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New Technology May Get Home Humidity Under Control

By Jay Stein on
Source: Алёна Синичкина

High indoor humidity threatens our health and building structures. A new technology enables air conditioners to effectively dehumidify using off-the-shelf equipment, with little additional cost or energy consumption.

Excessive indoor air humidity is bad for both humans and houses. It’s uncomfortable for people to be in highly humid spaces, but that’s the least of their problems. They also face increased risk for a variety of illnesses, and the structure of their homes and internal finishes can be damaged. Excess humidity is such a widespread problem that US consumers spend hundreds of millions of dollars a year on residential dehumidifiers to dry out their homes.

Despite all that spending, the dehumidifier is not the most common technology used to control indoor humidity. Instead, it’s the ubiquitous central air conditioner (and heat pump). This equipment is capable of removing humidity, but it’s not especially good at this task. Mainly, air conditioners cool down air. They do dehumidify it somewhat, but much more of the energy input to air conditioners goes for air cooling. Also, few central air conditioners are capable of responding to high humidity. Mostly their controls don’t measure it, and even if they did, they don’t have any way to signal to the air conditioner to shift into high-dehumidification operation. 

This unfortunate situation is likely to only worsen over time. Homes are being built to more effectively keep out heat, so air conditioners run less, and so, dehumidify less. Also, contemporary high-efficiency air conditioners are less capable of removing moisture than less-efficient earlier models.

Researchers working for Building America, a US Department of Energy program focused on innovations in residential building energy efficiency and indoor air quality, cobbled together a new technology that makes air conditioners and heat pumps smarter when it comes to managing humidity. Employing basic off-the-shelf equipment, with just a few simple control and mechanical modifications, it enables air conditioners to sense indoor humidity levels, and switch into a high-dehumidification mode when needed.

In tests, this new technology, which the researchers dubbed Advanced HVAC Humidity Control, did well. It maintained indoor air at acceptable humidity levels while consuming little additional energy. Adding Advanced HVAC Humidity Control to a new air conditioner cost about half that of installing a whole-house dehumidifier.

As impressive as these results are, Advanced HVAC Humidity Control isn’t ready for the mass market yet. More research needs to be done in more buildings, including different house types and locations. Ultimately, the HVAC industry would have to develop it into a standard product, so consumers can ask for it and contractors can be trained to install it.

If Advanced HVAC Humidity Control makes it through those steps, it has the potential to enable far more homeowners to manage residential indoor humidity with little additional energy consumption. Scientists and entrepreneurs are working on new technologies that more efficiently remove humidity from indoor air, but they’re years away from an off-the-shelf residential product. Until then, Advanced HVAC Humidity Control deserves more investment and product development by the residential HVAC industry.

What’s wrong with excess indoor humidity?

There’s always some water entrained in indoor air. For the most part, as long as it’s in the “Goldilocks Zone,” neither too high or too low, it’s a good thing. It helps us maintain healthy skin and reduces respiratory tract irritation.

Relative humidity, the main metric by which humidity is judged, is the ratio of how much water vapor is contained within a defined quantity of air, divided by the maximum amount of water that air could theoretically contain. In general, residential air is best contained within the range of 40-60% RH. Lower, the air is too dry. Higher, it’s too wet.

When indoor air is too humid, occupants usually feel uncomfortable, and they often waste energy by turning down the thermostat. More concerning is that damp air promotes mold, mildew, fungus, and bacteria growth, and those pathogens increase the risk of allergies, asthma, eczema, and bronchitis. Also, the wetter the air is, the more likely it is that water will condense on indoor surfaces, such as windows, or within walls, and damage framing, sheathing, insulation, and interior finishes.

In the US, these problems are most acute in the Hot-Humid climate zone, which stretches from Texas to Florida (See this publication for a map of US climate zones), but much of the country east of Kansas’ western border can be troubled by excess indoor humidity at some point.

How humidity is commonly controlled in homes

The most important way to manage humidity is to ensure the building shell has sufficient integrity to eliminate water leaks and minimize air leakage. Sealing roofs, caulking windows, and waterproofing crawlspaces are all good examples.

For water vapor that makes it past the building shell, or is released internally by people, showers, and kettles, many homeowners install whole-house dehumidifiers. If properly sized and installed they work well. Drawbacks are that they typically cost a few thousand dollars to install, can consume a few hundred dollars a year worth of electricity, and require periodic maintenance.

Far more US homes rely on air conditioners for dehumidification than dehumidifiers. About 90% of US homes feature some sort of of air conditioning equipment, but only about 20% have dehumidifiers.

The problem with using air conditioners to manage humidity, is that they’re mainly focused on maintaining temperature. Air conditioners do two things to make air more comfortable. Mostly, they simply cool down the air passing through them, lowering its temperature. Engineers call this effect sensible cooling. To a lesser extent, they also dehumidify air. They do so by passing air over cold metal surfaces, known as coils, and some of the water entrained in the air condenses out onto those coils, much the same way water beads up on a cold glass. Engineers call this effect latent cooling.

Of the energy input into an air conditioner, most of it goes towards sensible cooling, leaving much less available for dehumidification. The amounts of energy attributed to sensible vs. latent cooling are generally fixed for any given air conditioner, and there’s virtually nothing we as users can do to change them. (Engineers do have a way to modify them, but more on that later.) When those amounts are out of balance with a home, such that an air conditioner is putting too little energy into dehumidification, the indoor humidity is going to rise.

There’s another problem that keeps air conditioners from adequately dehumidifying. When an air conditioner turns on, the cooling coil is usually too warm to condense out water vapor. It may well cool the air but do little or no dehumidification. It can take as long as nearly a half-hour of operation for an air conditioner to reach its full dehumidification potential. This time period is known as ramp-up, and sometimes, if the cooling load is especially low, or the air conditioner is too large for the space it’s cooling, it might spend more time in ramp-up than in steady-state operation. When that happens, you can turn down the thermostat, but the house may remain too humid for comfort and safety.

Humidity problems are worsening

As bad as the home humidity situation already is, it’s likely to get worse. Homes are being built with heat-resistant windows, thicker insulation, and lower infiltration rates, so as to require less cooling. That’s a good thing, as lower cooling loads reduce energy consumption. But, lower cooling loads require fewer air conditioner operating hours, which means they do less dehumidifying. 

Air conditioners are also getting more efficient. Over the past 30 years, the minimum standard efficiency rating (the Seasonal Energy Efficiency Ratio) required by the Federal government increased by 40-50%, depending on which part of the country you’re in. One way manufacturers managed to meet those higher standards is by increasing the amount of energy going towards sensible cooling and decreasing the amount going for latent cooling. Currently, it’s common for four times as much energy to go towards sensible cooling as goes for latent cooling.

Lastly, the drive towards building electrification is encouraging people to install larger heat pumps, capable of meeting the entire building heating load. Peak heating loads are often greater than peak cooling loads. When heat pumps are sized to meet the heating load, during the cooling season, they’re much bigger than they need to be. That means they run even fewer hours in cooling mode, doing even less dehumidification.

How to solve the dehumidification dilemma

People facing excessive humidity have a few options. They can install a dehumidifier, although that’s expensive and energy consuming. Nate Adams, an HVAC guru who publishes at House Whisperer Blog, advocates for using electric resistance heat to warm back up cool dry air just after the cooling coil. The electric heat counters the sensible cooling done by the air conditioner, causing the air conditioner to run longer, doing more dehumidification. Energy efficiency advocates blanch at using energy to simultaneously cool and heat air, but if that energy consumption is protecting people’s health and building structures, who’s to say it’s not well spent? Nate’s documented his results, showing he managed humidity well, at less first cost and similar operating cost to a whole-house dehumidifier. 

Probably more people would pay for improved dehumidification if it were less expensive and energy consuming than current options, and there’s a good chance Advanced HVAC Humidity Control can fill that niche. It’s based on a simple insight. HVAC engineers have long known that slowing down airflow across an air conditioner coil causes it to do less sensible cooling and dehumidify more. Indeed, an air conditioner using this technique was patented in 1991, although, as far as I can tell, it was never developed into a commercial product. It took the advent of cheap humidity sensors and the widespread availability of variable speed fans to make this concept feasible for the mass market.

The Building America researchers developed Advanced HVAC Humidity Control by combining off-the-shelf components in an innovative way. They first selected a thermostat with a built-in humidistat and set it up in such a way that they could control air conditioners based on both temperature and humidity. The air conditioners they selected were basic single-speed models, which were modified by their manufacturers to increase their capacity for dehumidification. Those air conditioners and thermostats were then combined with variable speed fans, which were controlled to slow down when high humidity was measured. When there was a call for cooling, but the relative humidity was less than 60%, the fans were operated so that they flowed air at about one-eighth less volume than what’s considered standard for cooling operation. When relative humidity exceeded 60%, the fans slowed down to one-quarter less than standard. The researchers also implemented a complicated procedure for ramp-up, which included slowing down airflow by as much as half. 

Test results are impressive

In three test homes, which were located in Texas, Louisiana, and Georgia, Advanced HVAC Humidity Control succeeded in keeping the indoor relative humidity below 60%, 90% of the time, or better. The occupants at one test house were so comfortable in their dryer conditions that they raised their thermostat setting to a higher temperature, saving a bit of energy.

All the test houses did consume more energy than they otherwise would have, but that was expected. Condensing out additional water vapor takes energy. Also, modifying the air conditioners to enhance their dehumidification capabilities made them a bit less efficient. In one house, such modifications dropped its equipment from SEER 16 to 15. The additional energy consumption was minimal, and far less than dehumidifiers would have consumed. One house’s annual cooling electricity consumption went up by 4.8%, which would have cost about $28, at the average national rate in place at the time. It only cost about $1,000 per house to make the upgrades, including humidistats and variable speed fans, which is about half of what it would have cost to install central dehumidifiers.

The Building America researchers also found that the systems they observed operated mostly in ramp-up mode. In one house, the air conditioner ran in ramp-up 80% of its operating time. This finding reaffirms the importance the Building America researchers placed on addressing both steady state and ramp-up operation. Lastly, the researchers concluded that Advanced HVAC Humidity Control Isn’t limited to any particular equipment brands, models, and efficiency levels, and that it could be applied to two-stage or variable-speed compressor systems. They also concluded that it could be combined with supplemental dehumidifiers, or heat recovery ventilators.

What it will take to scale up for the mass market

As enticing as the results achieved by the Building America researchers are, much more work remains to turn Advanced HVAC Humidity Control into a standard product that consumers in high-humidity areas can ask for. Here’s what needs to be done.

More research. Three test houses doth not a mass market product make. More research needs to be done to confirm the results of the first tests and refine the technique. Also, research needs to be done to investigate performance in other house types and climate zones. Is this technique limited to new systems or can it be retrofit to existing systems? There are a lot of moving parts here, including performance, first cost, additional energy consumption, and maintenance. In detail, how does Advanced HVAC Humidity Control compare to other alternatives, including whole-house dehumidifiers and electric resistance reheat?

Productization. If you wanted to improve the dehumidification capability of your air conditioner, you might be able to find a contractor who could apply the techniques the Building America researchers laid out in their report. However, it would be expensive custom work, and it would take a highly-skilled and risk-tolerant contractor. This technique won’t be available to the mass market until one or more manufacturers come out with approved sets of equipment and control packages, and train contractors to install them.

Standardization. At some point, when multiple manufacturers offer air conditioners that can respond to high humidity, the industry may well want to develop standards for how it’s implemented. That way, consumers can be confident that regardless of manufacturer, they can be assured a minimum level of performance and quality.

