Abstract
European National Calculation Methods (NCM), such as the UK Standard Assessment Procedure (SAP), are used to make standardised and simplified assessments of building energy performance. These NCMs contain simplifications to aid ease of use and comparability of resulting Energy Performance Certificates (EPC). By comparing SAP with a modern, dynamic modelling system, this study quantifies internal temperatures and thereby heating energy consumption. Results show that for the considered test house SAP results correspond closely to a dynamic model using an idealistic heating system, with perfect control and instant responsiveness. However, the introduction of a dynamic, physically realistic gas fired boiler and water based heating system to the model results in a consistent increase in internal temperature (0.5 °C) and energy demand (by ca. 1000 kWh/a). Variation of further parameters within the dynamic model, controls and heat source size, are presented and compared to SAP results and assumptions. The inclusion of more realistic dynamics in building energy modelling for NCMs may provide a better basis for effective decision making with respect to a wide range of heating systems.
Highlights
The EU 2030 emissions reduction target of 40% [1] requires significant changes in the residential sector, which accounts for 1/3 of energy usage [2]
This paper describes a cross-model comparison between a fully dynamic building and heating system energy model (Building Technology Simulation Library, BTSL) and a quasi-steady state national calculation method (SAP) developed for use as part of an Energy Performance Certificates (EPC)
The calculation models utilized in this study, Standard Assessment Procedure (SAP) and BTSL, are both examples of bottom-up engineering models, in this sense they both rely on building information and estimated end use energy demands to estimate delivered energy using the thermodynamic properties of the heating equipment and building heat loss
Summary
The EU 2030 emissions reduction target of 40% [1] requires significant changes in the residential sector, which accounts for 1/3 of energy usage [2]. The European Commission provides the Energy Performance of Buildings Directive (EPBD) as a framework for simplified static models to assess retrofit activities and provide the decision maker with information about predicted energy consumption [4]. EU member states are required to implement building Energy Performance Certificates (EPC) utilising results from the use of National Calculation Methods (NCM). Discrepancies between calculated energy consumption and that experienced during building use are well documented in the literature [5]. Residential, non-domestic [6,7] and historic buildings [8] all show a gap between the predicted and actual energy consumption. The energy consumption calculated by NCMs follows the same trend has been observed [9,10]
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