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DEC Certificates – Almost Everything There is to Know

Written by Steve from CarbonCulture Team on 15th April 2015

Here at CarbonCulture, we love to know how buildings perform against their peers. As in the world of teenagers, so in the world of buildings, there are exams, certifications and certification authorities. In this post, I'm going to do my best to try and explain the certifications with which we concern ourselves, a little about how they work and how we use them. We'd like to open out the conversation about certifications, so please read this with an open mind, and a critical eye.

Display Energy Certificates (DECs)

Display Energy Certificates (DECs, from here on) are our bread and butter. You may have spotted these guys when visiting museums, galleries and other public buildings - that's because since January 9th, 2013 any public (non domestic) building with a floor area over 500m² has to display a valid DEC prominently at all times, by law. This is really great because it means you can check out the energy efficiency of the most interesting buildings in the UK! What's even better, is that we've made these available on our building pages, so that you don't even have to go searching for them. 

What do they mean?

“DECs are designed to promote the improvement of the energy performance of buildings. They are based upon the actual energy performance of a building and increase transparency about the energy efficiency of public buildings.”

A DEC is a (quite complex) evaluation of the in-use status of a building. That is to say that it concerns itself with exactly how the building is used (in terms of energy) by the people who occupy it, and compares usage against a 'model' building of the same type. The DEC ultimately grades the subject building into one of 7 categories (A, the best through to G, the worst) - and as the DEC baseline is based on a model building, one can compare the subject building against its peer-group. DECs are based on the actual amount of metered energy used by the building over the last 12 months within the validity period of the DEC.

Now, how can a peer-group of buildings be defined? Well, there are several characteristics of a building which tend not to change too often, and it is these characteristics (we call them 'meta-data') that allow the definition of a peer group, and hence a comparison can be made against the peers.

Validity period of DECs

Where the building has a total useful floor area of more than 1,000m², the DEC is valid for 12 months. The accompanying advisory report is valid for seven years. Where the building has a total useful floor area of between 500m² and 1000m², the DEC and advisory report are valid for 10 years.

A DEC must be accompanied by an advisory report and the owner of the building must have a valid one available. The advisory report highlights recommendations to improve the energy performance of the building (i.e. its fabric and associated services such as heating, ventilation and lighting).  

How do CarbonCulture use DECs?

As I mentioned earlier, a particularly useful aspect of DECs is that they measure energy efficiency of the building when it is in use. This means that we have a baseline against which we can compare real-time energy use. So, at any point in the day for which we have data, we can say if the building is being used more or less efficiently than it's own DEC grading. The colours that you may have seen on our individual  building pages are derived from the DEC rating. When the graph is green, this means that - relative to the building's DEC - it is running more efficiently; yellow means it's running approximately at its DEC rating; oranges and reds mean it is running less efficiently.

What this means is that you can take two graphs of totally different buildings (ie in different peer-groups) and say how well they are doing against their own ratings; hence you can say that building A is doing 'better' than building B. There's nothing like a bit of inter-group competition.


Energy Performance Certificates (EPCs)

Energy Performance Certificates (EPCs) look quite a lot like DECs. They share their A-G rating (though, confusingly, also have A*, and the scoring is inverted meaning that 100 is very good, but means zero emissions), and colour scheme. However, that is where the similarities end. They are required to be created for any building if it is to be rented, sold or built as of 2007, and are valid for 10 years.

What do they mean?

EPCs are a form of design-based certification. This means that they don't actually consider the finer details of how energy is used in a building (ie, how the occupants are using it). Rather, buildings are assessed on their designed efficiency - aspects like whether or not a roof is insulated, what sort of boiler is used, if the windows are double glazed, etc. Buildings are still compared against a model building, as with the DECs, but there is no sense of how much energy is actually consumed within the building.

How do CarbonCulture use EPCs?

Because of the way EPCs and DECs differ, we aren't able to use them in the same way. It would be great to take any building with an EPC (and because they are required by law in the UK, that is a huge set!) and compare it to any other just by looking at the colours; sadly this isn't the case. In order to avoid confusion about the comparability of buildings with only an EPC, we do not use these colours on the energy graphs.

We love how DECs allow those without a huge amount of knowledge about the energy sector to do a simple comparison of building performance, and this is all due to great work in meta-data collection, and good reporting. While EPCs provide a really great starting point for figuring out potential, you can't beat solid energy performance data for making decisions and making things better and more efficient.

For more information about DECs click here

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