EROH- energy return on heat

2021.05.06 – Ian Page

This new term was introduced in a Joule paper, proposing a methodology for evaluating the use of various primary fuels for various categories of heating.

While it admits that it's a flawed measure, it's better to have some measure!

The paper is introductory, and might lead non expert readers to the wrong conclusions, so some way to go, but it led me to a thought on an extension to the slivers series (i.e. take a limited resource, decide what your climate objective is, and develop a series of slivers of applications of increasing effectiveness to establish a strategy for using the limited resource.)

(Joule 5 531-550 mar 17 2001)

In this case the estimates of the temperature of heat needed for various segments of American and EU industry show that 1/3 to 1/2 of heat needed is at fairly low temperatures (less than 200C) the "boiler "category. This is cost effectively achieved with heat pumps up to around this temperature (higher presumably if it can use input waste heat as the source for the heat pump such as the heat of fermentation in a brewery).

This led to the thought that if we must burn some fossil fuels during the phasing out period, perhaps we could treat them as an artificially limited resource during that time and set short term policy appropriately. The objective would be to maximize the reduction in CO2 volume generated before 2050, thus a small reduction in an application segment early can have as much effect as a larger reduction in an application segment later.

This suggests that given that gas, oil and coal can deliver very high temperatures, which are perhaps more of a cost challenge for electrical or renewable hydrogen heating. Perhaps we need to first eliminate the use of these for low temperature heating. For example, using burning gas at two thousand degrees C to heat water to just 60 C for radiators or hot water supply in the home, seems a really bad use of fossils if you treat the CO2 that we can afford to generate/fossils as a limited resource.

This class includes space and water heating in homes, offices and industry, as well as quite a lot of industrial activities involving less than a couple of hundred degrees. These are easily accessible to heat pumps, waste heat reuse, insulation, and waste heat upgrading with heat pumps as appropriate. Since the technologies exist, although it may be necessary to encourage them into mass production volume and lower cost, they would be the obvious initial slivers to target with carrot and stick policy.

The use of fossils for generating electricity is thermodynamically more efficient at higher temperatures, however electricity is already usually cheaper and easier to generate from renewables so this isn't a temporarily justifiable use under this analysis and policy should obviously be to eliminate it as fast as possible by massive renewable investment. (except for gas fired stations for the few weeks a year when renewables don't yet provide secure supply)

With oil the main use is for vehicles and petrochemicals, not heating (it’s too expensive)- it's much easier to see the slivers for vehicles where the limit factor is battery production (replace large high use long distance vehicles first, then medium sized high use commercial vehicles and last consumer low use vehicles - not what is being done). Petrochemicals is a harder and more diffuse problem but a smaller segment. Targeting first the rapid replacement of the process that turns natural gas into hydrogen (a very high-volume application) with electrical generation of hydrogen from water, before tackling the wide variety of other processes that follow on, seems to be the obvious first sliver.  This is expected to be cost effective by 2030 but could be brought in earlier as a result of policies which might increase early volume and bring the break-even date forward.

Coal, in the limited form of the highest grade of coal for making steel, is as yet not easy to replace. It will probably be replaced by green hydrogen. Getting rid of the vast quantities of thermal low-quality coal used for electricity generation is probably a higher priority sliver in the short term.

This approach doesn't take the pressure off eliminating later slivers where urgent research and development of a wide variety of new processes is needed. It does suggest a way of focusing attention on already existing technology solutions where these can make a significant early contribution (e.g., all home and office gas fired heating could be replaced within ten years- the typical boiler lifetime with heat pumps or solar water heating depending on the country).

While some activities and policy proposals (e.g., from the UK CCC) are more or less aligned with this, there is still scope for earlier action with greater effect in general.