Heat Pump Cycle (2D): Vapour-Compression Refrigerant Loop

Mode

Conditions

Outdoor temperature 2 °C

Indoor target temperature 21 °C

Compressor speed 60%

Compressor isentropic efficiency 45%

Live Readout

COP

—

Electrical input

— kW

Heat delivered

— kW

Heat absorbed outside

— kW

Condenser temp

— °C

Evaporator temp

— °C

How it works

A heat pump moves heat "uphill" — from a colder reservoir to a warmer one — by cycling a refrigerant through four stages: the compressor raises its pressure and temperature (consuming electrical work W), the condenser releases heat Qh as the hot gas condenses to liquid, the expansion valve throttles the liquid to low pressure (Joule–Thomson cooling, no heat exchange), and the evaporator absorbs heat Qc as the cold liquid boils back into gas.

Carnot COP (heating) = Th / (Th − Tc)
Real COP  = η · Carnot COP   (η ≈ 0.4–0.5 for real compressors)
Qh = COP · W        (heat delivered indoors)
Qc = Qh − W          (heat pulled from outside air)

Th and Tc are the condenser/evaporator absolute temperatures (kelvin), so COP always improves as the indoor–outdoor gap shrinks and degrades sharply on cold days — exactly what the readout shows as you slide the outdoor temperature down. In cooling mode the cycle runs in reverse: the evaporator sits indoors and Qc becomes the useful cooling effect.

Hot high-pressure gas Warm liquid Cold low-pressure liquid/gas