The heat pump system you refer to is called a reverse-cycle chiller. It basically uses a standard high-efficiency heat pump to produce heat during winter and cool air in the summer.
A typical air-source heat pump heats or cools a refrigerant that flows directly through an indoor coil. Air blows over the coil to heat or cool your house.
A reverse-cycle chiller heats or cools water in an insulated tank. The water then flows through the indoor coil. The entire system will cost 15 percent to 25 percent more to install than a standard heat pump/electric furnace combination.
The advantage of a reverse-cycle system is that it can avoid the need for backup resistance heat during extremely cold times of the winter.
That advantage results from transferring heat to an insulated water tank.
During the summer, this large reverse-cycle heat pump’s cooling capacity chills the water in the insulated tank to 40 degrees or so. The chilled water is run through a coil in the blower system, which cools and dehumidifies indoor air just like a standard heat pump. The heat pump can cycle on and off as needed to chill the water in the tank independently of the indoor blower.
Another key advantage of having the heated water tank is its wintertime defrost mode. An air-source heat pump regularly switches to the cooling mode to defrost ice that collects on the outdoor condenser coils. During this time, expensive electric resistance heat comes on or chilly air blows out the registers.
With a reverse-cycle chiller, the heat to defrost the coils comes from the heated water tank so warm air continues to blow out the registers.
Reverse-cyle bonus savings
A reverse-cycle chiller provides other options for efficient heating.
The water could heat pipes installed in the floor for efficient radiant heating. This is one of the most efficient heating methods because you can feel comfortable at a lower room air temperature. This option is more feasible for new construction, but it can be used if you have a basement providing access to the underside of the floor above.
During the summer, an optional refrigeration heat reclaimer can be used. Instead of the heat pump exhausting the heat to the outdoor air in the cooling mode, it can be used to heat your domestic hot water for free. During the winter, the heat pump can be used to heat your domestic hot water in addition to the house.