Glossary
| Term | Meaning |
|---|---|
| Heat pump | Machine that moves heat from a cold source to a warmer sink using work |
| COP | Coefficient of performance: useful heat ÷ electricity used |
| Refrigerant | Working fluid that boils and condenses in the circuit |
| Evaporator | Heat exchanger where refrigerant boils and absorbs heat |
| Condenser | Heat exchanger where refrigerant condenses and releases heat |
| Compressor | Pump that raises refrigerant pressure and temperature |
| Expansion device | Restriction that drops refrigerant pressure (capillary, TXV, EEV) |
| TXV | Thermostatic expansion valve, controlled by a suction-line bulb |
| EEV | Electronic expansion valve, moved by a stepper motor and controller |
| Superheat | Vapour temperature above its saturation temperature |
| Subcooling | Liquid temperature below its saturation temperature |
| Saturation temperature | Boiling or condensing temperature at a given pressure |
| Enthalpy | Heat content per kg of refrigerant, kJ/kg |
| P-h diagram | Chart of pressure vs enthalpy used to plot the cycle |
| Temperature lift | Condensing temperature minus evaporating temperature |
| Carnot COP | Theoretical maximum COP from absolute temperatures |
| Approach | Temperature gap between refrigerant and air or water in an exchanger |
| Counterflow | Two fluids flowing in opposite directions in an exchanger |
| BPHE | Brazed plate heat exchanger |
| Hermetic compressor | Motor and compressor sealed in one welded shell |
| Inverter | Variable-speed drive for the compressor motor |
| 4-way reversing valve | Valve that swaps high and low sides for defrost or cooling |
| NTC thermistor | Temperature sensor whose resistance falls as temperature rises |
| HP / LP switch | High- and low-pressure safety switches |
| Defrost | Melting frost from the evaporator coil |
| EVI | Enhanced vapour injection, improves low-ambient capacity |
| Crankcase heater | Heater that keeps refrigerant out of compressor oil when off |
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