‘Why Automate Windows' Part 2

'Window Orientation and Cabling'

Will Perkins - Managing Director - SE Controls

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.

The process of opening windows of any orientation can be automated to provide easy access to the outside air for natural ventilation or for the provision of smoke ventilation no matter where the windows are located. There are various types of window openings currently available:

‘Hung’ on the outer frame, ‘hung’ refers to the part of the frame which is hinged allowing the vent pane to open, ‘top hung’ refers to a window which is hinged at the top, ‘top hung - open out’ suggests that the window is hinged at the top and opens outward. There are many types of arrangement using these two parameters, including ‘bottom hung - open out’ providing a hopper type window, generally used for smoke ventilation.

‘Hung’ windows can be fitted on ‘butt’ hinges to the outer frame, but more frequently are fitted on ‘variable geometry friction hinges’. These are usually made of stainless steel and are concealed in the space around the vent frame to outer frame and are actually fitted near to the ‘hung’ outer frame member, being placed on corresponding jambs. They are known as variable geometry as the hinges often move the vent frame away from the ‘hung’ outer frame once they are opened.

Centre pivot, or offset pivot windows have simple pivot points on the jambs and can rotate 180 degrees for easy cleaning. These are available in both horizontal and vertical pivot arrangements.

Both ‘hung’ and ‘pivot’ arrangements can be used in sloped facades or roofs.

Glazed or solid banks of opening louvres can also be incorporated into an effective natural and/or smoke ventilation system.

Parallel opening windows are becoming a frequent feature in modern architecture, offering  a simple ‘push out’ arrangements taking the whole vent away from the facade line and offer an excellent mode of ventilation.

All these arrangements can have one or more actuators fitted to provide simple operation and security. In order to calculate the number and size of the actuators required the size and weight of the window needs to be identified, together with its material, the hinge mechanism, and what free area is needed for ventilation. Free area is the area open to allow for ventilation which needs to take into consideration cills and reveals which compromises the free area.

The Geometric Free Area (GFA) of the opening window is calculated as the leading edge of the opening vent ‘x’ the distance opening, plus the two open triangles on each side of the open vent. The GFA can never exceed the maximum opening in the outer frame, or the ‘throat’ as which air can pass. Building Regulation, Approved Document B 2007, states that the method of calculation should only include the leading edge of the opening vents by the maximum opening of the window. Here adjustments may need to be made to the calculation regarding both possible obstructions and the presence of reveals and cills.

Depending on the opening, or stoke distance of the vent to outer frame, a variable efficiency is achieved for the free area provided, this is known as the coefficient of discharge (CV). Depending on the design of the windows and the area being ventilated, this is crucial to efficient operation and the design of the window configuration that needs to be detailed at the early design stages. More importantly the provision of free area for smoke ventilation is crucial in case of fire - again early involvement of a ventilation specialist is crucial.

Once the windows are designed, actuators will need to be placed on brackets to ensure that when a window vent opens the chain actuator operates to the geometry of the opening window. It is vital that this is correctly achieved for all opening positions of the vent to ensure long life of the actuator and correct operation as specified. A poorly designed actuator fixing can cause the actuator to clash with the outer frame which may not be noticeable, but will ultimately lead to damage to the frame and failure of the actuator Early confirmation of design details will ensure that the correct parts and preparations are completed on the windows to make site fixing effective and efficient, accurate and most of all to a high standard. Cabling between the actuator and the control panels seems like a straightforward task, but not one that should be tackled without prior planning, particularly if 240v actuators are being used. If tails are going to be left are these going to run through the window material, if so are bushes required and internal preps to the windows and or curtain wall? What material, what colour of cable should be used - who is going to install and where to? So many questions - all of these need to be answered at the design stages so that a safe and efficient installed system is provided.

To meet the aesthetic requirements of the client, consideration and detailing at early design stages again is crucial. Whilst the sheathing colours of cables may not match the colours of the window system, actuators can be powder coated to match the internal finish of the window making the installation as neat as possible.

As mentioned throughout this series, one of the most important aspects in delivering a cost effective and efficient system is the early involvement of a natural ventilation and smoke control specialist. A complete installation involves many trades working side by side and one experienced specialist overviewing the whole provision.

In the next and final issue we will cover the control of the actuators and the contractual process along with covering 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 dedicated 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.