Heat pumps are essential components of residential heating and cooling systems. They are installed outside the home and function similarly to air conditioners by cooling the living space. However, heat pumps offer an additional feature—they can also provide heat. These heat pump systems extract heat from the outdoor air during colder months and transfer it indoors. Conversely, they remove heat from indoor air in warmer months to cool the home. Heat pumps use electricity and rely on refrigerant to transfer heat, ensuring year-round comfort. Their dual functionality eliminates the need for separate heating systems, making them a convenient option for homeowners. Additionally, heat pumps are environmentally friendly as they do not burn fossil fuels like traditional furnaces.
There are two primary types of heat pumps: air-source and ground-source. Air-source heat pumps are more commonly used in residential settings as they transfer heat between indoor and outdoor air. Ground-source heat pumps, also known as geothermal heat pumps, transfer heat between indoor air and the ground. While ground-source heat pumps have higher installation costs, they tend to be more efficient and have lower operating expenses due to the consistent ground temperature throughout the year.
How does heat pump work？
Heat pumps work by transferring heat from one location to another using various air or heat sources. Air-source heat pumps move heat between indoor and outdoor air, while ground-source heat pumps transfer heat between indoor air and the ground. Although the focus will be on air-source heat pumps, the basic principles remain the same for both types.
Contrary to their name, heat pumps do not generate heat. Instead, they absorb heat energy from the outside air, even in cold temperatures, and transfer it to the indoor air. In cooling mode, a heat pump operates similarly to an air conditioner, absorbing heat from the indoor air and releasing it through the outdoor unit. When choosing the right system for your home, factors such as home size and local climate should be considered. Consulting a local HVAC expert, like those from Carrier, can provide valuable insights and help you make an informed decision.
Heat pumps are more commonly used in mild climates where temperatures rarely drop below freezing. In colder regions, they can be combined with furnaces to provide energy-efficient heating, except on the coldest days. This combination, known as a dual fuel system, maximizes energy efficiency and cost-effectiveness.
A typical air source heat pump system consists of two major components: an outdoor unit and an indoor air handler unit. The outdoor unit resembles the outdoor unit of a split-system air conditioning system and contains a coil and a fan. The coil functions as either a condenser or an evaporator, depending on the mode (cooling or heating). The fan blows outside air across the coil to facilitate the heat exchange. Similarly, the indoor unit, known as the air handler unit, consists of a coil and a fan. The coil acts as an evaporator or a condenser, and the fan distributes the conditioned air throughout the home. The refrigerant, a vital component of the heat pump system, absorbs and releases heat as it circulates through the system. Other crucial elements include the compressor, which pressurizes the refrigerant and moves it throughout the system, and the reversing valve that changes the refrigerant flow direction to switch between heating and cooling modes. And the expansion valve, which regulates the refrigerant flow, reducing pressure and temperature.
Heat pumps cool or heat by redistributing heat from the air or ground. A refrigerant circulates between the indoor air handler unit and the outdoor compressor, facilitating heat transfer. In cooling mode, the heat pump absorbs heat from inside the home and releases it outside. In heating mode, the heat pump absorbs heat from the outdoor air or ground, even in cold temperatures, and releases it indoors.
Understanding the principles of heat transfer is crucial to comprehend how heat pumps work. Heat energy naturally moves to areas with lower temperatures and less pressure. Heat pumps take advantage of this physical property by transferring heat from warmer areas to cooler ones. This process enables them to operate effectively.
In cooling mode, the heat pump's refrigerant is pumped through an expansion device in the indoor coil (evaporator). The coil absorbs heat energy from the indoor air, cooling it. As a result, the refrigerant heats up and evaporates into a gas. The gaseous refrigerant then passes through a compressor, where it is pressurized and further heated. Next, the outdoor unit's fan blows outside air across the condenser coils, causing the refrigerant's heat to transfer to the outside air. This process cools the refrigerant, causing it to condense back into a liquid state. Finally, the expansion valve reduces the pressure of the warm liquid refrigerant, cooling it further and preparing it to restart the cycle.
In heating mode, the flow of refrigerant is reversed using the reversing valve. The outside air or ground becomes the heat source, releasing heat energy inside the home. The outdoor coil acts as an evaporator, absorbing heat from the cool liquid refrigerant and converting it into a cold gas. The compressor pressurizes the gas, causing it to become hot. The indoor coil, acting as the condenser, cools the hot gas by passing air over it. This process heats the air and condenses the gas into a warm liquid. As the liquid refrigerant enters the outdoor unit, its pressure is reduced, transforming it back into a cool liquid and restarting the cycle.
To summarize, heat pumps are versatile and efficient systems for both cooling and heating. By utilizing a reversing valve, they can transfer heat in different directions. Heat energy is absorbed by the evaporator coil, transferred in the refrigerant, and released by the condenser coil as air is blown over it. Heat pumps provide a reliable method of heat transfer, ensuring comfortable temperatures in residential settings.