Target CO2 emission rate (TER): the dos and don’ts

What is the TER?

For a new non-domestic building or a substantial extension to an existing one (kindly take this as read throughout) the TER is the calculated target CO2 emission rate, expressed in kilograms of carbon dioxide (CO2) per square metre of total useful floor area (TUFA) per annum.

Introduced as part of the 2006 revisions to Part L of the UK Building Regulations and covered by Regulation 17B, it implements Article 4 of the EU’s Energy Performance of Buildings Directive (2002/91/EC), or EPBD.

Why does it matter?

If the client for a new non-domestic building wishes it to comply with Regulation 17C of the UK Building Regulations, then the team he or she engages to take the project from conception to completion and handover must ensure that the annual CO2 emission rate calculated for it as actually constructed (and including some elements of building and system performance as tested and commissioned) – the building CO2 emission rate or BER – does not exceed the target level defined by the TER.

How is it derived?

The derivation of the TER for new non-domestic buildings is shown in Figure 1 (overleaf). While a TER is also applied to new dwellings, its definition is not identical to that shown in Figure 1 and will not be considered further here.

TER as regulation

At the most obvious and superficial level, meeting the TER is a Building Regulation – not an energy efficiency option. As such, it has to be met just like regulations relating to structural integrity, fire safety or disabled access.

The importance of this regulatory function should not be underestimated. Part L requirements for air permeability testing and a properly managed commissioning procedure will undoubtedly help to match as-built performance to design potential, and its requirements for metering and a building log-book may (if enforced!) help owners or tenants to operate their new buildings as efficiently as their design ultimately permits – but the TER is the only measure that really forces new buildings, by law, to be designed to a lower CO2 emission rate than they otherwise might have been.

The same Article 4 of the EPBD that led to the introduction of minimum energy performance requirements for new buildings – TER in the UK – also requires that these be regularly reviewed at intervals not exceeding five years. If the political will is there to achieve very substantial future cuts in UK CO2 emissions, the next revision of Part L will undoubtedly require higher values of both (energy efficiency) improvement factor and low-or-zero-carbon benchmark to be used in calculating the TER.

While in practical terms it is, of course, only the combined effect of these two factors that actually matters, nevertheless the split does serve to provide the thoughtful observer with a timely reminder that a point will be reached beyond which further reductions in target levels will only be met through use of low-or-zero-carbon (LZC) technologies – the writing is on the wall!

TER as fundamental change in approach

At a more fundamental level the TER represents a holistic approach to reducing the CO2 emission rate of new buildings. It is not simply a “services thing”, but a criterion for the whole building – the building and its engineering services, taken as an energy-consuming and emission-producing whole.

Only the whole building can meet – or fail to meet – its TER. With the passing of the “elemental method” for compliance with Part L (for which we should shed few tears), current requirements for the minimum performance of individual components of the building – fabric, fittings, boilers, chillers, fans, lighting – remain largely to ensure that real opportunities for reducing CO2 emission are not wasted by inappropriate or unreasonable offsets between the performances of the different components. They are not a guide to what must be done to only just meet the TER.

This approach cannot easily be achieved if the different disciplines within the design team work in relative isolation from each other. The holistic approach was intended to make the members of the design team – architects and building services engineers in particular – combine their complementary knowledge, skills and experience more closely from the first concept of a building to its completion and handover.

Such a fundamental change in approach makes significant new demands of both architects and building services engineers. The younger members of both professions will cope with this; indeed most will probably welcome it. Their academic training will typically have emphasised holistic concepts (and they have more incentive to take climate change seriously). The same may not be true of older architects and engineers who have spent careers working in relative isolation on their own bits of the problem.

Notwithstanding the importance attached to building the new “special relationship” between architects and building services engineers, the holistic approach extends to everyone involved in the project. This includes client, quantity surveyor, principal contractor and sub-contractors – and not just the m&e guys either. The QS has an important role, since a long-term view and life-cycle costing approach is most compatible with the TER’s holistic approach; a short-term view and fixation on capital cost will almost certainly be in conflict with it. In the modern vernacular the TER is for team players.

If the TER is so significant, surely everyone is familiar with it?

Not necessarily. Not every building services engineer is a “designer”, even assuming the widest possible definition of the term.

Moreover, even among those who are, a not-insignificant number will undertake new-build work only occasionally. This will naturally apply more to the many smaller consultancy practices up and down the country.

Meeting the TER: The ‘Don’ts’

Don’t regard the TER as your (or the client’s) enemy. Meeting and even bettering the TER will give the client a better building – typically more comfortable for the occupants (more productive?) and cheaper to run.

Don’t design to “only just” meet the TER. Right from the start, aim to better it by a reasonable margin that all parties to the design can agree on. This might vary according to the complexity of the particular project or some other characteristic (but not the budget).

Since most people will not find it intuitive to think in terms of kgCO2/m2 per annum, the Asset Rating (see Figure 1) provides a simple and convenient measure. A sensible margin might then be at least 3.5 percentage points of Asset Rating (a margin of about 5%, on current target levels).

Then, if you have to trim the design post-tender or the air permeability test doesn’t quite meet the design aim, you will not have to bite your fingernails over the final calculation of the BER. It’s a pretty safe assumption to make that the further a project has progressed, the more awkward, time-consuming and expensive it will be to define and implement emission-reducing remedial measures.

