Heat pumps operate on electricity and have been in homes for 70 years. However, technological advancements only recently made them practical for colder climates like New England. According to the TED-Ed website, over half the homes in frigid Norway are equipped with heat pumps.
Heat pumps are more energy efficient and less costly to operate than conventional oil, propane, gas or coal-fired systems because they don’t generate heat–they simply move heat. This means they also produce less greenhouse gas.
In colder climates like Suffield, heat pumps are outfitted with legs to keep them above accumulating snow.
They can be expensive to install, but tax credits, rebates and incentives help reduce the cost. In the summer, they also double as air conditioners when their operation is reversed. They work with boilers, hot water heaters, forced hot air systems, and homes without ducting (mini-splits).
We’ll discuss the most popular kind of heat pump, which extracts heat from the air. Another style extracts heat from underground, where temperatures are more consistent. Since it requires digging, piping and complex components, it’s more expensive and comprises only a small percentage of installations.
How heat pumps work
So how does a heat pump extract heat from outside air when temperatures are 12º, for example? Here’s a simplified explanation.
For starters, you need to understand an important law of nature: heat is always attracted to cold.
Think of a heat pump as a closed loop. Tubing that contains refrigerant passes through two sets of coils, one inside the house and the other outside.
Let’s start outside. A fan draws air through the coil, which contains tubing filled with refrigerant. On a 12º day, the refrigerant will be colder. Let’s say 3º. The fan blows the 12º air through the coil, and since the tubing contains 3º refrigerant, the comparatively warmer 12º air will be absorbed by the colder refrigerant since heat is always attracted to cold. In this example, there’s a 9-degree temperature difference.
But that difference is not enough to warm your home, so the refrigerant is compressed, raising its temperature. The heated refrigerant in the tubing then passes through the second coil inside the house, where a fan blows the comparatively cooler inside air across the heated coils. Again, the warmth of the refrigerant is given off to the cold air since heat is always attracted to cold. That’s how your house is heated.
But we’re not done. After the refrigerant warms your home, it needs to be cooled again to travel outside in the closed loop to attract more heat.
That’s done by expanding the compressed refrigerant, which causes its temperature to drop. When it flows through the outside coil, it’s again at 3º and ready to absorb more heat from the 12º air. The cycle starts over.
Again, this is a simplified explanation. In practice, the refrigerant changes from a liquid to a gas as it flows through different parts of the system. That is important for its operation but not for a basic understanding. Heat pumps work harder and are less efficient in the winter but are unaffected by wind chills. The latest systems can warm your Suffield house when outside temperatures are as low as -13º.