Developed by HHIC and Progressive Energy Ltd
Technical Bulletin 157 – CO, CO2 and combustion ratio checks using an electronic combustion gas analyser (ECGA) when carrying out works on a natural gas appliance being supplied with natural gas containing up to 20 vol% hydrogen
This Technical Bulletin provides guidance to Gas Safe registered businesses and engineers on the effects of introducing a hydrogen blend up to 20 vol% within natural gas supplies on CO, CO2 and combustion ratio checks.
Following research undertaken by the HyDeploy project(1) at Keele University, the Heating and Hotwater Industry Council (HHIC), in collaboration with boiler manufacturers, gas detection manufacturers and Progressive Energy, have developed generic guidance on the flue gas analysis effects of introducing a blend of hydrogen up to 20 vol% into the natural gas supply.
Appliance research was conducted at Keele University as part of the HyDeploy project. Four pairs of domestic boilers were installed and operated continuously: one set of the four was supplied with natural gas, and the other set was supplied with natural gas blended with hydrogen up to 20 vol%. The four pairs were provided by four different manufacturers.
Utilising both a direct-reading CO2 ECGA and calculated-CO2 (indirect reading) ECGA, each conforming to BS 7967(2), combustion parameters were measured for all eight boilers, along with the gas composition being supplied to the boilers at the time of the measurement. The error of each instrument as they relate to CO and CO2 readings was +/-10ppm and +/-0.3% respectively.
The measured results of both the natural gas supplied and hydrogen blend supplied boilers were then compared against the Wobbe number of the gas being supplied to the boilers at the time of measurement.
The Wobbe number is the interchangeability parameter of gas quality and is used to set the limits of gas quality that can be transported within UK gas networks.
The GB Wobbe range is defined by the 1996 Gas Safety (Management) Regulations (GSMR)(3): at the time of writing this Technical Bulletin, the range is 47.2–51.41 MJ/m3 under normal conditions.
To aid the analysis, a combustion model was developed to predict the expected range of flue gas analysis results based on the GSMR Wobbe range, to allow comparison with the results obtained both from the natural gas supplied and hydrogen blend supplied boilers.
The results of the analysis found that both CO and CO2 concentration reduce as hydrogen is blended into natural gas supplies. As hydrogen is blended into natural gas supplies, the Wobbe of the gas reduces.
The degree of reduction measured in both CO and CO2 concentration was in line with the expected change due to a change in Wobbe number (ie, two natural gases of equal Wobbe, one containing a hydrogen blend and the other containing no hydrogen were found to have equivalent CO and CO2 concentrations).
These results are in line with previous research carried out on the relationship between flue gas results and natural gas quality(4).
The results of the research show that, although hydrogen blending has an effect on flue gas analysis results, the measured effect is not due to the introduction of the hydrogen but the effect hydrogen has on the Wobbe number of the gas.
Therefore, as long as the Wobbe range of hydrogenblended natural gas remains within the GSMR limits for natural gas, there will be NO change in the range of flue gas analysis results expected from appliances.
This was found to be true both for direct-CO2 ECGAs and calculated-CO2 ECGAs.
Therefore, no change in the criteria for combustion checks or calibration of analysers should be required to enable safe and accurate combustion checks to be carried out on an appliance being supplied with a blend of natural gas containing up to 20 vol% hydrogen (for example, no change to TB 143(5) is required to take account of the potential presence of a hydrogen blend up to 20 vol%).
The results of the research were peer reviewed by HSE, all four boiler manufacturers that supplied boilers for the research and the two gas detection manufacturers whose instruments were used to take the measurements.
Note 1: For details of current gas safety legislation, building legislation and industry standards for the geographical areas covered by Gas Safe Register, see the Legislative, Normative & Informative Document List (LNIDL)(6) by logging into your online account at www.gassaferegister.co.uk/sign-in
Note 2: For general information about the process behind the development of Gas Safe Register Technical Bulletins and the expectations for all stakeholders, see TB 1000(7) by logging into your online account at www.gassaferegister.co.uk/sign-in
(1) HyDeploy project (https://hydeploy.co.uk/)
(2) BS 7967: 2015 – Guide for the use of electronic portable combustion gas analysers for the measurement of carbon monoxide in dwellings and the combustion performance of domestic gas-fired appliances
(3) GSMR, 1996. UK Gas Safety (Management) Regulations, 1996, UK Statutory Instruments 1996, No. 551
(4) T. Williams, G. McKay, M. Brown (2004), Assessment of the impact of gas quality on the performance of domestic appliances (a pilot study), DNV GL (formally Advantica)
(5) Technical Bulletin 143 – CO and combustion ratio checks using an Electronic Combustion Gas Analyser (ECGA) when commissioning a condensing boiler incorporating air/ gas ratio control valve technology
(6) LNIDL – Gas Safe Register Legislative, Normative & Informative Document List
(7) TB 1000 – An introduction to Gas Safe Register Technical Bulletins