ENERGY SAVING


then air- to-air heat pumps are attractive, especially reversible units, if increasing summer temperatures make a/c desirable, or indeed essential, for the well-being of the very young and old. The real problem for the UK is caused by the ~ 23 million domestic gas-fi red, hydronic central heating systems operating at higher output temperatures than are readily achievable by heat pumps. Units are already available that can replace gas boilers and by running longer can deliver the required heat…provided insulation is also upgraded, not an easy task in older British housing stock.


Alternatively, existing gas boilers could already use natural gas diluted with 20% hydrogen, to reduce CO2 emissions. Pure hydrogen condensing boilers have been developed which would avoid abandoning the considerable investment in the grid. The problem is the transition from 20 to 100% hydrogen. Does the householder pay for the replacement of natural gas boilers before the end of their working lives by hydrogen boilers, or does the government provide subsidies? Maybe the key development are kits that allow the conversion of existing boilers to hydrogen? Then there is the ‘interesting’ logistical problem of transitioning whole towns from natural gas to hydrogen. Heat pumps avoid such problems provided the capacity of electrical transmission network is progressively upgraded as the number of heat pumps increases. Maybe hybrid heat pump/gas boiler units are the answer allowing space heating load to be divided between the electricity and gas grids? The heat pump component can be sized for optimum effi ciency with the hydrogen-fi red boiler unit providing peak heating and hot water. Water electrolysis co-produces gaseous oxygen, which can be vented to the atmosphere, but this wastes a valuable resource. If biomass is burnt in pure oxygen in a closed system, then highly concentrated CO2 is already ‘captured’ ready for sequestration. An electrolysis/biomass combustion plant would generate both hydrogen and electricity simultaneously removing CO2 from the atmosphere. In other words, it is both carbon negative and can utilise existing electricity and gas grids. Although it has technical elegance, the approach could only satisfy a modest part of the space heating demand. But it would also allow the continued use of natural gas by generating hydrolytic ‘blue’ hydrogen without


effi cient, the system will enable better matching of renewables to demand. The technology can be viewed as a thermal pump operating with air as the working fl uid and thus has interesting implications for large scale users of refrigeration…food processing plants, cold warehouses, supermarkets and databanks. Evaporating liquid air during the energy recovery stage could be used for refrigeration with the power generated used to drive, perhaps by direct coupling, conventional Rankin cycle units using low GWP refrigerants.


adding more CO2 to the atmosphere, although the suggestion might be anathema to idealistic environmentalists. Viewing hydrogen and heat pumps as competitors for the space heating market may be too simplistic, perhaps they should be viewed as complementary?


Liquid air is being developed as an energy storage technology to buff er intermittent renewable generators, notably wind and PV. Although the overall process is only ~60%


In summary, various factors, technical, economic and environmental, will determine which thermal pumping technologies come to dominate in the ‘Age of Renewables’. To maximise the cost benefi t to the customer and simultaneously minimise environmental impact one should keep an open mind about which technologies are likely to prevail. Trying to enforce selection by ill-advised ideologically- driven regulations and subsidies could result in sub-optimal technical solutions and waste of national resources. Global warming is too serious a problem to be a political football game.


www.acr-news.com


January 2021


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