Metrics. Once products are standardized, governments and industry organizations can develop metrics that enable consumers to compare products from different manufacturers. One example is the SEER rating for air conditioners. Metrics for humidity responsiveness could include performance as well as energy efficiency. A leader in this field is Ankit Kalanki, a researcher with RMI’s Carbon-Free Buildings Program. Kalanki is in discussions with several HVAC standard-setting organizations regarding incorporating dehumidification performance into their energy efficiency standards.

What’s next?

Productizing Advanced HVAC Humidity Control would be an excellent advance for the domestic residential HVAC industry, but it’s unlikely to be the final one. The next technical horizon for the industry to march towards would be to develop air conditioners that dehumidify and cool effectively while consuming less energy than current equipment. 

One such initiative already underway is the Global Cooling Prize, a collaboration among the environmental think tank RMI, the Government of India’s Department of Science and Technology, and many others. The purpose is to incentivize the development of a residential room air conditioner that not only exhibits one-fifth the climate impact of the most commonly sold room air conditioners in the Indian market, but can also maintain 60% relative humidity throughout virtually the entire cooling season. The two companies that won the prize developed units that integrated mainly existing technology in innovative ways. It will be many years before their innovations are incorporated into the central systems that dominate the US market.

Another promising research focus is to incorporate chemical dehumidification technology into air conditioners. Current dehumidifiers are based on the same vapor compression technology as air conditioners. Chemical dehumidifiers are potentially much more energy efficient. A separate cooling system could then be optimized for sensible cooling only. Innovative companies in this area include Blue Frontier and Transaera. Currently, these companies are mainly developing equipment for commercial and industrial buildings, and they will need a few years of product development before they’re ready to bring residential products to market.

In the meantime, as these innovations are being honed, Advanced HVAC Humidity Control, or a similar technology based on the same underlying principles, seems to be an ideal next step for the domestic HVAC industry to enable its customers to better manage humidity.

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Refrigerants Will Be a Big Deal in 2025

By Jay Stein on

Image by: Phyxter.ai

The refrigerant that charged up air conditioners and heat pumps for the last 15 years is going away in 2025, and replaced by two new more climate-friendly ones. Whether you’re buying a new system, or you want to help battle the misinformation and confusion that’s likely to ensue, here’s what you need to know.

On January 1st, 2025, a new US Environmental Protection Agency rule will effectively ban the refrigerant that’s been used in air conditioners and heat pumps for the last 14 years. R-410A is being banned because of its excessive contribution to climate change, and two new more climate-friendly refrigerants will be used in equipment manufactured after that date.

You may be wondering why, if you’re not in the heating and air conditioning business, you should care about these changes. After all, this isn’t the first time something like this happened. In 2010, the EPA banned R-22, which at the time had been the residential air conditioner standard for over fifty years, because it was depleting the ozone layer. That’s when R-410A became the new standard. If you’re like most people, you never knew what refrigerant was in your air conditioner, other than it was Freon, or something like that.

This round of refrigerant re-regulation is going to be different. Contractors and retailers are already telling customers what refrigerant is in their units. Not only will those customers be concerned, but they will be confused by a wave of misinformation that’s likely to surge. In the face of this confusion and misinformation, even if you’re not in the market for a new system, if you’re a regular reader of this blog, your friends and relatives will be turning to you for advice. Here’s what they’ll be concerned about.

First, for the first time since the late 1950s, when the domestic industry settled on R-22, there will be two standard refrigerants for newly manufactured air conditioners and heat pumps: R-32 and R-454B. Manufacturers are already selecting one of the new refrigerants for their product lines, and are using their selections in their sales pitches. Refrigerant is now another distinguishing factor between manufacturers, in addition to price, efficiency, and reliability. Some folks who don’t even have a working understanding of the refrigeration cycle will be sorting through that information to figure out which refrigerant is the best one for them. 

Second, both of these new refrigerants are slightly flammable. What enables refrigerants to be climate friendly is a tendency to break down rapidly in the atmosphere, and that tends to make them flammable. The new refrigerants are so slightly flammable that they’re unlikely to ignite. If they do, they’re unlikely to cause much damage. Furthermore, regulators and industry leaders developed a set of safety features that will further ensure they are safely used. Even so, since the founding of the home air conditioning industry in the 1930s, manufacturers only used nonflammable refrigerants. The introduction of even slightly flammable refrigerants is bound to make some consumers anxious.

What will you tell them? Hopefully, you’ll say that the EPA’s decision was necessary to keep refrigerants from becoming a major contributor to climate change. That they needn’t agonize over which of the two new refrigerants to choose because the differences between them are slight, and there are more important factors that will determine the success of any air conditioner or heat pump installation. And that if this equipment is installed properly, it is extremely unlikely it will jeopardize their health or property.

In these highly polarized times, in which both anxiety and misinformation are abundant,  it’s challenging to formulate and implement public policies to address climate change. This new round of refrigerant re-regulation is an example of the sorts of public policies that are both needed and will require public support to succeed. The more folks who understand why these policies are necessary, and why this isn’t a radical environmentalist plot to incinerate Americans in their homes, the more likely it will be that the general public supports these regulations, and climate change policies in general.

Do you want to help build such understanding and support? Then, simply, read on. 

The situation

In October, 2023, the US Environmental Protection Agency issued a rule designed to reduce the climate impact of residential air conditioner and heat pump refrigerants. This rule had its origin in scientific studies over a dozen years earlier that found that as the climate warms, and humanity gets richer, the amount of air conditioning we’re using is rising rapidly. As we install more air conditioning systems, charged with refrigerants, more of those refrigerants are leaking into the atmosphere. 

The refrigerants we currently use are powerful global warming agents, thousands of times more potent per pound than carbon dioxide. The scientists conducting those studies concluded that before long, atmospheric warming attributed to refrigerants would be equivalent to a substantial portion of the warming attributed to carbon dioxide itself. The only meaningful public policy remedy would be to switch to refrigerants that contributed far less to climate change. That insight led policymakers to craft an international agreement, which led to US Federal government legislation, which then culminated in the EPA rule.

The metric the EPA uses to regulate refrigerants is Global Warming Potential. It expresses how much more a refrigerant warms the climate than does carbon dioxide, which features a GWP of 1. A refrigerant with a GWP of 1,000 would be about a thousand times per pound a more potent greenhouse gas than carbon dioxide.

Starting in 2025, the EPA will require all newly manufactured air conditioners and heat pumps to contain refrigerants featuring a GWP of 700 or less. R-410A, the current standard for this equipment, features a GWP of 2090, so it can’t clear this bar. Of the refrigerants the EPA approved for this sector, equipment manufacturers are largely choosing between two, R-32 (GWP 675) and R-454B (GWP 470).

This new rule only applies to equipment manufactured in 2025 or later. Already installed equipment can continue to operate indefinitely with the refrigerant it was originally charged with. No one need chain themselves to their air conditioner to keep it from being dragged away by jackbooted thugs from the EPA.

There will likely be enough R-410A to continue to service existing equipment indefinitely, but if you’d like to switch over your existing equipment to one of the new lower-GWP refrigerants, you won’t be able to. With few exceptions, equipment is manufactured to work with a single refrigerant and can’t be charged with another.

Of course, when everyone puts up their 2025 calendars, there will still be air conditioners and heat pumps manufactured in 2024 still in stock. Split systems (with separate indoor and outdoor units) manufactured before 2025, and containing R-410A, can continue to be installed until the end of 2025. Window units and other self-contained systems can continue to be sold until January 1, 2028. How long R-410A equipment remains available, it’s impossible to say.

Mild flammability explained

Ever since the emergence of the home air conditioning industry about 90 years ago, manufacturers produced equipment charged with non-flammable refrigerants. But about a dozen years ago, when scientists began to search for a low-GWP alternative to R-410A, they came to a distressing realization: it wasn’t possible to identify a residential refrigerant that was both low-GWP and nonflammable. What enables a refrigerant to exhibit a low-GWP rating is that if it leaks into the atmosphere, it reacts with oxygen and breaks down quickly. Such reactivity tends to make things flammable.

When those scientists came to accept that the next refrigerant generation would be flammable, they developed a new category, mildly flammable, and identified chemicals that fit within it. Although mildly flammable refrigerants can be ignited, they will only do so within a limited range of air-refrigerant mixtures. Too much air, or too much refrigerant, and the mixture won’t ignite. A good way to keep a mildly flammable refrigerant from igniting is to mix it up with more air.

Also, for a mildly flammable refrigerant to ignite, there has to be a high energy flame present, like a candle or a cigarette lighter. A static electricity spark, a hair dryer, or a toaster won’t start a fire. Should a fire start, the flames are slow moving and they go out when the high energy flame is extinguished. Indeed, the flames are so lethargic, their burning velocity is much slower than a baby can crawl. Although it might seem scary to use them, mildly flammable refrigerants have been used for several years now in millions of air conditioning and heat pump systems around the world. I’m not aware of any reports of these refrigerants causing catastrophic fires.

Even with the minimum risk they pose, US regulators and the HVAC industry spent over $7 million developing measures to enable mildly flammable refrigerants to be used safely. They include special techniques for joining pipes and fittings, and enhanced leak testing. Any system containing more than 3.91 lb. of refrigerant will be required to include a refrigerant leak detector, and in some cases, systems containing less refrigerant will also feature leak detectors. 

Since there’s usually about 2-4 lb. of refrigerant per ton of equipment capacity, nearly all systems larger than a ton or two require leak detectors. Should these detectors ever sense a significant leak, they’ll turn on the system’s central distribution fan to dilute the leaked refrigerant with air, and turn off any gas furnaces or water heaters. 

These safety features don’t come for free. While it’s too soon for a comprehensive study on how much they add to the cost of a system, I’ve seen anecdotal reports that range from a few hundred dollars to a few thousand dollars. 

With these safety measures in place, it’s unlikely that mildly flammable refrigerants will harm anyone or cause catastrophic property damage. What’s more concerning are the logistics of getting these systems installed. Currently, few domestic contractors have worked with either of the new refrigerants or their safety systems. System buyers will want to be sure their installers are trained and are following the installation instructions.

Also, these refrigerants are new to building code officials. Early installations may get caught up in red tape as building inspectors work to enforce recently implemented codes and standards. Nearly all building code jurisdictions in the US recently adopted new codes enabling them to approve installations containing mildly flammable refrigerants. There are, however, a few laggards. To see if your state’s building departments are ready, you can check out this map from the Air-Conditioning, Heating, and Refrigeration Institute. Alternatively, you might find it easier to just call up your local building department.

Meet R-32

R-32 consists of a single chemical named difluoromethane, which is composed of carbon, hydrogen, and fluorine. Although it was only recently approved in the US to be used in air conditioning systems as a single chemical refrigerant, it’s long been used as a component in approved mixtures. R-410A, the standard for residential air conditioning for the last 15 years, is a 50-50 mixture of R-32 and a flame retardant. Because R-32 is mildly flammable, it couldn’t be used on its own in the US until approved safety systems for these refrigerants were developed.

R-32’s GWP is about one-third that of R-410A, and it’s about 5% more efficient. Those improved characteristics come at a price. R-32 is about 60% more expensive than R-410A according to eRefrigerants.com. Given the amount of refrigerant most residential systems hold, it would probably add less than $100 to the cost of an installed system.

Manufacturers already committed to use R-32 in their products include Daikin, Fujitsu, and LG, all of which are Asian-based, and have been using the refrigerant in their products for years. Goodman and Amana, which are recognizable North American brands but owned by Daikin, also opted for R-32.

