Impacts of large chilled water temperature difference on thermal comfort, equipment sizes, and energy saving potential

Abstract

The heating, ventilation, and air-conditioning system accounts for nearly half of the building's total electricity consumption, and chillers are the biggest consumer. Optimizing the design and control of chiller plants is critical for building decarbonization. This study evaluated the impacts of large chilled water temperature difference (CHW-DT) on the equipment sizes, thermal comfort, and energy saving potential. An office building in Beijing was modeled in EnergyPlus and calibrated by measured data. Three retrofit scenarios of chilled water systems were studied. Firstly, the impacts of large CHW-DT on occupants' thermal comfort were presented. The equipment was sized based on 5 °C CHW-DT and operated at larger CHW-DT. Secondly, the impacts of large CHW-DT on equipment sizes were studied. The equipment was sized based on the operating CHW-DT to maintain thermal comfort. Thirdly, an optimal CHW-DT control strategy was developed to save energy consumption without changing the equipment sizes. The uncertainty analysis of Fanger model inputs was done for the first two scenarios. The results showed that using large CHW-DT without changing terminal sizes caused a significant decrease in occupants' thermal comfort. The uncomfortable hour percentage during the cooling period changed from 0.48% to 37.50% when CHW-DT increased from 5 °C to 10 °C. It was costly to increase the terminal sizes to maintain occupants' thermal comfort when applying large CHW-DT. The simple payback periods ranged from 10.7 to 27.7 years. Compared with baseline, the proposed daily optimal CHW-DT control strategy reduced annual energy consumption by 12% without changing terminal sizes and thermal comfort. The case study demonstrated that the proposed daily optimal CHW-DT control strategy had a high energy saving potential for chilled water systems.