ABSTRACT
A large credit company has decided to relocate and centralise its offices and operations from a number of city centre sites in Northampton to the outskirts on a ‘green’ field site. Their present buildings are air conditioned but, the concept for the new building is an ‘environmentally friendly’, natural ventilated, low rise, one with a street style atrium. Only a small area of the building requires air conditioning for operational reasons. At an early stage of the conceptual design the client expressed certain concerns over whether natural ventilation would be adequate to maintain comfort in view of the extent to which the company relies on computers and associated peripheral equipment. The heat released from equipment in typical areas of their existing offices was surveyed and used as parameters in thermal models. Initial temperature predictions indicated that on the basis of natural ventilation alone internal temperatures would only exceed 26°C in the afternoons of a few days in a typical year. However, the client decided that the internal temperature should be limited to a maximum of 25°C during the warmest days of a typical summer. Intentionally providing a margin for exceptional summers and the risk of climate change. The client also required the option to install full air conditioning at some future time for investment purposes. Comparisons were made between full air conditioning, various mixed mode strategies. The design solution is a mixed mode building comprising both natural and mechanical systems that will operate predominantly in the natural mode. Natural ventilation is provided by fixed open trickle ventilators, opening windows, and automatically controlled vertical open lights in the atrium roof and side wall glazing. The mechanical systems include forced ventilation (displacement) and direct cooling (chilled beams), only intended for use when natural systems are inadequate. The paper is a design case study that describes the philosophy behind the design and, the analyses and modelling techniques used to determine the provision for natural ventilation. Keywords: Air conditioning, Energy efficiency, Mixed mode, Natural ventilation, Opening windows, Overnight cooling, Passive cooling, Trickle vents.
