VOICES | COMMERCIAL HYDROGEN APPLIANCES Making hydrogen work for commercial buildings Any conversion from natural gas to hydrogen in the grid must cater for commercial and industrial heating. Enertek Internationals Paul Needley and Frazer-Nash Consultancys Stephen Livermore explore the challenges T here is significant interest in the decarbonisation of heat by converting the UK natural gas grid to hydrogen. Of the 23 million homes connected to the network, around 90% have boilers for space and water heating, and about half have gas hobs and fires. Although domestic heat makes up more than half of the UK heat demand, the Stephen Livermore provision of space heating, hot water and cooking for commercial and industrial properties accounts for more than 25%. Any network conversion to hydrogen will need to cater for larger-scale commercial and industrial heating, too. Overall provision of heat for space heating, hot water and cooking in our homes and businesses accounts for more than 35% of UK energy consumption, according to BEIS. The government has signalled its intention for affordable, low carbon energy through the Clean Growth Paul Needley Strategy, and achieving this is likely to require almost full decarbonisation of heat in buildings. There has been increasing interest in the potential conversion of the UK gas grid to hydrogen. As intimated in the Prime Ministers 10-point plan, any conversion of the network is likely to start by blending natural gas with up to 20% hydrogen. Hydrogen has a high energy density per unit mass, but a low volumetric energy density, so a 20% blend only equates to around 7% decarbonisation. There are advantages to this approach, however. It will enable the hydrogen supply chain to be ramped up and it has a minimal effect on appliance performance domestic and most commercial appliances are already tested for ignition performance with 23% hydrogen as part of certification for use on natural gas. In practice, 20% is likely to be a limit for blending because of certification and technical issues. After that, it will be a jump up to 100% hydrogen. For the past four years, the government through the Hy4Heat programme has been exploring the feasibility of developing appliances that can run on 100% hydrogen, and a number are undergoing trials. Recently, commercial appliances have also been developed. For a given delivery pressure, hydrogen and natural gas provide a similar energy flux when injected through a burner. This is characterised by the Wobbe Index and means that from an energy production metric, at least natural gas and hydrogen are relatively comparable. The key benefit of hydrogen over natural gas is that, at the point of combustion, there are no carbon emissions. Initial findings from the Hy4Heat programme also suggest that NOx emissions a major air pollutant are lower for hydrogen than natural gas. Technical hurdles There are technical hurdles to deal with. Hydrogen has a greater flammability range and this poses a risk of ignition before the point of combustion. It also has a greater flame speed and is more prone to light-back, where the flame can propagate back upstream. These challenges can be overcome by: changing the gas and air mixing point and method; smaller burner port diameters; multiple ports; and specifying UV flame detection, except in open spaces, where fast-acting thermocouples suffice. Hydrogen flames are less visible and produce more water vapour (see panel, How hydrogen and natural gas differ). The engineering challenges for developing commercial hydrogen appliances are similar to those faced with domestic appliances, except on a larger scale. On some commercial catering appliances, ignition is manual and requires opening the appliance door, but this is likely to be acceptable for hydrogen appliances, as the gas tends to disperse quickly. It is estimated that there are around 1.5 million commercial gas appliances in the 2 million or so non-domestic premises in the UK1 less than 5% of the number of domestic appliances. As with homes, space-heating appliances are the most prevalent, with around 500,000 boilers in the range 30kW to 1MW. It is estimated that 80% of these boilers are <150kW,1 so commercial hydrogen boiler development has focused on It is estimated that there are around 1.5 million commercial gas appliances PAUL NEEDLEY is managing director at Enertek International and STEPHEN LIVERMORE is senior consultant at FrazerNash Consultancy 34 May 2021 www.cibsejournal.com CIBSE May 21 pp34-35 Hydrogen appliances Supp.indd 34 23/04/2021 16:25