Innovative thinking has done away with problems that have long dogged electric heat pumps — and both scientists and environmentalists are excited about the possibilities
Russia’s invasion of Ukraine and the subsequent energy crisis has been one of the most significant events in awakening the world to the necessity of ending its reliance on fossil fuels and moving to renewable resources of energy.
Several recent innovations aim to make a 200-year-old technology more efficient and attractive for adoption worldwide. The technology is heat pumps. More prevalent in the U.S. than overseas, heat pumps make up only 10% of heating requirements worldwide, and yet it is one of the most eco-friendly forms of heating and cooling a home.
Several recent innovations aim to make heat pump technology even more efficient than it already is, potentially opening the door for greater adoption.
Where Heat Pumps Got Their Start
Heat pump technology is much older than you'd imagine. Lord Kelvin, a British mathematician, physicist, and engineer, first proposed using heat pump systems in 1852 in a mineral extraction process. After two years of experimenting and building, the first heat pump was designed and employed for industrial use. This version worked by heating brine in order to extract salt from fluid. As energy crises occurred in the 1950s and 1970s, heat pumps grew in popularity as an alternative to fossil fuels – which is where the world finds itself again today.
How Do Heat Pumps Work
Put succinctly, heat pumps are electrical devices that move heat from the outdoors into people’s homes. When there isn’t much heat in the air, they come with heating coils that compensate for the diminished heat sources.
As the theory of heat pumps goes, if you can seize heat, you can use it. Heat pumps capture the heat outside the home and transfer it to radiators or forced-air heating. Inside of the heat pump, refrigerant flows around the system and when it encounters heat it absorbs it. A compressor then forces the refrigerant to a higher pressure, which raises the temperature to the point where it can heat your house. The increased pressure pushes the refrigerant molecules closer together, increasing their motion. The refrigerant later expands, cooling as it does, and the cycle repeats.
This cycle works in reverse in the summer, allowing heat pumps to provide cooling.
The cool (no pun intended) thing about heat pumps, and what makes them more efficient, is that they can move multiple kilowatt-hours of heat for each kWh of electricity they use. Heat pump efficiencies are measured in terms of their “coefficient of performance” (COP). A COP of 3, for example, means 1kWh of power yields 3 kWh of heat. That’s a 300% efficiency. The amount of COP depends on a variety of factors such as the strength of your heat pump and the outside temperature.
So Why Aren’t Heat Pumps More Popular?
Much more efficient than gas heaters, standard heat pumps are prone to icing up. This can make for very cold evenings as homeowners wait for their units to thaw in the following day’s daytime temperatures.
Heat pumps are also significantly more expensive than gas heating units, and because natural gas prices have remained low for decades, the incentive to change hasn’t existed.
Many who live in colder climates have also perceived heat pumps as inadequate in producing enough heat to keep their homes comfortable. Homeowners who live in drafty older homes believe gas boilers a safer bet as they can supply hotter water (140-160 degrees F) to radiators. Heat pumps tend to be most efficient when heating water to 100 degrees F.
Modern-day heat pumps make these arguments obsolete. There are multiple devices on the market that work well even when outside temperatures drop as low as negative 10 degrees F. One of the world leaders in heat pump use is Norway, where many homeowners use heat pumps with a gas furnace as backup. This reduces reliance on fossil fuels tremendously.
Innovations in heat pump design are producing units that are more efficient, better suited to houses with less insulation, and (once microchip and distribution issues are solved following the pandemic) less expensive.
What’s on the Horizon with Heat Pumps
Zhibin Yu at the University of Glasgow thinks he has a solution to the problem of heat pumps icing up. He and his colleagues have built a working heat pump prototype heat pump that stores leftover heat in a small water tank which helps the heat pump use less energy. The unit separately reroutes some of this residual warmth to parts of the heat pump that are exposed to cold air, allowing it to defrost itself without disrupting the heat supply to the house.
This system could help improve a unit’s COP by between 3 and 10 percent, while costing less than existing designs with comparable functionality.
Rick Greenough, an energy systems engineer in the UK, is experimenting with storing heat in the ground during warmer months where it can be used by a heat pump when the weather turns cool. A circulating fluid transfers excess heat from solar hot-water panels into shallow boreholes in the soil, raising the soil temperature to a rough maximum of 66 degrees F. In winter, the heat pump can draw on that stored heat to run more efficiently when the temperatures drop.
A third option on the horizon is called a high-temperature heat pump, expected to debut this year. These heat pumps use CO2 as a refrigerant. In the heating and cooling cycle, these units use a water tank where a layer of cooler water rests underneath hotter water. The lower, cooler layer adjusts the temperature of the coolant as needed and can send the hotter water at the top to radiators at temperatures as high as 185 degrees F.
This device has been tested in Holland and the results are encouraging. Twenty homeowners tested the units for several years, and in June 2022 were given the option of taking back their gas boilers. All stayed with the heat pump as they found it less costly and more efficient.
Neighborhood Heat Pumps
Where home-by-home installations are costly, researchers are looking at developing large systems that serve entire neighborhoods called district systems. These can draw warmth from nearby rivers or sea inlets (which can hold temperatures that are higher than the air) and via a long pipe, use it to heat the refrigerant. The hot refrigerant passes its heat to water in the district heating loop which is then piped into individual homes.