Continuing on from our topic opener, ‘Closing the Performance Gap’, it would be sensible to start answering some of those questions we asked. Why are our buildings consuming more than they’re designed to? Where are the leaks leading to high fuel bills? What can be done to plug the gap?
We see the gap, we recognise the problem, but before we can establish how to close it, we need to know what’s in it and why. Last year CIBSE published a report TM54 Evaluating Operational Energy of Buildings at the Design Stage that identified which individual sources contribute to the gap. Standard methodologies to produce EPCs (SAP for Domestic and NCM for Non-Domestic) are built on the principle of benchmarks to assess compliance, their purpose is to produce relative rather than absolute results. It is not that the methodologies are inaccurate, it is that there are factors outside their scope that cannot be included for a compliance assessment. The ‘outside the scope’ factors are inherent standard assumptions regarding occupancy, temperatures and setup commissioning; if we are to include these inside our assessment scope, we are better able to identify the sources of our performance gap. At the design of a new build or the assessment of an existing building, we should consider:
- reviewing occupancy hours,
- temperature settings,
- and additional equipment consumption
to allow for a more realistic analysis of actual energy consumption.
A Practical Approach
Now we know the usual suspects, we’ve just got to update the methodologies, right? Wrong. The methodologies serve a very valid purpose, it is our role to use the knowledge we have and assess our buildings using a measured approach that appreciates both the theoretical and practical factors affecting energy consumption. The BSRIA (British Services Research and Information Association) have published a guide outlining a management approach to closing the gap – the Soft Landings process extends the involvement of designers and integrates all stakeholders (construction, users, designers) collaboratively rather than simultaneously.
More recently we have seen rise to Building Information Modelling (BIM), an approach which uses the digital 3-D representations of buildings (e.g. geometry) to be the core of analysis and uses the most accurate data for each facet of that building available. Using advances in software compatibility BIM allows all stakeholders to share and use single points of reliable data to model the optimum design, construction, operation and decommissioning of a building.
So we have Soft Landings and BIM but how are we going to apply them to our existing assets?
One size fits none
Understanding buildings is easy when they’re not already built. With the vast majority of our 2050 building stock already built, we have a great challenge of understanding our current assets. The Holy Grail is to identify the full scope and estimate the extent of all of our energy consumption within it. Good news is, we can say we’ve identified the full scope (TM54), the challenge is estimation. Existing buildings do not have the data sources to efficiently conduct a full BIM exercise but what if we can recreate some of that data? Using the principles of TM54, Soft Landings and BIM, but with data used from standard methodologies, actual billing and industry knowledge, you can produce a model that is an accurate representation of an existing building in use.
For existing buildings it is critical to use a robust methodology to arrive at results such as paybacks and capital expenditure, results which should be at the core of any decision making regarding building improvement. If we fail to appreciate our building’s in-situ performance we will fail to realise the true potential of upgrading our buildings.
Author: Stuart Gray – Associate, Sustain Ltd