You may have heard the term “heat pump” from your home inspector or HVAC technician, but aren’t really sure what it means. Heat pumps look like an air conditioning unit, and they do work like A/C for cooling, but they also work in reverse to heat your home. To help you understand, let’s discuss exactly how they work and what the major components and benefits of a heat pump are.
What is a heat pump?
A heat pump works like an air conditioner during the cooling season. In the heating season, it can be switched to work in reverse. Simply put, when in cooling mode, it cools the inside and pumps the heat to the outside of your home. When in heating mode, the heat pump pulls heat from the outside environment and pumps it to the inside of your home.
In technical terms, a heat pump basically transfers heat from one environment to another. This is done when the heat pump is part of your HVAC system. The heat pump does not generate heat, but rather pulls the heat from the outside air, a water source, or a geothermal source.
Even in the winter, there is latent heat outside. However, for most systems, a heat pump using outside air does not operate efficiently when the temperature drops below 40 degrees.
What are the benefits of a heat pump?
Heat pumps only use electricity to move air through the system. This makes them efficient and cost-effective. Depending on where you live, compared to an electric resistance furnace or baseboard heaters, a heat pump can reduce the electricity used to heat by as much as 50%. Newer high-efficiency heat pumps do a better job at reducing humidity as compared to an air conditioning system. For more information on heat pumps and to see how they may help you save energy, visit this energy.gov website.
What are the components of a heat pump?
There are several components to a heat pump system. Below is a description of the major parts.
· Exterior Unit - The exterior unit of the heat pump is typically called the air conditioning or A/C unit. This is the familiar unit you see that has the housing, fan, copper coil system, and cooling fins. The fan pulls air in through the copper coils and blows it out of the top of the unit.
· Interior Unit - The interior unit of the heat pump is typically a part of the furnace system or an air handler. This unit also has a copper coil system and a fan to move air through the coils as well as the distribution ductwork of your home.
· Compressor - As the refrigerant moves through the compressor, the pressure is increased, which makes the refrigerant hot. This pressure also helps to move the refrigerant through the coil system.
· Evaporator - The evaporator is the set of coils housed within the interior unit.
· Condenser - The condenser is the set of copper coils housed within the exterior unit.
· Reversing Valve - The reversing valve switches the flow of the refrigerant through the system. In one direction, the system functions as an air conditioner; in the other direction, the system functions as a heat pump.
· Expansion Valve - The expansion valve regulates the refrigerant pressure and temperature within the system.
· Refrigerant - The refrigerant is the liquid or gas that is contained inside the copper coil system. The coil system is a continuous loop connecting the exterior and interior units. The refrigerant may also be called freon, 410A, or R22. Although it is called a refrigerant, it is actually a liquid or gas that transfers heat or cold. It can easily change temperature from very cold to very hot by adjusting its pressure.
How does a heat pump work?
In general, a heat pump uses electricity and its components as a way to transfer heat from one environment to another through a medium we call refrigerant. Using a fan, the heat or cold within the refrigerant is transferred from the coil system to the air around it. Along with the fan, a distribution of ducts moves the air to the desired areas of your home.
Cooling Mode
In the cooling mode, the refrigerant moves through the compressor in the outdoor unit coil system. This creates a higher pressure in the refrigerant and converts it from a liquid to a very hot gas.
The coil system in the exterior unit functions as a condenser, and the fan in the exterior unit pulls cooler air through the coil system. The refrigerant absorbs the lower temperature, which lowers the refrigerant pressure and transfers the heat to the exterior atmosphere.
As the refrigerant travels through the system, it passes through the expansion valve, which regulates the pressure. The lower pressure converts the refrigerant back to a liquid, which becomes very cold. As the cold liquid flows through the interior unit’s evaporator coil, the fan moves warm air across and through the coils, cooling and dehumidifying the air, which is then distributed throughout the home.
Heating Mode
When in the heating mode, the reversing valve is switched, thus reversing the entire system. The refrigerant travels through the compressor, making it a hot gas. As the hot gas travels through the interior unit coil system, the fan blows air across the coils to heat the air.
The refrigerant absorbs the cooler indoor air through the coils and the pressure lowers. As the refrigerant travels through the expansion valve, it becomes a cold liquid.
As the refrigerant passes through the coil system of the exterior unit, the fan draws warmer air through the coils and back through the compressor, making it very hot.
Summary
Heat pumps are an efficient way to heat and cool homes, but they have their limits depending on if they are using air, water, or geothermal as their heating or cooling source. If using air in the northern states, it is not uncommon for a heat pump system to have a backup electric induction heat source in the furnace for when temperatures are consistently below 40 degrees.
At HomePro Inspections, our home inspectors are trained to inspect heat pump systems and their operation. Any issues are documented in your home inspection report and recommended for resolution by a qualified professional.
Visit our website to learn more or to schedule your home inspection in the Rochester, Owatonna, and Faribault, MN areas. You can contact us today at (507) 202-8942 or utilize our online “Schedule Now” feature to set up an appointment.