Air handling units
CENTRE TAKES A DIP INTO AHU EFFICIENCY A
ir management specialist Mansfield Pollard was appointed by Nuffield Health to upgrade the swimming pool air handling
units at the newly acquired Fitness & Wellbeing Crawley Central Club in West Sussex. The swimming pools were served by a pair of
Calorex AHUs, which were in a poor state of repair and difficult to maintain due to their complexity and use of refrigeration circuits for dehumidification. Both units were sited in a small roof top plantroom with no clear route through the building, making access very challenging. Nuffield Health wanted its new solution to be easy to maintain and energy efficient. It also wanted minimal disruption. In effect the gym didn’t want their customers to know that the changeover was taking place. After several surveys and meetings with the client a proposal was put forward. The plan was to strip out and replace the pair of existing Calorex units with a single AHU built to withstand the aggressive environment of a swimming pool and increase energy efficiency with a more easily maintainable unit. Using CIBSE and ‘Sport England’ guidelines, and thermal modelling of the swimming pools, a performance specification was agreed for the AHU, which was: • Pool water between 28˚C and 30˚C
(air temperature 1˚C above water temperature)
The pool water is maintained between a set point of 28 and 30˚C which is predefined and determined by the gym services manager. The swimming pool air temperature is to be maintained 1˚C higher than pool water temperature. This creates a more comfortable environment for the bathers. • Air Change rate 7acph (4m3
/s)
Minimum fresh air 30% or against occupancy, 12 l/s pp and 1p / 4m2
, whichever is the greatest.
Humidity to be maintained between 50% and 70%, allow RH at higher levels in winter to use recirculated air and reduce heat load. Keep pool under slightly negative pressure to prevent moisture being driven into walls. Night time recirculation mode to save energy limited by humidity requirements. A final design was proposed with a thermal wheel heat recovery AHU (due to space restraints), incorporating night time air recirculation, filters and LPHW heating. Dehumidification would be performed by mixing fresh air and the whole system controlled by a TREND controller linked with the site’s BMS
system. All the AHU components and the internal materials were treated to withstand the aggressive chlorine based environment. To allow the pool to remain open, a temporary fan system was connected to the ductwork serving the pool area. On the supply a fan and coil were positioned on the duct entry to the pool to provide tempered fresh air during the works, all this being installed
overnight so the pool could open as normal. With no accessible routes to the plantroom the
removal of the old equipment and installation of new equipment had to be carried out by crane positioned adjacent to a multi-storey car park. These lifts also had to be performed overnight. Thanks to planning and coordination between the specialist engineers and designers, within two weeks Mansfield Pollard had completed the installation including new pipework and electrical installations with a reconfiguration of the ductwork serving the swimming pools. Over a single night the temporary ventilation installation was disconnected and the new AHU reconnected to the swimming pool. The AHU and associated systems were commissioned and set to work.
ENERGY EFFICIENCY IMPROVED RUNNING COSTS REDUCED
COMPACT SIZE CREATED NEW STORAGE SPACE
EXTREMELY RELIABLE
TO ENSURE CONSTANT TEMPERATURE
www.heatingandventilating.net
September 2017
25
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