To recover the heat of compression, a heat exchanger can be installed in the hot-gas line between the compressor and the condenser of the chiller. A typical arrangement in conjunction with a domestic hot-water system is shown in the figure below. Hot-gas temperature depends on head pressure but is usually around 180 .
Cold water is circulated through the heat exchanger by the circulating pump.
When hot water is not being used, water is pumped back through the heat exchanger, the water heater or both. A mixing valve is provided to maintain the desired temperature. Energy can suitably be reclaimed from refrigerant-system hot gas when there is a steady and concurrent demand for refrigeration and heat and when refrigeration systems operate for 750 or more hours per year. If the exchanger is located outdoors, drains must be provided to prevent freezing. Energy savings are dependent on many variables such as how much and when excess heat is available and how much and when excess heat can be used.