Absorption heat pumps are driven by boiling an environmentally benign refrigerant solution in a generator (or desorber) chamber. The high-pressure vapor condenses to a liquid while giving up heat in a condenser. The liquid then passes through a pressure-reducing valve and evaporates by absorbing heat in an evaporator. Finally, the vapor is reabsorbed into the solution in an absorber chamber. The driving energy comes from the thermal energy used for boiling, plus a all amount of electricity for pumping the solution from the absorber back to the generator.
In the heating mode, heat is taken from outside air when the refrigerant evaporates and delivered to the building interior when it condenses. In the cooling mode, the function of the two heat-exchanger coils is reversed, so heat moves from inside to outside.
Absorption heat pumps can double the efficiency of natural gas heating (to give a heating COP of 1.6 to 2.1). They can also reduce the impact of electric peak loads in cooling by the more efficient use of natural gas (with a cooling COP of 0.8 to 1.4).
Researchers at the BTC are working on two types of absorption heat pumps: