SA-12-001 -- Simulations of Chilled Water Cooling Coil Delta-T Characteristics

Increasing loop chilled water return and supply temperature difference or delta-T is an effective way to improve the chilled water system efficiency and save chiller plant operating costs. In some chiller plants, the delta-T can be expected to fall to about one-half to two-thirds of design at low loads due to various causes, such as coil load, air entering and leaving temperatures, and chilled water supply temperature. Computational simulation is a useful and flexible tool to study cooling coil delta-T characteristics under various conditions. This paper simulated the cooling coil delta-T profiles with different geometric configurations and various waterside and airside conditions using an effectiveness-NTU model. The waterside heat convection coefficient was modeled with a combined correlation. The simulation results show that the existing waterside correlations generated significantly different delta- T profiles. With variant geometric configurations, the coil delta-T at full load may be higher, equal, or lower than that at part load. The complexity of cooling coil delta-T characteristics indicates that it is hard to make conclusions about the coil delta-T change with cooling loads.