1. Department of Design and Innovation
2. Energy and Environment Research Unit, Faculty of Technology, The Open University, Walton Hall, Milton Keynes MK7 6AA, England
3. Building Research Establishment, Bucknalls Lane, Garston, Watford WD2 7JR, England
4. Rickaby Thompson Associates Ltd, Witan Court, 296 Witan Gate West, Central Milton Keynes MK9 1EJ, England