Meet R-454B

R-454B is a blend containing 68.9% R-32 and 31.1% of an ultra-low GWP refrigerant from a new family known as hydrofluoroolefins. These refrigerants are composed of hydrogen, carbon, and fluorine, just like R-32, but feature a different chemical structure. Hydrofluoroolefins are remarkable in that they exhibit single-digit GWP, but are often mildly flammable. The particular hydrofluoroolefin used in R-454B was developed by the Dupont corporation for the automotive market, and is widely used. If you bought a car in the last few years, it probably came charged with it. It costs about 2½ times as much as R-32.

R-454B’s GWP is about 30% lower than R-32’s, but it is slightly less efficient, perhaps as little as 1% less. Because it contains a hydrofluoroolefin, R-454B costs about 25% more than R-32 and about twice as much as R-410A.

Many of the major North American air conditioner and heat pump manufacturers adopted R-454B, including Trane, Carrier, Lennox, and Rheem.

Which one is best?

So, if we’ve got two refrigerants, one of them has got to be better than the other, right? Which one is best depends on your what you want to achieve. Do you want the cheapest refrigerant? Then R-32 is your choice, although for a typical split system, choosing R-454B would at most add just a few hundred dollars to the overall installed cost of an R-32 system. That doesn’t seem like a big deal for a purchase that runs somewhere between five and twenty thousand dollars. 

Do you want the most efficient one? Again, R-32 would be your choice. How about the lowest GWP? Here, R-454B has the edge. However, the overall lifetime climate impact of an air conditioner or heat pump depends on much more than refrigerant GWP. You’ve also got to take into account overall system efficiency, annual operating hours, the cleanliness of the local electric grid, how much refrigerant the system contains, how much refrigerant leaks during its lifetime, and how much refrigerant is reclaimed at the end. In some cases, R-32, with its higher efficiency, could well contribute less to climate change. Indeed, the HVAC manufacturer Daikin calculated out such a scenario, although the difference in climate emissions between the two refrigerants was less than 1%.

For any given system, it’s not worth breaking out the laptop and going through all the calculations that Daikin did. You’ll probably find that the difference is slight. The equipment selected and installation quality will have a far bigger influence on system outcomes than refrigerant choice. Also, it’s not as though an installer is going to ask which refrigerant you prefer. Equipment will come from the factory designed and manufactured to work with only a single refrigerant.

My suggestion is that you find an installer who does high quality work and select equipment from the manufacturers that installer likes to work with. In the end, it will matter little whether that equipment is charged with R-32 or R-454B. Your time and energy are better spent finding an excellent contractor.

Practice non-attachment

Don’t get too attached to either of these refrigerants. There’s at least one more round of re-regulation coming from the EPA, and probably several. When that next rule goes into effect, and by how much it lowers the GWP bar, no one can currently say. With a GWP of less than 500, R-454B might survive the next round, but not the one after that. Ultimately, it’s likely that propane, or some other similar hydrocarbon, with a GWP close to zero and no fluorine, will emerge as the long-term standard refrigerant for residential air conditioners and heat pumps. It remains to be seen what sort of safety systems will be required for such highly flammable refrigerants.

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Wait! Propane is the heat pump refrigerant of the future?

By Jay Stein on

Image courtesy of Koolex

Charging heat pumps and air conditioners with propane refrigerant can help mitigate climate change and other environmental problems. That may seem scary, as propane is highly flammable, but with advanced technology we can use it safely.

Refrigerants flow through the innards of every air conditioner and heat pump. Their alternate evaporation and condensation move energy from cold to hot, thereby heating and cooling our homes and buildings. But as magical as the refrigeration cycle seems, refrigerants have a dark side. They leak into the atmosphere and contribute to climate change and other environmental problems.

We can mitigate those problems by charging heat pumps and air conditioners with propane. Unlike current refrigerants—which are composed of hydrogen, fluorine, and carbon—propane contains only hydrogen and carbon. It breaks down rapidly in the atmosphere into naturally occurring chemicals, and contributes little to climate change and not at all to fluorine pollution. 

Other benefits include that propane is efficient, inexpensive, and widely available. Given all these benefits, we’re already moving, in the US and globally, down the path towards making propane the standard refrigerant for heat pumps and air conditioners.

There’s only one major problem with propane refrigerant, and it’s a doozy: it’s highly flammable. In the US, we haven’t used flammable refrigerants in homes for nearly a century. Using propane refrigerant sounds scary, and there will undoubtedly be people who stoke those fears by presenting out-of-context information. Don’t forget that climate change and fluorine pollution also expose us to uncertainty and hazards.

Even though propane’s safety record is not perfect, there are numerous reasons why you can be excited about its potential and confident it will be used safely. It’s already being used in a variety of market niches in the US and around the globe. US regulators are moving cautiously and incrementally. Documented incidents involving injuries and property damage are rare. Advanced technology, much of which already exists, will help to assure safety. Rigorous technician training and certification will help avoid some of the biggest risks.

If you want to support the transition to propane refrigerant, one thing you can’t currently do in the US is buy a propane-charged heat pump or air conditioner. But, you can support the Environmental Investigation Agency, a non-profit organization that advocates for propane by interacting with government agencies and informing the public.

Propane returns

In the late 19th and early 20th century, propane was a popular refrigerant, largely used in industrial ice making machines. At the time, the home refrigerator industry was in its infancy and heat pumps weren’t yet manufactured. The refrigeration systems back then were not especially leakproof. While there are documented cases from that era of fires being caused by leaking refrigerants, it’s not clear how many were caused by propane. 

Noxious odors from refrigerant leaks may have been a more widespread problem, given that two of the main competing refrigerants were ammonia and sulphur dioxide. Unlike those refrigerants, propane doesn’t irritate eyes and bronchial passageways. Indeed, in 1922, an advertisement in Ice and Refrigeration magazine, touted propane as “The Odorless Safety Refrigerant.” That wasn’t enough to make propane a major player in the nascent home refrigerator market.

The Frigidaire company’s search for a nontoxic and nonflammable refrigerant was a major factor driving the invention of chlorofluorocarbon refrigerants in 1928. Sold under the trade name Freon, these chemicals—composed of chlorine, fluorine, and carbon—came to dominate the refrigeration and air conditioning industries for over half a century. During Freon’s reign, most US residential building codes prohibited propane refrigerant and it largely disappeared from the the market. 

The damage Freon did to the ozone layer came to be its undoing. Its eventual banning began with the signing of the Montreal Protocol in 1987. Freon was the first refrigerant banned for environmental reasons, but certainly not the last. It took less than 30 years until the next international agreement on refrigerants, which resulted in the EPA banning the chemicals that replaced Freon because of their impact on the climate. It will likely take even fewer years for the latest refrigerant generation to be banned.

With each of these successive waves of refrigerant introduction and subsequent banning, propane has made its way into more applications. Eventually, after a few more rounds, it may be the only refrigerant left to be used in heat pumps and air conditioners.

Problem with current refrigerants #1: climate change

The main reason why current refrigerants will get banned is that they contribute too much to climate change. In theory, that shouldn’t be a problem. Heating and air conditioning technicians are supposed to install systems that don’t leak, and when those systems reach the end of their life, technicians are required by law to capture and recycle the refrigerants. In reality, these systems leak more, and technicians capture far less used refrigerant, than they should. Perhaps 3% to 4% of air conditioner and heat pump refrigerants leak annually, on average. When you consider that there are over a billion air conditioners worldwide, that adds up to a lot of leaked refrigerant.

Once they leak into the atmosphere, the impact refrigerants have on the climate is typically expressed using the term Global Warming Potential, or GWP for short. It expresses how much more a refrigerant warms the climate than does carbon dioxide. Carbon dioxide features a GWP of 1. A refrigerant with a GWP of 1,000 would, in theory, be about a thousand times more potent greenhouse gas than carbon dioxide.

Starting January 1, 2025, the EPA will require all air conditioner and heat pump refrigerants to feature a GWP of 700 or less. That’s about 1/3rd the GWP of the current standard refrigerant (R-410A). While the EPA’s new limit is certainly an improvement, it’s likely the Agency will eventually lower it. According to the EPA, propane’s GWP is 3, so it’s unlikely to ever be banned on that basis. By the way, the EPA’s regulations only apply to newly installed systems. The Agency doesn’t require the refrigerants in existing systems be changed out, and the new refrigerants can’t be used in older systems.

How much would switching to propane reduce refrigerant’s climate impact? A team of scientists, mostly from the International Institute for Applied Systems Analysis, an Austria based research organization that supports sustainable development public policies, explored this question. They modeled the global temperature impact of three different scenarios: 1) Continue using the current standard refrigerant, R-410A, in all newly manufactured split air conditioning units worldwide. 2) Switch over those same units to R-32, the most common low-GWP refrigerant replacing R-410A. 3) Switch over to propane. They concluded that switching to propane would avoid three times as much temperature rise by the end of the century, as switching to R-32. They also concluded that “propane as a refrigerant can play a key role in creating a more sustainable split AC sector.”

Problem with current refrigerants #2: fluorine

Refrigerants may get caught up in the international drive to ban some fluorine-bearing chemicals. The technical name for these chemicals is per- and polyfluoroalkyl substances, but they’re better known by their abbreviation, PFAS. They’re also known as forever chemicals, as they can persist for a long time in the environment. They’ve been linked to a lot of adverse health effects, including increased cancers and decreased fertility.

Some fluorine-bearing refrigerants are characterized as PFAS, and some of them break down in the environment into chemicals that some scientists characterize as PFAS. For example, one recently formulated refrigerant that will soon be used in heat pumps breaks down into trifluoroacetic acid, also known as TFA. This acid accumulates in waterways and gets into drinking water supplies. Even at low concentrations, TFA is potentially harmful to human health and aquatic life. 

Several research teams recently found concerning levels of TFA in drinking water and elsewhere in the global environment. The chemical and HVAC industries don’t dispute these findings, but they do dispute the severity of the threat posed by TFA. One research team, financed by an industry trade group, concluded that “with the current knowledge of the effects of TFA on humans and ecosystems, the projected emissions through 2040 would not be detrimental.” 

While the debate over TFA rages, it looks like the first regulatory body to take action on refrigerant-related fluorine pollution could be the European Union. The European Parliament recently forged an informal agreement that would ban all fluorine-bearing refrigerants from being used in newly-manufactured split air conditioners and heat pumps by 2035. It still needs to go through a formal approval process before it passes into law.

In the US, the EPA is developing its own PFAS Strategic Roadmap which will set timelines and specific actions the agency plans to take in this area. The Roadmap doesn’t include refrigerants, but lots of scientists and environmentalists are calling for the agency to expand its scope.

Seven reasons to expect a safe transition to propane

How concerned should you be if one day in the future you find yourself in a house or building with propane-charged equipment? Not much, and here’s why.

1. Propane refrigerant is already being used in equipment around the globe

Propane charged air conditioners are currently sold in the UK, Germany, India, and China. In the US, it’s used in small commercial units like beverage coolers, frozen drink machines, ice makers, and ice cream freezers. Most refrigerators now come charged with isobutane, which, like propane, is a hydrocarbon and highly flammable. You may have a flammable refrigerant in your home without knowing it. As all this equipment is being used, the industry is learning how to work with propane ever more safely.

2. US regulators are moving cautiously and incrementally

What makes refrigerants exhibit low GWP is that they react with oxygen and break down quickly, should they ever leak into the atmosphere. That same ability to react with oxygen also makes them flammable. When US regulators realized they couldn’t reduce the climate impact of refrigerants without increasing their flammability, they decided to compromise. The latest refrigerants, approved for US heat pumps and air conditioners starting in 2025, only moderately reduce GWP, and are only slightly flammable. These refrigerants can be ignited, but only under limited circumstances, and only in the presence of a high energy flame, like a candle or cigarette lighter. A hair dryer, toaster, or electric space heater won’t do it. Over time, as the domestic industry gains experience with these slightly-flammable refrigerants, regulators will likely decrease GWP limits, and increase flammability, incrementally.

