Investigation into the application of a solar-assisted air-conditioning system in Hong Kong

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Investigation into the application of a solar-assisted air-conditioning system in Hong Kong


Author: Mo, Man Ki Aggie
Title: Investigation into the application of a solar-assisted air-conditioning system in Hong Kong
Degree: M.Eng.
Year: 2012
Subject: Solar air conditioning -- China -- Hong Kong.
Air conditioning.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xiv, 165 leaves : ill. (chiefly col.) ; 30 cm.
Language: English
InnoPac Record:
Abstract: In the hot and humid climate regions like Hong Kong, conventional air-conditioning (AC) systems controlling the temperature and the humidity of the supply air simultaneously operate inefficient due to the over-cooling and re-heating processes. Handling the latent load separately by using liquid desiccant is a promising way to reduce the energy use from the AC system. This study aims to investigate the feasibility of applying the solar hybrid liquid desiccant cooling system (SHLDCS) in Hong Kong. Two building models including a typical office building and a hotel were developed in this study. To understand the performance of the proposed system, computer simulation was performed. Mass and energy balance equations of different components was integrated in the simulation porgramme. In order to develop the energy saving potential of the proposed system, two types of improved measures, i.e. configuration optimization measures and control optimization measures, were also evaluated. The adoption of the measures was mainly based on its energy performance. Simulation results found that the major difference of the cooling load between the office building and the hotel is that the hotel has a higher latent load. But both of their latent load proportions reach its highest levels which are around 50% and 30% of the total cooling load respectively between April to October. Results show that the sensible-to-heat ratio of the office building and the hotel is relative low in Hong Kong, which are 0.66 and 0.51 correspondingly. Therefore, using the conventional air-conditioning system in Hong Kong is considered as unsuitable.
System simulation results show that the dehumidification capacity of the basic SHLDCS (base case) is always lower than the required moisture removal rate under the natural mode operation. Furthermore, energy does not saved if the heater is completely powered by electricity. Solar thermal energy proves itself attractive due to the 5.6% of total annual energy reduction compared with the conventional AC system if the heater is energized by solar energy. However, with this small amount of energy reduction, the basic SHLDCS has a low feasibility to apply in Hong Kong. In this study, not all improved measures are adopted. The best configuration arrangement comprises the air-to-air heat exchanger (P2) and the auxiliary heater. The energy saving potential is further expanded from 5.6% to 8.5% compared with the conventional AC system. Results also prove that cooling tower (i.e. natural mode) cannot act as the only cooling source for the SHLDCS in the humid climate as it provides insufficient cooling capacity for the desiccant. To remove the entire high latent load, an auxiliary cooler is used to further cool the desiccant solution (i.e. cooling mode). Results indicate a larger desiccant mass flow rate was not beneficial as the energy consumption is increased. Significant energy saving is achieved by the optimum SHLDCS which reduces 17.8% and 32.4% of the annual energy and electricity consumed by the conventional AC system. Due to this high energy saving potential, Hong Kong has a high feasibility to apply the improved SHLDCS.

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