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Commercial buildings in London may use mechanical ventilation

Mechanical ventilation: Essential in commercial buildings?

The fact that mechanical ventilation has only occurred in the last 100 years or so proves that there hasn’t always been a need for mechanical ventilation, and only natural ventilation systems existed.

Today, there exists a great number of houses that only use natural ventilation, and gain the required amount through operable windows. The use of HVAC units is not a necessity in all circumstances, and in many situations, mechanical ventilation has been used unnecessarily.

Natvent conducted research into the use of natural ventilation in commercial buildings on behalf of the European Commission in 1998 and discovered that “mechanical ventilation systems are often installed in office buildings where good natural ventilation would have been sufficient to obtain comfortable indoor climate and good air quality.”

This research could show that the ‘need’ for mechanical ventilation is only a perceived one in some situations, and construction firms are more inclined to choose a design strategy which is easier or one that they have more experience in applying. The study also found that there is a “lack of information on natural ventilation in standards and guidelines, and also a lack of published data on case studies of the performance of buildings whichincorporate natural ventilation.”

This would make it harder for architects to satisfy standards such as ASHRAE standard 55 or ISO 7730. Nevertheless, there are manyexamples of buildings that have purely used natural ventilation, proving thatin certain climates and situations that mechanical ventilation is not needed.There are many natural ventilation solutions that can provide adequate airquality in buildings. Passive stack ventilation uses pressure differences inair. Because hot air rises, a building can be designed in a way where air canflow through windows and other openings, and rise as the particles get warmer.This air escapes through the top of the building, providing cooling for thebuilding, normally through a chimney.

This can be improved further using a thermal chimney that enhances the natural stack ventilation effect, as the chimney will heat the warm air further creating a suction. Night purge ventilation can be used where the building has openings during the night, which allows cool air into thebuilding, and by sealing the building during the day and with the rightbuilding fabric it will keep the cool air present.

One example of a project that has used natural ventilation is the construction of the Coventry University Library, which is in a city centre and also a deep plan construction of 50 metres by 50. It contains natural ventilation in every area except for the areas which contain computers. This shows that even though a building is very large and deep, it is possible to ventilate to an acceptable standard to an extent. If this were to be a smaller library with a much smaller computer suite, one can assume the need for mechanical ventilation wouldn’t exist. Nevertheless, this is a large university library which is built to accommodate a lot of students at one time, and for their comfort mechanical ventilation is only needed in one sector of the building because the heat generated from all the computers would make the roomuncomfortable. On top of that, Coventry is a city which is not as dense asother cities such as London, which has a much larger population of people,standing at around “12 million” for the London Metropolitan region, compared toCoventry which has a population “of around 345,385”. The denser a city it is,the bigger the population and the higher the pollution and noise pollution,which influence the ability to use natural ventilation.

Also, the denser a city is, the hotter it will be due to factors such as the wind. Many natural ventilation techniques rely on wind to bring in cooler air into the building. Furthermore, the option to be able to construct a building further away from the main busy roads may be harder in a denser city due to planning restrictions. For these types of buildings quite a lot of the time they would have to be situated further away and have more space around them from the main areas of their city, otherwise mechanical ventilation would be used in most the building.

A reason mechanical ventilation is used is because there is a variance in standards between buildings and rooms of different function, especially between residential and commercial buildings. For a residential facility, ASHRAE determine the outdoor air requirements for living areas to beat “not less than 15 cfm (7.5L/s) per person”. This compared with the outdoor air requirement for a commercial office space being at the value of 8.5 L/s per person. This shows that comfort levels vary depending on the type of activity in buildings, creating an obstacle to achieve these standards. The obstacle gets bigger depending on the type of environment; for example, a residential building in a dense city will be harder to reach the standard than in a rural area with better wind flow. This creates a need for mechanical ventilation since there is a preference to HVAC units as there is a wealth information and knowledge on how to apply this method of ventilation and a lack of for an alternative,which has been outlined in the Natvent study.

If these issues in the industry were to be improved by having lots more information on natural ventilation, it could be possible for many companies in different areas to be able to create a suitable environment without using mechanical ventilation. Current trends in the construction industry and historical methods have proven that mechanical ventilation isn’t needed all the time, as “today in Switzerland, Belgium, Denmark and UK a significant percentage of new office buildings have natural ventilation.” This could prove that the need doesn’t exist for every type of situation, but only over time as populations have grown in areas and standards have been raised there has been a demand on more efficient systems such as HVAC at the expense of a higher energy consumption.