Energy Matters | Issue 4 | 2020
14
Measuring the Performance Gap Chris Ricketts, Consultancy Business Manager
TECHNICAL www.elmhurstenergyconsultancy.co.uk
The problem is that homes have been shown to routinely perform worse than expected, and often by a significant amount (an average of 60% underperformance in the largest study undertaken). We need measurement of thermal performance at a larger scale to validate these findings and to ultimately understand how to more efficiently insulate our homes, and to design methods and policies to improve their delivered in-use performance. You can’t manage what you don’t measure.
How Measured Energy Performance works
20% of all energy use in the UK is for heating homes, making it the single biggest user of energy. It’s a big cost to residents and a big contributor to the country’s carbon emissions. To meet targets set by the government, building regulations set out a series of minimum requirements for both new and existing buildings which aim to balance energy efficiency, carbon emission savings and running cost. RdSAP and SAP are useful methodologies when calculating a building’s relative energy efficiency and carbon emissions but are not without their limitations. Measured Energy Performance is a new service from Elmhurst Consultancy that can measure the actual energy performance of homes.
You can’t manage what you don’t measure Compliance modelling is useful to assess the energy efficiency of buildings under standardized conditions to determine if minimum performance requirements are met. However, a number of research projects over the years have highlighted a performance gap between their outputs, such as Energy Performance Certificate (EPCs), compared to the measured energy use during occupation. This poses the risk of misleading consumers, failing to account for the true occupancy behaviours of residents in how they use their homes, and, for society at large, the UK housing stock may not in fact be achieving the regulated targets that have been set out by Government.
Measured Energy Performance uses Smart HTC technology to measure the thermal performance of a house, defined by the ‘Heat Transfer Coefficient’ or HTC. The HTC encompasses all of the heat lost from a dwelling during the winter, through the walls, roof, floor and windows by conduction and radiation and by air movement and convection paths through gaps and cracks in the building fabric. That makes it the ultimate barometer of how well the overall fabric of the home keeps heat in and cold out. The same HTC value is calculated as part of all SAP, RdSAP and PHPP calculations, thus enabling direct comparison of predicted and measured performance, with variables such as occupancy energy use behaviours and weather all accounted for. Elmhurst has developed the concept of a measured energy performance report which will use the Smart HTC calculation at its core whilst presenting a very clear comparison of the SAP design intent against the performance of what has been delivered.
