Natural ventilation — something in the air
In the second of a series of articles examining issues within the building-controls sector, Graeme Rees of Trend Controls answers readers’ questions about the application and use of natural ventilation.
Q: What is natural ventilation and how is it used within a building?
A: Put simply, natural ventilation is a means of allowing fresh air into a building space while at the same time removing stale air. It does this through passive means — using forces such as wind and pressure differences instead of mechanical ventilation systems or fans.
There are different methods of naturally ventilating a building but perhaps the most common, which will be familiar to us all, is the opening and closing of windows. Nowadays this can be fully automated, with strategically placed windows and vents providing air supply and exhaust.
Q: How can natural ventilation address the problem of excessive CO2?
A: We’ve all experienced the effects of excessive CO2 in a building — a stuffy environment makes it difficult to concentrate and hard to remain alert and focused. For schools and other educational establishments this is an area of great concern, and studies have shown that students in a naturally ventilated classroom achieve significantly better results.
According to research by David P. Wyon in his 1996 study titled ‘Indoor environmental effects on productivity’, a lack of ventilation in buildings can reduce productivity by at least 15% because of symptoms such as headaches, fatigue, irritated eyes and difficulty in concentrating
Also, the Danish Technological Institute, in a study published in 2007, suggested that a naturally ventilated building produces 40% less CO2 than a comparable mechanically ventilated building.
Q: What financial benefits does a naturally ventilated system bring building owners and occupiers?
A: As well as making sure that a building has clean air, The Carbon Trust has found that a naturally ventilated building could have half the energy costs of a mechanically ventilated building.
In addition to the lower investment costs as a result of having less, or perhaps no, mechanical-ventilation plant, there is a reduction in ongoing lifecycle costs from having a smaller amount of plant to service and maintain, as well as a smaller risk of breakdown. The routine cleaning and hygiene maintenance of ductwork — essential to comply with health and safety legislation — is also avoided.
Q: How does natural ventilation work as part of a building energy management system (BEMS)?
A: The control of natural-ventilation systems is often provided as a standalone solution. While this can regulate ventilation in a building, there may be circumstances where it is in conflict with other HVAC plant — with uneconomical results. One example is having windows to provide fresh air whilst heating or air conditioning plant is running.
Such conflicts lead to inefficient and wasteful use of energy and can also have a negative impact on the initial installation cost, as installing a temperature sensor for the heating system and a separate temperature sensor for the natural-ventilation system is unnecessarily expensive. Making natural-ventilation controls an integral part of an overall BEMS solution not only reduces the initial investment cost but also ensures that all building systems are working efficiently with on another.
Also the supply chain involved with specifying and installing a natural-ventilation system can be quite fragmented, with different design and installation parties involved. This results in contractual confusion, supply and responsibility clashes during the construction project, and leads to a complex warranty, service and support situation.
To avoid such a scenario, having a seamless solution from a single provider — which also takes on the design element — is most beneficial. This will ensure the most energy-efficient methods are employed whilst delivering comfort to users.
Q: What are the key considerations when specifying a natural ventilation system?
A: Not only will customers demand a system that delivers clean air, energy reduction, comfortable conditions and minimal impact on the building’s occupants, they will also want a system that is quiet.
In a learning environment or office space, where natural ventilation is provided by automated actuation of windows, it is very important to specify devices with very low noise ratings. Doing so ensures that control motors do not whine but are nearly silent.
Security is another important consideration — one would never leave the windows open at home when unoccupied, nor leave windows wide open when it is raining.
Also important is knowing the exact position of a window and the effectiveness of the ventilation itself. Millimetre-by-millimetre control is essential to achieve the most effective natural ventilation as a window that is open too wide or too little will actually impede the ventilation of a space. Many systems only open and close in three or four steps, which is less effective and, therefore, less efficient.
Graeme Rees is product manager with Trend Control Systems.