Here in the UK, as of 2010, around 45% of total CO2 emissions were from buildings; 27% from domestic buildings and 18% from non-domestic (commercial) buildings. Energy prices are a major concern to consumers and increasing amounts of people are falling into ‘fuel poverty’, spending more than 10% of their income on energy in their homes. Understanding the energy performance of buildings is critical, to allow informed comparison of buildings and to recommend and implement improvements.
Further to David’s recent blog posting, hopefully this article provides a good overview of the UK system.
The UK is a member state of the European Union (EU) and by legal directive, it is a requirement for all member states to implement the EPBD (Energy Performance of Buildings Directive) 2002/91/EC, which defines energy rating for the production of Energy Performance Certificates (EPCs) and Display Energy Certificates (DECs), towards climate change targets agreed in the Kyoto Protocol. The UK government must enforce the use of EPCs and DECs in certain situations, and direct policy to encourage and eventually mandate their use, to pre-determined timescales.
The United Kingdom is governed by parliament in London, England. The EPBD was implemented in each of the nations in the Energy Performance of Buildings (Certificates and Inspections) Regulations 2008, which had specific versions for England and Wales, Scotland and Northern Ireland, where national administrations exist with varying powers.
Energy Performance Certificates
The UK Energy Performance Certificate (EPC) is an asset rating, a prediction of energy use based on a simulation of the building design.
It separates performance into an Energy Efficiency Rating (the ‘overall efficiency’ – where a higher rating equates to lower running costs for the building) and the Environmental Impact Rating (a measurement of CO2 emissions – where a higher rating equates to a more ‘environmentally friendly’ building). The familiar A-G chart is used, representing a scale of 1-100, where a building with a rating of 100, “would cost almost nothing to heat and light and would cause almost no carbon emissions.”
An EPC is required for any building which “uses energy to condition an indoor climate”. Generally, this includes any building with heating, mechanical ventilation or air conditioning. The EPC must be commissioned when a building is constructed, refurbished, sold or let and they can only be produced by accredited energy assessors, who submit the EPC to a national register. The building owner must ensure that an EPC is available for prospective buyers.
The EPC is summarised by its rainbow charts, but in reality the document contains a more comprehensive advisory report. It includes a list of measures that could be carried out to improve the building, in order of their cost (with an approximate payback on the investment), for example loft insulation or a more efficient boiler. A balance has to be struck between the outlay cost of these improvements and the payback savings.
The EPC also estimates a second rating, indicating what the building could potentially achieve if some of these improvements were made. This information is presented to the consumer with cost-effective solutions for future energy savings.
Display Energy Certificates
The UK Display Energy Certificate (DEC) is an operational rating. Whereas EPCs are a prediction of energy use based on design, DECs are an actual measurement of in-use energy performance. The DEC displays the previous three years’ actual energy consumption, and must be procured after a building has been in use for a year. Real energy data must be used, including meter readings and bills. Smart meters are making the collection of the relevant data much easier. It must be renewed every year to maintain the currency of data.
It includes a chart, showing the change in CO2 emissions over the previous three year period (or less for new buildings) which allows improved performance to be easily understood. The DEC rating also allows comparison with a typical building of the same type, and with the asset rating of the building fabric. Just like the EPC, the DEC has an accompanying list of recommendations in an advisory report and can only be produced by accredited assessors.
The original legislation (in 2008) required that all public buildings with a floor area over 1000m2 displayed a DEC. The penalty is £500 for failure to display a DEC in a prominent place “clearly visible to the public” and £1,000 for failure to present, on request, a valid advisory report.
From January 2013, the Recast of the EPBD requires that public buildings over 500m2 must display DECs. This figure may fall to 250m2. Many organisations are calling for all public and private-sector commercial buildings to all be required to display DECs.
National Calculation Method
In the UK, energy efficiency assessment and rating is carried out in accordance with the National Calculation Method (NCM), as defined by the Department for Communities and Local Government.
The NCM is used to display compliance with UK Building Regulations in energy terms, evaluating the building design against a ‘notional’ building. This shows whether the proposed (built) building emission rate (BER) is less than the target emission rate (TER). Improved targets for UK Building Regulations every four years are imposed by updating the notional building, making it tougher to pass. The calculation includes structural build-up of walls, roof, floors, windows etc. and the energy efficiency of heating, hot water and lighting.
This information can be used to produce the EPC. There are two main ways to calculate the energy rating. Firstly, with approved ‘simplified’ software – based on SAP (the Standard Assessment Procedure) for dwellings and SBEM (Simplified Building Energy Model) for non-domestic buildings; or secondly, with dynamic simulation modelling (DSM) software for more complex designs. There is also a reduced data version of SAP for calculating the energy performance of existing dwellings, but not an equivalent for SBEM, so non-domestic buildings always require a full SBEM calculation. This requires an accurate ‘piece by piece’ description of the building geometry and services, although it does take into account that building type (hotel, supermarket, school) influences performance.
The process has many critics, as the assumptions made in the notional building mean that the EPC can be over-optimistic about the potential performance of the building. SAP and SBEM were only ever meant to be compliance-checking tools, but are frequently used to tweak the specification to achieve the target rate.
In my next blog entry, I will discuss the impact of recent changes to the EPC regulations, as well as challenges related to the effectiveness of EPCs and DECs and some pathways for moving forward with better building energy transparency in the UK.