Outdoor 0°CIndoor 0°CCOP 0Heat 0 kWElectric 0 kWFrost 0%FPS 0

Refrigerant loop: blue = cold, low pressure; red/orange = hot, high pressure. Compressor → condenser (heats the room) → expansion valve → evaporator (takes heat from the cold outdoor air). Drag to rotate, wheel to zoom.

Frost-Belt Heat Pump: Refrigerant Loop, COP and Defrost

Follow the refrigerant round the loop and see why a heat pump delivers 2–4 kWh of heat for 1 kWh of electricity — and why that number falls in the cold.

Virtual teaching model with simplified refrigerant properties. It is not installation, charging or servicing guidance.

Weather and house

Results

Pressure–enthalpy diagram

Dome = saturated liquid / vapour. 1 evaporator out, 2 compressor out, 3 condenser out, 4 after the expansion valve (same enthalpy as 3).

Indoor / outdoor temperature (24 h)

COP and electric power (24 h)

Missions

Independent numerical checks

Controls help

Drag or one finger: rotate. Wheel or pinch: zoom. Buttons Hero / Outdoor / Cutaway / Indoor (keys 1–4) jump to camera presets.
Space pauses. Time-lapse sets how many simulated seconds pass per real second.
The compressor speed is set by the thermostat: the colder the room compared with the setpoint, the faster it runs.

The science

The cycle. The compressor raises the refrigerant pressure; hot gas gives up heat in the condenser (inside) and turns to liquid; the expansion valve drops the pressure at constant enthalpy (h4 = h3); the cold wet vapour then absorbs heat from outdoor air in the evaporator. Heat delivered Qh = m·(h2 − h3), compressor work W = m·(h2 − h1), and Qh = Qc + W.

COP. COP = Qh / P_electric. The Carnot limit T_cond / (T_cond − T_evap) shows why a smaller temperature lift is better; a real unit reaches roughly 30–50 % of it.

Frost and defrost. When the coil is below 0 °C and the air is humid, frost grows, the coil conductance UA falls and the evaporating temperature drops. At 50 % frost the unit runs a short defrost, taking heat back from the room.

Simplifications. A single fluid with R32-like saturation and latent-heat model values (fitted to a few points, not full property tables), ideal-gas compression with a constant isentropic efficiency, no pressure drops, steady refrigerant state at each time step, one lumped room. Treat the numbers as teaching values [check against refrigerant property tables before quoting].

Sources of this kind: engineering thermodynamics textbooks, refrigerant property tables, seasonal-performance test standards.

Made with Blender (outdoor unit, cabinet, coils, room) and rendered with Three.js. Not affiliated with any manufacturer.