Seasonal underground cold storage system for air conditioning in cold climate regions

Pao Yue-kong Library Electronic Theses Database

Seasonal underground cold storage system for air conditioning in cold climate regions

 

Author: Dong, Ji Shuai
Title: Seasonal underground cold storage system for air conditioning in cold climate regions
Degree: M.Eng.
Year: 2016
Subject: Heat exchangers -- Design and construction.
Heat storage.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: ix, 88 pages : color illustrations
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2917131
URI: http://theses.lib.polyu.edu.hk/handle/200/8615
Abstract: Cooling demand has increased considerably due to growing population, increased thermal comfort requirements and heat dissipation associated with wider use of electrical appliances. To meet the increasing cooling demand, conventional air conditioning systems driven by electricity contributes to energy crisis, environmental problems and economic pressure. In association, an environmentally friendly and economically efficient seasonal underground cold storage (SUCS) air conditioning system is proposed for a detailed investigation. The proposed SUCS system aims to store the cold energy of the natural cold winter air for summer time air conditioning. The cold energy will be transferred and stored underground by the use of a coolant that circulates between an outdoor heat exchanger (OHEX) and a borehole heat exchanger (BHEX). In this study, the effectiveness of the OHEX with different design parameters (including air velocity, coolant velocity, coolant concentration, coolant temperature and heat transfer area) was investigated by using the NTU method, while the underground storage capacity was investigated by CFD simulation using ANSYS Fluent. Based on the NTU analysis, it was found that the influence of air velocity on the effectiveness of the OHEX is larger and negative as compared to the other parameters. To optimize the effectiveness of the OHEX amongst the studied parameters, it was found that air velocity should not be too high to lower the effectiveness, nor too low to keep the flows at the laminar zone. For the CFD analysis, simulation results indicate that soil temperature distribution is in radial form. Thus for space saving in practice, multiples of BHEX should be arranged within a smaller radial range. The influence of coolant inlet temperature on the heat transfer rate between the BHEX and soil was also investigated and a significant influence was found. The results of this study confirmed that a moderate air velocity with low temperature has a positive influence on the effectiveness of the OHEX and on heat transfer rate of between the BHEX and soil. It is therefore concluded that SUCS system is more effective for application in cold climate regions.

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