Many factories and buildings throw heat away. A chiller rejects heat at its cooling tower at about 32–37 °C. Laundries drain warm water. Dairies and pharma plants have warm effluent and condenser water.

These streams are too cool to use directly. A water-to-water heat pump lifts them to 55–80 °C. Because the source is warm and steady, COP is high, typically 4–6.

Both sides are water, so the machine is compact. The evaporator and condenser are both plate or shell-and-tube heat exchangers. There is no fan and no defrost.

Every cooling tower and drain carries heat away to be wasted. A waste-heat heat pump catches that heat and puts it back to work.

(All values typical.)

Worked example — Chiller heat recovery in a Chennai hospital

Condenser water flows at 20 m³/h, cooled from 37 °C to 32 °C. A water-to-water heat pump (typical COP 5) uses this heat.

• 1.163 kWh/m³·K is the heat capacity of water.
• Q source = 20 × 1.163 × 5 = 116 kW
• Q hot = 116 × 5 ÷ 4 = 145 kW of hot water heat
• Electrical input W = 145 − 116 = 29 kW
• Bonus: the cooling tower now rejects 116 kW less heat, saving fan power and make-up water.

Remember

• Warm, steady source → high COP.
• No fan, no defrost, compact.
• Check source flow and temperature over a full day, not one reading.
• Use a strainer and a plate HX that suits the water quality.