3. Documented incidents involving injuries and property damage are rare

In the modern era, starting with the Montreal Protocol, there have been some incidents of fires and explosions caused by propane refrigerant. I’ve only seen less than a half-dozen incidents documented, although I’m sure there are more. My sense is that the number of incidents is minuscule compared to the overall number of systems installed.

The most serious accident took place at a refrigerated warehouse in New Zealand in 2008, when a propane refrigerant explosion killed one fireman and injured another 7. In another accident, a service technician working on a system designed for a different refrigerant, didn’t realize it contained propane, and set off an explosion. In nearly all the documented incidents I’ve seen, standard safety measures weren’t utilized, service personnel ignored labeling, or untrained personnel didn’t follow safety protocols. All of these factors seem preventable with rigorous training and certification.

4. Charge limits help control risk

The smaller the amount of propane contained within a heat pump, the less damage a leak can cause. To manage the risks associated with flammable refrigerants, regulatory bodies often limit the amount of refrigerant that a particular device can be charged with. Typically, such charge limits are based on the amount of occupied space and the equipment serving it. 

In the US, charge limits are set by the EPA, usually in conjunction with other standard setting organizations. Currently, the Agency only approves propane for use in self-contained products, like window air conditioners. For these products, the EPA limits the amount of refrigerant they may contain by a complex formula. Allowable charge amounts vary depending on cooling capacity and equipment type, but the highest charge allowed is 1 kg. A typical gas grill tank holds as much as 9 kg.

To my knowledge, no one manufactures propane-charged self-contained units for the US market. Even if they did, it’s unlikely US consumers would heat and cool entire homes using them. In the US market, consumers prefer central and mini- split systems. For US manufacturers to produce propane charged versions of such equipment, the EPA would have to approve using propane for split systems and set charge limits. Indeed, environmental organizations are advocating for both of these actions.

One problem with charge limits is that because they’re based on safety, they can be set so low that they limit equipment efficiency. It doesn’t help to mitigate climate change if equipment consumes more electricity, which then releases more carbon dioxide emissions. It would make it more feasible for equipment manufacturers to meet charge limits with high efficiency if new technology enabled heat pumps to operate with less refrigerant. 

Researchers working at the Fraunhofer Institute, a German organization focused on technological innovation, recently demonstrated in the lab a 3½ ton propane charged heat pump containing about one-fifth the amount of refrigerant of commercially available systems. To achieve these impressive results, the research team evaluated more than 20 different combinations of heat exchangers and compressors. It remains to be seen if the technology developed by this project is picked up by equipment manufacturers.

5. Some systems put the entire propane charge outdoors

One way to protect building occupants is to place the entire refrigerant charge outdoors, contained within an air-to-water heat pump. Heat or coolth is transferred from the heat pump to the building via pipes containing either water or an antifreeze solution. Energy is exchanged between the water (or antifreeze) and occupied space using radiant floors, radiators, or fan-coil units. This will probably be the first way propane heat pumps are approved for use in the US. The main drawback is that it adds an additional heat exchanger, which adds expense and reduces efficiency.

Even though this format seems safe enough, given the profusion of gas grills located outside US homes, it still isn’t allowed by the EPA, but that could soon change. In September 2023, ASHRAE, the standard setting association for HVAC engineers, issued a proposal for public review to allow outdoor heat pumps to be charged with up to 4.9 kg of propane. If ASHRAE approves this proposal, the EPA probably will enact a similar regulation.

6. Additional safety features may be required

For some systems, with equipment inside buildings, regulators may want more safety than they can get from charge limits alone. At a minimum, labels and signs will be required that make it clear to service technicians which equipment and pipes contain propane. Additionally, regulations often require propane equipment be located a specified distance from ignition sources or completely isolated from open flames and hot surfaces. They may also require special electrical boxes that isolate electrical circuits to ensure that leaking refrigerant doesn’t come in contact with sparks or hot wires.

Another safety feature typically installed with propane systems is a refrigerant leak detector. When indoor refrigerant concentrations get to one-fourth of the level at which they’re problematic, these sensors set off alarms and trigger safety systems. Even with these detectors, avoiding leaks is critical, so special materials and techniques are required for pipes and joints, as well as rigorous field testing for newly installed systems. 

Some regulations require plastic blades for air distribution fans. These blades are typically made of metal but could potentially cause sparks if they rubbed against housing or cowling. Those sparks would be problematic if leaking refrigerant came in contact with them.

Research in this area is ongoing, and future systems may well require additional features yet to be developed.

7. Rigorous technician training and certification for technicians will be implemented

To ensure that safety protocols are followed impeccably, there will have to be a rigorous system of training and certifying installers and service personnel. Also, they’ll have to be well trained in service and decommissioning, both of which are especially vulnerable to accidents.

Looking at this list, two things are apparent. First, even though propane is inexpensive, installing safety features will drive up the cost of air conditioners and heat pumps. Second, even with the most rigorous training and inspections, all these features and protocols will not be perfectly enacted on every installation. Accidents will likely be rare, but they will not be completely eliminated. Then again, climate change and fluorine pollution aren’t risk free either.

Want to help?

If you like the idea of heat pumps and air conditioners charged with propane, and would like to help make them available in the US, there is a way for you to get involved. Support the Environmental Investigation Agency. Founded in 1982 by UK anti-whaling activists, it’s now a worldwide non-profit organization devoted to investigating and campaigning against environmental threats.

EIA’s climate division does a ton of work in the refrigerant area. To bring attention to how much grocery store refrigeration systems are leaking, the group sent activists into stores armed with refrigerant leak detectors. In addition to investigations, EIA produces reports on policies to mitigate refrigerant-related climate change and other pollution. It also lobbies the EPA and other major US standard organizations to support those policies. When the EPA was recently considering which policies to enact to transition to lower-GWP refrigerants, EIA organized a joint petition on behalf of several environmental groups that was influential within the agency. 

EIA has long advocated for regulations accepting propane refrigerant. Its US division is a registered 501(c)(3), and accepts donations.

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When will we get the heat pump thermostats we need?

By Jay Stein on

We want dual-fuel heating systems—electric heat pumps combined with gas furnaces for backup—to minimize our carbon footprints and utility bills. Currently, no one makes thermostats that would enable these systems to do these things, but if governments and manufacturers take action, that could change.

It was a dark and stormy night. In a house near Denver, Colorado, the indoor temperature dropped below 68℉, and the thermostat activated the heating system. This particular heating system combined both a heat pump and a natural gas furnace into a configuration known as a dual-fuel system, which is gaining traction as an archetype for inexpensively electrifying existing homes. 

This home was also equipped with a thermostat typical for duel-fuel systems that determined which heater to run based on outdoor temperature. As is common, the outdoor temperature control was set at 35℉, just to make sure the house would stay comfortable. Above that temperature the heat pump would run, and below it the furnace would. No one knew for sure that was actually the right temperature to maintain comfort. It was based on a rule of thumb, which in-turn was based on the performance of heat pumps made decades ago. 

When the outdoor temperature dropped below 35℉, the thermostat fired up the natural gas furnace. Unbeknownst to everyone sleeping peacefully in the house, operating the heat pump at that moment instead of the furnace, would have caused less carbon dioxide to be released, and it would have cost less to run. The thermostat wasn’t smart enough to figure that out. As a result, the family wasted money and an opportunity to reduce CO2 emissions.

It’s likely that the family would have wanted a smarter thermostat if they could have gotten one. When consumers are asked what motivated them to buy heat pumps, two of their top answers usually are that they wanted to cut their energy costs and reduce their environmental impacts. Given these sentiments, you’d think that for dual-fuel systems you’d be able to equip them with thermostats capable of either minimizing CO2 emissions or utility bills. Think again. They’re not available at any price.

In theory, we already have most of the technology needed to make such thermostats. To minimize emissions, the thermostat would need to know how clean the local electric grid is at any given moment (it changes frequently over the course of the day), and how efficient the heat pump is (which also varies). The thermostat would also need to know the emissions associated with the natural gas grid and the efficiency of the gas furnace (both are relatively constant). Provided with such information, the thermostat need only make a simple calculation.

Determining the least cost heater requires a similar calculation, with one major difference. Instead of knowing grid cleanliness, the thermostat would need to know the cost of electricity and natural gas at any given moment. Combining that cost information with equipment efficiency, the cost of operating both heaters could be calculated, and the least-cost one identified. It’s not possible to minimize both emissions and costs simultaneously, since only one thing can be minimized at a time. It would be possible for such a thermostat to include an algorithm that balanced emissions and costs based on the user’s preferences.

Performing such calculations wouldn’t require technology much more sophisticated than current smart thermostats, like those from Nest and Ecobee. Instead, we don’t have CO2– and cost-minimizing thermostats for two reasons. First, several of the needed information streams don’t yet exist. For example, there isn’t a good way for thermostats to know what the actual energy prices are at any given moment. Second, it’s hard for manufacturers to build markets for products that are so new consumers don’t even know they need them.

There are folks working on developing smarter heat pump thermostats, both in government laboratories and in manufacturers’ offices. Because there’s so much untapped value for these controls to access, it’s likely they will eventually come to market. That emergence will come a lot sooner if: utilities and equipment manufacturers get to work on developing the necessary information streams; the federal government invests in research and funds manufacturers’ development efforts; and lastly, environmental advocates get the word out on how these thermostats would save both money and emissions.

Why dual-fuel systems matter

The gas furnace is the most common heating device in the US. Over 40% of US homes are equipped with one. Millions of these homeowners are going to want to take advantage of the Inflation Reduction Act’s heat pump tax credits, but will find it’s expensive to retrofit heat pumps, with costs often running as high as $30,000. 

One trick to cut these costs down to just a few thousand dollars or less is for homeowners to wait until their air conditioners fail, replace them with heat pumps that cost little more than new air conditioners, and leave their gas furnaces in place as backup. This strategy avoids the expense associated with upgrading air distribution ducts and electric panels, both of which are often required. It might not be the ultimate long-term electrification strategy, but in the short-term, while we build public support, workforce volume, and manufacturing capacity, it’s an attractive one. To learn more about this strategy, see Replacing a central air conditioner? Get a heat pump instead. As more homeowners learn about it, they’re likely to drive a lot more heat pump installations.

If we’re going to maximize the benefits we get for our investments in these heat pumps we need better thermostats. The way virtually all dual-fuel thermostats currently work is that when there’s a call for heat, they turn on either the heat pump or the gas furnace based on either indoor or outdoor air temperature. These controls are fine for homes, where heat pumps are backed up by electric resistance heat, propane or fuel oil. These fuels are so expensive and carbon intensive that simply maximizing heat pump operation will come close to minimizing energy costs and CO2 emissions. 

Natural gas is different in that it’s much less expensive and carbon intensive than those other fuels. Whether or not it’s beneficial to run a heat pump instead of a gas furnace at any given moment depends on several factors that can vary by the hour, including heat pump efficiency and energy costs. Making a decision on which heater to run based on a single temperature setting can’t possibly account for such variability.

This lack of effective thermostats is not a reason to delay heat pump purchases. A dual-fuel system installed in most locations in the US, using controls readily available now, over its lifetime, will likely cost less to operate, and cause fewer CO2 emissions, than a standalone gas furnace. The problem is that when people install dual-fuel systems equipped with current thermostats, they’re not getting all the money and emissions savings available. Indeed, we’d all benefit from those savings.

