Heating & Cooling with Heat Pumps

September 23, 2020

Welcome to our third article in this Climate Change Week series. Today, we take a look at how to reduce our impact related to heating and cooling our buildings, focusing on one specific kind of technology: heat pumps.

Heating our homes takes an enormous amount of energy—it’s by far the largest energy use in our homes. And most of us heat by burning some sort of fossil fuel, in either a furnace (blows hot air around) or boiler (moves hot water around).

It’s surprising to some people that there’s a not-inconsequential fire burning in most homes’ basements. In addition to the greenhouse gas issues related to that combustion, there are two other serious concerns.

The first is leaks, especially with natural gas. Made up mostly of methane, natural gas is a very light gas that has a propensity to leak through gaskets and other joints along the entire supply chain up to and including in your home. Natural gas has no odor, so utilities add sulfur-based compounds called thiols, which smell like rotten eggs. But you won’t likely smell anything if the leak is very small. While these leaks are usually minute and don’t present a serious risk in terms of fires or explosions, they’re very common. So, if you add them all up, they become significant. And that’s very troubling because on a 20-year timescale, methane is about 85 times more potent a greenhouse gas than carbon dioxide.

The other concern is incomplete combustion. If your heating system (this also goes for cooking and water heating with fossil fuels) isn’t efficiently burning the fuel, it will release dangerous gases. The main one to be concerned with, because it’s the most common, is carbon monoxide, or CO. Also odorless, high levels of CO in your home can be deadly—more than 400 people die from CO poisoning in the U.S. every year. It can also be debilitating, with symptoms mimicking the common cold, including headache, dizziness, weakness, and upset stomach—CO poisoning sends more than 20,000 people to emergency rooms in this country every year (not including those linked to fires or explosions).

So, always be sure to have all your heating equipment regularly maintained and make sure you have working CO detectors throughout your home.

Or, better yet, cut that gas line altogether. There are lots of options for space heating without fossil fuels (gas, oil, or propane), including wood and pellet stoves, which can play a great role (though they come with CO risks, as well, since you’re still burning something). But it’s hard to beat heat pumps on safety, convenience, and environmental points.

Before we talk about the heat pumps, though, we need to talk about your heat load. That’s essentially how much heat your home will require to keep you comfortable in winter. If your home is very drafty and not well insulated, it will take a lot more heat to keep you at a comfortable 68 degrees than if you had a well-insulated and air-sealed home. So, first, always take a look at your home’s performance and do as much as you can to increase it. Energy audits are still free for any NY State resident, and are a great place to start (contact us, info below, or Get Your GreenBack Tompkins, for more information).

Now that your home is nice and comfy, we can talk about heating it. Heat pumps have been around for a long time—your refrigerator is a heat pump that pulls heat out of the inside of the refrigerator and dumps it in the room. And because heat pumps basically move heat from one place to another, rather than heating air or water by burning a fuel or putting enough electricity into the system to make wires hot, they are super-efficient. You may be aware of your gas furnace’s efficiency rating, and it may be as high as the mid-to-high 90s for a really good one (most older ones are closer to the 60-70% range, or worse); heat pumps can be as much as 500% efficient.

How’s that possible!? A heat pump is essentially made up of a compressor, condenser, expansion valve, and evaporator. As the refrigerant moves through each of these, it gives off heat (at the condenser) or takes in heat (at the evaporator). Because you’re simply compressing the refrigerant and moving it around it results in super high efficiencies of energy in (electricity to run the components) vs. energy out (heat).

So, while these systems can be expensive, they can save you a lot of money over time. According to the Northeast Energy Efficiency Partnership, the annual savings when using an air-source heat pump are around 3,000 kWh (or $459) when compared to electric resistance heaters, and 6,200 kWh (or $948) when compared to oil systems (at $0.153/kWh). Savings are even more for propane, and less for natural gas.

There are basically two kinds of heat pumps used for space heating (and cooling): air-source and ground-source, or geothermal, heat pumps. As their names imply, heat pumps work by moving heat from one space (inside your home) to or from either the air, in the case of air-source heat pumps (ASHP), or the ground, in the case of ground-source heat pumps (GSHP). For example, in winter, heat pumps move heat from outside to inside your home, and the process can be reversed in the summer to pull heat from inside your home and dump it outside, thus providing air conditioning!

How do you get any heat from outside in the middle of winter? With GSHPs it’s not as hard, since the ground temperature stays a constant 55 degrees or so, and the heat pump system circulates water (coolant, actually) through pipes laid in the ground (either horizontally about 6’ down or vertically in wells). So, in winter, starting with 55-degree coolant, it’s not terribly difficult to raise that to well over 100 degrees in the heat pump unit, and that heat can be transferred to either water or air and distributed throughout your home, in most cases via your existing distribution system.

