What contributes to the energy performance of a building?
The energy rating of a building is a complex calculation which is based on a combination of factors. The key factors are:
- the type of construction of the building (including walls, roofs, floors and glazing)
- whether parts (zones) of the building are used for different purposes e.g. office, factory etc and the occupancy profile for each zone
- heating, cooling, ventilation and hot water systems used
- lighting
The energy performance of non-dwellings is shown as a CO2 based index. The CO2 based rating a building receives depends on the energy used for space heating, water heating, ventilation and lighting, less any energy generated from energy generation technology installed in the building (such as solar water heating). The lower the number the lower the typical CO2 emissions (based on a scale of zero to 150 +).
The rating is adjusted for the total useful floor area of a building (see glossary of terms for a full definition) so it is independent of size for a given type of building.
The calculation process compares the carbon emissions of the building with those of a reference building. The reference building is an equivalent building (i.e. a building of the same size, shape and use as the actual building) constructed to a notional building designed to a specified standard.
Collecting the information required for an EPC
Once the energy assessor has been commissioned to produce an EPC, there are 3 main steps to performing the assessment. These are:
- gathering the relevant information about the building
- analyzing the information and identifying different zones of the building
- entering the information into an approved software programme. The appropriate methods for commercial buildings are simplified building energy model or dynamic simulation model
The energy assessor will need to understand the internal layout of the building and for what purposes it is designed to be used. This is to understand the energy demands of each individual space (zone) in accordance with its designed use.
The information that will be required to produce an EPC includes:
- analysing the information and identifying different zones of the building and their dimensions (either as verified from plans or as measured). This information may be readily provided from building plans
- the activities conducted within the zones, e.g. retail space, office space, kitchens, storage etc
- the heating and ventilation services for each zone, including type of system, metering, controls, fuel used, etc.
- the lighting and controls used for each zone
- the construction of the fabric of the building and thermal efficiency of the materials used: roof, floors, walls and glazing
If there are no plans for a building, the energy assessor will need to survey the building and gather the appropriate information. If you have up to date information and plans for your building this process will be less time consuming. The energy assessor is responsible for ensuring the information used in the energy calculations is accurate and, even where detailed plans are available for existing buildings must validate this information by making a site inspection.
Using data gatherers
In certain circumstances, data gatherers working under the supervision of the energy assessor can assist with producing EPCs for larger and more complex buildings and portfolios of buildings. However, the energy assessor must be in a position to verify the data and to supervise how and by whom it is collected.
The department has provided accreditation schemes with the following advice on the use of data gatherers:
There is no justification for using data gatherers on level three buildings, because the scale and complexity of level three buildings is not sufficient to justify their use on them.
The use of data gatherers on level three buildings is not permitted.
For level four and five buildings the energy assessor must:
- visit the and inspect all buildings for which they issue an EPC to ensure they can verify any data provided and be sure that it is appropriate for the building before the EPC is lodged on the central register. This also enables the non-domestic energy assessor to provide the building owner or landlord with the outcome
- record all the assistants used and the provenance of all data that has been used to produce the EPC
- provide evidence of supervision of the process. One way of demonstrating this would be via the use of ISO9001 procedures
- demonstrate the suitability of any assistants used – the energy assessors are responsible for ensuring that any assistants used are fit and proper and suitably qualified, for example by being a level three energy assessor or through membership of a recognised professional body. The energy assessor must be able to provide evidence to support an assistant’s suitability to do the work
The energy assessor must be able to demonstrate that the contractual arrangements of any assistants allow sufficient supervision and quality control by the energy assessor.
Employing assistants from the same company as the energy assessor would be one way of demonstrating this.
Remote lodgement business models, which is the practice of an energy assessor lodging a certificate which has been produced from data that has not been collected or verified in the manner described above by the energy assessor is not acceptable.
The definitions of level three and level four buildings and level five buildings, which are defined as those buildings for which the dynamic simulation model is used to carry out the assessment, are attached at Annex B.
Producing the EPC and recommendation report
This information will be fed into an approved software programme using a government approved energy assessment method. The appropriate software tools for commercial buildings are simplified building energy model (SBEM) or dynamic simulation model (DSM) (even if the building was originally used for residential accommodation). The software produces the certificate and the recommendation report for the building.
Only government approved software may be used to assess the energy performance of a building and to produce the EPC.
The software assesses the energy demands of each individual space in the building in accordance with the activity conducted within that space (e.g. office space, kitchens, storage space, etc). Different activities can result in different periods of occupancy and different required temperatures, as well as varying requirements for lighting and hot water supply. The energy consumption and carbon dioxide emissions are calculated by considering these demands in relation to the details of the building services.
The energy assessor will need to understand the internal layout of the building and for what purpose it is used. The energy assessor will need to validate (via plans and or a physical survey) zone distances, thermal insulation and building services.
The software will use the information provided by the energy assessor and standard performance tables and will produce the EPC and recommendation report. The recommendation report will help owners and occupiers to improve the energy efficiency of a building. The recommendations only include those improvements that are appropriate for the building that has been assessed. For each recommendation indicative paybacks are noted.
The recommendations are provided in 4 categories: short term payback (less than 3 years); medium term payback (between 3 and 7 years); long term payback (greater than 7 years); other recommendations (based on the energy assessor’s knowledge).
Once the energy assessor has produced the EPC it must be lodged on the central register. Lodging the certificate will generate a certificate report reference number which all valid EPCs must contain. The EPC must also be provided to the person who has commissioned the EPC at this stage.
Assessment of representative units
Certification for units in blocks can be based on the assessment of another unit in the same block. Representative units should all be in the same building or block. What makes one unit representative of another will be down to the judgment of the energy assessor as to whether the data used for one building would accurately reflect another. Material facts may include age and construction of the building, orientation, position within the block, type of heating, insulation and glazing.
If one unit in a block were surveyed in detail the energy assessor can copy the data model to prepare an EPC for another. The energy assessor needs to be satisfied that they are the same (or make any adjustments as required) and then submit the data to produce an EPC for the second unit. Where a number of assessments are based on the assessment of another representative unit, the energy assessor will need to visit a sufficient sample of the units to verify that they are indeed representative.
The use and occupancy patterns of a non-dwelling can be complex. Annex B highlights a number of situations that frequently occur and the requirements for an EPC. These examples may change over time and are not a definitive list of the possible situations which may occur.