The long road to 2019: can building fabric and onsite renewables really deliver zero carbon buildings? By Geoff Russell-Smith, general manager, Tarmac TermoDeck
2016 and 2019 zero targets for residential and most recently, non-domestic builds have ensured that the UK construction industry is like a weary traveller stuck at crossroads without a map. In one direction there is a road, which leads to the promise of offsite renewables, and in the other direction is a well-trodden path that takes us back to onsite renewables.
Before we can plot the correct roadmap to deliver zero carbon buildings by 2019, the industry needs clarification from government on the definition of this term. Under the current definition only energy generated onsite - through ground source heat pumps, solar panels, wind turbines or combined heat and power plants - can be used.
From some quarters of the construction industry there is a belief that a relaxation of the term to allow offsite technologies to mitigate a building's energy usage is the only way to meet the 2019 target.
Crucially, I believe that before we immediately call to relax the term, we should look at the carbon savings that thermally efficient buildings combined with innovative onsite technologies can already deliver.
It is expected that the definition of zero carbon will be reviewed by the end of this year. However, any relaxation of the zero carbon definition could potentially lead to more inefficient buildings which have offsite renewables 'bolted on,' rather than a building which is in itself thermally efficient. In addition, there is also no guarantee that offsite renewable contributions will not be 'double counted' on other developments. If this were to occur, a 2019 target for zero carbon buildings could be rendered pointless.
Onsite route
Making a building thermally efficient is the first step in the design process and should be the starting point before considering other ways of delivering carbon savings. We should also bear in mind that the selection of renewable technologies is only cost-effective when they are combined in an efficient building. For example, a thermally inefficient building using photovoltaic panels will always require a higher renewables input, resulting in the need for larger and more expensive solar arrays. It is only through careful selection and sizing of renewables in an energy efficient building that capital costs will be reduced.
In my opinion, it is clear that the real solution lies in making buildings more energy efficient and encouraging the development of innovative onsite renewables, which can work in tandem with other building systems.
The road to success
One approach which consistently delivers greater energy performing buildings is incorporating high thermal mass into the initial design of a building.
By opting for this route, a thermally efficient building can be achieved as heavyweight structures provide stable, comfortable temperatures to internal spaces. Because a building with an exposed concrete floor has a very high thermal mass and is over a large surface area close to the occupants, it can significantly influence the comfort levels for the users of the building. Passively, the concrete can absorb heat or radiate ‘coolth’ and will work to stabilise comfortable temperatures.
Importantly, in high thermal mass structures, external outdoor daily temperature variations are not reproduced inside the building, because the maximum heat level reached during the day is delayed by the thermal mass of the building and can be counterbalanced by strategies that make use of the cool of the night. This 'thermal lag' greatly reduces the need for further energy consumption.
Working in tandem
TermoDeck is one example of a system that actively exploits the high thermal mass of structural, hollowcore concrete slabs to control internal temperatures and distribute warmed or cooled fresh air through a building. It has already been incorporated into the sustainable designs of a number of buildings in the UK and works in tandem with onsite renewables.
One example is Howe Dell Primary school in Hertfordshire, which is testament to the success of combining TermoDeck with onsite renewables such as its interseasonal heat exchange system - a ground-breaking onsite renewable system which is located under the school's playground.
TermoDeck's flexibility means that it works equally well with groundbreaking onsite renewables such as the interseasonal heat exchange system or other renewables such as groundsource heat pumps.
The way forward
The road to 2019 maybe a long one, but only when we are armed with a clear roadmap will we be properly qualified to deliver this challenging target. However, before then we need to identify what advances have already been made to provide thermally efficient buildings and those onsite technologies which can deliver carbon savings. Experience shows that combining innovative technologies, which utilise the thermal mass of a building, such as TermoDeck with onsite renewables provides the real route forward in delivering more energy efficient buildings for the future.
