REFRIGERANTS
Inform, don’t ass-u-me H
Professor Dick Powell of Refrigerant Solutions asks: “Are heat pumps the right answer?”
eat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time – Clausius’ statement of the Second Law of Thermodynamics. A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative. Yet I was asking something which is the scientifi c equivalent of: Have you read a work of Shakespeare’s? C P Snow Rede Lecture 1959: The Two Cultures. “If the UK is going to retrofi t the 26 million
existing homes across the UK to be made low carbon - which is UK infrastructure policy - convincing the public to rip out a perfectly good heating system and install expensive to run ground source heat pumps is simply bonkers!” Stuart Fegan, GMB National Offi cer, GMB website; February 2019. Heat pumps are a practical demonstration of the Second Law of Thermodynamics; I was reminded recently of Snow’s oft-quoted remark about this Law when discussing climate change and the UK Government’s 2050 target for carbon neutrality with friends. I mentioned that, as our gas boilers wear out, we could be replacing them with heat pumps, prompting the query: “what is a heat pump?” When I answered that they were units similar to air conditioners that can deliver a quantity of heat three to four times greater than the electrical energy supplied by pumping heat
34 March 2020
from a low temperature source into the room, the responses were quizzical. Is this a practical joke? Have you fallen for an Internet scam? I don’t think it would be suitable for my house since I don’t have a heat source available. Where my friends might just be confused, the GMB, as the above quote shows, are anti-heat pump. They oppose them because “electricity costs four times as much as gas”, so many more households would be forced into fuel poverty as well as making obsolete the expertise of its gas engineer members. The union further advocates the long- term retention of the UK gas grid, with the replacement of natural gas by hydrogen. Even if the HVAC industry thinks heat pumps are the answer, we may have a credibility gap with the general public.
Renewable energy sources such as wind, photovoltaic, biomass and tidal, all primarily generate electrical power. To this list we can also add nuclear energy, which is likely to contribute to UK decarbonisation. Space heating will be competing with other energy sectors for electricity, notably transport, requiring the installation of more renewable generating capacity and expansion of the Grid, capital spending that will ultimately be paid for by consumers through their energy bills. Heat pumps therefore seem an obvious alternative to gas heating, helping to minimise the number of PV installations and wind farms and thus the capital cost of decarbonisation. While this may be true for new builds where modern levels of insulation and heat recovery ventilation can be incorporated in the design, the real problem lies with existing housing stock, a signifi cant proportion dating from the nineteenth century. Most present-day
UK central heating systems are hydronic, operating at around 650C for space heating and hot water. The effi ciency of a heat pump is very sensitive to the temperature diff erence between source and sink so its energy advantage is compromised on cold winter days and it may struggle to supply hot water. A solution off ered commercially is the ‘hybrid’ system, combining a heat pump and a condensing boiler, which is claimed to be 35% more energy effi cient than the boiler alone. While technically attractive, could a household on a limited budget aff ord the initial capital cost, even if their future energy costs are lower? The GMB raises a valid issue about the impact of the move away from gas heating on household fi nances. Furthermore, there is considerable commercial investment in the gas storage and distribution system which will become redundant as well the private investment in the 23m UK domestic, gas central heating systems. But is hydrogen the answer?
The progressive replacement of natural gas by hydrogen would allow the retention of the existing gas grid and boilers. Even now a 20/80 hydrogen/natural gas mixture could be used. Domestic boilers capable of burning 100% hydrogen have already been developed, the problem is sourcing the hydrogen. Renewable- powered water electrolysis, roughly 80% effi cient, appears to be the answer. In a condensing boiler, at roughly 90%
effi ciency, hydrogen would deliver an overall effi ciency of around 72% relative to the original electrical energy.
Yet if this electricity was used in a cheap electrical resistance heater the effi ciency would be about 95%, allowing for a 5% transmission
www.acr-news.com
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