Posted on 24/05/11
Making natural ventilation work
in unusual spaces
Historically all buildings were
naturally ventilated. Now with the increased awareness of the
environmental impact of high energy use and with global energy
prices rising rapidly, natural ventilation has become an attractive
solution to reduce energy usage while maintaining a healthy and
comfortable environment for occupants.
In the UK natural ventilation is
commonly adopted in schools, although many designers of large
scale office spaces are still reluctant to use natural ventilation
due to clients wanting very precise temperature limits and small
temperature fluctuations. However, there are now a growing number
of buildings being naturally ventilated which have very demanding
requirements for ventilation and comfort.
In museums and art galleries the need for the
preservation of the artwork and historic artefacts requires the
galleries that they are displayed in to have full climate control -
this includes the requirement for humidity and temperature control.
The climate control strategy is most commonly achieved by using
some form of mechanical ventilation combined with heating, cooling,
humidification and dehumidification equipment. With the tight
absolute humidity limits (usually relative humidity within 40% to
60%) and even tighter restrictions in terms of daily fluctuations
it is clear that natural ventilation can be non-trivial
to implement within galleries when the external humidity often
varies beyond these limits. However it is possible to naturally
ventilate museums and art galleries, but requires more thought than
other building types. The strategy will need to be designed for
each specific building and the specific external climate. Using the
effects of thermal mass and moisture buffering from the fabric of
the building in conjunction with good monitoring and controls, a
stable environment can be achieved in the galleries with natural
ventilation.
However, this kind of strategy will
not be possible as a stand-alone solution in more extreme climates
such as extremely humid or extremely dry, cold places. A different
approach may be needed such as putting the display material in
humidity-controlled cases so that only human comfort criteria
affect the requried internal gallery climate conditions. Pollutants
are another concern in museums and art galleries; these generally
include the amount of particulates and the concentration of
pollutant gasses such as SO2, O3, NO2, and NOx. In mechanical
ventilation systems filtration systems are often used to reduce the
concentration of the pollutants. However, recent research indicates
that the benefits of filtration in mechanical ventilation may not
be as great as previously thought. For example, particulate
pollutants are mostly taken inside by visitors rather than from the
ventilation and some gaseous pollutants such as hydrogen sulphide
can be generated from sources within the museum and are not just
from vehicle emissions (Air Pollution Levels In Air-Conditioned and
Naturally Ventilated Museums: A Pilot Study; May Cassa, Nigel
Blades and Tadj Oreszczyn). Pollutants can be minimised in a
naturally ventilated space by designing systems with openings away
from the main source of pollutants and the effects can be
avoided altogether with the use of display cases for the artefacts.
Some examples of naturally ventilated museums include the Alcazar
Castle - Spainand and the V&A National Museum of Childhood
at Bethnal Green.
Modern hospitals are generally
mechanically ventilated, mainly for the purpose of pollutant and
infection control. Current NHS policies require that principal
medical treatment rooms such as isolation rooms and operating
theatres are mechanically ventilated. This is mainly for the
isolation and prevention in the spread of airborne infections.
These principal medical treatment rooms generally require a higher
level of filtration, with strict guidelines on airflow direction
and pressurisation of the room. However, all other public spaces,
offices and patient wards can be naturally ventilated. Natural
ventilation removes the reliance on mechanical fans for high
ventilation rates required for hospitals. Apart from major energy
savings, there are other benefits associated with patient comfort
and health. One example of this is the Houghton Primary Care
Centre. It is the first large health care facility to be awarded a
BREEAM Outstanding rating (
http://www.shine-network.org.uk/downloads/events/JoeBiggs.pdf).
The ventilation design incorporates e-stack equipment as well as a
central ventilation spine to ventilate large communal areas and
some consultant rooms. (For more information on this topic see
http://www.who.int/water_sanitation_health/publications/natural_ventilation.pdf.)
Increasing energy prices and CO2
levels have prompted designers to design buildings which are more
energy efficient. Natural ventilation is increasingly used in
sustainable building designs. When the ventilation strategy is
carefully developed for the specific building and the particular
external climate, natural ventilation can be incorporated in even
the most challenging circumstances either as a part of a hybrid
design, or even as a stand-alone solution.
Yichen Gao
May 2011