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An interior view of the centre showing roof lighting to help reduce the electrical lighting load
In full operational mode, the centre has simultaneous requirements for heating and cooling, something which this technology can uniquely provide, and do so with a fraction of the hardware required by a conventional cooling system, as Sikora explains. “There’s an arrangement of pumps and valves in the plant room which will decide whether we are dumping heat into the ground, which will happen during the summer, or whether we are on net fashion extracting heat from the ground and delivering some of the cooling to the building.” Six independent air handling units look after the distribution of this heated and cooled air. Voids beneath the ramps in the central dome convey the treated air, which is dispatched into the space via slot grilles running horizontally at floor level. Paul Sikora explains the logistics of serving both heating and cooling loads. “If you have a lot of occupancy and you have to deal with odours or C02 build-up, that’s all picked up by sensors that look at the quality of the air coming back from your conditioned spaces. Then, as the air goes through the box, it first goes through a filter, then it will hit a coil which is served by cold water. If you need cooling or moisture removal, there will be chilled water going through that coil, and the temperature of the air is dropped going through it. After going through that radiator, it hits the second one, which will be served by the warmed water from the machine. If the air does need heating before it’s sent back into the room, warm water will be pumped into that coil, and so the valves and the fans and the mixing of the air is all controlled by instrumentation right at the air handling unit. What our equipment does is it provides a large reservoir full of chilled water and another one full of heated water and the system mixes and matches according to whatever requirements it has to satisfy.”
There’s one further element of this system which satisfies both energy and aesthetic imperatives in an ingeniously serendipitous way. Declan Leonard explains. “The air supply ducts to the building, we couldn’t just have big louvers on the side of a building to take in air, we had to take the air intakes back away from the building and the only way we could do that at the time was underground. We had to use concrete drainage pipes, the large 1500mm diameter ones you’d see on the side of the road. We used maybe 30m or 40m of those, back up along the hill, where we hid basically the intake point. The beauty of that was – and we modelled this on the software first –that during peak winter temperatures, we take in the air at say -3c up the hill. By the time it reaches the building, it has gained maybe five degrees of heat.” The concrete pipe in the ground remains at a more or less constant temperature throughout the year, so the process of taking in warm air for cooling in summer or cool air for warming in winter changes the temperature in the desired direction. The phenomenon, because it was pre-modelled on the software, allowed the engineering team to downsize the heatpump in proportion. “I don’t think that got much headlines but I think it’s the most energy efficient thing in the building because there’s absolutely no energy input into it at all.”
The bathrooms in the centre, where treated waste water is recycled for flushing toilets and urinals
All energy consumption requirements were plotted using thermal dynamic simulation software in order to optimise the energy spec. Here again, the project team found aesthetics and energy minimisation working in harmony. When it came to insulation however, the subterranean structure didn’t provide quite the performance that the engineers had expected. Declan Leonard explains. “Parts of that building are under a lot of soil, which one would assume would give you huge insulation properties but the reality is it gives you very very little. At 15m you get quite a bit but at 4m or 5m, the thermal conductivity of soil, especially when it’s wet, is of no use at all. Day one when we looked at it, we talked about not providing any insulation bar the soil itself, but we ended up putting 75mm of insulation over the majority of the building – except the back which was covered with 16m of soil. At that depth, it gave us the same effect as three inches of high performance polyurethane.” The key issue with the insulation was its compressive strength. With so much soil pressing it to the external shell of the structure, conventional insulation materials would have disintegrated. There was however a pre-existing solution available. A highly compressed material had already been developed for the heavily trafficked floors of industrial cold-rooms. “Basically the civil structure consultants gave us the load, which is quite a simple calculation, the weight per metre cubed of soil by the height, so the vendors of the insulation have a compressive strength. Once we found what we were after it was a reasonably simple exercise.” If the soil overhead lacked thermal properties, the concrete structure itself offered thermal properties that the engineers were able to draw on in order to optimise the building’s energy requirements. “Parts of the concrete structure are 800mm thick.” Declan Leonard explains. “In sustainable design, the more thermal mass you have, the more stable your environment will be. It will take a lot more heat to heat up that wall but once that’s heated, it’ll store the heat and release it at a slower rate than a lightweight building.” Factoring in these properties, together with a series of external weather files and internal temperature trends, an optimiser within the building management system manipulates heating and cooling in order to maintain that thermal stability.
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