VOICES | JOEL GUSTAFSSON Why heat pumps can help and hydrogen cant With the rapid decarbonising of electricity, Max Fordhams Joel Gustafsson says industry and government should encourage the uptake of heat pumps rather than be lulled into a false sense of security by hydrogen T he energy used to heat buildings is responsible for around 20% of the UKs carbon emissions.1 As a nation, we have committed to netzero carbon by 2050, and providing all heat for buildings from low carbon sources is a key component of the strategy.2 This should be both alarming and empowering to building services engineers. The decisions we make now, and the technologies we implement, will be operational for most, if not all, of the next 30 years. The world is currently 1C above pre-industrial levels Australia is on fire, Cape Town is running out of water and Cambridge hit 38.7C in summer 2019. Another 0.5C will exacerbate all of these impacts and many more, and this is the current best case. We cannot ignore the urgency. This means we need to get on with deploying the technologies that are available to us now and not wait for technological answers that are many decades away. It will be too late. How far away is hydrogen? JOEL GUSTAFSSON, partner, principal engineer and member of MF: Net Zero An immediate opportunity Using hydrogen for heat is not a means to reduce the CO2 emissions of the UK in the 2020s.5 So, what can we do? The answer lies in the proliferation of UK renewables. In the past five years, the carbon intensity of grid electricity has decreased by 60%. Coal-fired power stations have been decommissioned, and the cost of offshore wind has decreased. Both of these things happened much faster than predicted and the trends are accelerating.6 Meanwhile, the increased efficiency of electrical appliances has reduced peak loads from 61.7GW in 2002 to 50GW in 2018. Electricity is decarbonising rapidly, the grid has spare capacity, and we know how to turn it into heat with an efficiency of 300-400%.7 Electric heat pumps are completely orthodox in Scandinavia, France and many other countries. Yet, in the UK, we put their widespread deployment in the same bracket as burning hydrogen in boilers something that is at least 30 years away. The hydrogen solution is often proposed by those wishing to gain efficiencies by making use of existing infrastructure a completely sensible aim. Heat pumps can provide this when applied to existing heat networks to make excellent use of the physical installations put in place to enable combined heat and power (CHP). We should note that CHP is currently a technology that burns gas to displace low carbon electricity; the net result is that its heat-carbon intensity is 130% that of a gas boiler and 330% more than an electric heat pump8. Electricity is decarbonising, the grid has spare capacity, and we know how to turn it into heat with an efficiency of 300-400% It is impossible to mention low carbon heat without discussing hydrogen. The replacement of methane in our gas network with hydrogen seems instinctively simple. However, we cant allow ourselves to be lulled into a false sense of security; the technical and economic barriers that stand between us and a functioning hydrogen economy are almost as high now as they have been for the past 20 years. First, green hydrogen is made by electrolysis of water, using renewable electricity, in hydrolysers and subsequent compression into a network; around 35% of the energy is lost to this process.3 Second, the energy density of hydrogen per unit volume is one third that of methane. If we are to use it as a direct replacement, we will need three times more storage and distribution capacity than we currently have for methane. Lastly, burning it is inefficient. Hydrogen burns hotter than methane and the thermal losses within the boiler will increase such that current levels of combustion of efficiency are unlikely.4 In total, we lose around 50% of the electricity we put in using hydrogen in this way. Retrofit heat pumps Retrofit of CHP with heat pumps is possible, and can have an immediate impact. Two stages of vapour compression take heat from air at temperatures as low as -15C and raise it to 70C; with water, we can efficiently go to 90C.9 The refrigerants, either ammonia or a combination of butane and propane, have a near-zero global warming potential. Further, the buffer vessels that have been installed to accommodate the low turndown of CHP engines can be deployed to store heat from heat pumps, shift demand, 30 March 2020 www.cibsejournal.com CIBSE Mar20 pp30-31 Joel-Max.indd 30 21/02/2020 14:51