Zero is a very easy number to understand. Or is it?
Certainly a bank statement with zero at the bottom is wholly understandable, even if unwelcome, but in our area of building operation and management the concept of zero carbon or zero energy is much harder to get our heads around. This is why it is taking such a lot of brain power and time to come up with useful and meaningful definitions of zero carbon as it applies to buildings. Fudging the issue by saying "nearly zero" (which is what has been done in European Directives), doesn't really help.
It's important to get it right, because it's very probable that the buildings we design and deliver will, at some point in the future, have to demonstrate their energy and carbon signatures as a contractual obligation. The question is: how will successful performance be demonstrated so that payments on completion are not withheld, while wrangles about performance and outstanding perceived defects are resolved?
The difficulty comes in separating the various contributions to the building's energy use that lead to carbon dioxide emissions. An analogy with the energy labelling of motor cars is helpful here. The miles-per-gallon data displayed on the garage forecourt is derived from very carefully monitored laboratory testing of a sample vehicle. The 'driver' is standardised, as is the road profile. Although test results are very repeatable, it takes a very special kind of driver to reproduce these figures on the highway.
Buildings are a bit more tricky. Loads arise from ventilation losses, and from conduction through wall for example. The construction supply chain can reasonably take responsibility for these performance characteristics during design and construction, but what about the small power contributions and the behaviour of occupants? It is difficult enough to ensure that designs are faithfully engineered into actual structures, but it is impossible to know whether the occupants will behave as the designers have assumed in their calculations. We cannot put the completed structure in a test cell. In actual operation occupancy effects are very hard to measure and completely uncontrollable from our perspective. So, a "nearly zero" building may well not have a zero energy signature, but we cannot easily tell whether the issue is a faulty building or occupants that don't match the design assumptions.
Wholly controlled testing of completed buildings is simply not possible, both practically and economically, but there are a few things that can be done to identify the dark matter hidden in the gap between design intent and reality. Airtightness measurement is already included in the Building Regulations, and with the diagnostic tools we have (smoke tests, infrared imagery and endoscopes), defects can be found and the lessons learned taken to the next site. Newer methods, such as co-heating tests, are also emerging to evaluate in-situ whole building U-values, but on the whole our skills and competencies in analysing, predicting and communicating whole building performance is poor.
The occupancy effects are not a completely lost cause. There are methods such as TM22 2012 that have been designed to separate out the regulated and plug-in power electrical loads, but analysis takes time and can only be done with the benefit of a significant period of occupation. One consequence of this may be that the present concept of a single point of practical completion may have to be changed into something more like the commissioning period given to warships, where handover is subject to proving trials where operational readiness is a blend of constructor and operator responsibility. This will be a serious challenge to existing practice and will not be something easy to introduce.
We are required to deliver "nearly zero" buildings by 2019. If we are going to be expected to prove it, whatever "it" turns out to be, then there is a deal of work to be done if the legal profession are not to be given free lunches for decades to come.
This feature was written by Andrew Eastwell, BSRIA Chief Executive, and first published in the FETA magazine, December 2012.