Look, no wires
Malcolm Anson of Clarkson Controls gives an insight into what a truly wireless sensor system can achieve and why specifiers need to be careful in their selection of options.
The rise of building-management systems has spawned the need for a fast, reliable way for buildings to feed information back to those systems. Wireless sensor technologies are widely available for this purpose and are especially good options for retrofit projects. The reduction in installation and maintenance costs makes them a hugely appealing option, and a report by US firm Navigant Research in 2013 predicted annual worldwide shipments of wireless nodes for building controls will surpass 36 million by 2020.
It is vital, therefore, to choose the right wireless solution. The key is to understand that wireless does not necessarily mean cable-less. This issue, while adding a layer of complexity to the debate — not least when it comes to terminology — should inform consulting engineers and installers as to which is the best option for their job.
We coined the terms cable-less and wireless to clarify the difference between the two main types on the market.
Cable-less wireless sensors sleep most of the time. A change in temperature or whatever value is being sensed wakes the device, which then transmits the new value to a multi-channel receiver.
Because this type of sensor is in a ‘sleep’ mode for much of the time, its power requirements are quite low, so batteries or wiring for power is not necessary as it is powered by an onboard photo-voltaic cell with inbuilt power storage (such as the EnOcean system). Simple switches can also be used, which send signals using piezo generated power.
The other type of wireless, but cabled, sensors operate more like a cell net phone system, so the sensors will be communicating constantly with neighbouring sensors and onto a receiver. Because this type of sensor is constantly sending and receiving information, it needs to be constantly powered — so it needs a cable to it.
There are numerous pros and cons for each type of system. However, sensors that need constant power will require cabling, which effectively means that they lose the advantages of the ‘wireless’ approach, such as lower installation costs,. After all, installing a 2-core cable is no different to running three cores.
Another consideration for the cable-less, wireless, route is where the architect wants to avoid unsightly cabling and containment. Overall the truly wireless route offers a lower cost and more visually appealing approach.
However, specifiers and installers do need to be aware of the challenge of wireless that applies to both systems. A space fitted with wireless sensor technology before occupation may subsequently be sectioned up with partition walls and office furniture which will affect the wireless signal.
When tenants move in, the first thing they do is partition areas. They will then fit aluminium blinds between glass glazing which block the signals, as do large filing cabinets. The system may stop working, and subsequent investigation may discover a partition that wasn’t there when commissioning was carried out.
However, such issues can be dealt with speedily by applying signal boosters to the system.
There are, of course, certain instances in which the wireless sensor option will not be adequate. Try operating a wireless-only system in an old bank or building with walls a metre thick and see how much information your BMS receives.
Particularly in listed buildings, you’ve got to be careful with the fabric of the building. Old buildings have thick walls, which can prevent a signal getting through, so you might need lots of repeaters, for example, to collect the signal and transmit it on —giving it extra legs.
Even then, it would seem counter-intuitive to specify a wireless system that still requires running cables and causing disruption during the install.
You really need to be cable-less and wireless to take full advantage of the cost savings. With Enocean technology there are numerous manufacturers making complementary products, which is good news for installers as they are truly compatible and can be mixed and matched between the various manufacturers.
Malcolm Anson is managing director of Clarkson Controls.
