An investigation of solar powered absorption cooling systems for South Africa.
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Date
2012
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Abstract
Increased standards of living and indoor comfort demands have led to an increase in the demand
for air-conditioning in buildings in South Africa. Conventional vapor compression systems use
refrigerants that damage the ozone layer and contribute significantly to the global warming
effect. Therefore, there is an urgent need to implement environmentally cleaner ways of
satisfying this air-conditioning demand and absorption cooling systems have shown great
potential to do so.
This project is concerned with finding the technical and economic effectiveness of solar powered
absorption cooling systems for South African climatic conditions. Solar cooling systems are
made up of a solar collector array, water storage tank, absorption chiller and cooling tower for
heat rejection. In this study, two complete systems, one utilizing an open wet cooling tower and
another using a dry cooler were studied and their technical and economical performance
analyzed. One system was installed at Netcare Moot Hospital in Pretoria and comprised of a
solar collector array made up of 52 evacuated tube collectors, two 6000 litre hot water storage
tanks, 35kW LiBr-water absorption chiller, and a wet cooling tower. This system was coupled to
an existing vapor compression chiller so that cooling is provided even when no solar energy is
available. The installation controlled and remotely monitored through the internet and parameters
logged through a Carel Building Management System. The other system is at Vodacom World in
Midrand, Johannesburg and is an autonomous solar heating and cooling system aimed at
maintaining the building environment at comfort conditions throughout the year. It is made up of
a 116m2 evacuated tube collector array, a 6500litre hot water storage tank, 35kW LiBr-Water
absorption chiller, 1m3 of cold water storage, a dry cooler for the chiller, and two underground
rock storages to pre-cool the supply air to the building and the dry cooler respectively. Long
term system performance studies were carried out by varying the system control strategy for the
chiller, hot water storage tank, existing vapor compression chiller (in the case of the Moot
Hospital installation), hot water storage tank, dry cooler (for the Vodacom installation) and the
system Coefficient of Performances were calculated and life cycle cost analysis carried out. Due
to the fact that solar availability and cooling demand are approximately in phase, solar powered
absorption cooling presents a great opportunity for reducing peak electrical cooling energy
demand. It was also discovered that the economic effectiveness of the system increases with the
absorption chiller capacity, and it‟s more advisable to operate the solar absorption cooling
system with a vapor compression chiller as a backup for facilities that require uninterrupted
cooling. The solar autonomous system is oversized for most of the year since it is designed to
cover the peak cooling loads.
Description
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.
Keywords
Solar air conditioning--South Africa., Solar heating--South Africa., Solar energy--South Africa., Theses--Mechanical engineering.