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in the set time period – hence a small leak may not be identified.

Systems for communications and control

Single control panel solutions that provide fast feedback are available and relatively simple to use. They typically incorporate an LCD display

levels, as well as temperature, for controlling the ventilation to optimise energy consumption by controlling fan speed, and hence fan power and energy used to heat the air on cooler days. They can also isolate the gas supply in the event of fan failure or if the CO2

level exceeds

An example of a simple single control panel that provides fast feedback.

to monitor both carbon monoxide (CO) and atmospheric gas levels (ie methane and LPG). The system should be fitted with an on/off switch as well as being able to take a signal from one or more emergency gas isolation buttons. This panel may be capable of communicating with a building management systems (BMS) system to provide feedback of the kitchen’s operational status.

Gas safety proving

The supply of gas into the kitchen needs to be controlled and monitored safely. One of the practical issues is having confidence in the integrity of the gas supply pipework and appliances in the kitchen area. BS 6173 states that where a solenoid valve

is used, and where appliances are not fitted with a flame supervision device, there should be a means of proving that all the appliances are turned off before gas is allowed into the kitchen. The Institution of Gas Engineers and

Managers (IGEM) document, Strength testing,

tightness testing and direct purging of small, low pressure industrial and commercial natural gas installations IGE/UP/1A[5]

, states that the

closure of an electronic control valve (ECV) on a gas supply can result in the complete loss of pressure on the downstream side of the valve. This would then necessitate a tightness test,

and possibly purging (in large installations) before the resumption of the gas supply. This could happen even where flame safety

type devices are fitted to equipment, since they can continue to allow gas flow for up to 10 seconds following the closure of the ECV, resulting in a loss of gas pressure downstream of the ECV.

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A drop in the downstream system pressure

may also occur during periods when cooking is not taking place (eg overnight or at weekends) when, due to the allowable leakage rate on a given installation, the gas pressure downstream of the valve may drop significantly (although within the allowable pressure drop for the installation). Gas pressure proving provides a means of ensuring that all gas appliances are switched off before allowing gas into the kitchen. It also ensures that no gas is escaping from the pipework or the appliances, so ensuring the integrity of the installation. There are two principal methods of monitoring the gas proving. Differential pressure sensing is the more recently exploited method. This technique measures the pressure differential across the inlet and outlet supply of the ECV – rather than just the supply as with the other methods – hence the incoming gas pressure is not critical to the system operation. This, in turn, eliminates nuisance tripping. This method will also isolate the gas supply from the kitchen if the gas drops to a dangerously low pressure during use. However, as differential pressure monitoring takes varying supply pressures into consideration, it will not close the solenoid valve for transient changes of gas pressure, as may happen with other methods. This is known as a ‘dynamic’ means of gas proving. Older designs that rely on allowing a timed amount of gas through into the downstream pipework for a set time period are static in operation and so can miss small gas leaks. For example, if the incoming gas pressure

is slightly higher than when the system was installed, it would mean that more gas than anticipated could pass through the small valve

prescribed limits. The integrity of the gas installation can be checked automatically each time such a panel is switched on by utilising pressure differential technology. Natural and LPG gas, CO2 and oxygen depletion detectors can also be incorporated into such controls panels where necessary.

Conclusion

The drive for safety combined with energy efficiency and the need to improve the working environment has led to very high expectations in kitchen design and operation. Instrumentation design and functional capabilities have advanced greatly in the last few years to provide monitoring and control solutions that are simple, reliable and integrated. However the monitoring of the air for

safety and quality can only be used to support systems that have been correctly designed, installed and regularly maintained. © Chris Dearden and Tim Dwyer 2010

1. BS 6173/2009/11.1 Specification for the Installation of Gas-fired Appliances for Use in all Types of Catering Establishments. BSI,

2009

2. PD CEN/TR 1749: 2005, European Scheme for the Classification of Gas Appliances According to the Method of Evacuation of the Combustion Products (Types), ISBN

0580481034. 2005

3. DW172: Specification for Kitchen Ventilation

Systems. Heating and Ventilating Contractors’ Association, 2005

4. Gas safety in catering and hospitality - Catering Information Sheet No 23 (rev1).

HSE, 2007

5. IGE/UP/1A Edition 2 Strength testing,tightness testing and direct purging of small, low pressure industrial and commercial Natural Gas installations. IGEM, 2005

June 2010 CIBSE Journal

51

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