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Primary Secondary Variable AC Systems
The Primary side of the heating or cooling circuit contains the boilers or chillers as well as the primary pumps. In this circuit the boilers or chillers heat or cool the water which is circulated around by the primary pumps in a continuous loop between the chiller or boiler and the low loss header.
The secondary side of the system contains any of the plant items which transfer thermal energy into the rooms or equipment within the building. For example Fan Coil Units (FCU’s) Air handling units (AHU’s), Chilled beams or under floor heating as well as radiators etc. The secondary side can be made of multiple “secondary circuits” or just the one, this will vary with the design and load of the building.