Wednesday, March 15, 2023

"Everything you need to know about the wild world of heat pumps" is nowhere near everything you need to know about heat pumps


I had such high hopes for this MIT Technology Review article by Casey Crownhart . Finally, someone was talking about an important, ready-to-go technology for addressing climate change and the power grid. Unfortunately, other than a handy introductory explanation of how heat pumps work, we get the same old narratives, biased - - biased in favor of a technology I actually have been pushing, but biased nonetheless - - with all the same old bad habits, getting key details wrong, using questionable examples, making big logical leaps, omitting important problems, and ignoring the most promising aspects of the technology.

The claim that heat pumps don’t work well in really cold weather is often repeated by fossil-fuel companies, which have a competing product to sell.

There’s a kernel of truth here—heat pumps can be less efficient in extreme cold. As the temperature difference between inside and outside increases, a heat pump will have to work harder to gather heat from that outside air and disperse it into the room, so efficiencies drop.


There are heat pumps running everywhere from Alaska to Maine in the US. And about 60% of buildings in Norway are heated with heat pumps [Norway is an interesting case but a bad example. It has abundant electricity almost all of which comes from hydro which plays by a very different set of rules with respect to the power grid. -- MP], along with 40% in Sweden and Finland. [Sweden and Finland rely heavily on ground-source heat pumps, but we'll get back to that -- MP]

That first link points to a quite good Washington Post article by Anna Phillips on the increasing popularity of heat pumps in Maine, which is caused less by their advantages in winter (as the MIT piece implies) and more by the need for summer AC in New England due to climate change. Phillips also doesn't assume an argument can be ignored just because it comes from someone associated with the gas industry. 

Again from the WP:

The Maine Energy Marketers Association raised questions about heat pumps’ viability by suggesting they would tax the region’s electric grid. In 2021, ISO New England, the state’s power grid operator, warned of rolling blackouts because of supply chain issues affecting natural gas. Yet the trade group’s president blamed the situation on the state’s promotion of heat pumps.

“Our power grid is not equipped to handle the demand that is now being put on it,” Charles Summers said in a radio interview. Summers said he and his fellow industry group leaders in New England had sent letters to their governors “asking that states pushing so hard toward electrification, pushing complete conversion to heat pumps, just tap the brakes for a few minutes.”

 Strain on the power grid is the main devil in the details of electrification, whether you're talking about heat pumps or EVs, but it receives disturbingly little attention from journalists and commentators. Here is the only mention of the grid in the MIT piece.

 Heat pumps run using electricity from the grid. While fossil-fuel plants still help power grids around the world, renewables and low-carbon power sources also contribute. So with the current energy mix in all major markets, heat pumps are better for the climate than directly fossil-fuel-powered heating, Monschauer says.
[It's a bit a a digression from our primary point but ramping up immediate demand for electricity will almost inevitably shift the generation mix toward natural gas, particularly in situations where solar isn't much of an option such as winter in New England.]

 One of the main disadvantages of using electricity instead of something like natural gas or oil to heat or cool a house is that the power grid is far more affected by spikes. If everyone gets home at 5:45 On a winter's day and turns on their heat pump, or if everyone cranks up the AC on a hot Saturday afternoon, the results can be disastrous for the power grid, ranging from brownouts all the way to cascading power failures. By the same token, if everyone decides to conserve at the same time it really doesn't do a lot of good with electricity compared to something like heating oil.

Particularly with heat pumps, this problem can be a double whammy. A massive cold front/heat wave will cause a huge increase in people turning on the heat while at the same time making heat pumps far less efficient. We've already seen something like this in summer since the vast majority of air conditioners run on electricity. The existing infrastructure simply couldn't handle it if everyone currently heating with gas or oil suddenly went over solely to electricity.


What if there was a way that you could get everyone to use their heat pump only when it was somewhere between 50 to 60° outside? 

From the Department of Energy:

Geothermal heat pumps (GHPs), sometimes referred to as GeoExchange, earth-coupled, ground-source, or water-source heat pumps, have been in use since the late 1940s. They use the relatively constant temperature of the earth as the exchange medium instead of the outside air temperature.

Although many parts of the country experience seasonal temperature extremes -- from scorching heat in the summer to sub-zero cold in the winter—a few feet below the earth's surface the ground remains at a relatively constant temperature. Depending on latitude, ground temperatures range from 45°F (7°C) to 75°F (21°C). Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. The GHP takes advantage of these more favorable temperatures to become high efficient by exchanging heat with the earth through a ground heat exchanger.

As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, and, if so equipped, supply the house with hot water. Some models of geothermal systems are available with two-speed compressors and variable fans for more comfort and energy savings. Relative to air-source heat pumps, they are quieter, last longer, need little maintenance, and do not depend on the temperature of the outside air.

And from Wikipedia:

The US Environmental Protection Agency (EPA) has called ground source heat pumps the most energy-efficient, environmentally clean, and cost-effective space conditioning systems available. Heat pumps offer significant emission reductions potential, particularly where they are used for both heating and cooling and where the electricity is produced from renewable resources.

By comparison, here's the entire discussion of ground-source heat pumps from the MIT piece.

There’s already a wide range of heat pumps available today. About 85% of those installed are air-source heat pumps like the one I’ve described. These come in a wide range of shapes and sizes. But other models—so-called ground-source or geothermal heat pumps—gather heat from underground instead of collecting it from the air.
Just to summarize, the technology with the most promise for reducing the climate change impact of heating and cooling only gets one sentence while the biggest challenge we have to address doesn't even get mentioned. This is more or less what we've come to expect from coverage of global warming stories, which given the magnitude of the problem, isn't acceptable at all.


  1. I wrote about this topic for the Madison (NY) Eagle weekly newspaper.

    1. That is Madison _New_Jersey_. Tangled fingers ...