Analysis: study findings on the accuracy of Irish BER ratings present significant implications for policy and homeowner decision-making
By Tensay Hadush Meles, Niall Farrell, and John Curtis, ESRI
Improving building energy efficiency is widely considered as one of the most cost-effective approaches to combat climate change, with energy performance certificates serving as benchmarks. For example, in its 2019 Climate Action Plan, the Government of Ireland set a goal to upgrade half a million existing homes, about a quarter of the housing stock, to B2 Building Energy Rating (BER) scale by 2030 as part of the building decarbonisation strategy. To achieve this, the government provides grant support for home energy upgrades through an €8 billion retrofit scheme. Similar building energy performance policy benchmarks are used in other countries, including the European Union and the USA.
When national policies are defined relative to a certain BER scale, it motivates households to target the specific BER scale when investing in improving the energy efficiency of their dwellings. However, BER scales are generated based on projections from engineering estimates using standardised values for the number of occupants, energy use schedules, and other input data.
For instance, it calculates energy for space heating on the presumption that the heating system operates 8 hours per day (7am to 9am and 5pm to 11pm) for eight months of a year (October to May inclusive) to maintain the indoor temperature of the living room area to 21C and the rest of the dwelling to 18C. This implies that the effectiveness of BER scales related investment is determined by the accuracy of the BER scales in capturing actual dwelling-specific energy performance. Should a discrepancy between projected and actual energy performance exist, then household investment benefits and future climate policy targets might not be realised.
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In two related studies, we evaluate the accuracy of the Irish BER scales in capturing observed energy use for home heating and home heat loss. The studies focus on building fabric performance in isolation while excluding the influence of occupants' behaviour on energy consumption, as factors associated with occupants' energy consumption behaviour would complicate building energy performance comparisons. The first study looks at the drop in indoor temperature during the early morning hours (midnight to 06:00 a.m.) of winter months when the heating system is confirmed as being turned off.
Dwellings with better BER scales are expected to retain heat and minimise heat loss, thereby having relatively a lower drop in indoor temperature. The second study exploits differences in boiler operation for home heating while the indoor temperature hovers around the thermostat’s set point temperature during the main winter heating months. This serves as a proxy measure of the variations in energy use for home heating across the BER scales, attributed to building fabric performance alone. Dwellings with better BER scales are anticipated to have a shorter duration of boiler operation to maintain the indoor temperature within the thermostat set points.
Our analysis is based on detailed information collected every three minutes over a span of two years, obtained from smart thermostats provided by Hub Controls Ltd. This data includes household thermostat set point, indoor temperature, and heating unit operating status. Having access to this extensive data allows us to clearly isolate the sole effects of building fabric performance across dwellings with different BER scales. Besides, we factor in outdoor temperature, relative humidity, windspeed, levels of the thermostat set point, several building characteristics, and type and efficiency of the main home heating boiler when assessing the relationship between our key outcome of interest (home heat loss or energy use for home heating) and BER scales.
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Our findings show that improving building energy efficiency, as measured by BER scales, leads to a reduction in energy use for home heating and an increase in home heat retention. However, the differences in observed energy performance attributed to BER scales are considerably lower than what is projected. This does not imply that upgrading dwellings' energy efficiency is not beneficial. Instead, the findings suggest that BER scales do not capture the insulative performance of dwellings as accurately as we would have anticipated. This could be due to their reliance on standardised values and their nature as aggregate measures.
These results present significant implications for both policy and homeowner decision-making. Aligning energy efficiency investments to the achievement of a 'B2’ BER standard may lead to achieving targets at greater costs than necessary. A BER system that more accurately captures the insulative performance of individual dwellings could guide us toward a more cost-effective decarbonisation trajectory. This also affects homeowners, who factor in the change in BER, when planning home energy efficiency upgrades. A refined energy performance system that more accurately captures the performance of each individual home could guide homeowners toward investments tailored to their dwelling's specific characteristics. This could involve a more data-driven approach to evaluate and identify the most suitable upgrades.
Tensay Hadush Meles is a postdoctoral research fellow on climate change and energy transition at the Economic and Social Research Institute (ESRI). Niall Farrell is Senior Research Officer at ESRI and Adjunct Associate Professor at Trinity College Dublin. John Curtis is an applied micro-economist and Research Professor at ESRI.
The views expressed here are those of the author and do not represent or reflect the views of RTÉ
