Applicability of a liquid-desiccant air-conditioning system in energy-efficient buildings with high latent load

Abstract

To reduce global greenhouse gas emissions, the recent building trend is toward energy efficiency, achieved primarily by reducing the indoor sensible load. However, handling the indoor latent load has been overlooked. Reflecting this building trend, heat-pump-driven liquid-desiccant (HPLD) air-conditioning systems have emerged as a promising technology that effectively handles indoor latent loads in energy-efficient buildings with low indoor sensible heat ratios (SHR). However, the aforementioned building trend has not been simulated in previous studies. Thus, the performance analysis of HPLD air-conditioning systems has been investigated for only one type of building. In this study, the indoor thermal loads of four different energy-efficient types of high-latent-load buildings were estimated to simulate building trends. Then, the changes in indoor thermal comfort based on room conditions and energy consumption of the reference air-conditioning system (i.e., the vapor compression system) and the proposed HPLD air-conditioning system were compared as the energy efficiency of the buildings increased. The indoor thermal loads were estimated using TRNSYS18 software, and both air-conditioning systems were modelled via the integration of theoretical analyses and the effectiveness-NTU model. The simulation results show that the indoor SHR decreased from 0.8 on average in the reference building to 0.64 on average in the building with the highest energy efficiency. In the building with the highest energy efficiency, only 43.3% and 24% of summer operating hours were thermally comfortable when the reference system operated to meet only the supply-air target temperature and primarily the supply-air target humidity via the condensation dehumidification process, respectively. In contrast, owing to the decoupled control of air temperature and humidity, the proposed system could maintain a thermally comfortable room in all building types for almost 100% of summer operating hours. Finally, when both systems achieved the same thermal comfort satisfaction, the proposed system could save up to 33.2% of the operating energy compared to the reference system in energy-efficient buildings. Based on the results, it can be concluded that the proposed HPLD air-conditioning system adopting decoupled control is more efficient as the energy efficiency of buildings increases.