How Does A Heat Pump Work?

Popular in Europe and Asia, heat pumps are incredibly efficient systems used for heating and cooling homes and are becoming increasingly more popular in the U.S. They use minimal energy to transfer heat between two locations and work much like refrigerators. The simple systems are comprised of one or multiple discrete indoor units connected to an outdoor condenser unit. Outdoor units utilize either water or air sources along with a compressed refrigerant to draw hot or cold air into a home.

Heat Pump Efficiency

Heat pumps can cut energy bills by 40%, transferring heat from one space to another rather than burning fossil fuels to create heat. Traditionally, heat pumps have been a great option for moderate-climate living, but new technology is creating options for extreme weather climates where air-air heat pumps are not effective.

Advances in heat pumps are improving the system’s performance even more. Two-speed compressors enable heat pumps to work close to heating or cooling capacity, cutting energy expenditure. Dual-speed motors minimize drafts by regulating airflow while the most efficient heat pumps use a desuperheater to heat water 2-3 times more efficiently than conventional water heaters. The addition works by recovering waste heat from the pump’s cooling process.

Air-Air Heat Pump

Air-air heat pumps function most effectively in moderate climates. In air-air heat pumps (sometimes called air-source heat pumps) the two-way pump captures hot air from outside your home and releases it through an inside unit, reversing the process to cool indoor spaces. How does it work, exactly?

Heat pumps transfer heat energy between indoors and outdoors. A fan pushes air over copper tubes filled with a refrigerant (like the one on your refrigerator) that absorbs the heat. The liquid is compressed in one copper tube, forcing it to expel the captured heat. The heat is moved either indoors or out, heating or cooling the home. After compression, the refrigerant is depressurized (cooled) in another coil and channeled to the space (either inside or outside) where heat is being collected. In cold winter months, the refrigerant absorbs warm air from outside the home, releasing it inside. During warm months, the heat inside a home is absorbed by the refrigerant and released outside, leaving only cool air inside.

Air-air heat pumps do more than transfer heat. Conventional air conditioners actually act as dehumidifiers, sucking heat-trapping moisture from a home’s air, removing the stickiness of a hot day and cooling indoor spaces even more. Heat pumps do the same and high-efficiency heat pumps actually remove humidity more effectively than conventional duct and window systems, meaning they use less energy and cool more productively.

Absorption Heat Pump

Absorption heat pumps are an exception to the “no fossil fuels” rule. They are technically a version of air-air or air-source heat pumps, but absorption heat pumps are powered by propane, natural gas, or water heated by geothermal or solar power. The refrigerant, in this case, is ammonia water. Like in air-source heat pumps, the refrigerant is compressed in one copper coil, forcing it to release absorbed heat. After heat is released, the ammonia is evaporated off using a heat source that boils the water, and the cycle repeats. Absorption heat pumps are most commonly found in commercial spaces, though scaled systems for the home are increasing in popularity.

Geothermal (Ground-Source) Heat Pumps

Among the most energy efficient methods of heating, geothermal systems take advantage of the Earth’s natural cycles. Around four to six feet below the Earth’s surface, temperatures remain at a near-constant. Like air-air heat pumps, geothermal systems are comprised of two main parts, in this case, the heat pump and the ground loop. Geothermal heat pumps use either a closed-loop or open-loop system to transfer heat between your home and either air or water that is trapped below ground. In a closed-loop system, pipes carrying water or a heat-absorbing refrigerant cycle through pipes without leaving. In an open-loop system, heat captured from water is pumped from an exterior source such as a man-made pond or well. The water is cycled back into the source and the process repeats.

If you decide a hyper-efficient geothermal system is the best fit for you, a contractor will recommend which configuration works best for your home and lot. For lots of limited space, a Vertical-loop is designed with heat transfer tubes buried vertically in the ground. If you have the space, the heat transfer pipes in a Horizontal-loop system are buried shallow, extending horizontally at a grade rather than vertically. Geothermal systems are an ideal solution for extreme weather climates, but be ready to get that checkbook out. The lure of low operating costs must be a factor when considering the system’s high installation costs.

Reverse Cycle Chiller

Reverse cycle chiller heat pumps generate hot or cold water instead of air and are designed to work with existing radiant floor or forced-air heating systems. Reverse cycle chillers are another great option for climates that hover below freezing, all-electric homes, or homes in areas where natural gas is not an option. In reverse cycle chillers, an insulated tank of water is heated and cooled. Refrigerant coils capture the energy stored in water instead of air to heat or cool a home. Reverse cycle chillers are significantly less costly than geothermal systems and have a desuperheater coil option to allow it to replace an air conditioner as well as a furnace.

Single-Zone (Single-Head) Solutions

Single-zone systems connect one indoor unit to one outdoor condenser unit and are designed for a single room. Single-zone systems are great for home additions, where extending ductwork is costly and cumbersome, or in rooms where inconsistent heating and cooling is an issue.

Multi-Zone (Multi-Head) Solutions

Single-zone solutions are easily converted to multi-zone with the addition of one or more indoor units that all connect to a single outdoor unit. The multi-unit system works in the same way that single-zone systems do, using a refrigerant and copper compression coils. Each unit customizes the temperature in its individual space (kitchen, hallway, attic, etc.) Multi-zone systems are ideal for older homes with no room for ductwork, ENERGY STAR new construction homes and home additions, and existing homes where inconsistent heating and cooling is an issue.