Construction is about to start on Phase I of a business park in Luton which uses earth cooling to supply air to small office units. The Butterfield development for Easter Properties has been designed by Hamilton Associates. Each building is supplied with external air drawn through a 1.2m deep earth duct that runs for 80m to a protected screened air intake. Air is supplied into the office areas through a displacement system via a plenum floor. It is intended to be extremely simple and has one major advantage over natural ventilation: controlled night cooling can be achieved without having to open and close the windows automatically. It also has other benefits: the costs for the whole system are less than for a simple fan coil unit system; the temperatures in the office spaces can be kept at or below 26°C under 'normal' BCO loadings; and the CO 2 emissions are half those of a naturally ventilated building and 20 per cent of those for an air conditioned building. Atelier Ten developed a larger- scale proposition with Make and Carey Jones Architects for a competition project in Leeds with Urban Catalyst, which extended the idea to an eight-storey building.