EPC: EPC Conventions

CIBSE Low Carbon Energy Assessors who produce Energy Performance Certificates must be aware of the ‘conventions’, writes Andrew Geens, who has set a CPD questionnaire for readers

All Low Carbon Energy Assessors (LCEAs) accredited to produce Energy Performance Certificates (EPCs) must be familiar with the non-domestic EPC conventions. CIBSE Certification is required to verify that they are. In order to help demonstrate understanding of the conventions, CIBSE has provided this briefing and questionnaire on page 64 that may also be of interest to other members – particularly if they are planning to join the register themselves.

The latest version of the EPC conventions for England and Wales is available on the CIBSE Energy Centre website, www.cibseenergycentre.co.uk/assessor-area/ epc-conventions.html Amendments for Northern Ireland are also located here.

This article sets out to explain some of the key elements of this convention document and should be read in conjunction with it. In order to maintain and improve the quality of certificates and inspection reports generated as a result of the Energy Performance of Buildings Regulations 2007 (and 2008 in Northern Ireland), the Department for Communities and Local Government (CLG), has approved the formation of convention groups, one each covering EPCs, Display Energy Certificates (DECs) and air conditioning inspections.

The development of conventions is part of the ongoing work to standardise the assessment process, to ensure a uniformity of approach, and to assist energy assessors and their accreditation schemes; it is important to note that in some circumstances, following the convention may not be consistent with the judgement of an individual assessor. The guiding principle of the conventions is to remove the variability in assessment that comes from subjective decision-making. If everyone is making decisions guided by the conventions, the rating should always be the same regardless of which assessor produces the rating. The conventions are designed to improve the quality and accuracy of non-domestic EPCs. The conventions will, therefore, supersede any previous assessment guidance process including the iSBEM manual.

It is important that every CIBSE LCEA is familiar with the conventions and follows them when undertaking an EPC, even if there might be good reasons to adopt an alternative approach under some circumstances.

The conventions are presented in a table to reflect the tab structure in the standard iSBEM software, and are accompanied by an implementation date (see web link mentioned above). One important overarching principle to come from the convention group is that default values in iSBEM should only be used as a last resort, and that the reason for not being able to establish an actual figure must be recorded in site notes.

In order to avoid inconsistencies where different terms might mean different things to different people, a Glossary of Terms is provided to reduce the risk of variations in the ‘interpretation’ of the conventions.

Assessment level decision flow chart

There are three levels of EPC assessment, and their classification has changed since the legislation first came into force, so it is important to be familiar with the flow chart. Briefly, all new build assessments must be carried out by a Level 4 or Level 5 assessor. Assessment of simply heated and naturally ventilated existing buildings requires a Level 3 assessor; more complex buildings (heated using MTHW, HTHW or steam distribution or cooled using air conditioning with central plant) require a Level 4 assessor; and complex buildings (requiring dynamic simulation modelling, DSM, or having any of the features listed in the flow chart) require a Level 5 assessor.

Very few CIBSE LCEAs are qualified only as Level 3 assessors. Level 4 assessors are automatically qualified to assess Level 3 buildings. Level 5 assessors can assess Levels 3, 4 and 5, but only using the DSM software that they are qualified in. If they wish to assess Level 3 or Level 4 buildings using other software, they will need to demonstrate their competence (qualify) in the use of that software. The definitions of features that are significant in classifying a building as Level 5 are repeated after the flow chart.

Dimensions convention

Arguably, the energy assessment criterion with the most scope for variation is the measuring of dimensions, either from plans or on site. Do you include the thickness of party walls, intermediate floors and partitions? How do you measure irregular roof profiles or spaces with irregular geometry? Although probably not exhaustive, the conventions group seem to have produced measuring conventions for most situations that are likely to be encountered.

Local mechanical exhaust and ventilation rates

This convention has been developed in response to feedback that in many existing buildings it is difficult to establish local exhaust ventilation rates, and as previously stated, the use of the iSBEM default is to be avoided where possible, generally giving a worst case scenario. Assessors should attempt to use more appropriate figures wherever possible. The convention groups have used a table of air change rates per hour, taken from a number of sources including CIBSE Guides A and B. The intention is that assessors can use the following relationship between volume flow rate (Q)m3/s, room volume (V) m3 and air change rate (N) air changes/hour, to calculate the volume flow rate, that is:

The assessor can then divide this by the floor area to give a volume flow rate in l/s/m2 as required by the software, effectively making the flow rate a function of air change rate and room height (V/Area = room height). Anyone following this might recognise that ventilation rates are dictated by process or occupancy, which is usually proportional to floor area, so using room height in this way will result in inaccuracy in a small proportion of buildings with unusually high ceilings. This is a good example of the philosophy of the conventions to provide consistency all of the time, although in a small proportion of cases, accuracy may be a casualty.

The work of the EPC convention group is ongoing, and there is also a DEC convention group and air conditioning convention group. CIBSE is represented on all of these, so if you are aware of anything that needs standardising in this way, or have any feedback on the existing conventions let us know by emailing Andrew Geens, QA and technical development manager, at ageens@cibse.org

To complete the online questionnare and demonstrate your understanding of the conventions please go to www.cibsejournal. com/cpd. You can also post it to N Hurley, CIBSE, 222 Balham High Road, London SW12 9BS.

Completing the questionnaire will demonstrate that you have read and understood the conventions. If you do not complete it, we will have to contact you to establish that you have read and understood the conventions. If we are unable to do this we may be unable to continue to accredit you as an EPC assessor.

If you are a CIBSE member, the fact that you have successfully completed the questionnaire will be automatically uploaded into your CPD record. If you are not a CIBSE member you will have to update your CPD record manually to contain this information.

Andrew Geens is quality assurance and technical development manager, CIBSE Certification