Thermal performance measurement guidance released

The energy consumption in any building is driven by four key parameters: the thermal performance of the building itself, the efficiency of the heating and cooling systems, the actions of the occupants and the local weather conditions.

Of these, the thermal performance of the building itself is seen as most critical. This is because that while the other three parameters regularly change, the underlying thermal performance does not. If a building’s fabric is measured, understood and performing as expected everything else can flow from there.

Heating and ventilation can be better specified, designed and commissioned, allowing the influence of occupant behaviours and weather to become much easier to understand and account for. Ensuring good thermal performance is key to ensuring buildings are truly low energy and efficient throughout their operational lifespan.

In the absence of a measured understanding of building thermal performance, the building industry is reliant on modelling predictions and best guess estimates. For a new build home that is designed to be low energy, a discrepancy in as-built fabric performance can undermine the installed heating and ventilation systems effectiveness.

In retrofit, a misunderstanding of the building fabric can influence an entire retrofit strategy. Performance predictions are often conservative in nature, so thermal performance may be better than first thought. This will directly influence decisions around what insulation to install or what type and size of heating system to specify.

Building performance measurement specialists Build Test Solutions has produced a new thermal performance measurement guide to help building industry experts understand how they can best approach their own assessments of building thermal performance.

Split into five key stages, the guide starts with a process for surveying a building to find the assumed performance of each building element, such as floors and walls. Techniques and tools, such as SAP and RdSAP based energy performance certification (EPC) assessments, help determine the assumed performance of the whole building.

Once this assumption has been understood, it is time to measure actual performance, according to Richard Jack, Technical director at Build Test Solutions:

“The actual energy performance of buildings often varies significantly from predictions, with some studies showing over a one-hundred percent difference. That’s why in-situ performance measurements are so important. They provide the means to understand how a building really works and help us all to make much better decisions. “Good thermal performance is critical to ensuring buildings are truly low energy and efficient throughout their operational lifespan. Understanding the underlying factors that drive this performance allows you to set the best possible baseline and make decisions that can make a real difference.”

Stage three of the measurement guide explains the importance of comparing the predicted and actual performance against each other to understand the gaps. If those gaps exist, further diagnostic testing is needed at stage four. This should reveal the cause of the unexpected performance, which in many cases is linked to air movement or fabric heat loss, which are two of the largest contributors to performance gaps.

Finally, the guide explains how people can act on the results.

Richard added:

“Once you have the data, you are better able to identify performance trends, spot quality control issues or commission remedial works and upgrades. For those looking at major retrofit programmes this is essential. The measured insight can be used to inform the retrofit design and specification, as well as serve as a basis that the impact of works can be assessed once completed. “This feedback will help to improve future build processes, our understanding of materials and the ways that we can most effectively reduce energy use, leading to better performing buildings.”

You can download and view the report here.