be provided by only using the thermal energy stored overnight in the tanks .
The electrical load required for a directexpansion split type system is generally between 60 to 70 W / m 2 . The electrical load for a welldesigned chilled water system is in the region of 50 to 55 W / m 2 . The chiller-assist thermal storage system only requires between 20 W / m 2 and 28 W / m 2 of electrical power . During a power failure scenario , only the pumps and fan coil units require generator power . The BMS system keeps the heating elements from switching on under power failure conditions , ensuring that only 10 W / m 2 of generator power is required to provide 100 % of the full peak cooling load for up to 4 hours .
Two central air-cooled chillers are positioned in a freely ventilated plant area on the roof of the building . Three thermal storage tanks are situated in the basement . Chilled water is reticulated to in-ceiling fan coil units by means of a reversereturn variable speed pump chilled water pipe reticulation system .
The air is conditioned by in-ceiling fan coil units . The conditioned air is introduced into the occupied zone by means of constant volume ceiling diffusers . Each fan coil unit conditions a temperature zone varying in size between 25m 2 and 80m 2 . Dedicated units are allocated to sensitive areas i . e . executive offices , boardroom and meeting rooms . The motion sensors that control the lights are incorporated into the operation of the air-conditioning system . When an area is unoccupied , the air-conditioning units switch to an economiser mode . The unit ’ s temperature set-point is then adjusted to 26 ° C . This allows us to reduce the energy demand , but simultaneously , it enables us to reduce the pull-down time to bring the office ’ s temperature down to the set-point temperature .
The BMS / Fan Coil Manager allows for complete control flexibility . The HVAC system can either be controlled centrally by the facilities manager or individually from any desktop computer or laptop .
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