ANNUAL ENERGY-USING SIMULATION OF SEPARATE HEAT-PIPE HEAT EXCHANGER Dan-dan Zhu 1 , Da Yan 1 , and Zhen Li 2 1 Department of building science, Tsinghua University, Beijing, China 2 School of Aerospace, Tsinghua University, Beijing, China ABSTRACT A kind of separate heat-pipe heat exchanger (SHP exchanger), which can move heat from indoor air to outdoor air by making use of their temperature difference, uses much less energy consumption than air-conditioning system in base station due to none of compressor. This study built up an annual energy-using simulation module of SHP exchanger in DeST by building the model of SHP exchanger and accomplishing the coupling calculation of it and the model of dynamic thermal process in building. Besides, the verification and application of this simulation work shows that it can assist the design of air-conditioning system in base station. INTRODUCTION Millions of base stations have been built for data processing and transmission in mobile communication system in China in recent years. Statistics showed that the power consumption of base stations accounted for more than 90% the total power consumption of telecoms companies, in which air-conditioning system uses more than 40% power in base stations (Hu Wei et al., 2008). Therefore, it is how to reduce the power consumption for air-conditioning system that is the key to achieve base stations’ energy-saving. The size of base station is generally small, about 20 ～ 30 square meters and electrical equipment mainly includes communication equipment and air-conditioning system. As communication equipment operates continuously releasing high heat of 100～400W/m 2 , cooling is required even in winter. Besides, as there is little ventilation to insure air cleanliness and indoor moisture source, moisture load is so little that dehumidification is not required in air-conditioning. Now split-unit or precision air-conditioner is used in most base station in China, resulting in long-time operation and high power consumption. There are some methods to solve this problem in study and application, for instance, compressor frequency control, adaptive control of air-conditioner, new refrigerant and using natural cooling resource (Hou Fu-ping, 2006). For using natural cooling resource, there are plate-type heat exchanger or heat pipe exchanger and supplying outdoor air directly (Liu Jie et al., 2008). And of them Separate Heat Pipe exchanger (SHP exchanger), moving heat from indoor air to outdoor air by working fluid flowing in pipe when outdoor air temperature is below indoor one, is a very energy-saving way because of none compressor. As the heat transfer performance of SHP exchanger working in base station is related with many factors such as outdoor meteorological parameter, indoor casual gain, building parameter etc., its performance in all condition is required to calculate by simulation. However, the simulation study of heat pipe has mainly focused on heat pipe components so far, instance for, computational fluid dynamics (CFD) simulation of flowing fluid, heat transfer simulation of heat pipe unit (Wang Yue et al., 2000), and lacks simulation combining heat-pipe equipment and dynamic thermal process in building. So this study aims at building up a simulation module of SHP exchanger in the building energy simulation software—— DeST for the simulation of room temperature and energy consumption in all condition to help designing air-conditioning system in base station. OPERATING PRINCIPLE Heat-pipe is a high-efficient component of heat transfer by the flow and phase change of its working fluid with the advantage of large density of heat discharge, good isothermality and simple structure. The structure of SHP exchanger is as Figure 1 shown. The evaporator (the indoor unit) is located in the bottom of room with a fan and the condenser (the outdoor unit) is upper outdoor with another fan, which are connected by a gas pipe and a liquid pipe. When heat-pipe working, indoor air heats the evaporator to vaporize its working fluid resulting in the pressure rise in the evaporator that makes the vapor flow to the condenser through the gas pipe, where the vapor condenses into liquid with heat release, and then the liquid goes back to the evaporator because of its gravity and capillary force. In this way, the heat of indoor air is moved to the outdoor air. Proceedings of Building Simulation 2011: 12th Conference of International Building Performance Simulation Association, Sydney, 14-16 November. - 1168 -
