A clear vision: why zero carbon targets for non-domestic buildings will call for heavyweight answers
The recent budget announcement that all new non-domestic buildings will be required to be zero carbon by 2019 will clearly have far reaching implications for the design and specification of new buildings. Geoff Russell-Smith, general manager, Tarmac TermoDeck outlines how high thermal mass systems can provide a viable 'third way' alternative to air conditioned and naturally ventilated buildings.
With housebuilders already working to a carbon neutral target of 2016 and around a third of all building-related carbon emissions produced from non-domestic buildings, a target announcement for non-domestic buildings had been eagerly anticipated. At present, only energy generated on-site, through solar panels, wind turbines or combined heat and power plants, can be used. But now this deadline has been unveiled, Ministers are likely to come under pressure from the industry to relax the definition of 'zero carbon' to allow off-site renewable energy sources to mitigate a building's energy use. This is because practitioners have struggled to incorporate on-site renewables and meet the financial pay backs and capital returns of doing so. However, another way of looking at the problem is to make buildings even more energy efficient, so that the "compensating" renewables can achieve 'zero carbon' status more easily.
Implications for building design
The new target has far reaching implications for the design and specification of a planned building's heating, cooling and ventilation systems.
Selecting a system requires a complex and detailed assessment that will be driven by a number of factors including - building type and location, budget available, usage, complexity, comfort requirement, client preference, regulation compliance, political authority and expected energy and running costs. To meet this increasingly difficult challenge the design process will evolve and we will see the increased use of dynamic modelling techniques, more interactive use of the building fabric and greater integration of the sub-systems within the building.
There have broadly been two system options available to design teams - refrigerant-based air conditioning and natural ventilation. However, a third approach, the active use of high thermal mass combined with mechanical ventilation will become more prominent in this more demanding environment.
Unresolved matters
Air conditioning systems have for a long time been regarded as the 'preferred' solution or are considered to be the 'top-of-the-range' choice because those buildings in which they are implemented attained higher rental values. However, it is a misconception that air conditioning systems are the only means of achieving comfort conditions and premium rental values.
Our experience in the past eighteen months is that a massive change in the opinion of clients and developers has taken place. For example, they are now willing to sacrifice elements such as the previously sacrosanct suspended ceiling if a concrete exposed ceiling is required. Air conditioning is now also widely recognised as a significantly more energy-intensive process than mixed mode or natural ventilation and crucially, also produces high levels of carbon dioxide.
The capital costs of air conditioning are also significantly higher than alternative systems. While capital costs will always be central to specification decisions, it is also vitally important that the projected running costs over a building's lifetime are considered. However, introducing full air conditioning into a design can often add around 50 per cent to the eventual running costs of the building, in addition to further maintenance costs.
Air conditioning is frequently specified for non-domestic buildings including offices and public buildings but it can severely impairs comfort levels. Air conditioning can be noisy, unhealthy and windows cannot be opened which prevents fresh air from entering the building.
Death of the air conditioner?
The future of air conditioning and how it will fare with the introduction of energy performance ratings is currently in some doubt.
The Energy Performance of Buildings Directive (EPBD) requires Energy Performance Certificates for all non-domestic buildings, which will specify an energy rating. Although it is uncertain exactly how air conditioning type systems will score, many industry experts are anticipating that such systems will only be able to achieve a D or E rating as opposed to B or C ratings for other greener systems.
This will deliver a significant change. I believe that the requirement to have an Energy Performance Certificate will for the first time provide a value incentive for property managers and landlords to improve energy performance. I would also suggest that those companies, which have defined Corporate Social Responsibility (CSR) policies, will be most keen to occupy the highest rated buildings and property investors will use the certificates as a yardstick to measure financial return on their investments.
A natural option
Initially, naturally ventilated buildings might be seen as the low energy solution compared to refrigerant-based ventilation systems. However, it is important that specification decisions are practical and appropriate. This is because we face the prospect of the number of days with outside temperatures in excess of 25°C doubling by 2040, and tripling by 2080, it is vital that new buildings are designed to deal with future climatic conditions.
With variability in weather conditions and in particular, hotter summers choosing natural ventilation will compromise comfort levels if the air entering the building is hotter than desired level inside the building. Unfortunately, noise and air pollution also mean that opening a window is frequently not an option anymore - the air coming in is often as hot as the air inside the building. Studies reported in a presentation by BRE also confirmed that natural ventilation is not necessarily the best option. In 10 out of 16 schools tested, natural ventilation failed to deliver minimum 3 l/p/s and carbon dioxide levels exceeded desirable levels.
Achieving thermally efficient buildings
I believe there is a viable 'third way' to both air conditioning and natural ventilation. The use of high thermal mass systems have a proven track record of delivering greater energy performance over the lifetime of a building.
By incorporating high thermal mass into the initial design, 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.
Active versus passive use of thermal mass
The passive benefits of the high thermal mass properties of concrete can be significantly increased by the clever technique of passing the supply air through the thermal mass. The supply air passes through the holes in the hollowcore (which are primarily there to save concrete) at low velocities, allowing prolonged contact between the air and the slabs. In turn, this enables a far greater area of concrete to actively behave as a heat exchange medium that releases heat to, or absorbs heat from, the air in the slabs. This enables the design engineer to develop strategies to influence the occupied spaces by either heating or cooling the ceilings or heating or cooling the incoming air.
This system, known as TermoDeck 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.
In a well-insulated, airtight concrete building, which has good heat recovery, TermoDeck can successfully leverage the clear thermal mass benefits to produce an efficient environmental system. As a result, the system can replace the need for potentially inefficient air conditioning systems. Furthermore, it delivers 100 per cent fresh air with a level of reliability that natural ventilation cannot provide, ensuring an indoor atmosphere that is quiet, fresh and keeps occupants alert - whether they be employees, students or pupils!
Importantly, the system delivers proven results. The Innovate building, a commercial property in Leeds was awarded the highest ever BREEAM rating in 2007 - 87.55% - by utilising the high thermal mass of structural hollowcore concrete. Similarly, the Elizabeth Fry Building, a TermoDeck building at the University of East Anglia was built twelve years ago and is still cited as one of the UK's most energy efficient buildings.
It is clear that now the zero-carbon announcement for non-domestic buildings has been unveiled there will be far reaching changes to the way buildings are designed, specified and ultimately, operated. But most importantly, if we are to hit zero-carbon targets, it is imperative that the industry acts now by specifying systems, which can future proof our buildings against climate change.
