We’re often asked about natural ventilation of healthcare buildings and whilst many are suitable in principle, it is made more complicated by the need to separate the supply to the different spaces to minimise the risk of transferring infections. However, this isn’t a problem if it is designed into the building early on and in fact there is nothing to stop healthcare buildings being exemplars of good practice in low-energy design.
We’ve recently been involved with a low-energy healthcare building at Houghton le spring, near Sunderland. We knew early on that we would look to use the building’s thermal mass to help us – cooling the building fabric at night and using this to cool the hot incoming air the next day. We considered various options including a thermal plenum underneath the ground floor which air could be passed through before it enters the building. However, this proved logistically difficult as we needed to provide air to both the ground and first floors. There would also be quite a few hours in the summer when we would need to keep the inside cooler than the outside in order to meet the client’s comfort criteria. The problem is that cool air is denser than warm air so descends rather than rises up through the building. In the end we decided to develop a thermal wall above an under floor plenum which would allow the outside air to enter the building at high-level. Imagine two 50m long walls, 10m high running along the middle of the building built 0.5m apart and with dividers every metre. This give us 50 or so shafts and makes it possible to separate the air for the different spaces and access the different floors. Looking at a plan drawing of the building, the thermal wall is obvious but when you’re inside the actual building you probably wouldn’t know it is there if you weren’t looking for it as the architect did a great job blending it in with the internal features. However, locating it in the middle of the building did give us the logistical problem of designing the shafts around the corridors and access routes which need to pass through the wall – this bit was more of a logic puzzle than a technical challenge. This would not have been possible if we hadn’t joined the design team as early as we did.
Since the design was so unusual there was no standard equipment that would fit so we designed and manufactured some bespoke equipment to sit on top of the thermal wall to regulate the airflow through the building. These units, one on top of each of the shafts have actuated dampers to regulate the flow and also low-powered fans to provide some mechanical assistance where necessary- most likely on the hottest days when mechanically pushing air over the thermal mass can provide significant cooling with only little investment of fan energy.
The building opened a few weeks ago and we’ve already started monitoring the system. The Indian summer really helped us as we could run some preliminary tests on the summer cooling before next year, something we hadn’t imagined possible in October! We’ve also just found out that we’ll be part of a team led by Willmott Dixon who has been awarded funding from the Technology Strategy Board (TSB) to undertake a performance monitoring of the building over the next two years. This will allow us to undertake some detailed monitoring of the system and include this in a review of the overall building performance.