Air source heat pumps achieve high-efficiency heating and cooling based on the Carnot Cycle—a thermodynamic cycle that transfers heat from low-temperature sources (outdoor air) to high-temperature spaces (indoor areas, hot water tanks) with minimal electrical energy input. This article concisely explains its core logic, cycle process, and key parameters.

According to the Second Law of Thermodynamics, heat spontaneously flows from high-temperature to low-temperature objects. The Carnot Cycle reverses this process by using external work (electricity driving the compressor) to force heat transfer from outdoor air (low-temperature source) to indoor/hot water (high-temperature source). Its key advantage is high energy efficiency: the Coefficient of Performance (COP) is 3~5, meaning 1 unit of electricity produces 3~5 units of heat—far higher than electric heating (COP≈1).

The cycle relies on four components: compressor, condenser, expansion valve, evaporator, and refrigerant phase change (liquid ↔ gas). The core flow is:

[Outdoor Air] → Evaporator (Isothermal Heat Absorption) → Compressor (Adiabatic Compression) → Condenser (Isothermal Heat Release) → Expansion Valve (Adiabatic Expansion) → Evaporator (Cycle Restarts)

COP = Output Heat ÷ Electrical Energy Consumed. Ordinary models: 3~5; low-temperature models (with vapor injection): ≥2.5 at -25°C.

Theoretical COP_max = T_High ÷ (T_High - T_Low) (T in Kelvin). Smaller temperature difference between indoor and outdoor means higher efficiency.

Afour-way reversing valve switches the roles of evaporator and condenser, enabling heating (outdoor absorbs heat) and cooling (indoor absorbs heat).

The Carnot Cycle is the core of air source heat pumps, enabling energy-efficient heat transfer instead of heat generation. It is eco-friendly, energy-saving, and suitable for household, commercial, and industrial scenarios, supporting the "Dual Carbon" strategy.