Understanding How A Heat Pump Heats And Cools Your House
Your house uses a heat pump to warm it on those cools nights. The HVAC technician explained that the pump draws in warm air from the outside and uses it to warm the house. But how does that work when it's 40 degrees outside and 60 inside and you want to warm up the house a bit more? A heat pump makes use of the Second Law of Thermodynamics, and here is how that is used to warm, and cool, your home.
Heat Moves From Warm to Cool Objects
This law of physics states that systems tend to move from an ordered to a disordered state, much like a teenager's bedroom a couple of days after it has been cleaned. As the law pertains to temperature, cold, which is a more ordered state of the molecules, tends to move toward a disordered state where the molecules are moving faster, which is the definition of heat.
40 Degree Air Still Has Heat in It
Temperature is relative. You walk outside into 40-degree weather to walk the dog and it feels cold. But the air is still warmer than 30-degree air. Relative to 30-degree air, 40-degree air is warm and that is the warmth that your heat pump wants to capture for your home. To do this, your heat pump must produce colder air to draw the heat from the 40-degree air.
Your heat pump has coils which contain a refrigerant. This is a gas, which is also used in your refrigerator and car air conditioner. This gas is forced through an expansion valve which causes the gas to cool down. The gas is cooled to below the outside air temperature and circulated through coils outside of your house. The coils are now cooler than the outside air and attract the heat contained in the air. The heat is absorbed by the refrigerant and brought into the house.
One limitation is that heat pumps don't work well when the temperature is freezing outside. To function, the heat pump would need to cool the refrigerant to below freezing to get any heat out of the freezing air. People who live in colder climates will have a backup system, such as a gas or electric furnace.
Some heat pump systems come with a backup heat source in the form of electric strips. Every system does this differently, so have a manufacturers representative explain how their heat pump generates heat when the outside temperature gets close to freezing.
Cooling Your Home with a Heat Pump
One of the advantages of a heat pump is that you don't need to install a separate air conditioning unit to cool your house. The Second Law of Thermodynamics works for you here, too, by reversing the flow of the refrigerant. The refrigerant is cooled down lower than the temperature in your house and draws the heat out of the air. It forces that air outside then returns to pull more heat out of your house.
Whether you're heating or cooling your house, the heat pump manages the cycle without any intervention by you. Which is probably not the case when it comes to convincing your teenager to keep their room clean.