Cost optimization of passive house external walls

Abstract

The purpose of this thesis was to optimize the costs of Passive House external walls, using ISOVER insulation materials. The aim was to compare 5 different timber structures and 2 main ISOVER insulation products: KL-33 and KL-37. Thus, 10 wall structures were studied in this thesis.

The methodology is based on Life-Cycle Cost analysis. It consists of material costs calculation (initial costs) and energy losses’ costs calculation (life-cycle costs). Material costs were calculated for thermal insulation, vapor barriers and gypsum boards. Energy losses’ costs were calculated for 3 cases: 50 years study period with 2% annual energy price increase, 20 years study period with 2% annual energy price increase and 50 years study period with 5% annual energy price increase. The sum of material costs and energy losses costs shows the total costs for the structure during its life span.

Each structure has 6 variants with different thickness of thermal insulation. Thicknesses were chosen in such a way to provide U-values of structures from 0.07 W/m2K to 0.13 W/m2K. Calculations were made for 1 sq. m. of investigated structures. This method allows to find out the best solution (type of structure, insulation material and thickness of this material).

For calculation of technical characteristics of structures, DOF-THERM software and manual calculations were used. For cost calculation and cost optimization, Excel tool was used. All calculations were done according to Finnish and European building codes and standards.

The results show that in all cases Double timber frame structure with total insulation thickness 525 mm is the most economically advantageous solution.

One more important aspect revealed by the results is that the usage of cheaper insulation with higher thermal conductivity is more profitable when the study period is short and energy price increase is small.