Typical air conditioners use a pump to compress refrigerant. This compression makes the refrigerant very hot, making it easier to reject the heat in a heat exchanger to the outside air. As the hot gas is cooled it becomes a liquid. The compressor and this heat exchanger are the condensing unit.
The now cooler liquid refrigerant is routed to an expansion valve which returns the refrigerant to a gas. Thanks to this phase change, this gas is very cold, making it easier to gather heat in a heat exchanger from the inside air. The evaporator and this heat exchanger are the evaporator unit. Principle 36 – Phase Transition
The refrigerant then returns to the pump and cycles again.
The greater the difference in temperature between the refrigerant and the medium on the other side of the heat exchanger, the greater the system’s efficiency. So for an air conditioner to work efficiently, it benefits from the outside air being cool. Of course this is when you are least likely to need air conditioning.
Tall Cool Glass of Water
Instead, pool water can provide a great heat sink for home air conditioning systems, as described in this This Old House video. Not only does the cold water help the air conditioner run more efficiently, but that same heat transferred into the pool can make a swim more comfortable. Principle 22 – Blessing in Disguise