Different Types of HVAC Systems: What Is A Heat Pump?
You may have heard the advertisements for mini-split systems and wondered what those work. Before we can get into that, we need to define what a heat pump is. In order to understand what a heat pump is, you need to grasp what is called the 2nd Law of Thermodynamics, which states:
"Heat always flows from a higher temperature to a lower temperature, hot to cold."
A heat pump is a device that is able to transfer heat from one fluid at a lower temperature to another at a higher temperature. Heat pumps owe their name to the fact that they allow heat to be carried from a lower to a higher temperature level, essentially going against natural heat flow. In the summer, a heat pump removes heat from inside your home and replaces it with cool air; working just like a conventional, high-efficiency air conditioner.
In the winter, the system works in reverse. It removes available heat from the air outside your home (yes, there is heat in cold outdoor air) and moves it indoors, providing an even, comfortable temperature level throughout your home.
Air-to-air heat pumps are basically air conditioners with the capability of reversing their cycle to provide heating in the wintertime.
Like we said, during the summer, air conditioners remove heat from the house, and 'pushes it outside. Air source heat pumps have a switching system that allows them to operate in reverse in the winter, removing heat from the outside air, bringing it into the house. Since air source heat pumps are not actually creating heat, but moving it from one place to another, they are less expensive to operate than electric resistance heaters, and depending on the costs of both natural gas and electricity, possibly gas furnaces as well.
For climates with moderate heating and cooling needs, heat pumps offer an energy-efficient alternative to furnaces and air conditioners.
A great practical illustration that everyone can relate to is your refrigerator. It removes heat from inside to the metal tubes or grid in the back where the heat is absorbed by the air in your kitchen.
Like your refrigerator, heat pumps use electricity to move heat from a cool space to a warm space, making the cool space cooler and the warm space warmer.
Because they move heat rather than generate heat, heat pumps can provide up to 4 times the amount of energy they consume.
One drawback to air source heat pumps is that they get less efficient when the outside air temperature gets colder. It is harder to extract the residual heat from colder air.
Let's say in the West Michigan area, winter temperatures get below 20 degrees only about 15 percent of the heating season. That means that a heat pump provides sufficient heat for about 85 percent of the heating season. That's more than enough time to help you save energy and save money on your annual heating and cooling costs.
When outdoor temperatures drop below 20 degrees or so, a back-up heating system -- usually an existing gas furnace -- automatically provides supplemental heat.
The reason you don't see many air-to-air heat pumps in this area, natural gas is sufficiently cheaper than electricity that an air source heat pump is generally more expensive to operate than gas furnaces. For those who are unable to receive gas services, the air source heat pump is probably the best bet.
If you are heating with propane because natural gas isn't an option; it may be a great fit for you.