An innovative air source heat pump solution was required to reduce building carbon emissions, says Jodi Willis of energy and sustainability company MTT
MTT were instructed by our client, a commercial developer specialising in student accommodation, to design the MEP building services on a 400 bedroom new build development in London.
Our appointment was also to develop an energy strategy to be submitted to the Local Authority as part of the planning proposals demonstrating how the sustainability targets set within the Local Plan and emerging Local Development Framework could be met.
Initial proposals were to provide air source heating to the entire development with combined heat and power addressing the baseline domestic hot water loads with a top up from biomass fired boilers in order to meet the carbon emissions savings and also provide a proportion of renewables integration that approaches that of the London Plan target of 20 per cent.
Through discussions with the Planning Authority there was a real reluctance to accept both air source heating and biomass boilers. The aversion to air source heating emanated from the report published by the Energy Savings Trust on air source heating performance in the residential sector whilst the provision of biomass is discouraged due to air quality issues and fuel supply into a city centre location.
MTT were able to provide a technical response on the issue of air source by demonstrating that the installation for this project constituted a commercial application of the equipment and therefore provides a fully designed solution that would then be maintained and managed through a system of best practice controls and maintenance regime. The Energy Savings Trust report is aimed at the residential sector where the design, installation and subsequent maintenance was demonstrably the contributing factor to the lower performance figures stated.
The planning authority accepted the inclusion of air source heating and recognised its suitability and contribution to reducing carbon emissions.
The omission of biomass boilers was one that MTT and our client welcomed, since the capital costs associated with this element, the ongoing fuel costs and availability along with the maintenance implications were a major consideration. For MTT the inclusion of biomass provided particular challenges in the integration and control when interfacing with the other technologies.
The resultant services solution is a more conventional air source heating providing 100 per cent of the heating to the student rooms and common areas through a system of underfloor heating which is best suited to an air source solution, maximising the efficiency.
The baseline hot water requirements, which are in themselves significant in a modern development of this type - new build projects are, as we know, thermally efficient - are provided by the Combined Heat & Power Unit, whilst peak loads are addressed through use of conventional, high efficiency gas fired boilers.
This solution, along with the fabric and services improvements that go beyond the requirements of Part L of the Building Regulations, provides an overall carbon emissions saving of 32.8 per cent, with a contribution from air source heating of just under 10 per cent.
This equates to a saving of 67 tonnes of CO2 overall of which 20.5 tonnes is provided by the air source heating. The overall resultant energy consumption of the development is calculated to be 1,500MWH for gas to heating and hot water along with CHP input and 950MWH for electricity.
Although the reduction in Carbon emissions falls short of the target of 40 per cent required by the Local Authority, MTT demonstrated that the design team had made significant improvements from the baseline Part L compliant building in all areas including fabric performance, building services efficiencies, integration of centralised community style heating and hot water and the integration of what are classed as low and zero carbon technologies (LZCs) in the form of CHP and air source heating.
The local authority have accepted these proposals and the project is now progressing through detailed design with completion proposed for late 2012.