In this series of articles by Will Perkins we look at the provision of adaptive natural ventilation for healthy and efficient buildings and the safety provision of smoke ventilation. The series attempts to explain some of the pitfalls in the lack of early design and understanding of such systems.
One of the main reasons to automate windows is that of convenience. Not all windows are located at reachable height and may need a pole to operate, in some larger rooms and corridors many windows may need to be opened, so clearly an automated solution is preferable. On securing premises in the evening, automated systems can ensure all windows are closed prior to setting alarm systems. Other benefits can include ‘night time cooling’ strategies, when premises may not be occupied, and an automated solution can operate above ground windows on a time switch basis.
The integration of automated windows into a complete building management system can ensure the most efficient use of energy. Many of BREEAM excellent rated projects in the UK today use natural ventilation strategies based on window automation.
But why do we need to ventilate our buildings? According to Approved Document F and CIBSE it is mainly for health reasons offering the occupiers appropriate Indoor Air Quality (IAQ). Inadequately ventilated buildings can harbour such gases as radon, a naturally occurring gas in the earth, hydrogen sulphide, which often results from the bacterial breakdown of organic matter in the absence of oxygen, carbon monoxide, by combustion processes, dust, virus and fungal spores. The presence of any of these elements can prove to be the cause of ‘sick building syndrome’.
Today we are also much more aware of VOC’s (Volatile Organic Compounds), which have significant vapour pressures which can affect the environment and ultimately human health. In newly fitted buildings VOC’s are often present in high quantities in materials such as setting paint and new carpets, these ‘smells’ can easily be identified in the atmosphere. Whilst many are non-toxic at the levels present, VOC’s can still have chronic effects on health. Today anthropogenic VOC’s are tightly regulated, particularly in materials used indoors, but ventilation strategies can play a big part in negating the risk.
In busy buildings, body odour, an increase in moisture from breathing and build-up of CO2, often leads to lethargic working or learning environments, resulting in poor working performance – this issue has been well documented in schools where an ‘appropriate indoor air quality’ is crucial to learning ability.
It is crucial that the ventilation strategy is decided at the outset of the design process. By adopting either a completely natural ventilated solution or a hybrid mixed mode solution with mechanical cooling for in only the harshest of weather conditions, can significantly reduce a buildings running costs.
So we have covered the practical reasons and the need for ventilation in our buildings today, but how do we achieve the ‘automation’?
A window ‘actuator’ is usually an electrical device which is placed on the leading edge of a window to open and close a window to various degrees as required. These come in two basic types, a ‘chain’ actuator and a ‘linear’ actuator. Chain actuators are the most compact and operate by pushing a one way folding chain out from a flush motorised housing fitted to the frame or opening light. In areas where windows are much larger, linear actuators, based on fixed ‘screw’ and motor principle may be used.
Whilst these devices may seem to be simple, window actuators do come in a very wide range of sizes and typical offer the following choice specification:
Voltage: Either in 24V DC or mains 230V AC ratings. Where smoke control is required 24V DC actuators are used so that these can be operated from an independent battery back-up in case of fire and power outage in the building.
Load: Usually indicated in amperage and is very important to consider when specifying a complete system. Often cheaper units are less efficient and require greater loads which results in an increase of control panels to operate at the higher amperage, not to mention the increased energy requirements.
Force: Indicated in Newtons (9.81 N = 1Kg) and required to open and close the window safely in all weather conditions. Referring back to efficiency, the available force within the unit should be as efficient as possible to reduce the amperage required. Some larger windows may need two actuators to perform correctly.
Stroke: This is the distance the actuator travels creating the safe opening of the window normally indicated in millimetres.
Speed: Indicated in millimetres per second. This is an important consideration in smoke ventilation situations where smoke vents must fully open with a 60 second time limit.
Size: Units vary in size depending on their specification but housings are very important to be considered when looking at the space available within the reveal, the size of the vent and the stroke required.
Intelligence: Some basic actuators rely on simple switches to limit and run the actuator motor, where occupant intervention is required. Some more sophisticated devices offer resistance feedback and information on where the actuator is within its cycle by the use of incremental volt measurement.
The most important aspect of all these variables is getting the right actuator in the right place to do the job most effectively with the minimum of maintenance. As mentioned earlier it is crucial to get a specialist involved at the very early design stages to determine the most efficient product and designs available. Leaving the choice of actuator to the lowest common denominator – cost, can have a serious detrimental impact on an installations performance and on-going maintenance requirements.
In the next article we will cover free area calculations guidance under the new Approved Document B 2007, and how to achieve this effectively and safely.
SE Controls operate across the globe with offices in several continents, with specialists offering clients expert advice based on local legislative requirements. Visit the website at www.secontrols.com for further information. To discuss your requirements with SE Controls, or request literature, please call their head office in Lichfield on 01543 443060.