The art of natural ventilation
February 1st 2009 Natural ventilation is an effective solution to cooling a building economically and environmentally.Now with the ability to cool on hot still days Monodraught believes that it has the total solution to ventilating a building naturally
Natural Ventilation has been around for a very long time! Indeed,many people will have seen the original Wind Towers in the Middle East, which have been around for more than 2,000 years, Wind Towers were used to capture the prevailing wind from any direction and turn that wind through 90° into the dwelling below.
This is probably the very first time that wind was used actively and consistently in this way in the design of buildings to provide a ventilation system. Monodraught Windcatchers™ are based on the same design and on the same principles but benefit from sophisticated control dampers and indeed, intelligent control systems to accurately control this throughput of ventilation air. That is the very epitome of sustainable energy.
Other forms of 'natural ventilation' have, of course, also been around for a very long time! Single sided ventilation, or just opening windows, has always been a popular form of natural ventilation, since apart from a little bit of elbow grease, it costs nothing to operate! 'Crossflow ventilation' is probably the next most popular method but again, often relies on opening and closing windows, but it stands to reason, it is so much better than single sided ventilation, because at least there is a crossflow of air across the room.
More sophisticated designs for crossflow ventilation require a fairly complex arrangement of dampers and controls, since one of the many essential ingredients of effective natural ventilation is wind movement but because it is one of the vagaries, this has to be controlled between a 'no wind' situation and gale force blowing! Single sided ventilation or using opening windows is very often only effective during summer months when it is very hot and sunny – and then we open a window. If there is a gentle breeze blowing then it is fine and we immediately feel the benefit, but if it is a 'no wind' hot, muggy day, opening the window will not achieve very much! Crossflow ventilation is also pretty ineffective if there is no wind movement, although many designs rely on a difference in temperature between the lower part and the upper part of the room to create a 'thermal flow' of warm air rising and exiting the high level vents or openings.
In truth, of course, not only is this a pretty hit-or-miss 'wish list' but it also depends on a high build up of heat at high level to create this 'thermal movement'! If the temperature is 25°C+ outside, it is not much fun waiting for the temperature within the upper part of the room to increase above the external temperature to create that 'thermal flow'.
Stack ventilation or 'passive stack ventilation' has always been a very popular term and goes one step further than the single sided or crossflow natural ventilation principle by creating a stack effect.
Unfortunately, however, during hot summer months, it doesn't really help because for a passive stack to work effectively, it needs a 10°C temperature difference between inside and out. So what if it is 25°C outside to start with? 'Passive' of passive stack simply means no-one has to do anything.
However, the 'downside' of passive stack technology is that it is totally dependent on the elements, the weather, wind movement, and temperatures! Having said all that, natural ventilation must still be seen as the 'preferred option' to air conditioning in maintaining a healthy and environmentally-friendly building interior, as opposed to all the criticisms that have raged for years relating to 'air conditioned buildings'.
Many people have always complained that they get sore eyes, dry throats, and in many cases,people are concerned that other people's germs may be circulated and so leading to all the problems of SBS (Sick Building Syndrome). The other disadvantages of a conventional air conditioned building is that by its very nature, it demands constant maintenance with the changing or cleaning of filters; it is often noisy; usually the temperature generated is too cold; but worst of all, it uses up so much of our precious energy resources! Natural ventilation by comparison does not have any of these disadvantages. However, the importance of natural ventilation is 'controllability'.
"Top down ventilation", that is, using roof turrets that captures the wind from any direction, has proved to be one of the most reliable and popular forms of natural ventilation simply because it uses the natural elements of wind movement to channel relatively clean, fresh air from above roof level and the wind pressure pushes that fresh air supply through the Windcatcher system down into the building below. This tends to slightly pressurise the room below, forcing out the warmer stale air, which rises naturally to ceiling level and up and out through the leeward side of the roof mounted turret. Because this necessary air supply is entering (and leaving) through one predetermined roof unit, sophisticated controls can include temperature, CO2, air quality, seasonal and daily time settings, and most important of all, a simple but effective end-user override control to 'open and shut' these control dampers depending on the individual's personal whims.
However, even that advantage of pampering to the individual must have an intrinsic overall control, in as much as the main control panel must revert the controls to its original pre-programmed setting after 20 minutes.
But times are changing! It is true we had a 'rubbish' summer this year but we are being constantly reminded of the evidence of global warming, so who knows what will happen in 2009 and beyond? One thing is pretty certain, energy prices are likely to continue to go up and the desires to reduce our carbon footprint are growing by the day. So, effective natural ventilation does indeed have a very important part to play in buildings for the future.
So where is the problem? One of the perceived drawbacks or limitations of a natural ventilation strategy is, what happens on a hot sunny day when temperatures externally are around 25°C+ with little or no wind? What happens when temperatures continue to increase internally, from the effect of internal electric lighting, computers, photocopiers, other office equipment, and of course, from the people themselves? So – enter the Sola-boost! Designed to work in connection with a top down, roof turret ventilation system, Sola-boost is designed to utilise solar energy to drive an integral fan to increase the throughput of fresh air through the system, to either improve the natural ventilation rate of the Windcatcher system or when there is no wind whatsoever, to actually create that downdraught of fresh air. Even when the temperature externally is 25°C+, the very movement of fresh air through the building creates an adiabatic effect. This is very similar to having a desk fan. It cools you down but you know full well, it is still the same temperature of air that is blowing! It is just the movement of air itself on a hot, sweltering day, particularly if it is coming down from the ceiling and it is relatively fresh, clean air, that is so welcomed by everyone.
With the advantage of free night cooling, where the cool night air plunges down to floor level, purging the building of stale odours and warm air and leaves the building fresh and cool for the next day's onslaught! Now Sola-boost moves the whole natural ventilation process into the next generation of energy free 'air conditioning'or sustainable ventilation. More articles from Monodraught Limited: | 