But pulling heat out of our winter air? It’s not easy, but it is doable, and it does work very well even in our area. For a long time the technology just wasn’t able to do that when temperatures dropped below about 40 degrees—not very helpful in our area. But over the past 15 years or so things have improved to the point that many ASHPs continue to provide hot air in your home even when the outside temperature is in the negative double-digits. Because they’re often starting with much colder air, ASHPs aren’t quite as efficient as GSHPs, though they can still be 250-300% efficient. They also are cheaper to install, mainly because they don’t require the trenching or well-digging needed for GSHP systems.

ASHPs come in two main types, mini-split (also called “ductless”) and ducted (there are also air-to-water ASHP systems, though they are not yet as common in the U.S.). Split systems have an outside compressor/condenser unit and inside air-handling unit, often called a “head”, while ducted systems use your existing ductwork to distribute the heat (or cold air, in summer).

A form of heat pumps is also available to heat domestic water—what comes out of your faucets and shower. Called simply air-source or ground-source heat pump water heaters, or HPWHs, they heat water the same way they heat air (ground-source systems typically are built into a larger GSHP that’s providing space heating, while air-source HPWHs can be stand-alone units). They’re similarly super-efficient. The main consideration when thinking about installing one is that unlike their space-heating cousins, air-source HPWHs are installed indoors, which means they pull heat from the room they’re in to give it to the water. This is fine in a basement, where they’re ideal, but not great in a living space, where they can drop the temperature of the room in the wintertime by a few degrees (though that can be a good thing in the summertime).

All of these systems can be expensive. Again, they’re most cost-effective if you’re off-setting oil, propane, or electricity that’s feeding an appliance that’s using simple resistance heating (typically, baseboard or space heaters). And there are incentives available to help off-set the upfront cost. These have moved away from NYSERDA and are now administered by the major utilities. A homeowner in the NYSEG territory installing a typical GSHP system can get incentives of $7200 ($1500/10,000 BTUH of heating capacity, assuming a commonly cited reference size for single-family homes in NYS). There are also incentives for ASHPs ($1000/10,000 BTUH for a system serving the full home’s heat load) and for air-source and ground-source HPWHs ($700 and $900/unit, respectively). And there are additional incentives for qualified installers, which can go a long way to defraying the cost and hassle of their applying for the incentives on the homeowner’s behalf.

In our area, and many areas across the state, HeatSmart campaigns have been running for the past few years (the first one was right here in Tompkins County). These community group-led campaigns bring together vetted installers and community educators into a program that offers presentations about heat pumps along with discounts for signing up through the program. As I write this, the latest HeatSmart Tompkins campaign recently kicked off. We urge you to check them out at www.heatsmarttompkins.org, where, in addition to information about the campaign, you’ll find lots of great information about heat pumps, as well as testimonials and case studies.

One final thing that needs to be said about heat pumps is to acknowledge the issue of refrigerants. Refrigerants are essential to how heat pumps work, and they come at a high environmental cost. You may have heard about CFCs, or chlorofluorocarbons, which were phased out through the historic Montreal Protocol because they were responsible for causing holes in the earth’s ozone layer. They were mostly replaced by a class of chemicals called HFCs, or hydrofluorocarbons. These don’t damage the ozone layer, but they are very potent greenhouse gases, with some having as much as 9000 times the greenhouse gas potential of CO2.

The refrigerants don’t cause any harm to the atmosphere if they’re properly sealed inside a heat pump or refrigerator. But leaks can occur during installation and the life of the appliance. Even small leaks can have a big impact on emissions. And if the appliance isn’t properly scrapped, with the refrigerants recovered, at the end of its useful life, those refrigerants can leak out in large quantities then. Project Drawdown, the research group that’s ranked the top eighty-or-so actions that need to be taken to effectively reduce the amount of carbon in the atmosphere (and thus address climate change), ranks refrigerant management as fourth highest of the most effective strategies.

There are alternatives, and there’s currently an international agreement to phase out HFCs for more benign refrigerants. CO2 itself can be used as a refrigerant in many cases. But every refrigerant has its own unique properties and applications where they excel and manufacturers are struggling to incorporate CO2 and other more benign refrigerants into their appliances. So, at least for the next few years, you’re likely to get a heat pump that uses a refrigerant with a greenhouse gas potential hundreds or even thousands of times that of CO2.

Massively expanding the use of heat pumps could, therefore, result in an increase in greenhouse gases into the atmosphere. But heat pumps still represent a small fraction of equipment using refrigerants (think of every commercial air conditioner and cooler/freezer in all the grocery stores). And as long as installers are careful during installation and in recovering the refrigerants from equipment that’s being taken off-line, the benefits of using heat pumps far outweigh the harm they may cause.

For more information about heat pumps, contact Guillermo Metz, Energy & Climate Change Team Leader at gm52@cornell.edu or 607-272-2292, x185.

Last updated September 23, 2020