Greater London Authority

GLA Energy Assessment Guidance

The GLA has issued a revised Energy Assessment Guidance. This is to be used on preparing energy assessments as part of stategic planning applications (including developments of over 150 residential units, developments over 30 metres in height, developments on the Green Belt and on Metropolitan Open Land).

Applicants are encouraged to use the updated SAP 10 carbon emission factor of 233 grams of CO2/kWh in place of the very outdated factor from SAP 2012 of 519 grams of CO2/kWh.

Any applicants proposing to use the outdated SAP 2012 carbon emissions factors will need to provide a justification. If gas-engine CHP is also proposed, applicants will be expected to provide sufficient information to justify its use and to minimise the carbon and air quality impacts.

This new approach of the GLA will be in place for London from January 2019 – until the Government adopts new Building Regulations with updated carbon emission factors. It seems likely that many of the UK's Local Planning Authorities will follow the lead of the GLA.

See a full copy of the Mayor of London's Energy Assessment Guidance.

If short on time, see these quotes from the Introduction:

See a full copy of SAP 10.

The implications of adopting SAP 10

There are two main implications of the reduction in the grid carbon factor for electricity by 55%.

These long awaited steps are a major improvement in encouraging the decarbonisation of heating, but do they go far enough?

SAP 10 is relevant to assessing planning applications for future buildings, so it would be more logical to use the predicted grid carbon factor for half way through the life of heating equipment that is about to be installed. In the case of a ground source heat pump installation the groundworks (the expensive bit) have a life of over 100 years and the heat pump itself should last for 25 years. If the useful life of the installation is conservatively estimated at 40 years, then the relevant grid carbon factor to be used should be the factor estimated for 20 years time. BEIS estimates that the grid carbon factor will have fallen below 50 gCO2/kWh by 2038. This is a further fall of 78% from the figure of 233 published in SAP 10.

CO2 Emissions Calculator

The Carbon Emissions Calculator shows the current level of CO2 being issued in grams for each kWh of heat delivered by the most common forms of heating, on the assumption that the heat pumps are using electricity from the grid.

The amount of CO2 emitted by a gas boiler is constant at 215 grams of CO2 per kWh of heat delivered (assuming the boiler is 85% efficient). Gas issues far less CO2 than burning oil, which in turn emits much less than burning coal.

Carbon content UK Grid electricity

However, the very clear winner is to use a heat pump which issues no CO2 at all if it uses green electricity. Even if the heat pump uses grid electricity only a small fraction of the CO2 issued by a gas boiler will be issued by the Grid when supplying an efficient heat pump.

The Carbon Emissions Calculator shows the current amount. This has fallen rapidly from the amount that would have been issued in 2012 as the grid has been decarbonising rapidly. The historic and projected CO2 emissions are shown on the graph below.

The message is very clear: if we want to reduce carbon emissions from heating we can do so now by using heat pumps.

Air quality is also a key driver

A significant benefit of heat pumps over conventional gas boilers is that there is no combustion involved (combustion of gas emits nitrous oxides). Beside the direct advantages (safety), technical advantages (no need for flues) this is very beneficial for cities like London with poor levels of air quality.

Alternative forms of low carbon heating

Alternative forms of low carbon heating have also been considered including direct electric heating, which has a significantly higher running cost; and the burning of hydrogen which emits no CO2 at the point of combustion.

However, upgrading the gas grid to contain very small hydrogen molecules would incur a huge national cost and upgrading all the boilers to burn hydrogen would also be a significant task. Production of hydrogen by steam methane reformation emits large volumes of CO2. This would require the development of economic Carbon Capture and Storage to achieve carbon neutrality.

Hydrogen can also be derived from electrolysis powered by renewable electricity, although the overall efficiency would be less than 70% before, accounting for distribution losses. This compares to an efficiency of over 350% for a typical ground source heat pump.

It is clear that the only practical route to heating without CO2 emissions is to avoid combustion. The alternative is to use heat transfer: which means using heat pumps. There is no need to search for esoteric alternatives when tried-and-tested heat pumps are available now.