Influence of degree days calculation methods on the optimum thermal insulation thickness in life-cycle cost analysis for building envelopes in Mediterranean and Semi-Arid climates

• Published in: Journal of Building Engineering 2023-11, Vol.79, p.107783, Article 107783
• Main Authors: Verichev, Konstantin, Serrano-Jiménez, Antonio, Carpio, Manuel, Barrios-Padura, Ángela, Díaz-López, Carmen
• Format: Article
• Language: English
• Subjects: ASHRAE; Cooling degree-days; Heating degree-days; Life-cycle cost analysis; Optimum insulation thickness
• ISSN: 2352-7102; 2352-7102
• DOI: 10.1016/j.jobe.2023.107783

The life-cycle cost analysis (LCCA) is one of the most widely used and validated methods to identify the optimum insulation thickness of the building envelope. This method depends on two parameters—heating and cooling degree days (HDD, and CDD). There are various methods for HDD and CDD calculation, the results of which vary significantly depending on the climatic zone. Therefore, this study aimed to analyse the optimum expanded polystyrene insulation thicknesses of a typical wall in Andalusia, Spain, obtained by the LCCA method to demonstrate variations and uncertainties of the results of the LCCA method based on HDD and CDD calculated by the “hourly”, UKMO, and ASHRAE methods, and with different base temperatures in the conditions of Mediterranean and Semi-Arid climates. On average, the HDD values calculated by using the ASHRAE method were lower, by 12.5%, than those calculated using UKMO and the “hourly” method. The CDD values calculated using the ASHRAE method were lower, by 29%, than those obtained using UKMO and the “hourly” method. Consequently, the optimum insulation thicknesses determined based on CDD and HDD calculated using the ASHRAE method were, on average, 14% underestimated compared with the thicknesses obtained using the UKMO and “hourly” methods. The results obtained showed that with an increase in the continentality of the climate, it becomes crucial to correctly use one or another method for calculating degree days to determine the optimum insulation of the building envelope using the LCCA method, which, in turn, requires the development of validation methods. •The LCCA method was applied to determine the wall optimum insulation thickness.•The study was conducted in a region with a Mediterranean and Semi-Arid climates.•Optimum insulation thickness results depended on the degree days calculation method.•Three methods of calculating degree days were analysed—hourly, UKMO, and ASHRAE.•Thicknesses determined with use ASHRAE degree days always were underestimated.