Glossary
| Term | Meaning |
|---|---|
| Commissioning | Proving that an installed system works as designed and recording the results |
| Pre-commissioning | Checks done before the first start-up, with the compressor off |
| Interlock | A condition that must be met before the next step is allowed |
| Anti-short-cycle timer | Minimum compressor off time, typically 3 minutes |
| Set point | Target temperature the controller works towards |
| Differential (hysteresis) | Temperature band between switch-off and restart |
| Short cycling | Frequent compressor starts and stops |
| P&ID | Piping and instrumentation diagram, using standard symbols and tags |
| TT / PT / FT | Temperature, pressure and flow transmitter (ISA tags) |
| JQ | Power/energy meter tag (power totaliser) |
| Heating capacity (Q) | Heat delivered to the water, in kW |
| Specific heat (cp) | Energy to raise 1 kg by 1 K; water ≈ 4.18 kJ/kg·K |
| ΔT | Temperature difference, here outlet minus inlet water |
| COP | Coefficient of performance: heat out ÷ electricity in |
| Steady state | Running condition where readings no longer change |
| Saturation temperature | Boiling or condensing temperature at a given pressure |
| Superheat | Suction line temperature minus evaporating saturation temperature |
| Subcooling | Condensing saturation temperature minus liquid line temperature |
| P-h diagram | Chart of refrigerant pressure against enthalpy |
| Enthalpy | Heat content of refrigerant per kg, kJ/kg |
| Gauge vs absolute pressure | Absolute = gauge + about 1 bar (atmospheric) |
| Insulation resistance | Resistance between motor windings and earth; typical minimum 1 MΩ |
| True-RMS power meter | Meter that measures real power in kW, accounting for power factor |
| Performance test report | Factory record of a unit's tested capacity, power and COP |
| Handover | Formal transfer of the system and documents to the owner |
| Defrost | Cycle that melts frost from the outdoor coil |
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