Heat Pumps have received a lot of attention. However I have found a lot of people have heard of heat pumps but they just are not familiar with them and often ask the same questions. Here is a little heat pump 101.
Q: How does a heat pump work?
A: A Heat pump simply stated is a device which moves heat from one place to another. By definition your refrigerator is a heat pump, other examples of heat pumps are: window A/C, central A/C, the A/C in your car. However these examples are of a one way only device and typically are not called heat pumps. Let’s use the window A/C as an example, standing inside the home the A/C blows out cold air, and outside it is blowing hot air (moving heat from the inside to the outside). Now let’s make an adjustment: take the A/C unit out of the window and install it backwards with the controls on the outside. When you turn the unit on you will have cold air blowing outside and hot air blowing inside (moving heat from the outside to the inside). Now you have a two way heat pump although a crude one. The typical heat pump is the same as a central A/C except with the addition of a few components mainly a reversing valve which switches the direction of refrigerant flow thus switching the coils just like putting the window A/C in backwards. This is an example of an air to air heat pump. (Please don’t actually use a window unit installed backwards it will drip water inside your home, freeze up and the electrical compartment is not designed to be outside in the rain and snow).
Q: How can a heat pump heat my home when it is 35 degrees outside or when the earth loop water temp is about 35 degrees?
A: Heat will ALWAYS move from hot to cold. If the outside air or the earth loop water temp is say 35 degrees and the evaporator (cold coil) is operating at 20 degrees the heat will move from the 35 degree air or water into the 20 degree refrigerant. The refrigerant is compressed by the compressor, which causes heat of compression which will raise the temperature of the refrigerant to 150 degrees or so. Now the hot refrigerant is moved through the condenser (hot coil) and the 70 degree air in your home is passed through the 150 degree coil and the heat moves into the air heating it and your home. Switch to the Cooling mode and the process is reversed by the reversing valve.
Q: What does SEER stand for?
A: SEER stands for Seasonal Energy Efficiency Ratio which is an engineering term. Basically the higher the SEER the more efficient the equipment is. Heat pumps also have a COP rating which stands Co-efficiency Of Performance. I feel that COP is easier to understand, again the higher the COP the more efficient the unit. For example, a COP of 3.5 means that for every dollar you spend on energy the heat pump will produce $3.50 worth of heat. Every heat pump has a published specification table showing the units COP. I just picked a 14 SEER 3 ton heat pump and the table shows at 65 degrees outside temp the COP is 4.17 and at 10 degrees it is 2.31. This shows us that the warmer it is outside the higher the energy savings; however at 10 degrees the heat pump is still 231% efficient.
Q: What is the difference between an air to air heat pump and a geothermal heat pump?
A: An air to air heat pump will move the heat from the air outside to the air inside like the window unit in the first question. A geothermal or Ground Source Heat Hump will move the heat from the water which flows through the earth loop to the air in your home. You can think of this type of heat pump as water to air, and depending upon the complexity of the application they can be water to water also. The main difference between the two types of heat pump is the source of the heat. In the heating mode a GSHP will use an earth loop which is buried in the ground where the ground temp stays more or less constant. An air to air heat pump gets it heat from the air which changes from hour to hour and varies considerably. Also water is a more efficient media to transport heat. This is why the geothermal or Ground Source Heat Pump is the most efficient method of heating and cooling your home.
Check out the CPM Cost Per Million Btu’s page and see why the heat pump is the most energy efficient method of heating.