Nashua, NH homeowners continue to choose heat pumps, thanks in large part to their impeccable energy efficiency capabilities. Since our area is prone to long, cold winters, every bit of efficiency counts. However, we here at Joyce Cooling & Heating Inc. notice that the average homeowner doesn’t know much about how heat pumps work. That’s not surprising, given that they’re unlike any other heating systems on the market. Here’s a complete explanation of how heat pumps work, including the fascinating science that makes it all possible.
What Is a Heat Pump?
A heat pump is a device that collects heat energy from one place and moves it to another place. And although you may not know it, your home has likely depended on heat pumps for years. For example, air conditioners are a form of heat pump. In their case, they collect heat from inside your home and carry it outside. The refrigerator in your kitchen is also a type of heat pump. It collects heat from its interior, which lowers its temperature. Then, it expels the collected heat into your kitchen.
When you see an HVAC system referred to as a heat pump, however, it refers to something more specific. It implies an HVAC system that collects heat energy from the outside winter air, amplifies it, and carries it inside to heat your home. In addition, HVAC heat pumps can operate in reverse, too, acting as an air conditioner for your home in the summer.
How Heat Pumps Work
Just like an air conditioner, heat pumps manipulate the pressure of a refrigerant to allow it to absorb and release heat. In a heat pump’s case, the refrigerant is typically a substance with an extremely low boiling point, usually around -15 degrees Fahrenheit or lower. That’s the reason why heat pumps can capture heat energy from cold air.
Inside a heat pump in heat mode, the process begins with the refrigerant at low pressure, in liquid form. In that state, the refrigerant’s temperature will be below its already low boiling point. The cold liquid refrigerant travels through a heat exchanger located in the heat pump’s outdoor unit. As it passes through, a large fan blows outside air across the heat exchanger’s coils. That allows the refrigerant to absorb heat energy from the warmer air, raising its own temperature until it boils.
Once that happens, the now-warm refrigerant vapor travels to the heat pump’s compressor. The compressor increases the pressure on the refrigerant vapor, which raises its temperature to around 115 degrees Fahrenheit. After leaving the compressor, the hot refrigerant vapor travels into your home, where it passes through yet another heat exchanger.
This time, however, a large fan circulates air from your home across the heat exchanger. But because the refrigerant is now much hotter than the air the heat exchanger comes in contact with, it surrenders its heat to the air and condenses back into a liquid. The result is a steady stream of warm air that raises your home’s indoor temperature.
After releasing its heat, the now-cool, high-pressure liquid refrigerant travels back out to the heat pump’s outdoor unit. There, it passes through an expansion valve, which lowers its pressure and temperature so it can start the process all over again.
In cooling mode, a heat pump reverses the flow of its refrigerant using a reversing valve. The mechanical process still works the same, except that it’s gathering heat from inside your home and getting rid of it outside.
The Science Behind Heat Pumps
To understand how a heat pump can pull off its interesting modes of operation, you need to understand a little bit about physics. The first concept you need to understand is enthalpy. That’s the scientific term used to describe the heat energy found in a given substance relative to absolute zero. Absolute zero translates to -459.67 degrees Fahrenheit. All air will contain some heat energy as long as it’s above that temperature.
The second concept you need to understand is how atmospheric pressure affects the boiling points of liquids. At low atmospheric pressure, the boiling point of liquids will drop. That means it takes less heat energy to make it boil. Conversely, the boiling point of liquids rises at high atmospheric pressures. Heat pumps use a compressor to control the atmospheric pressure of their refrigerant, thus controlling their boiling point as well.
You also need to know that the atmospheric pressure exerted on a refrigerant will alter its temperature, too. When you increase the pressure on a refrigerant, its temperature increases relative to where it started. The opposite is true when you decrease the pressure on a refrigerant. That is the secret behind how a heat pump can take the small amount of heat energy found in the cold winter air and turn it into plentiful heat for your home.
Lastly, you also need to understand a key part of the second law of thermodynamics. It states, among other things, that heat will flow from hotter substances to colder substances spontaneously. That’s the mechanism that allows a heat pump to capture heat from cold air. By using a refrigerant that’s even colder than the air itself, the available heat energy naturally flows to the refrigerant via the metal surface of a heat exchanger. Inside your home, the same thing happens, except in reverse.
The Efficiency Benefits of Heat Pumps
As you probably noticed by now, heat pumps neither create nor destroy heat. That stands in stark contrast to a gas-fired furnace, for example. They convert gas to usable heat through the combustion process. In doing so, they waste some of the energy contained in the gas. As a result, the average gas furnace is only about 80% efficient. Even the most efficient gas furnaces only reach about 98.5% efficiency.
Heat pumps don’t consume energy to heat your home, though. They just use a bit of electricity to run a compressor and some fans. All the heat already exists in the outdoor air. As a result, a heat pump operating in ideal conditions can run at close to 400% efficiency in heating mode. In cooling mode, they’re not quite that efficient, but still routinely rank among the most efficient cooling options on the market.
Your Local Heat Pump Experts
If you like what you’ve just read about heat pumps and think that one might be right for your Nashua home or business, Joyce Cooling & Heating Inc. can help. We’ve served homes and businesses in Nashua since 1995, offering quality HVAC installation, repair, and maintenance services. We also specialize in water heaters, indoor air quality solutions, Wi-Fi thermostats, and high-velocity HVAC systems. You can count on everyone here at Joyce Cooling & Heating Inc. to provide excellent customer service and flawless workmanship. We’re Better Business Bureau accredited and maintain an A+ rating with them. If you’d like to inquire about a heat pump for your Nashua home or business, contact Joyce Cooling & Heating Inc. today.