Don’t expect meeting the TER to come free, either in capital cost or in professional fees. It will certainly require a fair amount of additional input from the design team, particularly the architect, building services engineer and quantity surveyor; and there will be a learning curve.

Don’t imagine that it is easy to get a building that is “only” heated and naturally ventilated throughout to achieve its TER; relying on good U-values and natural gas condensing boilers will typically not be enough. The simpler the building, the more important it becomes to consider closely the fundamentals of form, fabric, fuel and services.

Meeting the TER: The ‘Dos’

Do consider meeting the TER right from the first concept of a project and develop the design with this in mind – in just the same way as for the client’s requirements, structural needs, fire safety, disabled access, etc.

Do understand that CO2 emission is a function of both energy consumption and the CO2 Emission Factor (CEF) of the fuel used. Remember the CEF hierarchy of the common fuels used in buildings (see Table 1). CEFs are not cast in stone and will be affected both by the mix of generating technologies used to produce grid-supplied electricity in the UK and the source of its natural gas supplies.

Do understand that – with the highest CEF (which, unlike its unit cost, is independent of tariff structure) – grid-supplied electricity must be used at the highest efficiency possible.

Do aim to reduce thermal and electrical loads at source as far as possible, consistent with the client’s realistic needs. While small power loads are not currently taken into account in the TER, they have a substantial impact on both the need for comfort cooling and on the size, energy use and CO2 emissions of any plant and equipment for which there is a need (which will typically be based on vapour-compression-cycle refrigeration plant using high-CEF grid-supplied electricity as its fuel).

Do design for the lowest air permeability that can be achieved routinely. For example, aim for no more than 5m3/h/m2 and insist on achieving less than 7; then if the rest of the building is up to performance you will have no problem.

Do aim to approach an optimum use of daylight. In smaller heated and naturally ventilated buildings this may be the only way to get reductions in CO2 emission rate beyond the level of the Improvement Factor alone (see Figure 1) for the lighting end-use category.

Appreciate that – either to avoid the risk of overheating or to reduce cooling loads to reasonable levels – this may mean going beyond conventional internal blinds (which typically perform rather poorly) to external shading devices such as overhangs, fins, louvres, brise-soleil, awnings, etc.

Do go for the highest plant and equipment efficiencies that the client can afford, not just what meets the minimum requirement stated in Part L. The marginal cost of doing so will almost always have a short payback period. Remember that it is the seasonal efficiency of an item of plant or equipment that is important in meeting the TER.

Do include a solar energy system (for solar heating or pre-heating of domestic hot water) as standard good practice in design – unless there is a very specific reason that renders it inappropriate in a particular application (and ‘the budget’ should not be one of these).

Do pick up all of the small credits that are available towards the TER by making them part of your standard good practice in design. This includes metering/monitoring and targeting with out-of-range alarms for space heating or cooling and improvements in the electrical power factor of the building.

Do get used to using low-or-zero-carbon (LZC) energy sources, including on-site generation of electricity from renewable energy sources. Incorporate them within projects, even on a small scale, as standard good practice in design.

Current target levels are set at 23.5-28% below the total CO2 emission rate for the notional building, according to services strategy, and the LZC benchmark represents 29-36% of these values respectively. It is unlikely that future revisions to the target level will be met without LZC technologies; the most common are listed in Table 2. Use of LZC energy sources may in any case already be the subject of local planning policy, hence a requirement over and above that of meeting the TER.

Do appreciate that the CO2 emission rate credit received for 1kWh/m2 a year of electricity generated on-site from a renewable energy source is equivalent to the reduction in emission rate for 1.35kWh/m2 a year of grid-supplied electricity saved in some other way.

Do reduce both the energy required for any purpose (by energy-efficiency techniques) and the CO2 emission associated with producing it (through LZC technology).

Do understand that all-electric buildings that employ only resistance heating elements will typically have considerable difficulty in meeting the TER unless a more-or-less substantial proportion of the electricity used is generated on-site from renewable energy sources.

Do expect to calculate the BER several times during the course of a typical project – not just “as constructed”, as required by Building Regulation 20D, but at least also “as designed”; more than this may be worthwhile routinely, and essential in particular cases.

You might, for example, consider it worthwhile to make it standard good practice to establish a model within iSBEM as soon as it can be defined in a reasonably complete way and update it at key stages or to reflect any major changes – so that there are no surprises when the final calculation is made. Expect this to take more time and cost more money.

Do use the ubiquitous iSBEM/SBEM software tool for your own advantage. Although formally for compliance rather than design – and never intended to be all things to all people (after all, it’s from the government and it’s free) – if used sensibly and with an awareness of its limitations, it can nevertheless allow the generic analysis of quite a wide range of “what-if?” scenarios at various stages of a project.

Don’t be afraid to use the more detailed technical output reports generated for the project – the “sim” files. It is not difficult to set up a spreadsheet to import this data and analyse it graphically. A well-chosen graph can provide a wealth of information about your successes (or failures). Figure 2 gives one simple example.

Do remember the holistic approach can be summed up as “3FS” – form, fabric, fuel and services.

Original print headline - Prime target