Mechanical cooling is required in the facility throughout the year. This is a result of several fan systems (compartment units) that are incapable of using outside air to satisfy interior space cooling loads through the winter. <The chiller is required to operate a minimum of around 3 hours per night in order to store enough chilled water to satisfy the cooling load of the tower.>
It is recommended that the existing chilled water system be modified to allow for Hydronic Free Cooling. Evaporative cooling at the cooling tower would be used to generate chilled water directly when outside temperature is low enough. This would allow the chiller to be bypassed and turned off when the outdoor air temperature is less than about 5° C. <Because the chilled water storage tanks will allow the free cooling to occur at night, the free cooling season will be extended. Also, the free cooling will be capable of operating at higher outdoor air temperatures, since the cooling can be operated 24 hours per day at a smaller temperature difference.>
This measure would involve installation of a plate-and-frame heat exchanger, significant repiping around the chilled water plant, and training of the building staff on the intent and operation of the new equipment.
The heat exchanger must be easily isolated and cleaned. Plate-and-frame heat exchangers can be taken apart relatively easily for service. Smaller applications can use a much less expensive brazed-plate heat exchanger, which must be piped on both sides with isolation valves and takeoff ports for pressure flushing.
Issues and Concerns
Some sources claim it is possible to pipe the system in such a way that chilled water is diverted directly to the cooling tower, saving the cost of a heat exchanger and forming a direct cooling system. This approach is strongly discouraged. Tower water picks up dirt and oxygen from outside, which would be carried through the chilled water distribution, damaging interior surfaces of piping, valves and auxiliary components.
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