The quest for a dual-fuel heat pump thermostat that minimizes greenhouse gas emissions

A dual-fuel thermostat that minimizes CO2 emissions is actually not that far from fruition. That’s because an information stream for quantifying marginal carbon dioxide emissions currently exists. It’s offered by WattTime, a nonprofit organization founded by UC Berkeley researchers. WattTime puts out an Application Programming Interface (an arrangement that enables multiple computers to communicate with each other, usually over the internet, abbreviated as API) containing real-time electric grid marginal emissions factors, updated every five minutes, for virtually the entire continental US, and most of Canada, Australia, and Europe. 

As the electric grid goes through the day, solar power ramps up and down, wind power does the same, and grid operators respond by firing up and shutting down various fossil fuel and other generators. The mix of all these different electric power sources also varies depending on where you are on the grid. WattTime figures out, for numerous locations, what generation sources will power the next devices to draw electricity from the grid, and quantifies their emission intensity in pounds of CO2 per Megawatt-hour of electricity consumed. See the graph just below for an example of what an ordinary day of such data looks like.

Image courtesy of WattTime

Already, several companies offer products that make use of WattTime’s data to reduce CO2 emissions. Enel X Way enables electric vehicle owners to charge only when the cleanest power is available. The recently released Google Nest Renew thermostat is able to shift heating and cooling operation to times when less CO2 would be emitted.

Since a CO2-minimizing thermostat would only be a bit more complex than what Google is doing with its Nest Renew product, it seems that it should be feasible. I asked Geoff Hancock, a WattTime product manager when he thought it would come to market, and he responded “This is inevitable. My feeling is that a WattTime-enabled heat pump could be commercially available in two years.” Currently, similar concepts are being investigated by several groups, including Oak Ridge National Laboratory and the Western Cooling Efficiency Center.

Accessing heating equipment efficiency

Whether you want a dual-fuel thermostat to minimize operating costs or CO2 emissions, it would need to know what the heat pump efficiency is whenever there was a call for heat. That’s tricky to do, as heat pump efficiency varies largely based on outdoor temperature. The colder it is outside, the harder the heat pump has to work to extract heat from outdoor air. For example, at 40℉, some heat pumps provide about 4½ units of heat to a home for every unit of electricity input, but only about 2¼ at 10℉. These numbers vary quite a bit between different heat pump models. To determine heat pump efficiency at any given moment, the thermostat would need to know both the outdoor air temperature and the characteristics of the installed heat pump.

Knowing the outdoor air temperature is the easy part. Some thermostats already include outdoor temperature sensors. Others are able to get the local temperature from weather services over the internet. 

Knowing how the efficiency of a heat pump varies with outdoor temperature is more complicated. Heat pumps are currently tested for their heating efficiency at a few standardized outdoor air temperatures between 17℉ and 47℉, with the option to also test at 5℉. The results of these tests are compiled by the Air Conditioning, Heating, and Refrigeration Institute, an industry trade group. One way to enable thermostats to access equipment efficiency information would be for AHRI to put out an API containing those efficiency test results. Installers would need to simply enter the heat pump’s make and model number into the thermostat,

Once the thermostat could access both outdoor air temperature and the efficiency test results, it could readily determine moment-by-moment heat pump efficiency. The thermostat would also need to know the furnace efficiency, but that’s a much simpler proposition. Furnace efficiency ratings are also compiled by AHRI and they vary little with external conditions. Installers would only have to program a single efficiency number into the thermostat.

Accessing real-time marginal utility costs

Most people never know what the actual price is of the electricity and natural gas they consume. Mostly they just pay the bottom line number on their bills. I have occasionally figured out my marginal cost of energy—the cost of the next kWh and therm we consume—and it’s tedious work. Even then, I only know my cost of energy at the end of the billing cycle, well after I’ve actually consumed it.

A cost-minimizing thermostat would need to know the marginal cost of electricity and natural gas in real time, and both can change monthly, or even more frequently. For example, between November of last year and this March, my gas marginal rate changed by 34%. My electric rate changed only by 1%, but soon my utility will switch me over to a time-of-use rate. When that happens, my electric rate will change several times a day, by as much as 67% during the heating season.

A cost-minimizing thermostat would need to access real-time utility costs via an API. Such an API doesn’t exist now and it would be a major undertaking to develop one. There are hundreds of utilities in North America, and most offer multiple rates. An API administrator would need to continually monitor all those utilities and rates for filings and notifications, and then quickly make hundreds of updates. This might be a job for artificial intelligence.

Once a thermostat had access to both equipment efficiency and real-time utility rates, it would be a simple calculation to determine which heater to run at any given moment.

The state-of-the-art for dual-fuel heat pump thermostats

The most advanced dual-fuel heat pump thermostat that I’m aware of is the one that Mitsubishi Electric provides with its intelli-HEAT heat pump. According to Mitsubishi, this heat pump can be combined with most natural gas furnaces, and it uses artificial intelligence to reduce both energy costs and greenhouse gas emissions. Obviously, it’s not capable of the cost minimizing calculations described immediately above—many of the needed information streams don’t exist yet—but it does some impressive things nonetheless.

For example, if the thermostat senses that during the heating season the room temperature is dropping, even with the heat pump operating, and that situation persists for nearly a half-hour, it will switch to the gas furnace to take over. Its artificial intelligence feature over time learns the conditions at which the heat pump can’t maintain comfort, and switches more quickly to the furnace. This is a much more effective means to increase heat pump operating hours, while maintaining comfort, than to use a single outdoor switchover temperature.

Mitsubishi Electric is working to improve the intelli-HEAT thermostat’s capabilities to reduce operating costs, anticipating that eventually the information streams needed will become available.

The old chicken and egg problem

To gain more insight on when a a CO2-minimizing thermostat might come to market, I contacted Daniel Meyers, the founder and CEO of Flair. His company makes several innovative thermostats, including one that enables mini-split heat pumps to be controlled from smart phones. He told me “I’d love a business justification to incorporate a carbon driven algorithm for selecting equipment but I don’t think there are currently any market mechanisms that are easy to plug into.” In other words, just like any manufacturer, he’s reluctant to invest in a product for which market demand doesn’t yet exist.

In the annals of corporate product development, this is a classic problem: What comes first, the market demand or the product? Customers can’t demand a product they don’t know they need, and they often don’t know they need it until someone makes it and markets it to them.

Building a market for cost- and CO2-minimizing thermostats is going to take some nudges from policymakers, manufacturers, utilities, environmental advocates, and investors. For example, utilities and heat pump manufacturers could get to work developing the APIs these thermostats need. The US Department of Energy could kick in money for research, and for manufacturers to develop and test prototypes. State and municipal heat pump program administrators could signal to manufacturers that when these thermostats are available, they will require their installation for dual-fuel systems. Environmental advocates could begin educating consumers about the benefits of these thermostats. It’s time for all these groups to get to work.

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Big Changes Afoot for Heat Pumps

By Jay Stein on

Heat pumps are becoming more efficient, less expensive, and more climate friendly. Understanding the legislation and regulations driving these changes is vital for consumers, policy wonks, investors, and electrification advocates.

There’s a perfect storm going on in the heat pump market. Policymakers and environmental advocates are touting this equipment as a solution to both climate change, and European dependence on Russian natural gas. Simultaneously, a plethora of legislation and regulations are emerging that are roiling the industry. These include new efficiency metrics, efficiency standards, federal tax credits, and refrigerant rules. Combined, they will make heat pumps more efficient, less expensive, and more climate friendly. They are also causing quite a bit of confusion for nearly everyone.

If you are a consumer in the heat pump market, an environmental advocate who wants to speak knowledgeably about building electrification, or just someone who wants to impress friends at cocktail parties, never fear. Read on to learn how the heat pump market is changing and why those changes will help mitigate climate change.

What you need to know about heat pump efficiency ratings

Whether you are planning to replace your air conditioner with a heat pump, or you are looking to influence public policy, you need to have a working understanding of two efficiency ratings: Heating Seasonal Performance Factor (HSPF) and Seasonal Energy Efficiency Ratio (SEER). The US Department of Energy requires that all heat pumps sold in the country be labeled with these ratings, and they are the basis for determining eligibility for virtually all government and utility efficiency programs.

They’re similar to the Environmental Protection Agency’s “miles per gallon” ratings for cars, and are determined by laboratory tests under standardized conditions. Two ratings are needed because heat pumps both heat and cool. HSPF expresses heating season efficiency and SEER expresses cooling season efficiency. The higher the ratings, the more efficient the equipment.

Manufacturers do a lot of research and development to boost their ratings, and charge more for higher rated products. Also, they’re used by designers, contractors, policymakers, and building code officials. The Air-Conditioning, Heating, and Refrigeration Institute, an industry trade group, provides an online directory that compiles the ratings. AHRI also governs how the ratings are determined, and continually upgrades them to be more representative of actual in-field performance.

Heat pump ratings V2.0

Now that you’ve got a working understanding of HSPF and SEER, I’m going to pull the rug out from under you. As of New Year’s Day 2023, they were superseded by new ratings named HSPF2 and SEER2. You might think of them as version 2.0.

The new ratings are similar to their predecessors in most ways, with one notable exception: they were modified to more accurately reflect the amount of work heat pump indoor fans do to push air through ducts. The SEER2 and HSPF2 ratings include five times more indoor fan power than the old ratings. That change results in lower, but likely more realistic, ratings.

There’s no simple formula to take a piece of equipment rated under the old system and calculate its new ratings. Instead, manufacturers redesigned and tested their products based on the new ratings. That said, we do have an approximation of how much lower they are. 

According to AHRI, if you had a group of ducted heat pumps, and you calculated their average HSPF, the average HSPF2 of that sample would probably be about 15 percent lower. The average SEER2 would probably be about 5 percent lower than the average SEER. Again, these ratios wouldn’t be precise for any individual unit, but for a group average, they’d probably be close. Also, this exercise is theoretical and you couldn’t actually do these calculations yourself. As new equipment comes out, it’s only being labeled with the new ratings, and not the old.

How much more representative of actual in-field performance are the new ratings? We don’t know yet. Researchers working for a coalition of utilties and other associations are currently collecting data to answer this question. Their final report is expected to be released later this year.

For heat pump buyers, the most important thing to know is to not directly compare the old ratings to the new ratings. Just because a new heat pump’s HSPF2 is lower than the HSPF of an older heat pump, doesn’t mean that the new heat pump is less efficient. Instead, just ignore the old equipment with the old ratings, and focus on equipment with the version 2.0 ratings.

Heat pumps get more efficient

Another change that took effect on January 1, 2023, was that new heat pump minimum efficiency standards kicked in. Just as the the US DOE sets minimum efficiency standards for light bulbs and washing machines, it also sets standards for heat pumps. Starting this year, the kinds of heat pumps most commonly used in US homes, manufactured after January 1 and sold in the US, must be rated at least 14.3 SEER2 and 7.5 HSPF2.

The new standards are about 7% better than the ones they superseded, but it’s hard to say for sure, since the old minimums were based on the old rating system. Heat pumps manufactured before January 1, 2023, can continue to be sold indefinitely.

For heat pump buyers, there’s not much to do. If you’re looking for the cheapest system you can buy, just know that the least-efficient and least-expensive systems will be a bit more efficient and a bit more expensive than they were last year. 

You might be able to get a screaming deal if you head over to the dealer’s showroom immediately and see if they have any of last year’s units still in stock. Not that I would recommend doing that. With the incentives available from both the federal government and other local programs, you may well find that high-efficiency heat pumps cost little or no more than their minimum-efficient counterparts, and cost less to operate.

