Energy performance of indirect evaporative heat recovery system in Hong Kong

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Energy performance of indirect evaporative heat recovery system in Hong Kong


Author: Chu, Wai-shing
Title: Energy performance of indirect evaporative heat recovery system in Hong Kong
Degree: M.Sc.
Year: 2002
Subject: Hong Kong Polytechnic University -- Dissertations
Energy conservation
Evaporative cooling
Hot-air heating
Hot-water heating
Department: Multi-disciplinary Studies
Dept. of Building Services Engineering
Pages: 126 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record:
Abstract: Some engineers claimed that Indirect Evaporative Heat Recovery (IEHR) is not effective for application in humid area. This dissertation will find out whether this is true or not by analysis and actual measurement of the performance of an IEHRS installed in Hong Kong under humid weather condition. In this study, the IEHRS installed at the Kowloon Park Swimming Pool plant room was monitored. The system is used to pre-cool the primary air before entering the air conditioning system for the swimming pool entrance lobby. The cooling mediums for giving up energy inside the IEHRS are the exhaust room air and the cold condensate collected from the Primary Air Handling Unit (PAU). Air and condensate flow meters, temperature and humidity sensors were installed on the IEHRS to measure the incoming primary air, exhaust room air and condensate properties. Computer programs were written to analyse the energy performance of the system based on the collected data. The data collection lasted for 4 months in an interval of 2 minutes from October 2001 to January 2002. The data collected within these 4 months was used to calculate the total energy change of the incoming primary air and exhaust room air before and after passing through the IEHRS. It was able to predict the energy effectiveness of the IEHRS during the hot summer and cold winter periods through calculations. It was found that during the winter period the saved energy cost due to the merit of the IEHRS could balance the overhead and operation cost of the IEHRS and much more saving could be achieved in summer time to pay back the capital investment. It was also noted that the higher the outdoor temperature, the more saving in energy was achieved. On the other hand, the increase in outdoor humidity did not lower down the rate of evaporation as the evaporation occurred at the exhaust air side and its humidity was relatively constant. In fact, the increase in outdoor humidity increased the supply of condensate from the PAU, which in turn increased the sensible heat transfer from the condensate to the incoming primary air. Further, it was observed that in some days, the temperature of the incoming primary air was lower than the one of the exhaust room air, so that the incoming primary air was heated in the IEHRS rather than cooling down. If meaning is not necessary, the fresh air should bypass the IEHRS when its temperature is lower than the exhaust room air. The components for evaporative process, which includes the condensate feed pump and condensate re-circulate pump, should be shut off as the heat extraction by means of evaporation is not required. After analysing the \installation cost, the operation cost and the saving in energy cost, the pay back period of the equipment is estimated to be around 9.01 years which is within the life span of the equipment. The achieved saving in energy by incorporating the IEHRS also indicates a possibility in selecting smaller capacity plant equipment when a new plant is designed. The down size in plant equipment can greatly lower the first capital investment. The work in this dissertation not only proved that IEHRS is worth to be used in Hong Kong's humid summer environment, but also showed the way for carrying out future study in this area. It has also developed the necessary software tools for analysing the system performance and the recorded data.

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