Decarbonization for non-engineers: how heat pumps work
Electrifying heating and cooling systems to decarbonize a building by installing heat pumps is a common and effective approach. This article explains how heat pumps work, without any engineering jargon.
One of the most common recommendations for building decarbonization is to electrify heating and cooling systems. Electrifying these systems shifts the heating and cooling load for a building from burning fossil fuels to electricity, which can be generated by renewable and clean sources. One way to do this is by installing heat pumps.
For a non-engineer such as myself, explanations of heat pumps can get overcomplicated and overwhelming pretty quickly. This article breaks down the most common types of heat pumps, how they work, and when they may be a good choice for a building.
What are the most common types of heat pumps?
Heat pumps provide both heating and cooling by transferring heat. In the winter, they extract heat from sources like water, air, or the ground and use refrigerant to transfer it to indoor spaces or water. The process is then reversed to offer cooling in warmer weather.
Air-source heat pumps (ASHPs) are designed for both heating and cooling. In winter, they draw heat from the outside air to warm interiors, and in summer, they transfer indoor heat outdoors.
Standard ASHPs perform optimally above 25°F, but their efficiency diminishes in colder conditions. To address this, cold-climate heat pumps are engineered to operate effectively at much lower temperatures, some even below an outside air temperature of 0°F.
An ASHP includes an outdoor unit and an indoor unit connected by piping that carries refrigerant for heat exchange.
Figure 1. — This illustration shows how air-source heat pumps work on a fundamental level.
Ground-source heat pumps (GSHPs) (a.k.a. geothermal) transfer heat from the ground to warm interiors in the winter and move heat from the indoors back into the ground in the summer to cool spaces. Because they use the earth’s stable underground temperatures, GSHPs provide reliable heating and cooling throughout the year, even in cold climates. While their initial installation costs may be high, GSHPs typically offer lower long-term operating expenses due to fewer components requiring replacement.
A typical GSHP system consists of a heat pump connected to a ground loop heat exchanger, making them an excellent choice for both individual buildings and district energy systems.
Figure 2. — This illustration shows how ground-source heat pumps work on a fundamental level.
Other important considerations
Variable refrigerant flow
If individual rooms or zones of a building have different heating and cooling needs, variable refrigerant flow (VRF) heat pumps can be helpful technology to add to a ground- or air-sourced heat pump. An example of when this may be helpful is when one zone of a building needs cooling, such as a space holding supercomputers, while the rest of the building needs to be heated. VRF heat pumps can simultaneously heat and cool rooms within a building, keeping all areas at a comfortable temperature for occupants.
Distribution systems
While “air-source” and “ground-source” refer to the source of the heat a heat pump transfers, heat pumps also have indoor components that distribute the heat around the building. Many times this choice depends on the system of heat distribution already in a building. For example, a building where heat is distributed using ductwork may use an air-to-air heat system whereas a building with radiators using hot water to circulate heat may use an air-to-water system. This can simplify the process of electrifying the heating system.
Refrigerants
Refrigerants commonly used in the past, like R-32 and R-410A, possess a relatively high global warming potential (GWP) and are currently being phased out worldwide. Manufacturers and system designers are shifting towards refrigerants with significantly lower GWP. Choosing heat pumps with lower GWP refrigerants contributes to climate objectives, ensures adherence to future regulatory requirements, and reduces the likelihood of equipment replacement due to refrigerant obsolescence.
Efficiency and the cost of electricity
Although the cost of electricity per unit of energy is typically higher than that of natural gas, modern electric HVAC technologies are significantly more efficient than natural gas-fueled equipment. The efficiency of a technology can be measured by calculating the ratio of heat produced to one unit of power consumed. This ratio is called a “coefficient of performance” (COP).
Standard natural gas furnaces have a COP of 0.8–0.9, since they lose energy as exhaust. Electric resistance heaters have a COP of 1.0, or 100% efficiency, which while more efficient than natural gas, is not enough of an improvement to compensate for the higher cost of electricity. Modern electric heat pumps; however, boast a COP of 3.0 or higher. They achieve this by transferring existing heat rather than generating it, and use minimal electricity to power the compressor and fans. This allows them to deliver significantly more energy than they consume, leading to substantial energy savings.
Putting in a heat pump system, or any decarbonization solution, is a decision with factors that differ from building to building. GreenerU is here to be your decarbonization partner, so please reach out to us with any questions you have!
Recent Articles
GreenerU is thrilled to announce that our heat recovery project, in partnership with Elevated Design, Inc., for the Roxbury Tenants of Harvard's Levinson Tower won the Building Decarb Intervention category of the 2025 BE+ Green Building Showcase awards!
More
Using “waste heat,” or heat generated from various campus processes that is usually lost to the environment, as a source of energy is a bit like finding a twenty dollar bill in your pocket that you forgot was there: it’s a resource you’ve always had. You just need to capture it to use it.
More
As much as we don’t want to admit it, failure does happen. Whether equipment failure comes as a surprise or as a predictable result of age, having a plan can make or break the long-term success of your response.
More