Planning SHEV window drives – how to proceed
Installation situation, fire protection strategy, stroke and power: 4 steps will provide you with electric and object-specific window drives for smoke extraction.
Do you have to submit a building application and implement the requirements from a fire protection strategy? Or prepare tenders for the individual trades? Then let us help you with these four tips for finding the right window drives for your natural smoke and heat exhaust ventilation (SHEV)
Function and angle of installation: how much space do you have for installing your window openers?
When selecting window drives, it almost always makes sense to start by figuring out which functions you want them to include. Do you want them to be limited to smoke extraction in case of fire, or should they also help ventilate the building naturally on a day-to-day basis? The window drives from D+H – with the exception of the pure ventilation drives of the VCD Series – have been approved for ventilation as well as SHEV. This means that you are free to choose window drives however you see fit. The question of what you want to accomplish with your drives also has a critical impact on where the drives will need to be placed in the building. What ventilation cross sections do you have to achieve? What smoke-vent area requirements have to be met? Insofar as these requirements exist, they are contained in the fire protection strategy for the building (see below "Fire protection strategy, stroke and power"). As a result, they provide a clear overview of the locations in the building where certain windows need to be opened.
The specific angle of installation in turn further narrows down your window drive selection. Are the windows you're planning to open located in the façade or in the roof? And what type of opening (bottom-hung, top-hung, side-hung, projected top-hung, parallel opening or side-hung) do you have in mind?
Depending on the specific conditions of the building and space you have for installation, you have a variety of options available to choose from. D+H offers a wide range of window drive models: from lock drives for locking windows to special drives for louvres and even the most conventional types of chain drives and rack and pinion drives. The last two drive models differ in particular in their design and mode of operation. While chain drives open windows through a flexible chain, the rack and pinion drive opens the windows using a rigid, robust rod. Chain drives can therefore not only be mounted on top, but can also be integrated into window profiles. In contrast to rack and pinion drives, this type of electric window opener does not protrude into the room, making it easy to combine it with shading elements, for example. Chain drives satisfy the most stringent requirements with respect to both function and aesthetics. Rack and pinion drives, on the other hand, are notable for their power. They have a robust design that makes them especially suitable for roof usage, perhaps for moving skylights or very heavy windows.
Power and networking: How long are the cable routes, and what window drive connection is planned?
Early in the window drive planning phase, you should get an overview of how long you expect your cable routes might end up being. Depending on the size of the structure, you have to decide between 24-volt drives and 230-volt drives. For smaller office buildings or stairwells, a 24-volt power supply can be perfectly suitable. In this case, the required cabling work is always very little. However, when it comes to more complex buildings with several storeys or large industrial halls, a 230 V solution is in most cases more functional and cost-effective. This is because, thanks to the high voltage, the 230 V window drives require much lower cable cross-sections than the 24 V drives. According to Thomas Rößler, Fire Protection Planner and Managing Director at D+H Deutschland GmbH, this voltage level results in savings of several thousand euros, assuming a total of 100 metres of wiring routes in the complete SHEV system for control panels and cables.
In addition to the cost factor, there is an additional argument for why you should opt for 230 V window drives in larger buildings. The lower cable cross-sections make the cables lighter and mean that they take up less space. This makes the job of the architects easier. They can design a building that meets their standards in terms of function as well as their requirements for structural engineering and aesthetics. Generally, D+H window drives are available in a 24 V and a 230 V design. This affects your building design as early as the electrical planning stage, because you have to think about the voltage in depth and make a choice regarding what kind of SHEV controller you will select. And keep in mind that D+H always recommends that its customers at least keep the cabling plans in mind while deciding on the specific window drive technology. This also includes any possible networking with some form of building automation or bus control system.
Fire protection strategy, stroke and power: What window drives do you need in order to meet the requirements for smoke-vent areas?
Provided that a fire protection strategy exists for your building project, it specifies what smoke extraction area requirements the building must meet. This means how large the opening areas of the windows have to be to ensure that they can provide safe smoke extraction in the event of a fire. The smoke-vent areas can be separated into geometric and aerodynamic extraction areas. The aerodynamically effective smoke-vent area must be implemented in cases where an NSHEV system is required by construction law in accordance with EN 12101-2.
If the smoke exhaust requires a geometric smoke-vent area, then this area can be calculated using a simple formula. You calculate this figure by multiplying the light opening width (LO) by the width of the clearances (WC). For side-hung windows, the height of the clearances (HC) has to be multiplied by the opening width. Calculating the geometric smoke extraction area helps you in figuring out whether the stroke lengths of your selected window drives are sufficient for the fire protection specifications.
In addition to the stroke length, however, the force of the window drives is also essential to your selection. Depending on what window sizes you are using for your structure and/or how much your windows weigh, your window drives require different compressive and tensile forces. Even the opening variations (see "Function and angle of installation" above) affect the required forces. The greater these forces are, the more current consumption the drives have. This relationship is critical for selecting the right smoke vent control Panels. As such, the narrow chain drives from the CDC Series require a power supply of 0.6 amperes, for example, at a maximum force of pressure of 250 newtons. The powerful rack and pinion drive of the DXD series, on the other hand, requires a power supply of 2,5 ampere at a force of up to 3000 newtons.
To make it far easier to decide on your structure-specific window drives and to aid the process with digitisation, D+H developed the myCalc software. You can provide this software with specific data about your window, such as the width and height of the window sashes as well as the profile. In combination with the additional requirements you provide regarding stroke lengths or opening angles and exterior influences such as snow or wind load, the program then calculates the best window drives for you, including the installation solution (bracket sets). You can also use this software to run straightforward calculations for the geometric and aerodynamic smoke-vent areas.
Machinery Directive and protective measures: Does the risk assessment have to be carried out early on in the planning phase?
If the bottom edges of the sashes on your windows fail to reach a minimum installation height of 2.5 m, you are obligated to carry out a risk assessment for your power-operated window. Why is this assessment necessary? Imagine your window opening and closing without taking possible dangers into consideration. Even if a person has their finger inside of the closing edge, the drive does not slow down or stop during the closing process. At forces up to 300 N, such a scenario could end up being quite painful. To prevent this from happening, a risk assessment for these systems must be carried out as per the EN 14351-1 product standard for windows and external doors based on the 2006/42/EC Machinery Directive. This is the obligation of the installer, the one who combines the drive or drive system with the window (e.g. the metalworker, window manufacturer or SHEV installer). The installer is liable in the event that the corresponding safety and health protection requirements are not met. However, in this process, a risk assessment is performed in the planning stage, well before installation starts. This means that the system consisting of the drive and window needs to have been designed and produced under consideration of the results of the risk assessment. You can find more information on this in our brochure "Air + Solution".
D+H draws upon technical expertise to provide support for planning window drives
Based on the fee structure for architectural and engineering services (HOAI), service phase 2 (SP2) is a suitable point in time for you to turn to D+H for assistance with your window drive planning. D+H provides you with guidance throughout SHEV system project planning – from selecting the right smoke extraction and ventilation elements to installation and commissioning. When you turn to D+H for planning support early on, you can be confident in the way the tender document text for the selected technologies has been defined. These documents will allow the rest of the project to be implemented smoothly and without major changes in planning. This also ensures that you can prepare your construction application or your tenders efficiently.
Your checklist for planning your structure-specific drive technology:
- Designing the required window drives with respect to ventilation and smoke extraction functions and angle of installation
- Planning the power supply, cable routes and networking to the building management system or through bus communication systems
- Calculating the required window drives with respect to smoke-vent areas, force and stroke
- Performing a risk assessment and implementing the protective measures