Projects resulted in 1 678kW during peak electrical tariffs , as opposed to the total 2 556kW a conventional chilled water system would have had . The thermal storage system was designed to satisfy 50 % of the peak day kW .
Hot water for space heating purposes is available at any time of the year , regardless of the cooling demand or plant cooling operating status . The peak heating capacity of the system is 870kW .
The sequence of operations relating to the various plant modes is achieved by the control system which is made up of various valves , actuators and controllers , and follows the dictates of the design .
The plant along with ancillary components such as buffer tanks , glycol management , ice inventory and expansion / makeup systems are located on the roof of the main campus building .
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Chilled and hot water hydronic circuits The chilled water pumping arrangement is a closed loop constant-primary and variable flow secondary system de-coupled by means of a plate heat exchanger . The heat exchanger also allows for the glycol solution to be contained in the plantroom only .
Chilled water generated by the chillers is supplied at 4.5 ° C and -6.0 ° C for normal and ice production modes respectively . Chilled water is supplied to the building at 8.0 ° C by the N + 1 variable flow vertical centrifugal pumps located on the roof plant .
Air Handling Units ( AHU ) and Fan Coil Units ( FCU ) are generally fitted with 2-way modulating control valves , except for the hydraulically remote units which are fitted with 3-way modulating control valves to ensure minimum circuit flowrates and to eliminate dead-leg scenarios .
Hot water is supplied to the building by means of a closed loop by N + 1 variable flow , vertical centrifugal primary hot water pumps supplying hot water to the building at 45 ° C . The AHU and FCU heating control valve arrangement is similar to the cooling system .
Air-side system strategy The majority of the building area is open-plan and is served by ‘ All Air ’ 4-pipe variable air volume air handling units located on the roof . Economy cooling has been employed in this system to optimise energy usage . The principle is such that when ambient conditions are favourable enough to satisfy the building demand without the need for mechanical cooling , 100 % outdoor air is supplied to the building by actuating a series of dampers .
Insulated supply air ducts distribute conditioned air via riser shafts in each of the cores to the floors allocated to specific AHUs . The design of the system incorporates zoning of areas relative to their load characteristics with each zone assigned to respective AHUs .
1 and 2 : Air handling plant arrangement around a typical core .
Typical return air fan arrangement .
Air handling unit piping connections .
www . hvacronline . co . za RACA Journal I November 2020 25