Project
Not only did the team on this project have to pull a rabbit out of the hat with a 16-working-day turnaround , but it is also said to now be home to the largest VRF air handling unit on the continent .
As a plant replacement project , the original plant located at William Moffett shopping centre in Gqeberha ( formerly Port Elizabeth ), was estimated at about 1 400kW supplied by two water-cooled chillers in a sort of back-to-back installation in the sense that the chiller plant room was located adjacent to the coil arrangement with very short pipe runs .
When the team from VMG Consultants ( VMG ) visited the site the first time , it was very clear that the old plant was in a bad way and had experienced trouble for some time with certain components being disassembled and one compressor removed and lying on the plant room floor . From the plant layout and modifications , VMG assumed that compressor short-cycling and re-circulation of cooling tower air , were two of the likely culprits .
The original plant layout included a plant room housing the two water-cooled chillers , a plant room housing the coils and two backward curved centrifugal supply air fans , a plant room housing the filters and a manually set fresh air damper , two cooling towers set in a deep outside plant area constrained by high walls on three sides and interconnecting chilled water and condenser water piping between these elements . The total length of the chilled water piping was not more than about 20m . There was no buffer tank , and this almost certainly was a contributing factor for the degradation of the original plant installation because chillers require a minimum water quantity in order to avoid short cycling . The pipe runs were suspected to be far too short . Chiller-suppliers would advise that this is often a common fault with installations using this type of equipment .
The effect of this would be likened to starting and switching your car engine off continuously where it would obviously not last very long . Without sufficient water in the system there is accelerated wear on the compressors . The compressor will start , it will cool down the minimum amount of water in the system very quickly , and then switch off , repeating continuously .
PROVIDING AN APPROPRIATE CURRENT-DAY SOLUTION Having been involved for some time in assisting this supermarket chain to develop and upgrade their store specifications , so much has changed from the “ old days when we used a calculator , a standard one-page calculation sheet , and a few well used data sheets and tables ” according to VMG ’ s managing member Nigel Pengelly .
www . hvacronline . co . za RACA Journal I August 2021 33