The Road to Merton
As more local authorities use planning policy to encourage low carbon development, on-site renewable technologies are no longer confined to one-off ‘best practice’ developments. Geoff Russell-Smith, general manager, TermoDeck explains how concrete-based thermal mass systems can also combine with proven renewable technologies to deliver further carbon savings.
In 2003, Merton Borough Council became the first local authority in the UK to use its planning powers to dictate that non-residential developments over 1,000 sq metres should utilise onsite renewable technologies to reduce annual carbon emissions by 10 per cent across all new developments.
New planning powers
Today, Merton no longer stands alone as a solitary beacon of best practice. Around 75 local authorities from Croydon to North Devon have taken proactive steps to follow this approach, which has been dubbed the ‘Merton Rule’.
The message for all practitioners involved in the planning, design and energy management of non-residential buildings is clear. Further changes to planning policy will dictate that renewable technologies like biomass boilers, ground source heat pumps and solar panels become mainstream.
Building on renewables
This is good news. However, I believe that the key to building, and successfully managing, low carbon commercial buildings is the integration of renewable energy sources into thermally efficient new builds. In the London Renewables document, a preferred hierarchy states that renewables should be considered once the potential to maximise a building’s energy efficiency and Combined Heat & Power (CHP) have been fully explored.
This makes complete sense. Minimising the 100 per cent energy figure makes achieving the 10 per cent renewables content easier and cheaper. Not only is this important to realising further carbon savings, but an inefficient building can also incur significantly greater capital plant costs and operational life-time costs.
High cost of inefficiency
To date, the selection and installation of renewable technologies only becomes cost-effective when considered over the whole life cycle of a building. For example, a thermally inefficient building using photovoltaic (PV) solar panels requires a higher renewables input, resulting in the need for larger and more expensive solar arrays. Conversely, the renewable element on an energy-efficient building will require a lower input, which helps to decrease capital cost involved and improve payback calculations.
Achieving thermally efficient buildings
One approach to achieving thermally efficient buildings is to incorporate high thermal mass into the initial design. Heavyweight structures, like concrete-cored buildings, have a very high thermal mass, enabling them to deliver stable temperatures to internal spaces by ensuring there is a resistance to the flow of heat or conversely, ‘coolth’, through the building’s dense material. Once dense materials like concrete reach their maximum internal temperature, the slow release of heat helps maintain comfortable room temperatures for a period of time after the initial heat input has been made.
Comfort control
Importantly, in high thermal mass structures, external diurnal 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 until counterbalanced by the cool of the night. This ‘thermal lag’ greatly reduces the need for further energy consumption.
The passive use of thermal mass is a solid start in good building design practice. However, to achieve the more rigorous energy performances demanded by new legislation, a more active approach is required, such as the use of the TermoDeck system.
TermoDeck exploits the high thermal mass of structural, hollowcore concrete slabs to control internal temperatures and distribute warmed or cooled fresh air through a building. The supply air passes through the hollowcore at low velocities allowing prolonged contact between the air and the slabs. In turn, this enables the concrete to behave as a passive heat exchange element that releases heat to, or absorbs heat from, the air in the slabs.
In a well-insulated, airtight concrete building, which has good heat recovery, TermoDeck can successfully utilise the thermal mass benefits of concrete to produce an efficient environmental system. As a result, the system can replace the need for potentially inefficient refrigerant-based air conditioning systems.
A combined approach
TermoDeck also has the vast potential to be used in buildings that utilise renewable technologies and can work in tandem with them to help deliver greater thermal efficiency, whilst also contributing to reduced carbon emission targets.
Currently being built, the new Phase 3 building at Malvern Hills Science Park, Worcestershire, is one the first buildings in the UK to combine both TermoDeck and ground source heat pumps. Boreholes have been drilled to enable four 90Kw ground source heat pumps to add heat or cooling capacity into the building. Couch Perry Wilkes, the building services consultants on the project, saw ground source heat pumps as the ideal renewable option to reduce the already low energy profile of the building.
Beyond Merton
Already, a small number of local authorities are seeking carbon reduction targets beyond the 10 per cent prescribed by the Merton Rule. It is clear that many authorities in the UK will be following the lead set by Merton. It is also apparent that the 10 per cent renewable factor will increase to 20 per cent and beyond in the years to come. This will create new challenges for building design. High thermal mass systems like TermoDeck are one such way in which these demanding targets can be met, by achieving savings on carbon emissions and reduced running costs, whilst also providing comfortable internal environments for new buildings.
4 December 2007