New federal tax credits make heat pumps cheaper

Starting in 2023, and continuing for the next decade, the federal government is increasing the income tax credits available for heat pump installations. For most taxpayers, those credits are now worth 30% of the cost of their heat pump project, up to $2,000. Sounds simple, right? Turns out, there are a lot of complications: not all heat pumps are eligible for the credit, there are limits to how much money one can claim in a given year, and there are special programs for low-and-medium income folks.

Of all these complications the one that’s likely to lead to the most confusion and frustration is the slate of eligibility requirements. To ensure that the tax credits are only being spent on efficient heat pumps, the federal government outsourced to the Consortium for Energy Efficiency the job of setting the bar. CEE is a non-profit organization that has long worked with efficiency program administrators to coordinate with industry, trade associations, government agencies, and each other. 

CEE regularly compiles minimum eligibility ratings for a wide variety of efficiency technologies, including heat pumps. If you’ve ever gotten a rebate from a utility energy efficiency program, there’s a good chance that CEE established the efficiency specifications. 

Why is CEE specifying efficiencies when we already have the DOE doing that? They serve different purposes. The DOE specifies the minimum efficiency equipment that manufacturers can produce. CEE specifies which equipment qualifies for incentives from efficiency programs.

If you want to take a look at CEE’s 2023 specifications for heat pumps, you can do so here. Warning: It’s not set up for industry novices. Whether or not a heat pump qualifies depends on what kind of equipment it is (ducted, ductless, or single-packaged), where in the country it’s being installed (North or South), and whether it meets up to five different criteria. 

If you’re interested in determining whether a given heat pump qualifies for the federal tax credit, you can collect the data you need from the AHRI directory, but it’s not easy. There’s a lot to collect and some calculations are required. To make things easier, CEE is joining forces with AHRI to develop a directory that lists qualifying products. You can find that directory here, only at the time of writing, it’s not been populated yet. Until it is, check with the manufacturers regarding their products’ eligibility.

Out with the old refrigerants, in with the new

Heat pumps, just like air conditioners, refrigerators, and freezers, are filled with refrigerants, which by expanding and condensing, move energy from cold to hot. Should refrigerants leak out into the atmosphere, which they do with alarming frequency, they can contribute to a variety of environmental problems, including climate change.

The EPA is planning to restrict the use of the refrigerant that currently dominates the heat pump market in favor of new refrigerants that contribute far less to climate change. The agency proposed such a rule in December, 2022. It’s expected this rule will be finalized later this year and will go into effect January 1, 2025. It will only affect newly manufactured equipment, and not the refrigerants contained within existing equipment.

There are currently two commercially available and EPA-approved refrigerants that can meet the proposed rule: R-32 and R-454B. Both are slightly more efficient than the current refrigerant and otherwise perform similarly in heat pumps. Even so, they represent an important departure from the refrigerants used in the US for the last century.

What enables refrigerants to have low climate impact is they readily react with oxygen in the atmosphere and break down. That capability also tends to make them flammable, and virtually all US building codes explicitly outlaw flammable refrigerants inside buildings. However, these new climate-friendly refrigerants are classified as “mildly flammable.” They can be ignited, but not easily. For example, they’re about as flammable as ammonia, which you may be storing under your kitchen sink.

To enable mildly flammable refrigerants to be used safely, industry researchers developed new sensors, controls, and piping techniques, but there’s still a lot of work left to do to incorporate them into standard practice. Designers and installers are being trained, and the nation’s building codes are being amended to include rules for the new safety equipment and techniques.

As states and other jurisdictions get ready, manufacturers are developing products that can meet the new regulations. Daikin, the world’s largest air conditioner and heat pump manufacturer, is already shipping products charged with R-32 to a half-dozen states: Florida, Oregon, Washington, North Carolina, Maine, and Vermont. By late 2024, it’s likely that qualifying products from virtually all the major manufacturers will be widely available.

For heat pump buyers, be aware that over the course of 2025 and 2026, contractors and building code departments are going to be working with new techniques and regulations. Both buyers and policymakers will want to check to ensure that local building codes will be ready to accept equipment with mildly flammable refrigerants. Most building code departments will be ready, but a few won’t. Be prepared for some confusion and resistance as the industry gets used to working with these new refrigerants.

Final thoughts

Now you know why heat pump industry professionals are living on ibuprofen and antacid tablets. You also know many of the things you’ll need to successfully install or advocate for public policies for heat pumps.

One conclusion I urge you not to take away from this post is that you’d be better off waiting for the new more climate-friendly refrigerants to be in place. Yes, those future heat pumps will contribute less to climate change. But the benefits of replacing heat from burnt fossil fuels with heat pumping, far outweigh the benefits of more climate-friendly refrigerants. We’ll all be better off to have more heat pumps sooner rather than later.

Besides, if you want to wait for this market to settle down, you’re going to be waiting a long time. Heat pumps are benefitting from lots of research and development. There are sure to be more new standards, technologies, and refrigerants in the future. Don’t wait for them. The heat pumps we have now are more than good enough to drive down energy costs and mitigate climate change.

Replacing a central air conditioner? Get a heat pump instead.

By Jay Stein on

Every day in the US, homeowners replace thousands of central air conditioners. They’d save money and reduce climate emissions if they replaced them with heat pumps.

I’ve got a 20-year old air conditioner and when it fails, which will likely be soon, I’m going to replace it with a heat pump. If you’ve got a central air conditioner in your home, I want you to join me. Here’s why.

Heat pumps are simply air conditioners with a reverse gear. In the summer, they cool down your house and move the heat outdoors. In the winter, they run in reverse, sucking heat from outside (even when it’s very cold) and moving it into your home. For every unit of electricity you put into them, they can move anywhere from two to five units of heat.

If you replace your air conditioner with a heat pump, you’ll most likely reduce your heating season utility bills, reduce climate emissions, and help advance our country’s move away from fossil fuels. Best of all, you’ll get those benefits at little to no more money than you were already planning to spend (assuming you were going to replace your existing air conditioner).

The difference between manufacturing a heat pump and an air conditioner is small, largely consisting of a factory-installed valve and some additional controls. In the field, heat pumps also require a few additional components and controls. The installed cost differential between the two is usually less than $2,000. The recently enacted Inflation Reduction Act offers offers a 30% tax credit on a qualified heat pump, up to $2,000. Chances are good that the IRA’s tax credit, combined with any local incentives, will come close to covering, or even exceeding, any additional costs you might face.

Every day, on average, about 10,000 air conditioners are replaced in the US, and that equipment that will remain in place for another 15 to 20 years. That moment when an air conditioner needs replacement offers an opportunity to add another heat pump to the nation’s fleet at little expense or trouble. I won’t let that moment go to waste, and I urge you to not to either. 

The devil’s in the details

Since my proposed action seems simple on the surface, but actually involves quite a bit of complexity, please allow me to flesh out the details. Even though the life of a residential central air conditioner is considered to be about 15 years, ours has lasted so much longer because my wife and I rarely use it. We live in Boulder, Colorado, and mostly cool the house using outdoor air and a whole-house fan. Our air conditioner is so old that if even the slightest thing goes wrong with it, we won’t repair it. We’ll just junk it.

When that happens, or maybe even next spring, we plan to replace it with one of the higher efficiency heat pumps on the market. We’ll probably just replace it with a unit that features the same cooling capacity as the existing unit. That way we won’t need to add any additional circuits to our electric panel, and our existing air ducts won’t need any modification. Both of those actions can be expensive to accomplish, with costs in the range of thousands, or even tens of thousands of dollars.

Instead, we’ll face two different categories of much smaller costs. First will be the heat pump upgrade charge, a new thermostat, and a few specialized components. Those items will likely add up to less than $2,000, which equals the amount of money we expect to save via the Federal tax credit.

The second category is a charge that won’t be an issue for us, but might be for others. The IRA’s newly expanded tax credit comes with a requirement that claimants buy a more efficient heat pump than the government standard. How much more hasn’t been finalized yet. We’re planning on buying one of the most efficient units on the market and will likely easily clear that bar. If you would likely purchase standard efficiency equipment, maybe because you live in an area with little heating and cooling load, you’ll face an additional upgrade charge. Check to see if your local utility or municipality offers incentives that offset at least some of that cost. 

On the heating side, we’ll leave our existing 98% efficient natural gas furnace in place for backup, as our new heat pump might not be big enough to keep our house up to temperature on the coldest days. We’ll also replace our thermostat with one that will switch over to the furnace when it gets so cold outside that the heat pump can’t keep up. It’s possible to get a thermostat that switches over to backup when it’s typically cheaper to run our furnace than our heat pump, but we’ll just set things up so we use as little natural gas as possible.

The average household in the contiguous 48 US states that goes through with a plan similar to ours, also known as hybrid heating, will save $253 off its annual heating bill, and reduce its annual global warming emissions by 1.25 metric tons. People with propane, oil, or electric resistance heat will save more, and those with natural gas heat will save less. Those projections come to us from a policy and research team affiliated with CLASP, an international nonprofit whose mission is to improve the energy efficiency of appliances and equipment.

In addition to our personal benefits, there will also be societal benefits. Every year in the US consumers purchase over 6 million central air conditioners. If a sizable portion of these are upgraded to heat pumps that will help expand the business ecosystem that supports heat pump installations and service, and pave the way for future programs that eliminate all fossil-fuel-burning heating systems.

What’s not to like?

While I’m excited about replacing my air conditioner with a heat pump, I have heard a few criticisms of my plan. They mostly center around the idea that it doesn’t go far enough, because it only offsets a portion of fossil-fuel heating energy and leaves gas furnaces and other backup heating systems in place. My take on these arguments is that once again we’re witnessing the ongoing battle of the perfect versus the good, and that we should grab whatever good opportunities to reduce greenhouse gas emissions that present themselves now. Here are the criticisms I’ve heard and my thoughts on them:

Not enough energy savings. The CLASP research team expects that hybrid heating systems will reduce backup heating system energy consumption on average (in the 48 contiguous states) by about 36%. In tests in Michigan, combining heat pumps with propane furnaces reduced furnace energy consumption by about 50%. Some folks advocate for whole-home electrification programs that achieve far more energy savings by motivating homeowners to improve the thermal performance of their walls and windows, junk their old heating systems, cap off their fuel lines, and install heat pumps that are big enough to provide all, or nearly all, of their home’s heating needs. 

That concept has been shown to achieve whole-home energy savings, not just heating system savings, of 58% to 79%, depending on which climate zone the home is in. While achieving such energy savings is attractive, it’s also expensive. Analysts from the American Council for an Energy Efficient Economy project that individual projects would cost from $42,000 to $57,000. The IRA does contain some funding to enable low-income households to engage in such extensive retrofits, but for folks just claiming the heat pump tax credit, it’s not nearly enough to drive many such retrofits. While I wouldn’t want to dissuade anyone who wants to do a whole-home electrification retrofit, the old saying, “Half a loaf is better than none,” seems to apply here.

Hybrid heating leaves gas furnaces connected to the natural gas supply grid. Natural gas is largely composed of methane, which is a much more potent greenhouse gas than carbon dioxide. Methane escaping from natural gas production sites and pipelines is one of the leading contributors to overall US climate emissions. I’ve had environmentalists tell me that they objected to the hybrid heating approach because it left natural gas burning equipment in place. They said they wanted to completely replace that equipment so that, ultimately, the gas grid could be shut down, and all the methane emissions associated with it eliminated. 

As enticing as their vision may be, let’s not discount the value of methane leaks avoided by hybrid heating systems. Far more methane emissions take place at the production stage of the natural gas supply system (which includes the wells and processing facilities), than in the furnace and distribution piping within the home, according to University of California researchers. That means that even though gas burning equipment is left in place, just reducing gas consumption will ultimately reduce demand at the production stage, significantly reducing methane leakage. That reduction may not be enough to please everyone, but it’s more than enough to not be dismissed.

