Heat pumps as a source of heating can use air, water or earth. The Air-water system is the best out of the available option because it combines the approachability of air as a source of heat, small investments, simple installation, vast reliability of the system and easy maintenance.
The air-water heat pump works on the principle of energy exchange between freons and the outside air. The freaon evaporates in low temperature if brought via valve to the pressure point of evaporation. The heat energy from the outside air allows for the evaporation of freon whose steam is then by compressing brought to a higher pressure level and higher temperature using the alternator freon-water. This energy is then used to heat the water. Condensed freons are then again via regulation filter brought to the evaporation pressure level for instant outside air temperature and so the process is repeated as long as there is a need for heating.
The water pump sends warm water into the radiators, floor heating, sanitary water boiler, fan-coil aparatus or other heating elements. In a combined version the heating-cooling process is achieved by reducing the water temperature to 7 degrees Celsius and then circulating it through filters and converters (fan-coils where the fans blowing provides cool air) or through floor or wall heating systems. This way a balanced cooling is achieved which can limit the lowest temperature so that condensation on the surface doesn't happen.
Today we have air-water heat pumps which within their cooling proces creates free hot water by spending 8-10 times less electricity than normally. The preparation of sanitary water is done by switching the system from cooling or heating regime to water heating regime.