How Do Heat Pumps Actually Work?

When it comes to HVAC (heating, ventilation, and air conditioning) systems, there are a lot of options to choose from. Many homes have gas furnaces, which are a great source of heat, but can be less efficient than heat pumps in milder winter temperatures. The most efficient heat source in milder weather would be a heat pump system.

In the Richmond area, a heat pump system is a great HVAC option for efficient heating and also heating performance. What makes this system so efficient is its ability to pump heat in either direction to provide both heating and air conditioning to your home.

How? Instead of burning fuel to create heat (can be inefficient and expensive) in milder climates, a heat pump uses the behavior of heat itself to move heat from one place to another. So, what exactly does that mean, you ask? In a nutshell, the key to understanding this is basic physics– heat always wants to move to a location with a lower temperature (just like we dream of heading to a beach house in Maine during the dog days of summer). But seriously- imagine how a hot cup of coffee always cools down when left on a counter, and how the countertop beneath the hot cup is warmed up as the coffee cools down. This is an example of heat transfer, and a rough parallel to how a heat pump works.

A heat pump is a closed-loop system made up of two parts: an outside compressor and an indoor fan unit (air handler). Refrigerant is the almost-magical element that connects these two parts, through a series of coils and pipes. Heat pump technology takes advantage of the fact that refrigerant fluid has a very low boiling point (below zero) that is also affected by pressure. Remember- heat always wants to move to a location with a lower temperature. Raising the pressure can greatly increase heat in the fluid, allowing it to transfer that heat into less-hot air (like on a hot summer day) through the condenser coil. Meanwhile, lowering the pressure can change the liquid to gas, which causes it to cool very quickly. Blow air over this cooled coil and voila–we have air conditioning! If you’ve ever used a can of compressed air to clean your keyboard or a tank of propane to grill, you’ve probably noticed the canister or tank gets cold when the gas is being released. This is the same mechanism that heat-pumps use to provide air conditioning!

Because of its low boiling point and ability to be easily manipulated with pressure, the refrigerant in a heat pump is able to draw heat from the air outside in cold weather- because even when it feels cold, there is still heat energy in the air. Heated refrigerant moves through copper pipes to the indoor fan unit where it is exchanged- the heat from the pipes transfers into the cooler air of the house, and the re-chilled refrigerant cycles back to the unit outdoors to collect heat from the air once again. In the summer this cycle is reversed, with the indoor unit’s pipes absorbing heat from inside the house, and releasing that heat to the outdoors.

While this mechanism works effortlessly at higher temperatures, the colder the outdoor temperatures are, the harder the heat pump needs to work to transfer heat to indoors. It’s hard to squeeze heat out of the air when it’s close to freezing. Fortunately, Richmond Virginia’s winter climate is right in the optimal range for heat pumps to operate very efficiently. Most heat pumps have an auxiliary heater that turns on when the heat pump struggles to maintain temperature. When temperatures drop below 35 degrees, gas heat is generally more efficient, but there are systems available that can automatically alternate between a furnace and a heat pump in winter depending on which one is more efficient- based on the temperature outdoors.