Case study Post-occupancy evaluation
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The wildly varying electrical consumption on site is very much down to occupant behaviour
use of biomass is now rising rapidly and should reach 70% after some technical and supply problems were resolved. ‘Things are moving in the right direction,’ he notes. The wildly varying electrical consumption on site
is also very much down to occupant behaviour. The highest users at Clay Fields consume 64.7 kWh/year per sq m, substantially above the national average of 47.7 kWh/year per sq metre, while the lowest users consume just 17.6 kWh/year per sq m. These figures include electricity consumption that is beyond the control of the building team, such as televisions and white goods like tumble driers. ‘Thirty-seven to 45% of total carbon emissions are out
of the designer’s hands,’ asserts Gill. Buro Happold also discovered the use of ‘regulated’ electricity at Clay Fields – lighting, pumps (for central heating) and the mechanical ventilation and heat recovery system (MVHR) – varies widely. But the variation is not as wide as for ‘unregulated’ use – that is, of various appliances such as in cooking. So involving and motivating users in reducing energy use in this area will be important for further reductions in future. Water consumption also varies widely, with the
Electrical consumption on the site is logged
biggest users measured at 196 litres per person per day, far exceeding the national average of 148 litres. However, average water consumption at Clay Fields was well below the national figure, at 91 litres, while the most sparing occupiers consumed just 28 litres per person per day. The rainwater harvesting system, which supplies grey water for toilet flushing and garden irrigation, is believed to be providing 24 litres per person per day. Gill suggests that water consumption may fall further if there were some way of showing occupiers how much stored rainwater is in their tanks on any given day; for example, if the tank is empty, they may think twice about watering the garden. However, Gill notes: ‘The occupiers aren’t too worried about water consumption because it is relatively cheap and they don’t feel they are wasting it.’ l
The POE results
Post-occupation evaluation of Clay Fields development in Elmswell, Suffolk, by Buro Happold. Data collected between September 2008 and November 2009.
Space heating and hot water, kWh/yr Great Britain average per sq m: Mid-Suffolk average per sq m: Clay Fields design target per sq m:
191.5 172 121
Clay Fields average actual performance per sq m: 92.9
Clay Fields highest per sq m: Clay Fields lowest per sq m:
144.9 46
Estimated average energy requirement for space heating per sq m at Clay Field:
Estimated average energy requirement for hot water per sq m at Clay Field:
Electricity in kWh/yr Great Britain average per sq : Mid-Suffolk average per sq m: Clay Fields design target per sq m:
Clay Fields average actual performance, per sq m:
Clay Fields highest per sq m: Clay Fields lowest per sq m:
73 20
47.7*** 61.9*** 13.9*
40.9** 64.7** 17.6**
* ‘Regulated’ electricity only, ie MVHR, lighting, pumps ** Includes unregulated electricity, ie other appliances *** Is both regulated + unregulated electricity combined
Average MVHR electricity use at Clay Fields, per sq m:
Electricity used for lighting at Clay Fields, per sq m:
Other electricity use at Clay Fields, per sq m:
Water litres/person/day Great Britain average: 148 Clay Field highest: 196
40 CIBSE Journal September 2010 6.7 4.8 to 9.8 (estimated) 24.6 to 29.6 (estimated)
Clay Fields average: 91 Clay Fields lowest: 28
www.cibsejournal.com
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