The issues are manifold and include technical development within the controls industry and its interface with IT technology;the influence of government legislation,primarily Part L of the Building Regulations and the Energy Performance of Buildings Directive EPBD),but the WEEE Directive and IPPC Directive should not be ignored; and ensuring that there is a skilled workforce in place that understands and can implement it.

Technology

When control systems developed by different manufacturers employ different protocols,interoperability is only possible if there is a device to translate between them.Creating these translators,commonly called gateways,may not be a realistic option for many users as it can be expensive,leaving the end-user feeling boxed-in by their vendor as no other control system can talk to their present system.

Comité Europeén de Normalisation(CEN)Technical Committee 247, Working Group 4,has been tasked with standardising ‘system neutral data transmission methods between products and systems for HVAC applications….to develop HVAC specific applications of existing communications methods, one for each level required’.

Working Group 4 has divided the communications within a building management system into three types of requirement:Management (workstation to workstation),Automation(plant controllers and workstations) and Field(terminal unit controls and communicating sensor devices).The rationale behind this three-tier structure is based on the need to support diverse quantities of devices,the differing amounts of information to be sent,the requirement for varying communication performance,and to support different types of transport media,i.e.the physical cable,etc.

There is a practical argument for employing different protocols at different levels within the building.The data transmitted between a temperature sensor and a controller has dissimilar networking requirements to the data that travels between an IT server and a workstation.As Ethernet was designed specifically to move very large quantities of data very infrequently,then it becomes obvious that perhaps it is not the best medium for transmitting a light switch or occupancy bit.The opposite is true at higher levels.When trying to read a temperature data archive from the server that may be a few KB in size,then RS485 may not be well suited.This topology better suits small packets of data travelling very frequently and would struggle to pass a large file across it efficiently.

We are now seeing a trend towards the use of standard IP data infrastructure cabling forming the backbone of the building management system(BMS)and other systems’ networks,replacing previous proprietary or other standard network types.

The strength of Internet technology lies in the fact that information is gathered where it is produced as its operation is based on the use of a browser.The browser receives information from the BMS via HTTP,the standard transfer protocol of the World Wide Web.The information is supplied ready for use so that the operator at the workstation does not need any specific BMS knowledge to display it.

To this end the BMS is equipped with a web server which converts information from the installation into HTML,code to be used by the browser.It is transmitted via the HTTP internet protocol and a TCP/IP(Transmission Control Protocol/Internet Protocol)connection to the browser. As the web server supplies all actual information,access is no longer required to the operator workstations should the installation change.This is particularly useful for multi-operator buildings or by remote control.

Government legislation

The Government believes that driving up the energy efficiency of buildings is critical to the success in achieving the carbon emission reduction targets in their Energy White paper and Energy Efficiency Action Plan.Part L requires reasonable provision to be made for the conservation of fuel and power by limiting heat loss through the building fabric and addressing the efficiency of services such as heating,lighting and mechanical ventilation.The operation of these services consumes energy which in turn generates carbon dioxide emissions amounting to 46 percent of the national total.The government is committed to the Kyoto Agreement and intends reducing greenhouse gases by 20 percent of the 1990 levels by 2010.

The EPBD focuses on new and large buildings(greater than 1000m2)and states that whenever a building is constructed,sold or rented out a certificate detailing its energy performance must be made available. In order to facilitate comparisons between buildings,the energy performance certificate must include reference values such as current legal standards and benchmarks.

It must also include recommendations for cost effective investments which can be undertaken in the building that will result in improved energy performance.

Most buildings already have the facility of a BMS together with HVAC controllers containing a wealth of energy saving features.The management station is capable of monitoring,actively reporting problems and storing important energy and environmental data and it is this data that is the key to being able to actively report where energy is being used.

So,having established that the nature of building control systems is to manage,the next step must be where to seek BMS advice. Manufacturers and installers of control systems are the obvious choice,being ideally situated to advise on selecting a new or upgrading an existing system so that it delivers the right conditions for the building and its occupants while meeting legislative requirements.

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