Chilled water is circulated by an arrangement of primary and secondary pumping to provide the coolant for the air-handling plant and fan-coil units. The chilled water is produced by air-cooled refrigeration plant in the louvred external compound at roof level.
Allowances for internal heat gains were based on nett office areas and the following technical specification:
Lighting: 10 Watts per square metre nett over all office areas.
Equipment: 25 Watts per square metre nett over all office areas.
Occupancy: Occupancy densities for the calculation of internal heat gains were based on one person for every 10 m² of nett area. Metabolic heat gains were based on C.I.B.S.E. standard data.
All internal heat gains were assumed to be evenly distributed throughout the open plan floor plates.
Fan-coil units are provided along the perimeter of the building at intervals of no greater than 6.0 metres.
Each perimeter fan-coil unit serves a depth from the external wall of approximately 4.8 metres. Fan coil units serving central areas are more widely spaced.
The FCU’s are controlled individually. Where possible, perimeter fan coil units are controlled by room temperature sensors mounted on the internal surface of structural columns. There are two FCU locations on each floor where the columns are too widely spaced to accommodate room temperature sensors. In these locations, temperature sensors are located in the return airstreams to their respective FCU’s.
Cooling Loads and Blinds
Tenants are required, as part of their fitting out work, to install window blinds to improve the visual comfort of staff reading computer screens. The use of blinds will also assist in reducing the discomfort arising from solar glare that may occur, especially during the early morning in east facing offices and in the late afternoon in west facing offices.
The presence of an internal blind was included in the analysis of solar heat gains which form part of the air conditioning calculations that also include equipment gains of 25W/m². Equipment gains of 25W/m², whilst satisfying the 2009 BCO Guide to Specification, are considered to be generous. Gains of this magnitude are representative of an office with a high density of computers where blinds become essential if the screens are to be read for long periods without causing discomfort.