A vapor-compression heat pump moves heat "uphill" from a cold waste-heat stream to a hotter process stream instead of generating that heat by burning fuel. Refrigerant boils at low pressure in the evaporator, absorbing heat from the source; the compressor raises its pressure and temperature using electrical work; it condenses at high pressure in the condenser, releasing that heat (plus the compressor work) into the process; then an expansion valve throttles it back down, dropping its temperature and pressure before it re-enters the evaporator.
COP_carnot = T_sink / (T_sink − T_source) [Kelvin]
COP_actual = η_compressor · COP_carnot
Q_delivered = COP_actual · W_electrical
Because the compressor only supplies the *lift*, not the whole heat, a well-matched heat pump can deliver 2–5 units of heat per unit of electricity — something no combustion process can do, since burning fuel directly tops out under 100% thermal efficiency.
- Waste-heat source — the temperature of free/cheap heat already available on site (cooling water, exhaust air, effluent).
- Process delivery temp — the temperature the industrial process actually needs; the further above the source, the smaller the Carnot ceiling.
- Compressor quality — real machines never reach the Carnot limit; multi-stage, well-designed compressors get closer to it than single-stage ones.
- Refrigerant flow — how fast refrigerant circulates the loop; does not change the COP, only how quickly heat moves.
The comparison box estimates CO₂ against burning gas directly in a boiler at 90% thermal efficiency, versus this heat pump's electricity drawn from an average grid — the assumption used across most industrial decarbonization studies for this technology.