Heat pumps cost more to run than gas furnaces in some places. The CLASP researchers found that for homes with oil, propane, or electric resistance heat, adding a heat pump will reduce utility bills everywhere in the 48 contiguous states. For people with natural gas heating, the CLASP researchers determined that almost all hybrid heating adopters would save money, but did identify 6 states in which homeowners would experience increased utility bills. Those expected increases were small, ranging from $9 to $66 per year. 

Nearly all hybrid heat pumps can be controlled so that their operating costs are less than that of a gas furnace. It’s just a matter of choosing the the right outdoor temperature to switch over from the heat pump to the furnace. That’s because the colder the outdoor temperature, the less efficiently the heat pump operates. The trick is to determine the temperature at which both the heat pump and the furnace exhibit equal operating costs.

The CLASP researchers assumed that the hybrid heating systems they analyzed would switch to backup heat at 41℉ everywhere, which is a reasonable assumption for a nationwide analysis. In the field, heat pumps in the higher operating cost states probably would be operated at a higher switchover temperature. To calculate the switchover temperature based on your local energy costs and selected heat pump, there’s an app for that. You can learn about it a dualfuelhp.com. 

In summation, when you look at the enormity of the problem—there are 54 million homes in the US that feature both air conditioners and heating systems according to the CLASP researchers—the inherent complexity and expense associated with completely replacing a sizable portion of those systems with heat pumps is an overwhelming task. Taking advantage of an opportunity now to add heat pumps millions of homes, with little cost and complexity, just seems like too good a deal to pass up. Later on, over time, we can make investments to improve home efficiency, reduce heating loads, and electrify more equipment.

Public policies that can help

If you decide to install a hybrid heating system you might find yourself bumping up against a few obstacles. Don’t worry, they’re all surmountable for a tenacious early adopter. If we want large numbers of homeowners to replace failed air conditioners with heat pumps, it’s going to take action by governments and trade associations to mitigate these obstacles. Here they are: Heat pumps aren’t produced and stocked by the industry in sufficient numbers to be instantly available to homeowners in many areas. Many contractors are not familiar with some of the subtle differences between installing an air conditioner and a heat pump. Many contractors are not well acquainted with the hybrid heating concept.

When air conditioners fail, they usually crap out during the summer, when temperatures are high, and homeowners want them replaced fast. If those homeowners are in northern climates, they may find that their local distributors don’t keep lots of heat pumps in stock. There’s a good reason for that. Those distributors don’t typically sell a lot of heat pumps. The problem is that few homeowners will want to wait around sweltering in the heat for a new heat pump to be shipped from the factory.  

The solution to this problem is for manufacturers to make more heat pumps, and fewer air conditioners, and for distributors to stock more of them. One way the federal government can help encourage both of these things is to use the Defense Production Act. The DPA empowers the US president to “allocate materials, services, and facilities” for national defense purposes. In June of this year, President Biden found that a shortage of heat pumps “would severely impair national defense capability,” and called for their domestic production capacity to be expanded. 

The US Department of Energy plans to use $250 million authorized by the IRA for this purpose. Exactly what the DOE will do with this money hasn’t been decided yet, but funding manufacturers to retool some of their air conditioner production lines would be a worthy use. Also, the government could guarantee to distributors who stock more heat pumps that it will cover the cost spread between heat pumps and air conditioners for units that don’t sell.

The hybrid heating concept can also be moved ahead by training contractors about some of the subtle differences between installing heat pumps and air conditioners. For example, with heat pumps, the outdoor units should be elevated so they stay above the snow. It would also help to enable contractors to explain hybrid heating to their customers and demonstrate the benefits.

Lastly, governments can market to consumers nationwide on the benefits and logistics of hybrid heating. That way, they’ll be prepared when their air conditioners fail. The more homeowners ask for heat pump replacements, the more distributors will keep them in stock. The campaign the EPA commissioned to disseminate information on its Energy Star program might make a good model. If the government does decide to pursue such a marketing campaign, I’ve got a slogan to propose: An opportunity to install a heat pump is a terrible thing to waste.

The More Heat Pumps the Merrier

By Jay Stein on

Concerns about climate-warming refrigerants leaking from heat pumps are valid. Even so, the benefits of installing heat pumps instead of natural gas furnaces far outweigh the drawbacks.

The number of cities moving to ban natural gas heating in new buildings, and encourage builders to install heat pumps instead, keeps growing. Early leaders include New York and Seattle. In California alone, 54 jurisdictions adopted codes that either restrict natural gas usage or outright require heat pumps in new construction. 

Following their lead, policymakers and environmental advocates responding to Russia’s Ukraine invasion, advanced heat-pump-boosting plans to lessen Europe’s dependence on Russian natural gas. One of the most prominent proposals came from the journalist and environmentalist Bill McKibben, who in an article titled Heat Pumps for Peace and Freedom, implored President Biden to “immediately invoke the Defense Production Act to get American manufacturers to start producing electric heat pumps in quantity, so we can ship them to Europe…” Biden hasn’t commented publicly on McKibben’s proposal, but separately, the White House did release a statement announcing support for the European Commission’s plan to increase heat pump deployments.

Some critics of amplifying heat pump installations noted that the vast majority of heat pumps currently produced in the US are charged with refrigerants that are potent greenhouse gases, and those refrigerants leak. As a result, or so they claim, turbocharging heat pump production and installation is bound to increase climate change.

While it is correct that the leaking refrigerant problem is serious, let’s not let the perfect be the enemy of the good. Research shows that the potential benefits to be gained by installing heat pumps instead of gas furnaces far outweigh the drawbacks of leaking refrigerants. Also, more climate-friendly refrigerants are on the way. Federal regulations, expected to take effect in 2025, will drive manufacturers to produce new climate-friendlier heat pumps. The push to install more heat pumps is a good thing that needn’t be slowed down over refrigerant concerns.

A new study that settles the question

For years now, leaders at the Natural Resources Defense Council, a US-based legal and scientific environmental advocacy group, heard concerns about the heat pump refrigerant problem. To investigate to what extent leaking refrigerants undermine the climate benefits of replacing natural gas furnaces with heat pumps, the organization funded a study by researchers working at the University of California, Davis.

The UC researchers used computer simulation to project the hour-by-hour energy consumption of an average US home in 99 US cities, first with a high-efficiency natural gas furnace, and then with a high-efficiency heat pump. Next, they used a database from the National Renewable Energy Laboratory to convert that energy consumption into carbon dioxide emissions. They also added in the leakage of natural gas and refrigerants, from gas pipes and heat pumps.

What they found was that for a weighted average of the US population, over a 15-year equipment lifetime, installing electric heat pumps instead of gas furnaces would reduce equivalent carbon dioxide emissions by a bit more than half. That projection assumes current refrigerants and starting out with the current mix of electric generation on the grid. The researchers expected savings to increase in the future as the grid gets cleaner and refrigerants are more climate friendly. The UC researchers also found that the savings would have been greater had there been no heat pump refrigerant leakage, but that leakage only reduced savings for current units by about 10%. As time goes on, that penalty decreases to just a few percentage points. 

Given these findings, the researchers concluded “…policies to expand heat pump deployment will only modestly impact refrigerant emissions from the residential sector, a change that is far outweighed by the significant reductions in carbon dioxide and methane emissions gained by deploying increasing numbers of heat pumps.”

More climate-friendly refrigerants are on the way

The US EPA is currently preparing new regulations that will essentially ban the refrigerant (R-410A) that is currently used in the vast majority of heat pumps and air conditioners sold in the US, and only allow newly manufactured equipment to be charged with a new generation of relatively climate-friendly refrigerants. It’s widely expected that those regulations will be released this summer, that they will only allow refrigerants that exhibit a bit less than about 40% of the climate warming impact of the current standard refrigerant, and that they will go into effect January 1, 2025.

Although the allowed refrigerants will be more climate friendly and efficient than the current standard, most of them are classified as “mildly flammable.” They can be ignited, but not easily. For example, they’re about as flammable as ammonia, which you may be storing under your kitchen sink.

To enable mildly flammable refrigerants to be used safely, industry researchers developed new sensors, controls, and piping techniques, but there’s still a lot of work left to do to incorporate them into standard practice. Designers and installers are being trained to work with this equipment, and the nation’s building codes need to be amended to include standards for the new safety equipment and techniques.

For the last century, virtually all US building codes explicitly outlawed flammable refrigerants inside buildings. In the US, there are thousands of building code jurisdictions, at the state, county, and municipal government level. Amending the codes for all these jurisdictions is a major undertaking. 

Leading the effort is the Air Conditioning, Heating, and Refrigeration Institute, a trade association which represents more than 300 companies. AHRI is advocating both statewide code amendments and state legislation, that empowers building code officials to accept the new slightly flammable refrigerants. According to Helen Walter-Terrinoni, AHRI’s vice-president for regulatory affairs, “Either code amendments or legislation is in place for markets representing one-third of annual sales. We expect to get to two-thirds by the end of next year.” 

Of the remaining code jurisdictions, there could well be some laggards. According to Elizabeth Ortlieb, a director with Alpyne Strategy, “I’ve seen recent reports that say it is unlikely that building codes in all 50 states will accommodate mildly flammable refrigerants by 2025.”

As states and other jurisdictions get ready, manufacturers will follow by shipping products with refrigerants that can meet the new regulations. Daikin, the world’s largest air conditioner and heat pump manufacturer, is already shipping products charged with the new refrigerants to a few states, including Florida, Oregon, and Washington. By late 2024, it’s likely that products from virtually all the major manufacturers will be widely available.

Let’s do the tighten up

In addition to advocating for climate-friendly refrigerants, both environmentalists and industry leaders are looking to prod installers and service people to take a more active role in preventing leaks. As Kristen Taddonio, a senior climate and energy advisor at the Institute for Governance and Sustainable Development, puts it, “What matters is the lifecycle climate performance of the system, including efficiency. If leaks are minimized, and the refrigerant is reclaimed at end-of-life, refrigerant should not contribute much to climate change.” 

By law, contractors are not allowed to intentionally vent refrigerant to the atmosphere and are required to reclaim refrigerant from retired equipment for reuse or destruction. However, far less refrigerant is being reclaimed then should be in theory, so it’s assumed that the missing refrigerant is being released. 

Recovering refrigerant from decommissioned systems is hard and expensive work, and when contractors go to sell what they’ve recovered, they find that it’s not all that valuable. Probably, if the economics were more attractive, more would be recovered. Both the policy makers and environmental advocates that I spoke with called for government action, including paying incentives to contractors to recover refrigerant, as well as more rigorous law enforcement. Furthermore, as more EPA regulations kick in, prices will likely go up, which should also make recovery more profitable. 

It’s getting better all the time

It’s clear that the climate change benefits of greater heat pump utilization far outweigh the impacts of their leaking refrigerants. Furthermore, as regulations come online, and new heat pumps come charged with climate-friendlier refrigerants, the net benefits of installing heat pumps will grow ever greater. In the event governments come up with the right means to motivate greater adherence to refrigerant recovery laws, that will be icing on the cake.

In the meantime, the refrigerant problem isn’t being ignored. To put it into context, according to Project Drawdown, a nonprofit organization that conducts rigorous assessments of climate solutions, the combined benefits of its Refrigerant Management and Alternative Refrigerants solutions are 25 times greater than those of its High Efficiency Heat Pumps solution. 

Given the results of the UC California study, how can that be? Refrigerants are used in many more applications than heat pumps, including transportation, refrigeration, and industrial food processing. There are also plenty of homes out there that incorporate air conditioners but not heat pumps.

