How Does a Heat Pump Work?
A heat pump works like an air conditioner but has a reversing valve in the outdoor unit that reverses the refrigerant flow. By reversing the refrigerant flow, the reversing valve effectively turns the air conditioner into a heating system.
This article will explain in detail how both an air conditioner and/or a heat pump can transfer heat from inside to outside (AC) or from outside to inside (HP).
Before we answer the specifics of how a heat pump works, you’ll first need to understand what a heat pump is and its important components.
⭐ What Is a Heat Pump?
A heat pump is a mechanical-compression cycle refrigeration system that can be used for cooling and heating.
Unlike traditional heating systems like furnaces, heat pumps utilize electrical energy and refrigerant to absorb and transfer heat from one place to another.
This is why they are considered more efficient than any other heating system because they don’t use fuel to create heat. They use an energy source to transfer.
✅ Example: Electric heating elements are known to be 100% efficient, so how can a heat pump be any better than that?
Well, when you put one kilowatt of electricity into an electric heating element, you will get one kilowatt of heat out (one kilowatt equals 3412.142 BTUs).
But when you put one kilowatt into a heat pump, you will get at least three kilowatts of heat out (10,236.426 BTUs).
This is called the COP or Co-efficient of Performance, and the basic principle is that the heat pump is more efficient because it doesn’t create heat.
It just moves it from the outdoor air to the air inside the home.
This allows them to transfer heat from the air or ground outside of a building to the inside or vice versa, making them an efficient and cost-effective option for heating and cooling.
Heat pumps remain effective at cooling a home’s indoor areas, even at high temperatures, just like an air conditioning system.
All heat pumps rely on five major components: an evaporator, a condenser, a compressor or pump, a metering device, and a reversing valve.
When functioning properly, heat pumps represent an energy-efficient option that can circulate either warm or cold air inside a home.
⭐ Components of a Heat Pump
Heat pumps consist of an indoor unit and an outdoor unit.
The outdoor unit looks similar to the outdoor compressor box of an air conditioning system, while the indoor unit handles air transfer inside the home.
Both indoor and outdoor units contain various sub-components, like condenser coils and evaporator coils.
Let’s take a closer look at the main components of a heat pump.
⚙️ Outdoor Unit
The outdoor unit has a coil that switches functions depending on whether homeowners use their heat pumps to heat or cool their homes.
The specialized coil functions as an evaporator coil in heating mode and as a condenser coil in cooling mode.
The outdoor unit’s fan blows air from outside the home and over the coil to create heat transfer.
⚙️ Indoor Unit
The indoor unit, commonly referred to as the air handler, also contains a coil and a fan—the coil functions similarly to the outdoor unit’s.
The indoor unit’s fan also functions the same way as the outdoor unit’s, except that the fan moves heat through the air ducts, distributing warm or cooled air to all rooms inside the home.
The refrigerant serves as a substance that undergoes repeated transitions from a liquid state to a gaseous state and back again.
As heat circulates through the heat pump system, the refrigerant either absorbs it or rejects it as needed.
⚙️ Thermal Expansion Valve
The expansion valve regulates the flow of the refrigerant as it moves throughout the system. This allows for a reduction in both the temperature of the refrigerant and the pressure applied to it.
⚙️ Reversing Valve
The reversing valve reverses the flow of refrigerant in the heat pump system. This allows the system to operate in two ways, switching between heating and cooling.
⭐ How Does a Heat Pump Work?
Heat pumps themselves do not generate heat but transfer heat from one place to another with the help of electrical energy.
A heat pump takes in heat energy from the outside air and transfers it indoors.
Heat pumps can also function as air conditioning systems by absorbing heat from the indoor air and transferring it outside.
Heat pumps can switch between heating and cooling modes based on the homeowner’s needs.
⚙️ Heat Pumps in Cooling Mode
How does a heat pump work in cooling mode?
The HP system pushes liquid refrigerant through the expansion valve on the indoor coil to cool a home.
The refrigerant absorbs heat energy from indoor air blown over the coils.
The resultant cool air then gets blown through the home’s ventilation ducts.
This process causes the liquid refrigerant to turn into gas as it absorbs the heat.
The gaseous refrigerant then flows into the compressor, where it gets pressurized.
The pressurized gas acquires even more heat and moves through the system to the coil in the outdoor unit.
The fan in the outdoor unit blows outdoor air across the coils, which act as a condenser.
The difference in temperature and pressure between the hot refrigerant and the outside air allows the unit to expel heat into the atmosphere.
As the refrigerant cools down, it reverts into liquid form, which then gets pumped through the system to the expansion valve in the indoor unit.
The expansion valve reduces the pressure of the liquid refrigerant and cools it further.
This refrigeration cycle repeats itself until the heat pump achieves the required temperature.
⚙️ Heat Pumps in Heating Mode
A heat pump works in the heating mode because the reversing valve reverses the flow of refrigerant in the air conditioner’s system, effectively turning it into a heat pump.
This reversal causes the outside air to become the heat source, absorbing heat energy outside and then transferring it inside.
The roles of the evaporator and the condenser also reverse.
The outdoor unit’s coil functions as the evaporator, and the indoor unit’s coil functions as the condenser.
