How is it that a machine (like a heat pump) can consume 1kw of power and produce an amount greater than that of heat? What am I misunderstanding?
In: 320
refrigerant based systems are drawing energy to power a compressor. An electric heat strip is like the baseline thing they compare heat pumps to. It’s the 1 in the equation. Compressor just pushes refrigerant around in a circuit, raising and lowering the pressure in specific places to absorb heat and reject it somewhere else and the energy required to do this is sometimes significantly less than resistive heating elements.
Latent heat is an important subject to try and grasp. Any time a substance has to change state from solid to a liquid or liquid to a gas it takes a lot of energy to do so. It’s why when you have ice in liquid water the water measures 32 degrees. The mixture can’t rise above 32 because any extra heat energy is being used to melt the ice, it’s only after the ice melts that the water is free to rise in temperature again. This measurable temperature is called sensible heat and now we can understand why the other is called latent heat, it’s not measurable on a thermometer. It takes something like 140 times the energy to heat 32 degree ice into 33 degree water than it would to raise 30 degree ice to 31 degree ice. It takes over 900 times the energy to raise 212 degree water to 213 degree steam (all fahrenheit here, sorry world) than it would to take 210 degree water and raise it to 211 degree water.
Refrigerant based systems exploit this by controlling the boiling and condensing temperatures of the refrigerant by controlling pressure. We know that water boils at 212F at sea level but in higher altitudes, less pressure, the boiling point of water comes down. it’s the same with refrigerant. A hot, high pressure liquid experiencing a large pressure drop will suddenly be way above its boiling temperature and because of this it has to pick up an enormous amount of heat to change phase into a gas, that’s pretty much what’s happening in an indoor coil on an AC unit. The outdoor coil in an AC unit is getting hot, high pressure gas pushed through it and the fan helps it reject enough heat to the outside air that it condenses back down to a liquid so the process can start again.
Probably more info than anyone needs, I’m not an engineer but this is my crude understanding of it, I work with this equipment and I have to think about this stuff a lot. All this to say that moving heat with refrigerant and a compressor consumes less energy than generating heat from electricity.
Latest Answers