Phase I of the National Energy Centre (1999)

The initial brief for the Centre was to create a building that would:

• use 40% less energy for space heating/cooling than CIBSE standards
• be constructed at no extra cost to more conventional buildings
• have a long design life and provide a stress-free working atmosphere
• allow flexible use of space with an area for meetings & displays
• maximise winter solar gain without over-heating in summer

Building Fabric

The strategy was to provide a high thermal inertia (mass) using:

• Exposed concrete ceiling on ground floor
• Multiple (dual) layer dense cement fibre boards on first floor ceiling
• Blockwork walls

- and the ability to vent overnight in summer. This was achieved through:

		Thickness (mm)	U-value
	Roof	Zinc skin above 50mm air gap 300mm insulation 80mm thermal board	0.13
	Walls	50mm air gap 80mm insulation	0.26
	Floor	315mm concrete slab 50mm insulation	0.15

Windows and Ventilation

The window design is: Softwood frames by Rationel Low-e glazing (centre U-value=1.9) Four narrow external light shelves One wide internal light shelf Vents with external louvres and lockable insulated doors to the interior are situated next to each window providing fresh air for occupants and allowing passive cross-ventilation of the working space.

Heating System

As the building has such a low heat demand, it was possible to install a domestic scale heating system based around an MHS Strata 1 condensing boiler. The boiler has a fully modulating heat output sliding between 20% and 100%. Its stainless steel heat exchanger is designed to return operating efficiencies from 88% to 96% (gross). This ensures that there are extremely low NOx and CO emissions. The unit also has a variable speed primary pump which allows the boiler to maintain the widest possible temperature difference across the heat exchanger (resulting a seasonal efficiency gain of some 7% to 10%). Control is through an electronic 7 day integrated timer and room thermostat, with a set back temperature for night and week-ends. Local temperature control is mainly by thermostatic radiator control valves (TRVs).
To avoid running the boiler at part loads in summer, instantaneous electric hot water units were fitted at each point of use.

Monitoring & Performance

An Eco-Warrior PC-based monitoring system was installed to log energy use and other relevant data, such as internal and external temperatures. Monitored data is verified against actual meter readings and utility bills. The strategy of providing a high thermal mass for the building has clearly worked very well, with occupants enjoying a very even climate inside the building with low energy use. In winter, this is generally achieved with the heating running more or less continuously from about 7.30 to 9.00 am, then requiring only short top-up bursts later in the day. For example, the small screen image shows internal and external temperatures on Thursday 15th February 2001. The external temperature rose from -3.5°C at night to a maximum of just 4.5°C by day, but the internal temperature at the monitoring point did not fluctuate by more than 1°C. And this was achieved with the central heating system only firing measurably in the first 1½ hours - later in the day, most of the heating requirement came from solar gain or incidental gains from the occupants and office equipment.

Summer energy use is very low, as the building is naturally ventilated. The internal temperature can rise as high as 24 or 25°C during prolonged periods of warm weather, but again fluctuates very little between day and night. Working conditions are more than acceptable, as staff can maintain a good cross-ventilation through opening vents beside the main windows, and the external overshading prevents the direct solar gains that are so useful in winter, when the lower sun angle allows warmth into the building.

The Eco-Warrior system also shows quite clearly how the lighting strategy is working. On bright days, throughout the year, there is often no lighting circuit consumption at all downstairs, with only limited use upstairs. In the example shown, the peak demand on the graph is just 1,600W serving an area of 400m². It is noticeable that the greatest lighting demand occurs when the cleaners come in at night and switch on all possible lights, proving that staff motivation is also an important part of minimising energy use.

Analysis of bills has shown that The National Energy Centre has achieved total energy use of considerably below the Building Research Establishment's Best Practice guidelines for a modern naturally ventilated office.