Wireless vs wired building energy management system

This article originally appeared as a BSRIA blog post, Choosing your BEMS, published in April 2013. It was written by Chris Monson, Strategic Marketing Manager of Trend Controls.

1 Introduction
2 The cost difference
3 The technical advantages
4 Deciding between the two
5 Find out more
- 5.1 Related articles on Designing Buildings Wiki

[edit] Introduction

When installing a building controls system or building energy management system (BEMS), businesses want the most efficient, economical and environmentally friendly solution available to suit their requirements. But how should you choose between applying a wired or wireless connected control system? What's the difference? And what are the benefits of each?

[edit] The cost difference

When it comes to making building control decisions, the major factor for selection and installation apart from appropriate usage is usually cost.

The cost for installing wired or wireless systems is largely determined by two things: parts and labour. These are in turn influenced by the scale of the installation project. The larger the project, the more parts, time and budget you're likely to need.

Whilst the parts for wired systems may be less than for wireless, wired system installation costs for time and labour are much higher when you factor in the additional costs for wiring and cabling. Because of this, wired solutions are best suited to smaller-scale projects.

Conversely, a wireless system has only one fixed overhead – the main receiver module – no cabling or lengthy installation required. Numerous sensors can operate with one receiver module, making wireless the most cost efficient solution for large projects with four or more sensors. A typical example of savings:

Wireless sensors plus 1 receiver will cost 30% less than fitting 4 wired controllers and wiring them back to the receiver.
12 wireless sensors cost approximately 50% less than a wired system.
Installing 32 wireless sensors would save over 60% of the cost of a wired system.

[edit] The technical advantages

“Never mind the cost – which one will actually work better?”

If the cost is not a hindrance, the prime considerations for any project are basic functionality and use. So what are the technical advantages and disadvantages of wired and wireless?

Wireless temperature sensors contain a thermistor sensing element and transmitter. Both are encased in a standard wall mounting / plant type enclosure, and up to 50 sensors can interact with a single receiver unit. Remembering the advantages of wireless for large-scale projects, a single receiver unit can be positioned up to 100m away from the sensors, so technically wireless can offer a very flexible solution. If correctly specified and configured, wired is a technical equal, and is not as susceptible to signal disruption. If disruption is a concern, most BEMS can be set to give an alert in the event of such a problem. ZigBee style networks are especially designed to avoid frequency disturbances and clashes with other devices, and were created in the late 1990's when installers realised that WiFi and Bluetooth were not sustainable wireless solutions. As such, the mesh system uses 2.4GHZ radio frequency, making it flexible and reliant – if one node breaks, others in the circuit can still communicate.

Alongside cost advantages and ease of installation, using wireless systems offer another obvious, technological edge – wireless is wireless, instantaneous and also 'plug and play'. This makes upgrading systems and introducing new technologies much simpler, though regular maintenance such as battery changes need to be factored into the time / cost equation.

[edit] Deciding between the two

Before any decisions are reached, buildings should first be audited to determine the most suitable solution – it is advisable to test how well wireless signals can be received and how likely disturbances are. If this is an issue wired may be your only option. After this, choosing the correct BEMS system depends on the size and usage of the building, the scale of the project and the budget. As a general rule, larger more extensive projects are best suited to wireless solutions.

--BSRIA