VOICES | BILL BORDASS BILL BORDASS FCIBSE is research and policy adviser to the Usable Buildings Trust bill@bordass.com ones, while 2+1 performance can be enhanced further by incorporating heat-rejecting glass. External shading may also attract birds and obstruct window opening and cleaning and, if one small piece blows off in the wind, facilities managers may rip the lot off the entire building for health and safety reasons. Frames for 2+1s cost more to make than for sealed units alone, but not that much more, and there are advantages: the sealed units last much longer because their perimeter seals dont get wet; the inner frames can be made from timber for better appearance, insulation and sustainability; and the external frame is usually aluminium for weather protection, but lightweight because the stiffness comes from the timber frame and the glass. If there was a proper market for them, costs would go down. How about making them deemed-to-satisfy in the Building Regulations? Further improvements can be made by ventilating the blind cavity, which is normally only partially sealed to avoid condensation. For example, the cavity can be: Cooled further if ventilated naturally from bottom-totop, or used for exhaust air in a pressurised building Used for heat recovery into the building, either by natural transpiration or drawn through by an extract system; this works particularly well in airtight flats that have kitchen/bathroom extracts running 24/7. In fact, if used as a supply air window, an effective U-value of less than 1W.m-2K can be achieved by using a single internal pane, not a double-glazed unit,3 so reducing capital and maintenance costs important in social housing. Now we are more aware of the need to limit overheating in the UK, will the 2+1 window come back into fashion? It has proved itself in UK projects, including the Elizabeth Fry Building4 at the University of East Anglia and the Open Universitys Design Studio refurbishment.5 We talk about innovation, hoping for the next big thing. But much innovation is purposeful improvement, based on feedback on what works and what doesnt. Sometimes this means going back to the future. I am encouraging British manufacturers to produce 2+1 windows and researchers to explore them, while examining the products on the European market. References: 1 UK housing: Fit for the future? Committee on Climate Change, February 2019. 2 This is argued convincingly by Professor Bent Flyvbjerg, now Chair of Major Programme Management at the Said Business School, Oxford in Five misunderstandings about case study research, Qualitative Inquiry 12(2) 219-245, April 2006. 3 Improving air quality in homes with supply air windows, BRE Information Paper IP 6/03, 2003. 4 Probe 14: Elizabeth Fry Building, Building Services Journal, 20-25, April 1998. 5 Naturally comfortable ofces a refurbishment project, Good Practice Case Study 308, BRECSU, BRE, March 1997. Uninterruptible Power Interpreted Look out for our free upcoming webinar A simple cooling solution for properties short on power. With 86% less electricity required, save your power, your time and your money getting on the grid. Thursday 16 May 2019 | 13.00 BST essaircon.com 020 8641 2346 Panasonic gas engine VRF and chillers | Robur gas powered chillers and heat pumps Brought to you by: CIBSE JOURNAL 24 April 2019 www.cibsejournal.com CIBSE Apr19 pp23-24 Bill Bordass.indd 24 22/03/2019 16:52