Last month I took part in a debate about the future of heating in CIBSE Journal with Phil Jones who runs the CIBSE CHP(Combined Heat and Power) group. In simple terms I was representing the case for an all-electric future, off the back of a paper I led in 2014, and Phil was presenting the case for gas CHP. (There was actually a lot of common ground; energy efficiency is being honoured mainly in the breach and electrification of heat is a big part of the future.)

You can read the full debate in the CIBSE journal here, in case I am misrepresenting Phil, but…

Phil’s position is that we need a variety of solutions with heat pumps providing heat in off-gas areas, and in cities Phil suggests that district heating is the way forward from CHP and, heat pumps. My position is simple; in almost all cases over any realistic lifetime, by any reasonable calculation methodology the hierarchy of low carbon heating, from low to high is:

  1. Heat Pumps – Lowest by miles
  2. Gas-fired boilers Second best
  3. Combined Heat and Power – Highest

This has been shown by teams from WSP|PB and Arup in reports and recently by Keepmoat in an article for CIBSE Journal.  This is why it doesn’t matter where you are or what thermal demand density there is, whether gas is available etc.; heat pumps are always better.

District heating probably needs to be part of a separate article but in a nutshell I think whether we use it or not should be left to project engineers. If there is a nearby energy from waste plant that will guarantee heat for a long period then that is great. But otherwise heat pumps should be policy, and mandatory unless there is a good reason why not. No CHP units or gas boilers, because then you are just adding losses onto an already high carbon system.

There are a host of other benefits to heat pumps in terms of no air pollution which is a big issue in our cities, they can eliminate overheating in new homes which is a big issue in southern cities (by not introducing as much heat and providing cooling if necessary), and they also improve energy security in the long term because electricity can come from whatever sources we decide; nuclear, renewables, gas, even coal if we need to do so. A gas system has to use gas and that is increasingly from abroad. Biomethane may change that but it can’t for the foreseeable future and even if it does exist in large quantities we can use it to generate zero carbon electricity.

I genuinely feel that the case for all-electric cities is now becoming unanswerable but an argument that is difficult, if not impossible to refute is that we can’t electrify our heating as the peak demand is circa 300GW and our electrical system has a capacity of around 60GW. My answers to this are:

  • Genuine energy efficiency is needed. We can reduce thermal demand, particularly of homes significantly with reasonably simple measures, such as double glazing, loft insulation, draught proofing and smart controls
  • Our power system is undergoing a revolution; energy storage, demand management, renewables, nuclear and flexible generation will mean our system will be able to generate what we need in a competitive marketplace
  • The process of electrification will take decades so there is time to adapt to the new demand

Having said that I could be wrong, as can anyone talking about the future and therefore I finished the debate with a proposed compromise on my electrification points

  • Don’t change the heating in existing buildings, but agree a programme of energy efficiency. Decide whether/how to change them to a decarbonised gas system, all-electric, hydrogen or other when/if these things are available
  • New developments should be all-electric. With very little need for space heating, they don’t create a massive increase in electrical demand, and we are only building at about 1% of our stock per year so we can do this easily
  • No CHP engines or other gas systems to be deployed until we have decarbonised the gas grid/converted it to hydrogen.

In this area I sway between despair and hope; more and more people are coming to the obvious conclusion to which any dispassionate analysis of the numbers leads; all-electric developments are the future and should be the present. On the other hand when talking to some people or groups there is still discussion about how we can use more CHP and gas, often on heat networks, to reduce carbon emissions and that is a worry. (Does anyone know how the GHG protocol emission factors get updated? I wonder if companies with a lot of CHP related energy will end up with emissions growing, at least relatively compared to others.)


PS. In the most exciting release of the year the government has just published the consultation on changes to the Standard Assessment Procedure (SAP) which is the methodology we use to make energy calculations and CO2 emission projections for homes. (The same factors will be used for non-domestic buildings as well I think.) I will put a full article response on about this as there is quite a lot in there but the big headline is that they are proposing a 23% reduction in the carbon emission factor we use for mains electricity (from 0.519 to 0.400 kgCO2 per kWh). This will have the benefit of going some way to recognising the benefit of all-electric systems compared to gas.

The current and proposed methodology for calculating this is wrong in my opinion for two reasons

  1. The calculation methodology suffers from a snapshot factor based on 2015 data when the changes won’t take effect until 2017, during which time there has been substantial changes in our electrical generation
  2. They have yet again refused to change to a lifetime CO2 emission factor; surely a building that is going to use a system for 20 years or so should use a 20 year average factor? (You can acknowledge that the uncertainty around the future by using a discount factor the further ahead you go).

The upshot of this is that we will still be massively overestimating the emissions from all-electric buildings and underestimating emissions from CHP engines; at least we seem to be moving in the right direction.

I would be really interested if anyone could tell me whether/how this will affect energy performance certificates of existing buildings. If I read it right then it will mean buildings with all-electric systems will improve and buildings with CHP systems will get worse?