The design incorporates natural ventilation strategies with 12M deep wings, open plan office areas and a series of ventilation methods including large window vents, small high-level window vents and bespoke baffled ventilators for trickle/ low volume ventilation to avoid draughts. High-level vents ensure that hot air can escape while incoming air tends to distribute across the concrete slab soffit. Actuators linked to a building management system operate inaccessible window ventilators.
The main Council Chamber has special low-level vents, which allow air to enter the Chamber through insulated sound attenuation chambers.
Geothermal heat exchange loops are buried under earth berms formed from the site spoil. The berms in themselves reduce the amount of spoil required to be removed from the site. The energy from the earth is used via heat pumps for heating and cooling pipes, which are cast into the coffered concrete slabs, which in turn either preheat the spaces in winter or precool them in summer utilising the mass of the exposed concrete.
A cooling tower is located on site and it is used for heat rejection from the slab cooling pipes in the hottest months. The tower uses sprayed water avoiding the use of refrigerants. The use of the tower reduces the amount of energy consumed in pumping fluid through the geothermal circuit.
The principles above are used in the Health Board block, but due to the requirement for cellular offices in this organisation an air handling unit was introduced to provide make-up air to the internal offices and to the atrium itself. In fact there are only three internal offices as most of the rooms are on a perimeter wall.
External stainless steel mesh screens as well as planting to southern aspect elevations provide solar and glare shading. Internal glass light shelves bounce light onto the soffit so that natural light penetrates deeper into the plan, as well as filtering direct glare. Glass is high performance with a U-value of 1.4W/sqMK, light transmittance of 66% and a solar factor of 34%. Internal translucent solar film blinds complete the light and solar protection design.
All openings and windows are air sealed to the building fabric with epdm membrane. Air Infiltration tests were carried out on the building to ensure that energy is not lost through leaks.
Roof insulation is CFC and HCFC free. 150mm is used to produce a U-value of 0.159 W/sq MK, lower than the new Building Regulation for dwellings and significantly lower than the requirements for buildings of this type. The consequent reduction in heat loss through the fabric will reduce energy requirements.
Wall insulation is typically 100mm, which produces a U-value of 0.3 W/sqMK. The insulation is outside the primary masonry of the building so that again the mass of the walls contribute to the thermal stability of the accommodation.
Solar energy collectors are located on the roof of the long office wings. The solar collectors heat hot water for WCs located at the end of the wings in order to avoid long hot water pipe runs.
Car parking for approximately 250 cars is provided. This has been designed so that under areas where cars park the hard surface is allowed to free-drain, through a no-fines concrete set in a grassgrid, into the earth where land drains operate. This avoids excessive water runoff into the local system and permits a lower size of drain.
Grey Water storage tanks are provided which use rainwater from the roofs to supply toilet cisterns within the scheme. This strategy reduces demand on mains water and all the energy consumed in its delivery.
The energy usage during the first months of usage was 159 KWh/ sq M per year.