WINDS OF CHANGE
The launch of Monodraught's Sola-Boost for use with its Windcatcher is such an ideal example of the energy-saving zeitgeist that it is surprising that no-one has come up with the concept before. Like all good ideas, it seems supremely obvious in retrospect, but its apparent simplicity belies a considerable amount of complexity.
The judges of the 2006 Interbuild Product Awards recognised this when they selected Sola-Boost as the winner in the building services category. They commented: 'Although simple in concept, this submission demonstrates that by employing new technologies with innovation, a product can be developed that can be applied either commercially or domestically.
It has the advantage of being able to respond directly to weather conditions and to be self-powered by solar energy.'
The company describes it simply as 'energy-free powered ventilation'.
In a sense, Sola-Boost is the icing on the cake. It uses solar energy to power a system which, in turn, provides considerable energy saving in buildings by avoiding the need for air conditioning. So, in order to understand the point of the Sola-Boost, one first needs to know about the Windcatcher.
THE WINDCATCHER Ventilation is key to creating a successful building environment.
This is increasingly so as global warming, coupled with the increased use of electrical heating appliances, makes the removal of heat the dominant issue for much of the year, particularly in summer.
Thermal comfort is a complex issue. British Standard BS EN ISO 7730 defines it as 'that condition of mind which expresses satisfaction with the thermal environment.' Even the Health and Safety Executive acknowledges that it is difficult to be precise and individual perceptions differ. It considers that if 80 per cent of the users of a building believe that they are experiencing thermal comfort, that is as much as one can hope to achieve.
It defines six key factors for thermal comfort, dividing them into two categories.
air velocity; and humidity.
clothing insulation; and metabolic heat.
Evidently, no manufactured product can address the last two of these factors, but considerable effort - and, in many cases, energy consumption - goes into addressing the first four.
The Monodraught Windcatcher deals with the issue of air movement and, through that, also with air temperature. Air velocity is important because it is air movement that will conduct heat away from the body.
With no air movement, people will sit in a cocoon of stagnant air, growing increasingly uncomfortable.
At the other extreme, too much air movement, commonly known as 'draughts', can make people become very uncomfortable.
The conventional way of generating air movement, and bringing cooler air into buildings is, of course, through opening windows. Architects and building managers are increasingly recognising the importance of this, not only for the technical advantages, but also for the psychological benefits that this brings to users, through the sense of control that it gives them. However, opening windows may only be partially successful as a ventilation strategy for the following reasons:
uneven effect, so users in some parts of the building benefit more than others, particularly in deeper plan buildings;
high winds can cause discomfort and may also result in papers blowing about inside; and ingress of environmental noise and pollution through open windows.
The virtue of the Mondraught Windcatcher is that it can supplement or even, in some instances, replace the ventilation that would normally come from opening windows.
NGS (the National Green Specification) describes the product as follows: 'The Monodraught Windcatcher system has proved to be the most effective method of providing natural ventilation to any commercial building, by encapsulating the prevailing wind from any direction. Clean, fresh air, relatively free from contamination or traffic pollution, is entrained at roof level and is carried down to the rooms below, through a controlled damper arrangement. The ventilation effect is similar to displacement ventilation.'
Night-time cooling is achieved without compromising the security of the building.
Warm, stale air is exhausted by the passive stack quadrants of the Monodraught system and replaced by cool fresh air, taken in from roof level.
In conceptual form, it is scarcely new technology, since 'windcatcher' towers were in use in the Middle East 2,000 years ago. In its current form, it was launched in 1995, deriving in turn from Monodraught's balanced ue system.
It works in the following way. Wind movement striking the Monodraught system is captured by the louvres serving the quadrants. Internal turning vanes on the windward side move the air through 90¦. The force of the wind is then driven down into the room or space below and, having a greater density than the internal air, this cooler incoming air ows down to oor level, while the less dense, warmer internal air rises and exits through the passive stack quadrants as a form of displacement ventilation. As the wind changes direction at rooftop level, the system quadrants also switch their function to continually provide incoming air and extract stale air from the building.
Such was the level of success of the Windcatcher that the company sold 2,570 units in the four years from 2002 to 2006. But, although very effective, the system is dependent on the existence of some wind. While the company says that the Windcatcher will work effectively in the summer, there may be times of the year when not as much wind is generated as desired.
SOLA-BOOST This is where the Sola-Boost comes in. It uses a 40W solar panel, bonded into the top of the Windcatcher to drive a 200mm-diameter fan. So, when the sun comes out, it activates the PV panel to power the fan and enhance the activity of the Windcatcher, without consuming electricity. This is a usage of solar power on a sympathetic cycle, since the energy is needed most at a time when there is likely to be more requirement for ventilation.
Monodraught has developed and patented a control system called PowerTrack, which prevents the fan from kicking in until solar power is being generated at a minimum level of 5V.
It then monitors the power 'continuously' - in fact, every five milliseconds. Then, once the solar panel is producing a minimum of 14V, a poweroptimisation feature comes into play, boosting the output to two and a half times the level that it would achieve with a directly connected system. In other words, at the time when the need for ventilation is highest, the output reaches a peak.
Since there could be times when this level of ventilation is excessive, it is possible to switch off the fan altogether, or to run it at half power. But the most important aspect is its ability to bring in cool, fresh air at the time when it is needed most, without the consumption of electricity.
It seems certain now that we have embarked on a series of increasingly warm and humid summers. All attempts to reduce our level of carbon consumption will fail if we become increasingly dependent on air conditioning. Yet, even buildings which are designed for maximum thermal mass, with plenty of natural ventilation and night purging, are likely to struggle in the most extreme conditions.
If a successful ventilation strategy cannot be introduced, then either building owners will feel obliged to introduce air conditioning, or the occupiers will take matters into their own hands and install personal electric-powered fans. In addition to the fact that these actually add to the heat load of buildings, they consume electricity that, at present, one can be confident does not come from renewable or carbon-neutral sources.
The Sola-Boost Windcatcher certainly cannot right all of these ills on its own.
But, in buildings that have been designed appropriately, it may tip the balance and prevent the installation of a non-sustainable ventilation strategy, whether planned or ad hoc. This is what certainly made the Sola-Boost a worthy award winner.