what is a heat pump? How does it work? Any pros or cons with system?

Start here: http://en.wikipedia.org/wiki/Heat_pump

It’s a contraption that tranfers heat through work. Air conditioners and refrigerators are a good example. They take heat ouf of a space. Refrigerators work by a compressor that compresses a gas outside and lets it expand on the inside while it circulates through tubes on the inside of the fridge. The compressor turns electricity into work compressing the gas. Then it lets that gas expand on the inside of the fridge, and this collects heat on the inside of the fridge. On compression the gas gets colder, dropping the heat. As it expands inside the fridge, it collects heat, only to later be compressed again on the outside to dump the heat out This doesn’t happen spontaneously, this needs work by the compressor, constant work by the compressor.

Check this guide, on page 3 there’s a nifty explanation with pros and cons of the system.

http://oee.nrcan.gc.ca/publications/infosource/pub/home/heating-heat-pump/booklet.pdf

Aqua pro Heat pump part 1.mp4