To put it simply a heat exchanger transfers heat from one thing to another.
A pool heat pump uses a combination of solar energy and electricity to heat the pool. The pump takes heat from the sun warmed air and upgrades it with a compressor and transfers it to the water. It works similar to a heat pump which works by extracting heat from the air outside and upgrades it with a compressor and transfers it into your home.
Pool heaters work by taking in the water and heating it via propane or gas. It has a higher operating cost than a heat pump even though the initial installation price is cheaper it ends up costing a lot more, however a pool heat pump is cheaper and more environmentally friendly.
New Zealand’s electricity infrastructure generates about [Pool heating heat exchanger]