While the problem of climate-warming refrigerants isn’t yet solved, we are making progress. The vast majority of refrigeration sectors have either already transitioned to climate-friendlier refrigerants, as the automotive sector has done, or the EPA is well underway developing new regulations that will be released over the course of the next few years. Lastly, this is just the world’s third wave of climate-driven refrigerant re-regulation. It’s unlikely to be the last.

Returning Workers Demanding Safe Indoor Air Are Driving a Revolution in Air Conditioning Systems

By Jay Stein on

Building air conditioning systems aren’t protecting the air we breathe and workers returning to buildings are demanding change. Upgrading those systems without contributing to climate change will take innovative public policies and technologies.

Source: Awair, Inc.

During the fall of 2020, between the second and third waves of the Covid-19 pandemic, the owner of the gym I work out at asked my advice on how to keep her building’s air safe from COVID-19. She asked because my wife had shared with her an article I’d written on upgrading heating, ventilating, and air conditioning (HVAC) systems to reduce airborne virus transmission.

Her quandary involved a proposal from her air conditioning contractor to install an electronic air cleaner. It was more expensive than she could afford, but if it would protect her members’ health and enable her gym to return to full occupancy, she was willing to look for the money.

I found some experts concerned that this system might not be effective or could produce harmful byproducts, so I advised her not to buy it. Instead, I suggested she ask her contractor to upgrade her system’s filters. 

Her contractor refused. She tried another contractor, but he also insisted on the same electronic air cleaner. I told her I’d find her a contractor, but none I contacted were interested in doing that work or set up to do it at a reasonable cost. 

In the end, she decided to focus on bringing in sufficient outdoor air, which she monitored with a handheld carbon dioxide meter. That wasn’t the most energy efficient choice available, but at least didn’t waste money on a questionable technology. 

A few weeks later I got an email newsletter from the proprietor of the restaurant a few blocks from my house, bragging about how he had installed the very same electronic air cleaner and how safe his dining room would now be. 

I drew several conclusions from this experience. Building owners and operators were attempting to upgrade their HVAC systems to mitigate infectious diseases, but didn’t know how in a way that was both effective and didn’t run up their energy bills. Neither did the technicians they relied on. And nobody had the information to determine how well their systems were now performing this task, or how upgrades could improve performance. 

As we anticipate the end of the pandemic and plan to return to buildings en masse, millions of building operators are facing the same HVAC upgrade demands. Doing these upgrades in the most energy efficient way could significantly improve health conditions with little to no increase in energy consumption. Upgrades made in a more typical way could increase HVAC energy consumption 2-5 times, adding to the energy demands that are driving climate change.

New public policies and technology can empower governments and trade associations to enable building operators and technicians to collect and interpret air quality data that informs healthy and energy-efficient solutions. Without a massive campaign on this front, however, building owners and operators may be left with solutions that waste energy, fail to protect building occupants, or both. 

The pandemic as teachable moment

“Before COVID-19, to the best of our knowledge, almost no engineering-based measures to limit community respiratory infection transmission had been employed in public buildings (excluding health care facilities) or transport infrastructure anywhere in the world, despite the frequency of such infections and the large health burden and economic losses they cause.” 

So wrote a group of nearly 40 of the world’s leading indoor air scientists in a recently published manifesto. This “Gang of 40,” as I call them, explained how respiratory infections are spread by tiny liquid droplets exhaled by infected people and circulated throughout building air. Not only have few building HVAC systems been designed to remove them or inactivate their contained viruses, many have been implicated in spreading them.

One culprit for this situation is a lack of indoor air regulations, standards, or guidelines. The U.S. Environmental Protection Agency doesn’t regulate indoor air the way it regulates outdoor air. The country’s most important standards for building ventilation come from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) — and with the exception of health care facilities, those standards don’t take infectious respiratory diseases into account. 

Surveys of workers taken during the pandemic indicate that this lack of standards is a big problem. One survey conducted by building technologies giant Honeywell found that 47% of U.S. executive-level workers believe “outdated ventilation systems” were the “biggest threat” to workplace safety. Concerns like these are bound to drive widespread HVAC system improvements.

The air the air is everywhere

Coronaviruses are not the only threats lurking in indoor air. Others include microscopic particles — known as PM2.5 and PM10 because they are 2.5 or 10 micrometers across or smaller — carbon monoxide, volatile organic compounds like formaldehyde and solvents, ozone, biological materials like mold and dust mites, nitrogen oxides, radon, and pathogens including viruses and bacteria. They come from indoor sources including fumes from combusted natural gas and wood, cleaning supplies, paint, furniture, pets, and our exhaled breath, as well as outdoor pollutants such as wildfire smoke and car exhaust that seep in through open windows and cracks in our buildings — or are brought in with ventilation air. 

Indoor pollutants can cause or exacerbate eye, nose, and throat irritation, headaches, fatigue, asthma and other respiratory diseases, heart disease, cancer, and cognitive impairment. Researchers have also found that high levels of PM2.5 are correlated with higher levels of COVID-19 infection. Any nationwide attempt to upgrade HVAC systems to minimize infectious disease transmission must also deal with these other contaminants as well.

It all starts with standards

When diseases were spread through food and water, governments passed standards for food and water processing, and put a cadre of officials in charge of enforcing them. The Gang of 40 called for a similar system for indoor air quality: “In the 21st century we need to establish the foundations to ensure that the air in our buildings is clean with a significantly reduced pathogen count, contributing to the building occupants’ health, just as we expect for the water coming out of our taps.”

Such an indoor air quality revolution would start with government standards setting limits for key indoor air contaminants, based on building types and uses. But meeting those standards will require monitors to see how buildings and individual spaces are meeting them.

Bring eyesight to the blind

The saying “you can’t manage what you can’t measure” applies here. For centuries, building owners and occupants have lacked information on indoor air quality. A new generation of relatively low-cost air monitors is starting to change that. They measure temperature, humidity, carbon dioxide, PM2.5, and total volatile organic compounds, although not all the available monitors measure all those parameters. Most hook up to some sort of phone app or dashboard and analyze how the levels measured compare to safe ranges — although without national standards, these safe ranges are often based on the manufacturers’ judgement. 

One example is the Awair Element, a smart-speaker-like box which sells for $299. It measures all the parameters listed above and features a rudimentary built-in display, as well as a smartphone app for more detailed information, trending, and analysis.

Last year, a team of scientists from locations as diverse as the Institute for Renewable Energy in Italy and the U.S.-based Lawrence Berkeley National Laboratory tested 8 different monitors under a variety of conditions, and found that the Awair product was the most accurate of the group. Making such measurements in a low-cost device is difficult, and even the Awair product registered errors in the range of 50% to 80% for some parameters and conditions. Still, the scientists concluded that such monitors “could be suitable for measurement-based indoor air quality management.”

Monitors like these could make us all much better informed indoor air consumers. Occupants could know when to open windows or leave when air is unsafe. Building operators could make data-informed decisions about how to adjust HVAC systems, or use smart controls to ramp up airflows to densely occupied rooms while turning down airflows to others. Operators and controls could make comprehensive decisions that both protect our health and minimize energy consumption.

The human factor

This revolution in indoor air quality monitoring will also require building operators skilled in using that data to improve HVAC system operation. It’s vital that they do so in a way that minimizes energy consumption as climate change is also an increasingly dire threat to human health. 

Indeed, numerous scientists have concluded that climate change is also worsening indoor air. Cleaning up indoor air at the expense of increased energy consumption just propels us further down that negative spiral. 

Breaking that cycle is going to take more than access to data. In the words of William Bahnfleth, an architectural engineering professor at Pennsylvania State University, and a leading member of the Gang of 40, “simply dumping data on building occupants or operators won’t be very helpful if they don’t understand it.”

Clearing the air

To understand how building technicians could use data to manage HVAC systems, let’s review the basics. To generalize, there are two kinds of indoor air pollutants: gaseous (like carbon monoxide and formaldehyde) and particles (like soot and viruses). There are also two basic techniques for removing those pollutants: dilute them with outdoor air or blow air through filters. 

Many building operators turn to outdoor air dilution because it’s relatively easy and works on virtually all indoor air contaminants. But it takes a lot of energy to warm up outdoor air in the winter and cool it down in the summer, and it can be downright counterproductive when outdoor air is more contaminated than indoor air — such as in the West during wildfire season.

Filtration is far less energy intensive but can also waste energy and damage fans and other equipment if the filters aren’t properly selected, sized and installed. Also, filtration only works on particles, not gaseous contaminants. 

The most energy-efficient means to manage indoor air quality in most buildings is to bring in just enough clean outdoor air to dilute gaseous pollutants to safe levels, and then remove particles via filtration. Filters are rated according to a metric dubbed Minimum Efficiency Reporting Value, which ranges from 1 to 20 in terms of effectiveness at removing particles. Most commercial building HVAC system filters feature MERV ratings from 6 to 8, but the sweet spot at which human health is effectively protected while consuming a minimal amount of energy is at MERV 13. (see image)

Source: Parham Azimi and Brent Stephens

Caption: This chart from Illinois Tech shows that filtration is a far less expensive and energy intensive means to reduce virus transmission via heating and air conditioning systems than outdoor air dilution. Filters more effective than MERV 13 (on the black line) cost more to deploy, but provide little reduction in virus transmission, while achieving that same level of protection with outdoor air (colored lines) is far more expensive.

What not to do

Electronic air cleaners whose vendors claim they can remove pathogens from airstreams or deactivate them are the subject of much controversy. Some of these devices work by electrically charging particles, like viruses, while others shine ultraviolet light inside ducts. Some were tested by well-respected laboratories and found not to produce the same results claimed by their promoters or were found to release harmful byproducts. Many manufacturers released their own tests that were found lacking by leading indoor air scientists. For example, one manufacturer tested a product intended to clean an entire room by placing it in a small box.

“If you are considering an in-duct air cleaner for your heating and air conditioning system, if you have to plug it in, then it deserves extra scrutiny,” said Dr. Brent Stephens, who runs the Built Environment Research Group at Illinois Tech. With such a profusion of conflicting test results, applying that scrutiny is not easy. It’s probably best to avoid electronic air cleaners until standardized test results are available.

Calls for training are gaining

In my observation, it’s rare that building operators and technicians reconfigure their systems to use MERV 13 or higher filters. But to be fair, upgrading existing HVAC systems to mitigate airborne infectious diseases and other contaminants is challenging, even for experts. According to a team of scientists from Johnson Controls and MIT, “the best course of action can vary significantly from building to building and even within the same building depending on weather conditions or occupant behavior.”

Certainly, smarter HVAC controls and software that analyzes indoor air data would help, but it’s hard to imagine they’d be sufficient. Pennsylvania State University’s Bahnfleth is calling for education and training programs from government agencies and ASHRAE to help disseminate the skills needed to put these technologies to effective use.

Air America

The agenda proposed by the Gang of 40 and others — standards, monitoring, and training — is at its earliest stages. Perhaps, as with past pandemics, when this one ends it will soon be forgotten, leading to few changes in public policy or technology. For those committed to a different outcome, there’s much to be done. Policy wonks can advocate for government action to support all three elements of the agenda. For investors, opportunities lie in the budding air monitoring market and companies with indoor air management expertise. 

As for the rest of us, there aren’t yet any easy answers. We can install air monitors, but what to do with the data is problematic. If our monitors tell us that our readings are out of range we can open our windows — if the outdoor air isn’t clogged with wildfire smoke. If particulates are too high, we can look for an HVAC contractor with the expertise to upgrade our filters to MERV 13. I wish I had a better answer for you, but this is a major problem and it’s going to take time to work out.

This article was originally published as How To Fight Both Indoor Air Pollution and Climate Change at the Same Time on Energy Central.

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