An air-to-air heat pump (with electric element backup) was installed as part of the construction of this new home, in 2008. The owner proceeded to add a backup by using a water to refrigerant heat exchanger to improve the efficiency of the system. The addition draws water from their deep well, runs it through the heat pump and dumps the water into a shallow well, so as to recharge the aquifer, creating an open loop system.
The water to refrigerant addition takes over for the air-to-air component when the temperature dips below 0 °C (32.0 °F). This temperature will be slowly raised, as the water to refrigerant system is more energy efficient. Where monthly electricity costs for electric air heating are ~$380, for air-to-air it is ~$300, and for water to refrigerant it is around $200, once the water to refrigerant system is fully engaged.
