Low-grade energy-bus air conditioning system using energy efficient three-fluid heat exchange terminals

Typical air conditioning terminals mainly focus on room temperature control, often neglecting adequate satisfactory room humidity management, resulting in poor thermal comfort. In addition, the direct heat exchange between refrigerant and air in these terminals cannot facilitate free-cooling using natural or waste cooling capacities. This study proposes a low-grade energy bus system that connects three-fluid heat exchange terminals, allowing for simultaneous control of room temperature and humidity. Furthermore, it enables the direct circulation of anti-icing fluid to each terminal for free cooling. Considering an office building in Nanjing, China, as an example, the annual operational performance of the proposed system is numerically studied and compared with two typical systems. The results reveal the following. 1) The three-fluid heat exchange terminals used can accurately regulate the room temperature and humidity, even when there are significant differences in the indoor cooling and dehumidification loads. 2) The annual system coefficient of performance (COP) of the proposed system increases from 3.3 to 3.9, leading to an annual energy saving rate of 14.4% compared to a typical water loop heat pump system in a typical office building in Nanjing, China. 3) Compared to commonly used room air conditioners, the proposed system is more energy-efficient.