How do you assess the energy efficiency of early architectural proposals?
We are often asked how to make buildings more energy efficient, and more particularly how the building envelope can be more efficient. Many in the industry rely only on U-values, but this does not tell the whole story...
Fabric energy efficiency is the result of the combination of four components: form factor, distribution of glazing, specifications (e.g. U-values) and junctions. Architects therefore have a significant role to play to deliver more efficient buildings.
Architecture and Energy Efficiency.
The distribution of glazing is widely understood and is generally influenced by other important considerations (views, design, daylight, overheating). The form factor, however is not considered as much as it could be. It is the ratio of external envelope to internal floor area. The higher the ratio, the more inefficient your building form becomes. Low energy specifications apply a performance level to this external envelope.
Unfortunately, there is often a lack of energy efficiency assessment of forms which leads to over-compensation with (very) low and expensive U-values. There really is more to energy efficient architecture than low U-values.
However, although it is undeniably more energy efficient to have low form factors (e.g. a square box), we also believe that that there is more to architecture than energy efficiency.
Fabric energy efficiency can therefore be a positive tension between architecture and energy efficiency. It is a very useful metric to measure the energy efficiency of architectural proposals as it combines form factor, distribution of glazing, U-values and junction quality into a single number, which can be used from early concept design through to construction as an indicator of ‘architectural energy efficiency’.
The compliance tools... and the better tools.
Part L calculation tools are generally not very accurate at predicting actual energy use. Other methodologies can inform design decisions more accurately: PHPP (the Passivhaus software) is an excellent tool and can also be used on non-Passivhaus low energy projects, particularly residential ones. The CIBSE TM54 methodology can be used on non-residential projects to predict actual energy use more accurately. It is important to remember that these softwares are only ‘tools’ though. They should be used iteratively, with intelligence and a thorough understanding of the construction implications.
Towards a more efficient, architecturally led design.
Architects remain in control. That is the way it should be. We can help those who want to deliver the wider ambition of the design and energy efficiency (as opposed to one or the other) and quantify the impact of various design options and explore possibilities.
Clients will also benefit from a greater focus on Fabric Energy Efficiency as it helps to deliver buildings which comply with energy and carbon targets and are more cost efficient.