Bulletin 85: Natural Ventilation

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Trend has introduced an intelligent window control package that can be fully integrated within its building energy management systems in order to maximise the benefits of natural ventilation. The use of MotorLinkTM technology allows window position to be controlled and monitored with unrivalled accuracy, as well as providing near silent operation and enhanced levels of safety and security. Because the technology is an integral part of the BEMS, control of the windows can be easily coordinated with that of the other HVAC services to boost energy savings and optimise conditions throughout the building. Since only one controls supplier is involved, confusion over contractual responsibilities is avoided.

Intelligent window/vent actuators and the motor controllers that power them make up the basic elements of the MotorLinkTM package. The BACNet-based motor control modules can operate on IP or MS/TP networks and communicate directly (IP version) or via a router (MS/TP) with the rest of the BEMS, where Trend IQ controls implement the natural ventilation strategy - determining when and how much each window should be opened or closed. Window operation is monitored through the BEMS supervisor (operator interface).

MotorLinkTM provides precise feedback of window position, enabling millimeter by millimeter control and thus ensuring a stable indoor environment in all weather conditions. As a consequence there is no requirement to regularly close the windows and reset them, which is necessary on non-feedback systems to prevent serious loss of control (eg, those using raise/lower actuators). The feedback feature also lets the building or facility manager view the exact position of any window and receive an early indication of possible faults, as well as showing if the controls have been over-ridden - using wall switches that allow manual opening/closing. There is a security benefit too as a signal can be sent to confirm that all or selected windows are fully closed outside normal hours.

Actuator speed can be varied to suit different situations. For instance, slower speed settings would typically be used in the automatic control mode to ensure very quiet operation. A higher speed would be more appropriate when the windows are manually activated via the wall switches as this would provide an immediate visual and audible response. Actuators are able to communicate with each other via their motor controller, allowing their movement to be fully synchronized (to a tolerance of less than 2mm). This avoids the risk of damage to windows with more than one actuator and facilitates exact alignment of window groups. The motor controller comes in 4 and 8 line versions and can drive up to maximum of 16 actuators; a line can control 4 actuators on separate windows or a synchronized pair on one.

When windows are closed, the pressure on their seals is eased by the actuators reversing a few millimeters, which helps extend seal life. They can also be programmed to stop and reverse if an object is encountered during closing.

Natural ventilation should not be treated in isolation from the rest of the building services. Window opening and closing must not only take into account such factors as external climatic conditions and room air quality, but must also be coordinated with control of the building’s heating and any air conditioning and supplementary mechanical ventilation. Without this, occupant comfort may suffer and energy consumption can be unnecessarily high.

However, trying to interface a BEMS with separately supplied window controls is far from straightforward and is unlikely to provide a fully effective solution. It can result in added complexity, increased installation costs and only limited communication between systems, and can also lead to conflict over who is responsible for resolving issues that arise. With the Trend solution – which is available through the company’s usual network of VARs (value added resellers) - there is a single system and single supplier, the latter carrying out all engineering and commissioning work (using standard Trend tools).

Monitoring and management of window operation is performed through the same Trend ‘963’ supervisors that are used for the other BEMS functions. In the rare cases where there is a requirement to view all of the many data points in the window actuators/controllers, it would be necessary to install a Trend Open Protocol Server (TOPS). This permits the transfer of a large number of BACNet points into ‘963’.

There are two main versions of the MotorLinkTM chain drive actuator, one with a 265mm stroke and the other 500mm. They are suitable for use on top-, bottom- and side-hung windows, either inward or outward opening, and cover window frame sizes up to 1.5m x 2.8m. All elements of the window control package are fully supported by Trend.

With energy costs increasing and the growing pressure on organisations to cut their carbon emissions, natural ventilation seems set to enjoy considerably wider use. Figures show that it can achieve a 40% reduction in CO2 emissions compared with purely mechanical ventilation. It can also produce a healthier environment for a building’s occupants and has been shown to reduce headaches, fatigue, eye irritation and loss of concentration, thereby improving productivity. Intelligent, integrated control is of course vital if the potential benefits of natural ventilation are to be fully exploited.

MotorLinkTM is patented technology developed by WindowMaster.