17 Aug 2021
The latest reincarnation of the London Plan requires developers to ‘evaluate operational energy performance’ on larger, non-domestic buildings.
This is better known as a TM54 calculation, but that title still doesn’t help explain what it actually is. Hopefully this article will.
Since 2005, every non-residential building has required an SBEM calculation to prove compliance with emission targets. This model predicts the building’s energy use and compares the results to Government set targets. This data is then used to generate the building’s Energy Performance Certificate.
The ‘S’ in SBEM stands for Simplified… It has purposefully been designed to offer a quick answer to a complicated question. But by being simplistic, SBEM doesn’t give very accurate predictions.
We need to remember the core purpose of SBEM is to comply with Building Regulations, and in that respect, it does the job. Sometimes it is used to calculate heating loads, or as a benchmark for the true performance of a building. But these more complicated questions go beyond what SBEM was designed to answer.
The ‘performance gap’ between SBEM and reality is well known – this is the disparity between the suggested energy use according to SBEM, and the real-life building.
And this is where TM54 steps up.
Building Regulations (and therefore SBEM) are only concerned with the energy used by heating, cooling, hot water, ventilation and lighting. It ignores office equipment, machinery, servers, kitchens, lifts, refrigerators… and anything else you can think of in a non-residential building.
SBEM also makes sweeping assumptions about how many people are using the building, what times of the day/week/month it is occupied, and what the thermostats are going to be set to.
To complete a TM54 calculation, the assessor needs much more information from the design team about how the building is going to be used. With these additional details they can over-ride the results of the original SBEM.
The assessor will add in the energy use from all the computers, cookers, production lines and plant rooms that SBEM ignores, they can adjust the expected number of people in each room and adjust when these people are going to be there. They can adjust the heating and cooling controls, and they can assign specific weather pattern data for the precise location of the building.
When these additional TM54 features are added into the mix, the estimated energy use of a building will normally be much higher than what SBEM originally predicted, but the results will also be far closer to the real-life performance.
But although the TM54 gives more accurate results, that comes at a cost. Literally. TM54 analysis is far more time consuming than the standard, ‘Simplified’ SBEM.
And now that the Greater London Authority has began requesting these reports on larger developments in the capital, expect other councils across the UK to take note.
If you have a planning condition which requires TM54 analysis, Energist’s Technical Team can help. Contact us for more details.