The first thing to say about wireless control is that it’s not new technology. The first scheme for radio control was patented over 100 years ago, and applications such as model aeroplanes and boats have been around for many years. More recently the use of radio waves has extended to all kinds of domestic and commercial applications, including cordless phones, intruder alarms systems and of course WiFi and wireless IT networks.

In buildings, wireless room sensors are widely available but at the moment they are mostly used for specific applications where hard-wired sensors would be inappropriate such as in historic buildings. So what does the future hold for wireless controls?

Refurbishments and retrofitting lend themselves to wireless, particularly when new partitions are built. Another key BMS-related application is for wireless sub-metering, especially in retrofitting heat, electricity and water meters in multi-tenanted buildings. The new European Directive for Energy End-use Efficiency and Energy Services puts an emphasis on the importance of smart metering in driving energy efficiency improvements. The fitting of wireless meters should make installing such metering a much more economic option in the future.

The unit costs of wireless sensors are higher than the equivalent wired kit, but installation costs will normally be much less and therefore there is rough parity in financial terms. Also, the wireless market is developing, and once wireless sensors benefit from the economies of mass production their cost advantages will become overwhelming. And that day is not far off.

The cost of the controllers, sensors, etc is only a small proportion (20% or less) of the total installed cost of a BMS. By far the largest part of the cost is the installation itself and the fitting of wired room sensors is a labour-intensive job. Within the estimates for installing a system, the fitting of each room temperature sensor will be costed at around £120 per sensor whilst the sensor itself will only cost a fraction of this.

There are some situations where the benefits of wireless are outweighed by cost and maintenance issues. For example, when it comes to control outputs on devices such as motorised valves and damper actuators, there is less benefit in using wireless communications because the power supply wiring will still have to be fitted and there is little extra cost in laying the control cabling. Another factor is that the wireless sensor will require batteries to be replaced before they go flat – batteries will only last up to five years even with optimum conditions. The sensor can alert the controller when the battery is low but facilities managers might well prefer to schedule battery replacement for every sensor at set intervals, eg four years.

There are also some concerns that wireless sensors will go AWOL in an office environment because occupants can get hold of them easily, and people might try to remove the battery for their own use. To counter this, some wireless sensors have an anti-tamper device that sends an alarm to the controller if removed from the wall. One controls manufacturer admitted that a wireless sensor in the company’s own head office BMS is still in communication with the system but its current whereabouts is unknown! At least with a wired system, you can follow the cable to locate the sensor if it has been moved.

Radio IT networks have proved an invaluable addition to office technology, particularly for small to medium sized businesses. Whilst data transmission rates cannot compare to a wired Ethernet system, radio networks are comfortably fast enough for most IT applications.

A key difference between IT and BMS networks is that the BMS does not require such a high speed capability. For example, IT radio networks based on variants of the IEEE 802.11 standard can handle data transmission speeds of up to 54 megabits per second. That speed of transmission is extremely useful when large amounts of data are regularly flowing through the network but a BMS does not have such a requirement.

This is one of the reasons that a recent standard, IEEE 802.15.4, was developed for applications such as BMS and it is based on ultra-low power, low data rates and high accuracy. Following on from this, an alliance of manufacturers has created ZigBee, a standard protocol based on 802.15.4. ZigBee compliant products are able to run on small, low-cost batteries and are ideally suited for wireless BMS sensors because the low data rates and intermittent signalling gives an extended battery life. ZigBee microchips will also be used in the home automation market and the mass production benefits will mean a very low unit cost – less than £2 each.

One of the leaders in this technology, Ember Corporation, has three Zigbee-compliant microchips on the market and is in the process of doubling the size of its research centre based in England at Cambridge Science Park.

The term ZigBee is derived from the method of communication used by honey bees – worker bees returning to the hive do a zig-zag dance to show the other bees where to find the nectar-bearing flowers.

In tandem with the development of radio networks is the use of mesh networking topologies which work in a similar way to mobile phone networks. For example, the wireless mesh network topology developed at MIT for industrial control and sensing is a peer-to-peer system called a multi-hop network. A node can send and receive messages and in a mesh network a node also functions as a router and can relay messages to its neighbours. Through the relaying process, a packet of wireless data will find its way to its destination, passing through intermediate nodes with reliable communication links. The network is self-configuring so that all devices can transmit from their original position without having to be moved. A weak signal or dead zone can be fixed simply by dropping a repeater node into place. The network error rate is low and can be further reduced if occasional re-transmits are allowed.

Much of the pace of wireless development is being driven by the consumer market. Wireless intruder alarm systems for the home are now commonplace and people are used to using WiFi with their laptops or reading their emails on a mobile phone. All the benefits of mass production will ensure that wireless BMS becomes an ever more affordable option – the labour costs associated with installing wired circuits will continue to rise faster than inflation whilst the real costs of wireless devices will fall.

Like most controls companies, Trend Control Systems, offers the options of wireless space and plant sensors to its systems. Chris Monson, the company’s Strategic Marketing Manager, says: “ I am confident that wireless sensors will become the norm in a BMS, but that there is little to be gained by fitting wireless control devices to valves, dampers, and so on.”

James Palmer, Sales Manager at North Controls, is bullish about the latest developments in wireless controls. “ZigBee is an important development because it will allow for smooth interoperability between different proprietary systems.”

The Building Controls Industry Association (BCIA) is at the forefront of bringing UK controls companies together to cooperate in facilitating interoperability between different proprietary protocols. This kind of cooperation will benefit all parties, (including end users) and help speed the take-up of wireless technology.

The challenge of providing seamless interoperability between different protocols is creating some exciting developments. Xsilogy has created the SensorWorx framework that allows system designers to create sensor network applications that integrate with legacy systems. SensorWorx integrates wireless sensors with wired building control systems and IT networks using different communications protocols.

IT giant Intel is working on its Mote technology, jointly developed with the University of California Berkeley at the Intel Research Berkeley laboratory. Intel Motes can serve as the building blocks for future wireless sensor networks bringing the cost advantages of small size and mass production.

Wireless control systems have been around for a long time, but with increasing demand from the BMS market it looks as though they are in for a period of exciting evolution.

If you’re interested in the development of building management systems and intelligent buildings, come along to the M&E Event at London Olympia on 10 and 11 October. Sign up for the free seminars on this and other exciting topics at www.buildingservicesevent.co.uk

Printer friendly version

Email this article to a friend