Luckily in my life, they just work but there’s gotta be way more to it than gas/electricity make air hot, refrigerant/coolant make air cold. Also what is refrigerant/coolant?
Also I’m sure it can vary in application so I’m mainly asking about buildings/residences.
In: Technology
The 2 most simple system for heating is gas and electric. You burn gas, generates heat, which then heat up a coil of fluids, which goes to a radiator and gives off heat. In electric heating, electricity is ran through a high resistance material, which heats up. Air is blown through the heating element.
For heat pump, this is the fascinating system. It pumps heat from one area to another. It uses a gas that can easily be converted between a gas and a liquid. The type of gas is specific to the temperature you’re trying to achieve, and that depends on its use case.
The principle is this: you take a gas, and compress it to a high pressure. When you compress a gas to a high pressure, it inadvertently gets hotter. That’s the “heat of compression” part of the first law of thermodynamics.
So now you have a hot gas as a source of heat. You run that hot gas through a radiator (condenser) and blow air across it, the air gets hot. This, inadvertently cools down the gas. When the high pressure-hot gas meets a cold surface (the condenser), it condenses into a liquid and remains at high pressure. Pretty much how a cold glass of water causes water to condense on the glass.
So now you have a high pressure-lower temp liquid in the system. To get this liquid to an even lower temperature, you need to turn it back into a gas. In order to turn it back into a gas, it needs to be in a low pressure area. To do so, you pass the liquid through either a thermal expansion valve or an orifice tube. Those devices acts as a gate. On one side of the gate, there is the high pressure liquid. On the other side of the gate, is a low pressure area. When the liquid passes through the gate, it meets a low pressure area, and quickly evaporates into a gas. This is governed by the enthalpy of vaporization part of the 2nd law of thermodynamics. When a liquid evaporates, it gets cold.
So now, you have a low pressure-cold gas. You pass it through another radiator (this is called the evaporator). Hot Air is blown through the evaporator, depositing its heat to the cold gas. This is how you get cooling. The cold gas is now a warmed-low pressure gas. The gas then, goes back to the compressor, which gets compressed again to a high pressure gas, inadvertently, gets hot again.
The heat pump system has the compressor, a radiator, an air handler, and another radiator. The 2 radiators switches role between condenser or evaporator depending on where you’re trying to move the heat. If you’re trying to cool the inside of your house, the radiator in the outside unit is the condenser, and the radiator in the air handler is the evaporator. If you’re heating the inside of your house, they switch roles.
The reason why your heat pump is able to extract heat from the outside in the winter, is because the temperature outside is still hotter than the temperature of the low pressure-low temperature gas. It’s only cold to you. Likewise, when it’s scorching outside, it can still cool your house because the air temperature outside is still colder than the high pressure-high temp gas.
Simply put, during the winter, the heat pump is trying to cool the outside, by moving heat to the inside. During the summer, the AC is trying to heat the outside by moving heat from the inside to the outside.
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