Advantages of using flue gas analysers

Telegan take an in-depth look at the advantages of using flue gas analysers.

In recent years flue gas analysers (FGAs) have become increasingly popular with professional heating engineers.

By drawing gases directly from the flue, FGAs provide vital first hand combustion data which eliminates the need for unnecessary and expensive stripping of healthy appliances.

FGAs also record compliance with new regulations, such as the newly issued BS7967, which covers safety aspects of carbon monoxide as well as requirements for CO:CO2 ratio parameters; and the European Design Standard EN50379, which covers portable electrical devices used to measure combustion flue gas parameters.

EN50379 will take over from current British Standards in the near future.

The Office of the Deputy Prime Minister has also recently issued requirements for the installation of high efficiency, condensing boilers.

These appliances can only achieve the high efficiency ratings claimed by the manufacturers if the gas/air mixture is set precisely - something that can easily be checked with an FGA.

All standard FGAs display data on CO, CO2, CO:CO2 ratio, O2, XS Air, nett and gross efficiency, flue temperature and pressure (while the flue test is running).

They measure CO, oxygen, pressure and temperature and use this data to determine all the other parameters.

For simplicity, all readings are taken via a single probe and the effect of any burner adjustment is shown in real time, making it easy to fine-tune for optimum efficiency.

The precise figure depends upon the appliance type: old-style balanced flue gas boilers generally peak around 70%, while condensing boilers can exceed 95%.

The CO:CO2 ratio in particular has been used as a 'health-check' for boilers for many years.

All common fuels convert carbon to CO2 during the combustion process.

In a perfect world all the carbon would be converted, but in practice this is impossible, with some of the carbon reacting only partially with O2 in the air, leaving CO in the flue gas.

With most appliances the CO is at a such a low concentration as to be virtually harmless.

Poorly ventilated, old or badly maintained installations may, however, emit dangerous levels of CO.

The ratio of CO to CO2 in the flue is therefore a simple test of safe combustion and conversion of carbon to CO2, with a low result suggesting a safe appliance.

The inclusion of ratio readings in appliance log books is now part of the Benchmark scheme to promote high standards in the UK central heating industry.

Some FGAs now have a dedicated CO "Room Test" function, which helps engineers comply with the CO safety part of BS7967.

The function provides minute-by-minute data which can be logged and printed directly from the FGA.

The pass/fail points are detailed in BS7967 and can form part of any prosecution of the installer or landlord if high CO in the atmosphere around appliances leads to injury or death.

The newest, full-function FGAs also have a differential thermometer (with K-type thermocouple inputs), a differential manometer (pressure sensor) and a gas escape or leak sensor.

The manometer allows an FGA to perform Let-by and Specific Tightness Tests and, on some units, there is a dedicated functionality to allow certain tests detailed in the Institution of Gas Engineers' procedure IGE/UP/1B.

Time-of test and pressure start/stop readings, with a customer signature column, can be stored and printed from the FGA.

The differential thermometer allows flow and return temperatures to be measured simultaneously.

This function can be used anywhere a potential temperature difference measurement is needed.

There are many different K-type probes available for a variety of applications.

The test is as valid for boiler flow and return as it is for specific radiators or individual temperature measurements.

Full-function FGAs provide a single instrument in place of many.

They usually have a comprehensive internal memory which stores all data from the tests undertaken.

This data can be downloaded to a PC or transferred via a Bluetooth connection to a handheld PDA.

The addition of a printer and the standard set of probes completes a comprehensive kit, and if the printer uses the same mains charger as the FGA, so much the better.

A print-out of the 4 logged reports (flue test/tightness/diff temp/CO room test) provides evidence of work carried out and can be signed off by the customer.

An explanation is always helpful as the average homeowner is only distantly aware what all these readings mean.

A final point is that it is particularly important to know the type of fuel being used by an appliance; an FGA testing a natural gas fired boiler flue, for example, will not provide accurate readings for an LPG fired unit.

It is therefore essential that users select the fuel type correctly.

Most FGAs provide a choice of fuels in the start-up sequence or as a set-up parameter.

As the number of different fuels being used by customers increase, FGA manufacturers need to provide increased options to heating engineers.

Biomass, biogas, coke and wood now join the standard list of five used over the last several years: natural gas, LPG, heavy oil, light oil and coal.

Weighing the quality versus cost issue in the FGA market is down to the individual, but CoGDEM (Council of Gas Detection and Environmental Manufacturers) recommends that all service engineers responsible for domestic or commercial appliance installation, maintenance and management should use them.

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