How do Heat Pumps Work?

In the US, central air conditioning is a popular form of temperature regulation in a home. Still, if you live in one of the many states that experience four seasons, a heat pump might be a better way to keep the air in your home warm or cool, depending on the time of year. A heat pump extracts heat from a low-temperature source and delivers it to a high-temperature place. The technology is relatively common and is used in various appliances in your home, like the refrigerator or air conditioning unit. Let’s learn a bit more about how an air-source heat pump works.


Components of a Heat Pump

Unlike a ground-source heat pump that uses heat from the ground, an air-source heat pump looks very similar to a central air conditioning unit and works much the same way. The system contains two main components – an outdoor unit and an indoor unit – each with several subparts:

Outdoor Unit
The outdoor unit contains a coil and a fan. The coil operates as a condenser or an evaporator, depending on which mode the heat pump is running in. The fan blows outside air over the coil to facilitate the heat exchange.

Indoor Unit
The indoor unit, commonly referred to as the air handler unit, is like the outdoor unit in that it contains a coil and a fan. The coil operates as a condenser or an evaporator, depending on which mode the heat pump is operating in. The fan moves air across the coil and through the ducts in the home.

Refrigerant is the substance that absorbs and rejects heat as it circulates through the heat pump system.

The compressor pressurizes the refrigerant and moves it through the heat pump system.

Reversing Valve
The reversing valve reverses the flow of the refrigerant, allowing the heat pump system to switch between heating and cooling.

Expansion Valve
The expansion valve acts as a metering device, regulating the flow and temperature of the refrigerant as it passes through the heat pump system.


How an Air-Source Heat Pump Works

One misconception many people hold about heat pumps is that they create heat. This is not the case. Rather, they redistribute heat from the air (or ground in the case of a ground-source heat pump) and use the refrigerant circulating between the indoor and outdoor units to transfer heat.

A heat pump can operate in one of two modes. In heating mode, the outdoor unit absorbs heat from the outside air and releases it indoors to heat your home. In cooling mode, the indoor unit absorbs heat from inside the home and releases it outdoors to cool your home. This is how the heat pump system works when it is operating in cooling mode:

  1. Liquid refrigerant is pumped through the expansion valve in the indoor coil, which acts as the evaporator. Air from inside the house is blown across the coils, where the refrigerant absorbs heat energy. The cool air is then blown through the ductwork in the home.

  2. The gaseous refrigerant then passes through the compressor, which pressurizes the gas and causes it to heat up. The pressurized refrigerant then moves through the heat pump system to the coil in the outdoor unit.

  3. A fan in the outdoor unit moves outside air across the coils, which are serving as condenser coils in cooling mode. Since the outside air is cooler than the gas refrigerant, heat is transferred from the refrigerant to the outside air. The refrigerant condenses back to a liquid as it cools and is pumped through the system to the expansion valve in the indoor unit.

  4. The expansion valve reduces the pressure of the liquid refrigerant, which significantly cools it. It is then ready to be pumped back to the evaporator coil in the indoor unit and restart the cycle.

As you can see, a heat pump operates similarly to a central air conditioning unit. However, unlike central air conditioning, a heat pump system can also operate in heating mode, making it a great option for homes during cooler months. When working in heating mode, the cycle is the same, except that the flow of refrigerant is reversed using the reversing valve. Then the heating source becomes the outside air (even when the temperature of the air is very low), the outside coil functions as an evaporator, and the indoor coil functions as a condenser. As a result, warm air is released throughout your home.

If you are interested in a heat pump system, get in touch with the experts at Napoleon to get the best recommendations for your home.