Unlike a forced air furnace, a heat pump doesn't use a fuel . Instead, it moves heat from one place to another . As a machine, the heat pump is commonly used in refrigerators, air conditioners, and heating systems.
A heat pump used in a heating system is a sort of ’backward’ air conditioner. In fact, there is usually a switch that converts it from one to the other. In the summer, it can be used as an air conditioner and in the winter, as a heater . A heat pump is commonly found in more moderate climates.
How Heat Pumps Work
In order to understand how a heat pump works, it's important to realize that even cold air contains heat , just to a smaller degree. A heat pump takes heat from outdoor air and moves it inside or takes heat from the air in your house and moves it outside.
When air is compressed (forced into a smaller space), the heat in the air is more concentrated and therefore the temperature of the air is much higher. The walls of that compressed space will radiate heat much faster to the surrounding area. When the heat has transferred and the air is allowed once again into an expanded space, the air will be cooler than before and able to absorb more energy to start the cycle all over again.
A heat pump uses a compressor and expansion valve to utilize this principle. If the heat pump is functioning as a heating system, heat from air in the outside coils will be absorbed by refrigerant in the coils and compressed. The heat in the air will then circulate through the inside coils and be transferred from the inside coils to the inside air . After the air circulates again through the outside coils and allowed to expand, it will once more absorb energy from the outside air.
Most heat pumps utilize the difference between indoor and outdoor temperatures, but a different variety of heat pump, a ground source heat pump , utilizes the difference between the temperature in your home and the temperature in the ground. It transfers heat from the earth to your home when functioning as a heating system or vice versa when functioning as an air conditioner.
Overall, a heat pump tends to be a more efficient method for heating than for cooling. The reason for this is that some energy is always lost as heat.
If the heat pump is being used for heating, the lost heat can be added to the heat being produced as a product. If the purpose is to cool, however, the heat may hopefully be kept away from the cool side, but doesn’t add at all to efficiency.
A heat pump also reduces humidity as it works.
Heat pumps have two different efficiency ratings, one for cooling (SEER) and one for heating (HSPF).
No system is perfect. Although the heat pump is very efficient, coils in the outdoor air will collect ice , which eventually needs to be removed. To do this, the heater must function as an air conditioner for a short period of time to heat the outside coils and remove the ice.
As a result, the heater must use burners or strip heaters for a little while to avoid pumping cool air into the house until it can switch back to heater mode.
Open fridge phenomenon
Because a refrigerator will actually produce more heat from the hot side than it will cold from the cool side, leaving your refrigerator door open to cool down your kitchen will actually produce the opposite effect, heating the room!
The extra work the heat pump has to do to maintain an ideal temperature within the fridge will result in so much energy lost as heat that the overall temperature in the room will be higher.
Heat pumps tend to be more efficient and cost effective than electric heaters. They are often more economical because they can be used year-round as both a heater and air conditioner. There is no need to buy a separate heater or air conditioner that is not even used for half of the year.
A heat pump is safer and cleaner than other heaters because it doesn't use fuel.