Energy Performance Certification: Misassessment due to assuming default heat losses

Ciara Ahern,Brian Norton

doi:10.1016/j.enbuild.2020.110229

Abstract

Energy Performance Certificates (EPCs), are issued when dwellings are constructed, sold or leased in the EU, are the foremost source of information on the energy performance of the EU’s building stock. Where the cost of obtaining the required data is prohibitive, EPC assessors use nationally applicable default-values. To avoid wrongly-higher EPC ratings for all existing dwellings, a standardised thermal bridging transmittance coefficient (Y-value) is typically adopted together with worst-case overall heat loss coefficients (U-values). These default U-values for roofs, walls and floors are drawn from building codes and regulations applicable at time of construction. Many older dwellings have undergone significant building fabric upgrades. Therefore, default U-values are considerably higher than the real U-values of those upgraded houses. This causes a systematic ‘default effect’ error in large national EPC datasets. For the dataset considered thermal default use overestimates potential primary energy savings from upgrading by 22% and by 70% in dwellings built before after and before thermal building regulations respectively. A methodology has been developed that derives from an EPC dataset, a method for calculating a realistic energy-improvement payback when use of pessimistic default U-values is unavoidable.

Highlights

Households consume 27% of end-use energy in the European Union (EU) 28 (Eurostat, 2016)
For dwellings with a NE/SW orientation primary energy consumption associated with both primary and secondary heating systems increased by 31% for post-thermal regulation dwellings and 92% for pre-thermal regulation dwellings when default U-values and a standardised Y-value is assumed
The use of pessimistic thermal defaults combined with the reality of significant thermal upgrading of pre-thermal regulation dwellings has led to significantly higher rated primary energy consumption associated with the space heating system

Summary

Introduction

Households consume 27% of end-use energy in the EU 28 (Eurostat, 2016). The extent and duration of the dominance of the thermal characteristics of pre-existing houses on this energy use depends on construction rates, floor areas and specifications of new dwellings (Simpson et al, 2016). Average replacement rates for existing housing stocks in the European Union (EU). Achieving lower energy use and associated greenhouse gas emissions requires energy refurbishment of these existing dwellings; together with greater efficiency and harnessing renewable technologies in the generation of energy supplied to houses (Kohler and Hassler, 2002; Lowe, 2007; Roberts, 2008; Schaefer et al, 2000; Simpson et al, 2016; Weiss et al, 2012).

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Discussion

Conclusion