For the refrigerant, it absorbed the waste heat of SDW in the
WHED, which was regarded as the evaporator. Then it was compressed
and then released the heat to water in the HWT which
served as condenser. Afterward, it was throttled by the capillary
tube and back to the WHED. When the water temperature in the
HWT was too low to take a bath, the electrical heater was started
up to raise the water temperature.