A model to study the effects of different control strategies on space humidity during part-load conditions

Many air conditioning systems have small moisture removal capacities and are not equipped to maintain space humidity under part-load conditions particularly during hot and humid periods. They are able to provide desired temperature control but humidity. The primary objective of this work is to identify control strategies that can be used to prevent significant indoor humidity degradation during part-load conditions. These control strategies are chilled water flow control, bypass air control, variable air volume control, run-around coil control and low face velocity/high coolant velocity control. Coil simulations have been employed to study the part-load performance of these control strategies. The coil model compares favourably with experimental data to within ±6.5%. Simulation examples are conducted for each control strategy under varying part-load conditions. Results from the coil model have indicated that some strategies are more effective than others in sustaining acceptable indoor humidity under part-load conditions. For instance, chilled water control strategy has been observed to produce highest indoor humidity throughout the range of conditions studied while variable air volume system provides highly effective dehumidification performance of the cooling coil. In addition, higher ventilation rates have been observed to increase the space humidity during part-load conditions.