The aim of this study was to elaborate and validate a reduced order model able to forecast solar heat gains as a function of the architectural parameters that determine the solar heat gains. The study focused on office buildings in Catalonia and Spain and their physical values were taken from the Spanish Building Technical Code and European Union Directive 2018/844. A reduced order model with three direct variables (solar heat gain coefficient, shade factor, window to wall ratio) and one indirect design variable (building orientation) was obtained and validated in respect to the International Performance Measurement and Verification Protocol. Building envelope properties were fixed and the values were taken from the national standards of Spain. This work validates solar heat gain coefficient as a primary variable in determining the annual solar heat gains in a building. Further work of developed model could result in building energy need quick evaluation tool in terms of solar heat gains for architects in building early stage as it has an advantage over detailed building simulation programs in terms of instant calculation and the limited need for predefined input data.

The ISO 52000–1:2017 is the overarching Energy Performance of Buildings (EPB) standard, providing the general framework of the EPB assessment. It is applicable to the assessment of overall energy use of a building, by measurement or calculation, and the calculation of energy performance in terms of primary energy or other energy-related metrics. ISO 52000–1 provides general profound guidelines, but also gives the freedom to adapt the guidelines with national standards and regulations. This article focuses on design stage energy performance assessment in the framework of syn.ikia project, which aims to deliver a blueprint for an Integrated Design Process of sustainable plus energy buildings and neighbourhoods, leading the way to plus energy districts and cities. This project has four demonstration sites and the one being in focus of this article is located in Catalonia, Spain. Even though this project and Spanish Technical code both are based on ISO 52000–1, the criteria of calculation boundaries of those two vary in some degree, and that can cause great difference in the primary energy balance. In the calculation of the energy balance the criteria of syn.ikia considers all common energy uses in a building, including heating, cooling, ventilation, dehumidification, domestic hot water and lighting, while the Spanish Technical Code excludes lighting consumption. The main difference however is caused due to the fact that in syn.ikia hypothesis the exported energy is being considered in the calculation of how much non-renewable energy is avoided from the grid, while Spanish Technical Code excludes it. For the evaluation of these differences, a simplified monthly primary energy calculation tool is developed during the evaluation framework of key performance indicators of the project. The analysis of the calculation framework hypothesis is presented, analyzing the effects of the assessment boundaries, different primary energy balance calculation hypothesis and building design alternatives.