Technical
COUNTERING RISING
COSTS OF ENERGY
By Arshad Ali Khan , director at EHAVAC ( Pty ) Ltd
In the past 20 years HVAC equipment technology has improved like never before . At the same time , energy costs have risen at an exponential rate .
Commercial establishments like malls or hospitals , and process industries like dairy , meat , mining , plastic and glass account
70 % to 80 % of their electrical power toward their HVAC systems .
On this background - demand for higher efficiency in HVAC system is becoming a priority . It means we must plan a project strategically . Before choosing the type of technology to address project needs , a client must investigate what is available on site that can possibly help in reducing recurring costs .
For example , office buildings need air conditioning . If the building in question is using solar photovoltaics ( PV ), then in this scenario one can choose water-cooled chillers for the building . Water-cooled chillers have better electrical efficiency than air-cooled chillers . Even water consumption can be reduced if a design incorporates water-to-water heat exchangers to replace air cooled cooling towers .
But if that building has ( or is going to install ) a generator then the use of absorption technology should take preference because in the generation of electric power , exhaust and jacket hot water waste is nearly 60 % of the useful energy . This waste heat can be tapped using an absorption chiller . For most office buildings this waste heat will produce sufficient chilled water to keep the air conditioning running . In other words , use of an absorption chiller reduces buildings ’ electric load considerably .
A water-cooled chiller is known to be the highest COP provider . ( Generally , in the range of 4 to 6 ) but this is not what is achieved by the system . The reason for this is the need for peripheral equipment e . g . a cooling tower - which in turn needs electric power to operate .
• How to bypass the cooling tower and not cooling water ?
• How to eliminate high water bills ?
5 ° K heated water dropped back to the water table around 30 to 50m away .
This 5 ° K hot water will make no changes in ground water temperature , as the water table is huge and moving . This creates benefits such as independence of ambient temperature and cooling water for the chiller is cooled without electric power . Total system efficiency increase ( real COP > 5 is achievable ), and Less Capex / maintenance results with a reduced recurring expense of water .
ABSORPTION CHILLERS There is a misconception about the efficiency , flexibility , and maintainability of absorption chillers . However , in recent years , absorption cooling technology has undergone significant changes that defy these assumptions .
Today ’ s absorption chillers have proven to be efficient , reliable performers in many industrial cooling applications around the world , usually as part of a natural-gas or combined heat and power ( CHP ) system .
They use water as a refrigerant and make efficient use of waste heat or low-cost natural gas , making absorption chillers a cost-effective solutions in circumstances where natural
These are the questions that prompted me to explore and find a solution that one may appreciate . Just think of the water table underneath the ground , under your feet . Ground water temperature is in the range of 12 to 18 ° C and its quantity is 100 times more than required . So , I need to pump ground water , make it pass through heat exchanger where heat transfer takes place and
Absorption chillers can produce sub-zero temperatures . Therefore , they are very useful in the food industry such as meat processing , fisheries and dairy facilities .
All images Supplied
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RACA Journal I January 2023 www . refrigerationandaircon . co . za