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can be upscaled to reach temperatures suitable for pasteurisation , scalding , and other processes requiring 120-150 ° C temperatures .
“ As an example of an in-use installation , we use between 10 % and 25 % of the total heat of rejection generated by the refrigeration plant . We achieve this by using a plate heat exchanger that we run the refrigeration plant ’ s hot gas line through ( which is roughly between 65 ° C and 95 ° C ). Water is then circulated out of an insulated hot water tank ( similar to a geyser ) through another plate heat exchanger . The water is then directed through a different ring main circuit throughout the facility and then tees-off to different departments . The water temperature is regulated by an actuator valve in the hot gas line which is controlled by a temperature sensor inside the water tank . The hot water in this example is kept between 55 ° C and 60 ° C for the application ,” says Smit .
Smit continues , “ For an average-sized supermarket , a 500-litre insulated hot water tank is generally adequate and with the ring main an insulated 22mm copper tubing circuit is preferable . If you had to heat up the water in that 500-litre water tank using an electrical heating element , you would have used about 9kW of energy . With heat reclaim from a refrigeration plant , you use zero extra energy . Similarly , if you use heat reclaim off a refrigeration plant for air handling , you also eliminate a lot of electrical heating elements which will show a huge cost saving .”
Heat recovery has been popular in comfort heating of spaces including commercial , residential and retail applications in European countries for a long time and here too , larger installations are able to push back heat from plants tying into district systems . “ Further applications of heat recovery include underfloor heating and hot gas defrost cycles . All of these solutions are an efficient way of harnessing an essentially free resource that can reduce the client ’ s carbon footprint ,” adds Bell .
PRACTICALITY AS A RETROFIT SOLUTION As a number of plants in the country age and are known to be inefficient , or owners are trying to stretch their assets and are continuously looking at part-replacement of components , a simple way to generate better efficiency is to strategically retrofit certain aspects .
“ If the system in question comprises a multiplex plant , retrofitting can be done by use of a plate heat exchanger as illustrated earlier or alternatively a heat pump can be installed to increase efficiency ,” Smit comments .
Van der Merwe advises , “ Although it is possible to retrofit older systems , you would need to evaluate this on a case-by-case basis and not just assume that it is possible for all the systems that are out there . There are a number of other aspects that need to be considered for example : if the piping profile is suitable , how the piping to the condensers has been installed , what changes would be required to the system , would rebuilding certain sections be required , and so on . If you change the parameters of some older systems , it often becomes critical to evaluate the original design and consult the equipment suppliers to make sure that additions will not be harmful to the installed system .”
LOOKING FORWARD IN HEAT RECOVERY Historically the drive to incorporate techniques such as heat recovery has been lacking because there is a general consensus that carried from the past , the cost of electricity was always extremely low and so there was no incentive to look at these sorts of solutions . Further , to incorporate other techniques was burdensome due to additional design work , calculations , and on site the installation of separate pipe systems and components was just extra effort .
Today and looking forward , harnessing free energy and utilising it in a number of applications will not only be practical , but it will also become critical as the world drives requirements to combat climate change , and so even locally we will not be protected from this push . We are likely to continue to see increased pressure to reduce carbon footprints and in South Africa this is directly related to our reliance on fossil fuels as the major energy provider .
Payback periods of capital investments are also reducing at a very fast pace , given the increasing operational costs facility owners have to keep in mind , and where every savings opportunity now has to be evaluated . With technology and advanced techniques across the board , plants can in future have a much smaller footprint too making them more affordable but more powerful at the same time .
“ The world is getting very close to that point of no return in terms of global warming . It is therefore sensible for everyone to start looking towards the future of what we call home and really start thinking more seriously about lowering our carbon footprints – exactly like harnessing the free ( or very low cost in the bigger picture ) resources . These include natural refrigerants – ceasing blowing off harmful refrigerants into the atmosphere and green energy . Global warming is going to affect everyone – even those who dismiss it because of placing profits first , and we need to take into account future generations ,” Bell concludes .
SOURCES 1 . Danfoss 2 . Energy Partners Engineering 3 . GEA Heating and Refrigeration Technologies 4 . Matador Refrigeration 5 . Oak Ridge National Laboratory 6 . South African Bureau of Standards 7 . General industry engagement RACA
www . hvacronline . co . za RACA Journal I February 2022 33