The most obvious is that, as the network cabling already exists to serve the IT system, there can be big cost savings on the BMS installation. Also, as the network is already managed and maintained, operational costs are, from the BMS viewpoint, greatly reduced.

In addition, the use of an existing network gives flexibility in the location of terminals to access the BMS, as they can simply be plugged into the nearest network port. If a convenient port isn't available, it's easy and inexpensive to provide a wireless Ethernet connection.

Finally, an Ethernet-based installation allows easy Internet access, which means that the BMS can be monitored and controlled from almost anywhere in the world. Costly dedicated telephone lines and modem links are no longer needed, yielding substantial savings when, for example, hundreds of stores need to be monitored from a supermarket chain's head office.

These enticing benefits are certainly achievable, but there is another side to the coin. Let's first consider the response of the BMS user's IT team. They are not likely to welcome the connection of ‘foreign’ equipment – the BMS – to their network. In particular, they are sure to have concerns about preventing unauthorized access to the BMS functions, and about ensuring that the BMS doesn't offer hackers a back-door into the IT systems.

They will also be concerned about the additional network traffic that the BMS will generate. In reality, this is unlikely to be a problem, but it is invariably necessary for BMS suppliers to demonstrate that the proposed solution will not overload the IT network.

With these factors in mind, it cannot be stressed too strongly that it is essential to involve the IT department from the earliest planning stages of any proposed shared-network BMS installation. If the IT team doesn't buy into the project, its chances of success are negligible.

Even the full commitment of the IT team doesn't, however, solve every potential problem. For example, it is quite normal to shut down IT networks from time to time for maintenance. The work is usually scheduled outside normal hours, so the loss of the IT functions is no problem. It is a quite different matter, however, for the BMS to be down for a weekend! Problems like this are not insurmountable, but they do need to be considered.

As the above points have made clear, deciding whether or not to adopt a shared-network BMS solution is by no means a trivial task. The answers to a few questions, however, can provide useful guidance.

First, is the installation for a new building? If so, unless the IT requirements of the future occupants are known, implementing a shared-network BMS solution will be difficult, if not impossible. Next, does the planned system involve remote access? If not, the benefits of network sharing will be reduced. It's also essential to decide whether the benefits of a shared network installation will outweigh the time and effort spent in coordinating the project with the IT team and ensuring that the IT and BMS systems will co-exist peacefully on the shared network. If the case is finely balanced, a halfway-house approach is possible. The BMS can initially be installed with its own separate Ethernet network and, should it prove desirable, this can easily be linked to the IT network at some future date. This approach doesn't cut installation costs, but it does potentially offer all of the other benefits of network sharing. Finally, remember that Ethernet, whether it uses its own network or a shared network, is not always the best choice for BMS. Devices connected to an Ethernet network must be no more than 95 metres from the nearest hub and, for a BMS in a large building, this can be a problem.

Technically, the solution is straightforward – install network extenders or more hubs. This does however mean higher costs and more complicated network management. A solution based on a traditional BMS networking protocol may, therefore, sometimes be a better choice, as these protocols usually allow long transmission distances without extenders or repeaters.

BMS installations which share a network with IT services can, in appropriate applications, combine big cost savings with outstanding flexibility. They are, however, by no means the best solution in every case, and they should be specified only after the issues discussed in this article have been given careful attention.

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