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Natural Ventilation in unusual places

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.

persian_natural_ventilationIn 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



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