The liquid refrigerant takes in heat while inside the outdoor unit and turns it into a cold gas.
The AC compressor applies pressure to the cold gas and heats it.
Air then passes over the newly created hot gas found inside the indoor condenser coil to warm the home.
As the air passes over the hot, gaseous refrigerant, the refrigerant condenses into warm liquid, flowing back to the outdoor unit.
As the liquid enters the outdoor unit, a metering device causes it to lose both pressure and temperature, cooling it down.
This cycle repeats as needed.
⭐ What Types of Heat Pumps Are There?
The three types of heat pumps are air-source heat pumps, water-source heat pumps, and geothermal heat pumps.
Each of the three types of heat pumps absorbs heat from the air, water, or ground outside the home, transfers that heat to the indoor unit, and distributes that heat throughout the home.
How Does an Air Source Heat Pump Work (ASHP)?
An air-source heat pump absorbs heat from the cold outdoor air using an air conditioner’s condensing unit but with the addition of a reversing valve.
The refrigerant that is used to absorb the heat energy is then pumped inside to the indoor coil (called an evaporator coil when used for AC), where the air handler circulates the home air across the indoor coil to warm the indoor areas of a home.
Even with the extremely cold outside air, newly designed low-temperature HPs are able to provide energy-efficient heating.
As energy costs increase, colder climates are causing homeowners to look for new ways to save money on heating their homes, and these systems are quickly becoming the sustainable choice.
An air source heat pump is the most similar to an air conditioner because it uses outside air to transfer heat.
How Does a Water Source Heat Pump Work (WSHP)?
A (WSHP) expels heat to a water pipe system in the summer and absorbs heat from the same system in winter.
Thus, WSHPs use water instead of air as a heat source to control the refrigerant temperature.
All other aspects of the operational process are the same as all other heat pump systems.
How Do Geothermal Heat Pumps or Ground Source Heat Pumps Work?
Ground source or geothermal heat pumps work by using the earth as a heat source or heat sink.
Ground source heat pumps exchange heat with the earth to control the refrigerant’s temperature.
All heat pumps come equipped with a reverse operation that enables them to serve both as heating and cooling systems.
Other models can also heat water for use within a home.
⭐ Benefits of Heat Pumps
Ducted or ductless heat pumps do more than regulate the temperature inside a home.
They provide several other benefits over alternative heating systems.
✅ Safety and Energy Efficiency
A heat pump remains safer and more energy-efficient than combustion-based heating systems, like an oil burner or a natural gas furnace.
As a result, heat pump owners enjoy significant savings on their energy bills.
Since heat pumps utilize electrical energy, they leave a minimal carbon footprint, making heat pumps a more environmentally-friendly option.
A heat pump can heat and cool a home, eliminating the need for air conditioners and furnaces.
This can amount to an upfront heat pump cost reduction when deciding on a climate-control system for a home.
✅ Improved Air Quality
Heat pumps also keep indoor air quality at a healthy level.
Like an air conditioner, the heat pump filters air by removing dust, mold spores, smoke, and other particles.
During summer, heat pumps also act as dehumidifiers and can also reduce condensation in rooms during the colder months.
✅ Low Maintenance
Heat pumps also require little maintenance.
A yearly check of the components keeps a heat pump running smoothly.
A heat pump can last as long as 50 years, although the average lifespan stands at 14.5 years.
Heat pumps remain a reliable, low-maintenance climate-control option that presents great value for money over other heating and cooling systems.
⭐ Where Do Heat Pumps Work Best?
There are two options for a heat pump to consider based on your climate zone; a standard system and a low-temperature system.
Standard Temperature Heat Pump
Heat pumps owe their high efficiency to the constant nature of thermal energy.
Thermal energy remains in the air even in freezing temperatures.
As a result, standard heat pumps function best with outdoor temperatures above 40°F (+4°C) and begin to lose their efficiency when temperatures drop that mark.
Standard heat pumps function less efficiently than furnaces when temperatures drop below 25°F (-4°C).
This reduction in efficiency occurs because of the reduced levels of thermal energy present at lower temperatures.
For example, air at 0°F (-17°C) contains about 85% of the thermal energy present at 70°F (21°C).
This difference in thermal energy causes a drop in the heat pump’s efficiency.
As a result, the heat pump works harder to make up for the difference between outdoor and indoor temperatures, which results in more electricity consumption.
Installing an auxiliary heating system can help heat pumps work even in freezing temperatures.
Low-Temperature Heat Pumps
Low-Temperature Heat Pumps work down to an outdoor air temperature of -35°F (-37°C) degrees.
The important thing to remember when sizing one of these systems is that at these lower temperatures, their rated capacity decreases to approximated 60%.
Because of this decrease in capacity, it makes it very hard to size the system as both a heating system and a cooling system.
The reason this is so difficult is that you can’t size the system to be your primary heat source without grossly oversizing it as an AC system.
Luckily, manufacturers have been designing these LTHPs as variable capacity systems, so consider the problem solved.
Size the system for heating and move on.
Though this will also increase the overall operating costs of your heat pump system.
Want to learn more about your home’s heat pump? Feel free to check out our other Heat Pump articles.
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