Optimizing air conditioning systems by considering the grades of sensible and latent heat loads

Traditional air conditioning systems uniformly treat all the sensible and latent heat loads of buildings by the lowest temperature chilled water, resulting in low efficiencies. Previous researchers proposed the temperature grades of staged loads and various energies, and the systems operate efficiently after being designed by grade matching. However, the method includes latent heat load with sensible heat load as the corresponding temperature grade; thus, the energy efficiency of the system designed can still be further improved. The latent heat systems have been experimentally improved, but the extent of applying appropriate humidity sinks and cooling and heating sources is unclear, and they are not comprehensively designed with sensible heat systems in the entire air conditioning systems. In this study, the humidity grade for the latent heat load and humidity sink is defined. A method for converting humidity grade to temperature grade is developed to obtain the potential of utilizing different humidity sinks, and cooling and heating sources in both sensible and latent load treatments. A grade-matching method is proposed to realize a more energy-efficient air conditioning system. A case study of an office building is used to demonstrate the method. The system designed using the proposed method improves energy-saving rates for heat pumps by 34.0% and 11.2% compared with the typical system (where latent and sensible heat subsystems are separately designed) and the system designed by the previous method (where the air treatments are limited to condensation dehumidification), respectively. This method is conducive to the more reasonable utilization of natural and waste cooling and heating sources for air treatment, and it reduces the capacities and energy consumptions of electric heat pump systems, resulting in significant energy savings.

Automated summary

This study proposes a more energy-efficient air conditioning system design method by defining humidity grades and developing a method to convert humidity grades to temperature grades. Through a case study, it is found that the system designed using this method can significantly improve the energy-saving rates for heat pumps.