Cutting costs not corners

As with other forms of electronic technology, the cost of BMS controllers has been gradually falling and there has been downward price pressure too on peripherals such as sensors, valves and actuators. Changes to the design of these different items of hardware have also had an effect on wider system costs.

For example, the development of controllers with modular input/output units makes it possible to put more i/o into a given space, thus allowing the panels to be smaller. As well saving on panel manufacturing costs, this can help solve the problem of building designers allowing less and less space for plant rooms.

The use of controllers that have Ethernet/TCP/IP connectivity can potentially have a much greater impact on overall costs. While there is some debate as to whether Ethernet is any cheaper than putting in a proprietary network (though it probably is), it does open up the possibility of the BMS being able to share a building’s IT infrastructure. This can mean substantial savings on electrical installation, which generally represents almost 50% of system costs.

Admittedly, in the case of new buildings it is rare for there to be an IT network in place when the BMS is fitted. However, with Ethernet increasingly being used by fire, security and other building systems, there is growing pressure on developers to ensure a common services infrastructure. Of course, if the BMS is being retrofitted - and currently some 70% of systems are retrofits – there is almost always an IT network to piggy back onto.

Field wiring accounts for an appreciable slice of electrical installation costs, though judicious design of system architecture will often allow it to be reduced. The advent of low cost radio-based temperature sensors means some can be done away with altogether. On most applications the installed cost of these units is significantly lower than fitting hard-wired sensors. Wireless technology is also now being used to speed system commissioning.

Those responsible for specifying building controls should also bear in mind that some can be easier to install than others. For example, a VAV terminal unit controller with an integral differential pressure transducer and damper actuator, simply have to be clamped to its VAV damper drive shaft. Fitting controls without these features is likely to be far more involved – which will inevitably mean higher labour costs.

The latest software for programming BMS controllers allows further savings to be made. Once a tortuous, error-prone and time-consuming process, system engineering was transformed by the introduction of graphical configuration tools. The subsequent upgrading and refinement of these has made it simpler still. With the very latest tools it is possible to create control strategy simply by selecting ‘blocks’ from a library of routines and linking them together.

Unfortunately, one of the most common ways of effecting savings involves stripping items out of the original control specification. True, capital costs can be cut to some extent by taking out functions like variable speed control of fans and/or pumps or full zone control of heating and cooling – but ultimately there is a much higher price to pay. And this is of course borne by the building user – largely in the form of greatly increased energy bills.

Graeme Rees,
Global Product Manager,
Trend Control Systems Ltd