Office c<strong>as</strong>e study cibse AwArd winner The design of the offices incorporated the idea of keeping the supply of fresh air to a minimum Predicted vs actual energy use John Williamson’s prediction for energy consumption w<strong>as</strong> unnecessarily high. Two years of monitoring h<strong>as</strong> shown the total operational energy consumption to be just 80k Wh/sq m/yr. He says that this is probably because computer use h<strong>as</strong> been lower than expected. Monitoring showed that internal summer temperatures did reach 26C maximum in the first summer. However, the re<strong>as</strong>on for this w<strong>as</strong> found to be due to an external 38 ventilation fans. His premise w<strong>as</strong> that the scheme would use less energy and the building would be more comfortable if the supply of air w<strong>as</strong> kept to the absolute minimum. This small amount of fresh air could then be cooled, perhaps using a small heat pump, before it is supplied. In summer, this solution would keep heat out of the building during the day and enable the ventilation fans to be turned off at night. He is currently applying for research funding to test his premise on part of the building’s ventilation system to find out whether this would be a more energy efficient ventilation solution for future P<strong>as</strong>sivhaus offices. sensor, damaged by a football, shutting down the night purge ventilation too soon. For heating, through two of the coldest winters on record, temperatures varied between 20C and 22C, depending on the occupier’s control of the radiators using thermostatic radiator valves. However, when the building is fully occupied the heat gains are sufficient to keep the radiators turned off which means the boiler is only used for a short time on calculation Methodolgy sq m kwh kwh/m 2 /a kwh/ Co 2 m 2 /a very cold mornings. As a result of this, and because the solar gains were higher than expected, the building’s space heating load of 14.8 kWh/sq m is also slightly lower than the 15 kWh/sq m/ yr predicted. To put this into perspective, the building’s g<strong>as</strong> bill w<strong>as</strong> £130 for a recent 12-month period. The photovoltaic panels have also performed better than predicted. ‘We installed the PVs to show how a small area of a The ventilation design w<strong>as</strong> further complicated by Powys County Council’s l<strong>as</strong>t-minute decision to add a computer server room to the scheme, which added an additional 720 W of heat. The council also decided to stick with its existing computer framework supplier rather than purch<strong>as</strong>e ultra-low energy machines. ‘Suddenly, IT energy use rocketed,’ Williamson laments. What’s more, the incre<strong>as</strong>ed ventilation needed to offset the additional heat gains pushed the scheme’s annual energy consumption up from 112 kWh/sq m/yr to 184 kWh/sq m/yr, far above the 120 kWh/sq m/yr allowed by P<strong>as</strong>sivhaus, jeopardising the building’s certification. Following these changes, Williamson w<strong>as</strong> forced to refine the design at the l<strong>as</strong>t minute. As a result, a brise-soleil w<strong>as</strong> added to the ground-floor glazing on the southern elevation. Extensive daylight control w<strong>as</strong> added to the T5 lighting to push its energy consumption below 10W/m2. Mechanical timers were installed to shut down all electrical sockets at night to eliminate standby losses. Movement detectors were added to the MVHR systems serving the computer rooms to enable the lights to be turned off and the ventilation turned to ‘low’ when the rooms are unoccupied. These units will run on medium speed when the room is in use; the high setting will only kick in when temperatures exceed the P<strong>as</strong>sivhaus low maintenance, reliable technology can make a big contribution to a low energy building,’ says Williamson. The panels have produced 5,987 kWh/ yr, which equates to about 20% of building’s needs. Unfortunately, because the PV installation w<strong>as</strong> grant-funded, Powys County Council cannot claim a feedin tariff; had it done so, says Williamson, the tariff would have been ‘more or less equivalent to the g<strong>as</strong> and electricity bills’. SPaCE HEatIng total oPEratIonal EnErgy total PV gEnEratIon (7kw array) total fuEl CarBon G<strong>as</strong> 08/10/09 - 08/10/10 (0.194kg/cO /kwh) 2 electricity 08/10/09 - 08/10/10 (0.568kg/co /kwh) 2 CoSt 08/10/09 - 08/10/10 EmISSIonS £/yr kwh kwh/m 2 /a kwh/ Co 2 m 2 /a £/yr £ kwh/a kwh/ Co 2 m 2 /a approx fit income £ P<strong>as</strong>sivhaus 335 Predicted 5,025 15.0 2.9 48,240 144 81.8 5250, 8.9 1,895.00 75.8 Canolfan Hyddgen 335 Actual 4,973 14.8 2.9 131.1 26,860 80 45.5 2409.82 2540.93 6,493 11.0 2,600.00 37.4 Canolfan Hyddgen Part l2 391 Actual 4,973 12.7 2.5 131.1 26,860 69 39.0 2409.82 2540.93 6,493 9.4 2,600.00 32.1 Bldg reg notional Part l2 391 Predicted 17,986 46 8.9 15,640 40 25.2 5,250 7.1 1,895 127.1 kwh/ Co 2 m 2 /a <strong>CIBSE</strong> <strong>Journal</strong> April 2011 www.cibsejournal.com
LIFE SUPPORT for energy efficient and sustainable homes Lungs Highly efficient heat exchanger - up to 9l% E<strong>as</strong>y to maintain filters Arteries Full range of matched ducting for optimum performance Ports accept l00 or l25mm ducting with no adaptors Tel: 01206 713800 www.titon.co.uk/hrv Heart Top quality, highly efficient fan motor keeps things running smoothly Brain Electronics balance, monitor and control air flow levels perfectly Airways Fully adjustable boost settings incre<strong>as</strong>e capacity when required Will your ventilation system be fully functioning? Call our consultants for a ‘Ventilation Health Check’ www.cibsejournal.com April 2011 <strong>CIBSE</strong> <strong>Journal</strong> 39
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