Chiller plant sizing by cooling load simulation as a means to avoid oversized plant

Many buildings in Hong Kong are equipped with oversized chiller plants, which often run at low part-load efficiency. In the paper, the conventional cooling load calculation method for plant sizing and the design criteria used in the calculation are reviewed. Factors that would contribute to overestimation of the required plant capacity are highlighted. With reference to six existing commercial buildings, design peak cooling loads estimated by using the conventional design load calculation method are compared with peak cooling loads predicted by detailed computer simulation, and with the capacities of the existing plants. In addition, the predicted energy use of the chillers based on their installed capacities are compared with the predicted energy use when the capacity of the plants are adjusted to the design cooling load determined using the conventional method, and to the peak load obtained by detailed simulation. It was found that the peak cooling load determined from a detailed simulation on the basis of a typical weather year of Hong Kong forms a good basis for plant sizing. Simulation calculations based on weather conditions for ten consecutive years indicates that a plant sized according to this method is able to meet the building cooling load to a sufficiently high degree of confidence.