Advanced water heat source units suitable for a wider range of applications such as high rise apartments, cold climates, coastal areas. Flexible installation options for high rise buildings as the units can be installed inside. They do not suffer the need to defrost and are ideal retro-fit to existing water cooled building systems. Able to operate with closed loop and open loop ground source water temperatures, bore hole and slinky applications are possible. It is also able to produce heat recovery via the water circuit between heat source units, making for a very economical system.