Building control jumps on the bus

Increasing safety requirements in building automation demand new procedures in the use of bus systems in buildings, for effective protection against fire for example. Harald Forster of Pilz explains

OPEN BUS SYSTEMS - such as the European Installation Bus (EIB) or the Local Operating Network (LON), have become generally accepted in building installations. However, the bus systems generally used within the housing technology have not always kept pace with the increasing safety requirements in buildings, in particular with regard to fire protection and smoke extraction.

More and more importance is being attached to safety within buildings, in particular with regard to potential risks such as fires, where people are mostly injured as a result of inhaling fumes. One measure involves an ingenious smoke extraction concept, in which escape routes are always kept free of smoke, and the fire brigade can extract smoke from targeted sections of the building, controlled through permanently installed ventilation systems.

Existing buildings are gradually being upgraded to include the latest technology. Much importance is being placed on a decentralised structure and flexibility. The entire safety system should be modular in design and should be easily expandable after the system has been commissioned. Use of a bus system is ideal for such requirements.

An installation in Dusseldorf was to be fitted with this new technology. The firm Kessler + Luch was appointed to do the design and had the task of finding a suitable bus system. It very quickly became obvious that standard bus systems would not be able to meet the specific requirements.

One of the basic requirements of this application was to be able to interrogate the status of the fire protection valves safely. Another indispensable safety requirement was to prevent the smoke extraction ventilators being switched on unintentionally. These functions can only be fulfilled using safety-related control systems and safe bus systems

Pilz's SafetyBUS p is an open bus system for the serial transfer of safety-related data. In addition to all the familiar benefits of standard bus systems - such as greater flexibility, less wiring and universal diagnostics - SafetyBUS p is designed to be suitable for use in safety systems in accordance with category 4 of EN 954-1 and AK 6 in accordance with DIN 19250. SafetyBUS p is the standard for the safety-related networking of plant and machinery. Barely two years since the system was launched, a wealth of on-board and decentralised modules are now available, providing the user with all the tools necessary to design a structured network.

Powerful argument

Although it was originally designed for plant and machine engineering, SafetyBUS p can provide ideal conditions to perform automation functions in the building sector. Variable baud rates and bus cable runs of up to three kilometres without the need for repeaters, a large selection of modules and connections to different standard bus systems such as Modbus, Interbus, Profibus, CANopen or DeviceNet make an overwhelming argument.

Protection against fire in buildings is guaranteed through the most diverse methods. Fire alarm control systems with corresponding alarms, sprinkler systems, fire control console and, most of all, fire protection valves, ensure that a fire is detected, tackled, displayed and notified quickly. Fire protection valves are an important part of the system. When everything is normal, all the fire protection valves are open, the ventilation and air-conditioning systems are all operational, and the installation runs via timed programs from the main control system. All switches on the fire control console are set at automatic.

If a fire breaks out, the affected fire protection valves will close, because the integral fuse solder will break in the heat, initiating the closure. This is basically a mechanical process, with no demands made on either electrics or electronics. End switches on the fire protection valves signal the closure to the programmable safety system safely.

This means that the special technology of the programmable safety system can guarantee that feedback from the valves matches the actual positions. Potential faults, such as shorts across the connection lines or external voltage sources will be detected by the safety-related system, which will always adopt a safe condition if a fault occurs. Specific fire protection valves can now be opened via the fire control console. If necessary, smoke extraction can be initiated, without anyone having to physically access the fire protection valve.

Maintenance of the fire protection valves also favours the use of a safe bus system. A functionality test of the valves must be carried out at regular intervals, to ensure that faultless operation is guaranteed in the case of an emergency. Previously this involved a lengthy procedure and a great deal of time. However, with SafetyBUS p and the PSS 3000 programmable safety system, it is now possible to test the fire protection valves easily and safely from the fire control console. This is possible due to the safe drive of the valves and the safe monitoring of their final position. This simple procedure increases the operational safety of the whole fire protection system considerably.

• Pilz
  Email c109@industrialnetworking.co.uk