Part load energy efficiency ratio
Approved document L, Conservation of Fuel and Power, Volume 2: Buildings other than dwellings, 2021 edition incorporating 2023 amendments, defines part load energy efficiency ratio as:
A ratio calculated by dividing the cooling energy delivered into the cooling system by the energy input to the cooling plant. Part load performance for individual chillers is determined assuming that chilled water is provided at 7°C out and 12°C in (at 100% load), under the conditions detailed in Table A2.
Table A2 Partial load efficiency ratio
| Percentage part load | 25% | 50% | 75% | 100% |
| Air-cooled chiller’s ambient air temperature (°C) | 20 | 25 | 30 | 35 |
| Water-cooled chiller’s entering cooling water temperature (°C) | 18 | 22 | 26 | 30 |
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