Evaluating the "as-built' performance of an eco-housing development in the UK

This paper uses a socio-technical building performance evaluation approach to forensically and systematically evaluate the actual performance of two case study dwellings located in a flagship eco-housing development in the UK, during the post-construction/initial occupation stage. The 12-month study captures the as-built' performance of the building envelope (principally heat loss) and installed equipment along with remote monitoring of energy use and environmental conditions, review of the handover processes and initial experiences of the occupants in relation to the home environment. It is found that actual annual energy use and CO2 emissions of the case study dwellings exceed design predictions by factors of 1.8 and 2.5, respectively. The main reasons for this gap are complex interdependencies that occur across the performance of building fabric and energy systems, usability of controls and occupant expectations and behaviour. Underperformance of mechanical ventilation and heat recovery systems and air source heat pumps results from inadequate commissioning and maintenance procedures and poor occupant control due to complex control interfaces. Furthermore, unclear user guidance and inadequate training during handover lead to poor occupant understanding of the mechanical ventilation and heat recovery systems and heat pumps, resulting in their misuse. The findings have proved that building performance evaluation processes are vital for examining operational outcomes and discovering performance-related issues that would otherwise go unreported and lead to bigger problems in future. Practical application: The methodological approach for evaluating housing performance adopted in this study provides design and construction teams with a practical approach to diagnose workmanship issues with building fabric and any installation or commissioning issues with energy systems and services. Maintenance regime of heating and ventilation system should be clarified at the installation and commissioning stage. Maintenance contracts should be set up for unfamiliar low carbon systems such as heat pumps, MVHR. Occupants need to be trained through graduated and extended handover that involves occupants trying out systems and controls in the presence of trained housing officers, supplemented by visual home user guides (developed by the architects) offering clear guidance on the daily and seasonal operation of systems and controls. Learning from such real-world case studies, from design to early occupation, is helpful in understanding the exact causes of the performance gap and how it can be addressed.