Posted on 17/10/11
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.
Stephen Livermore
R&D Engineer