Energy vs Carbon

Should a percentage target included in a Merton Rule-like policy be framed in terms of on-site energy use, or as a reduction in carbon emissions from predicted energy use?

The GLA and London boroughs have concluded that compliance should be in terms of carbon rather than energy. This is set out in informal guidance provided by GLA to the boroughs, and also in the draft design and construction elements of the overall London plan, and as a result developers and construction professionals are adopting this as the standard approach.

Many London boroughs followed Merton’s example and adopted targets based on 10% of energy generation for new build before the issue of how to measure compliance had been fully explored. This has created a slightly confusing situation where the policies all refer to a target of 10% of energy use, but compliance is being measured as having sufficient renewable energy generation on site to reduce carbon emissions from energy use by 10%.

Merton is now proposing a revised version of the policy for their draft LDF to clarify this issue: “The Council will require all developments, either new build or conversion, with a floor-space of 500m², or one or more residential units, to incorporate on-site renewable energy equipment to reduce predicted CO₂ emissions by at least 10%”.

The advantages of having the target in terms of carbon reduction are that:

• it fits with new Part L building regulations which assesses the energy performance of buildings in terms of their carbon emissions rather than energy use per se
• it fits with the central aim of the Energy White Paper to reduce CO₂ and put the UK on a path to a 60% cut in carbon emissions by 2050
• it recognises the fact that grid electricity has a higher carbon burden per unit than mains gas, and therefore that electricity generating renewables will save more carbon per unit of output than heat
• it would avoid potential anomalies such as all-electric heating

The Merton Rule policy should be interpreted through carbon emissions rather than raw energy usage.

The London Plan, relating to the Mayor’s strategy is also being interpreted as referring to the total “Primary energy demand” of a development and that this will be measured in terms of the “Carbon burden of the energy demand and use”. This interpretation will ensure that the market is not distorted, electric heating is not encouraged, and the strategy gives due credit to reductions in CO₂ emissions from the use of renewable energy resources.

To explain further: Heating with gas produces less CO₂ emissions than heating with electricity. Regardless of which energy is used it takes about 17,000 kilowatt hours per annum to heat an average 3 bed mid-terraced house. Therefore if the policy is to generate 10% of 17,000 kWhpa (1,700 kWhpa) then it will amount to the same amount of renewables on the roof whether gas or electricity is used.

However, if the electrical energy is converted into kilograms of CO₂ emissions per annum then an average home heated by gas emits about 4,500 kilograms of CO₂ per annum as compared to 7,000 kgCO₂pa for one heated by electricity. This is because gas for heating your home comes direct from the North Sea to your boiler, whereas electricity to heat your home comes from the gas being first piped to a power station where it is burnt to drive a generating turbine, and then as the electricity is carried down miles of copper cables to your home it looses some of its energy in the form of heat.

Therefore if we interpret the policy as requiring renewable energy to cut CO₂ emissions by at least 10% then it will take a lot more equipment on the roof than it would to generate 10% of the raw energy needs. This will act as a deterrent for developers who may be tempted to install electric heating into new buildings, which is often a cheaper capital outlay.

Electric heating should also be discouraged because it is much more expensive for the end user resulting in fuel poverty and undermining the competitiveness of local businesses by increasing their monthly energy bills.

Energy/Carbon calculation methodology: Determined by current Building Regs.

• Electric energy - 1 kwhpa = 0.568 kilograms of CO₂ per annum
• Gas energy      - 1 kwhpa = 0.19 kilograms of CO₂ per annum
  

The electricity calculation figure (circa 2004) are based on the carbon emissions associated with the general mix of fuels used for generation electricity averaged out across the year. As dirty coal fired stations come off line to be replaced by gas stations, or preferably renewables, then the kWh/ CO₂ figure will fall – however, this fall will be negated as the nuclear plants also close.

Establishing baselines
The baseline used for calculating the predicted CO₂ emissions of the development come from the Energy Consumption (ECON) Guides (in this case “Energy Efficiency in Industrial Buildings”, Sites Guide 18 and Benchmarking Tool for Industrial Buildings Guide 81), published (or listed) on the Carbon Trust website. A more comprehensive list of kilowatt hours per annum per square meter was compiled by Faber Maunsell for the London Renewables Toolkit – page 107: http://tinyurl.com/zdjh9

However, there is an urgent need to redefine the CO₂ baseline data on which to anchor the policy because all these ECON guides are out of date with some going back as far as the 1980s. The other baselines available are the CIBSE guides, though these are composites of other data sets and are also completely out of date because like the ECON guides they make no allowances for the new Building Regs that demand a far higher standard of energy efficiency. Therefore there is a pressing need for the Government to commission new benchmark and “best practice” guides. Until they are in place it is only possible to use a rule of thumb approach to accounting for Part L of the B Regs – which is to deduct about 8% from the ECON guides kWhpa per m2 figure.

An alternative to generic building type guides is to concentrate on the specific building itself. The idea would be that a forensic assessment is made of the predicted CO₂ emissions of the building, and that this is used as a benchmark for determining the 10%(+) policy. This is a sound approach – with a couple of caveats:

• First: it is likely that the process (probably in the form of software toolkits being developed by the BRE, GLA and others) to carry out the assessments will be extremely complex – too complex for small developers and local authorities without the resources to outsource the task to dedicated energy consultants. In the initial pre-application phase it will only be possible to identify basicCO ₂ figures anyway, and a simple excel spreadsheet will suffice.
• Second: there is the temptation to become fixated by this subject. The advice to local planning departments is to recognise that renewable energy is like any other specialist technical subject and inevitably prone to being populated by geeks, anoraks and obsessives. They rightly take a great pride in getting to the bottom of things – but this can sometimes be at the expense of everyday comprehension.
  

Despite these reservations, the site-specific CO₂ assessment approach is without doubt best for large and/or complex developments, but there is always a danger that fixating on it can become a wearying impediment. Mainstreaming renewables is the best way to cut CO₂ emissions, and the best way to do that is to engender a culture where doing so is effortless, methodical and to the point of being unworthy of particular mention.

Willow Lane CO₂ emissions
With reference to the Willow Lane, as a speculative development, it was impossible to establish a baseline energy/carbon footprint. Without knowing who the end users were going to be it was impossible to determine how much heating might be needed. As such it rules out water heating renewable technologies that might normally be used to pre-heat water for central heating and showers etc. This logic also applies to Ground Source Heat Exchange systems and Combined Heat & Power Units. Unlike electricity generating technologies it is impossible to sell the hot water on to a third party. The developer did not install heating (water boilers), or comprehensive lighting systems in the individual units, leaving the option of installing these to the final occupant. As such this confirms that the only energy/CO₂ baseline agreeable with Chancerygate was the electrical energy usage, and that only electricity generating technology can be used to meet the policy in this specific case.

Merton and Cadogan agreed that the original carbon footprint = 108,200 kilograms of CO₂ emissions per annum. Therefore (in theory) LBM expected the developer to cut that carbon footprint by 10% (10,820 kilograms of CO₂) through the use of renewable energy equipment. If however, the predicted CO₂ emissions were reduced through the use of energy saving measures in the design of the building, then the CO₂ reduction required through the use of renewable energy to meet the 10% would fall proportionately. With this in mind the policy should be considered as an incentive for the developer to design a more energy efficient building.

---

This guide has been extracted from this news article and The Merton Rule briefing, First Implementation