Guiding Teams by Hygrothermal, Energy, and Thermal Comfort Analysis while Managing Uncertainty
Managing uncertainty is core to all engineering analysis of building performance. Effective solutions are established when managing the risks associated with designs are balanced with the benefits to the clients and end users. Many engineering disciplines address uncertainty with statistical analysis, such as limit state design in structural engineering, where the probability of failure, loads, and other design parameters are stochastic variables. The same approach cannot currently be readily applied to moisture analysis of buildings, as there is often not enough information to make full statistical analysis practical. Design decisions must be made based on the available information and professional judgment and experience. Most building science problems involve numerous interrelated variables that must be considered when evaluating possible solutions. Assessing or quantifying the impact of each variable can be challenging and there is often no clear answer. As a result, feasible solutions and opportunities to optimize gains in performance are often discounted in practice due to inadequate information perceived risk. Such is the case for retrofitting older load bearing multi-wythe clay brick masonry buildings.
Theory tells us that adding insulation inboard of the brick will reduce heat flow, reduce drying, and increase the risk of freeze-thaw damage in cold climates. Designers have rightly asked the question if there are safe insulation levels from a durability perspective and how to effectively achieve both energy efficiency and thermal comfort goals. Hygrothermal and whole building energy analysis can help determine optimal insulation levels, but the value of such analysis can be limited if the uncertainty related to the existing brick properties and “as-built” construction are not adequately managed. This uncertainty can be managed by supplementing the analysis with information gained by field investigation and lab testing of brick samples.
This paper presents case studies where hygrothermal and building energy analysis were used to evaluate the risks and benefits of insulating existing multi-wythe clay brick masonry buildings using an interior insulation strategy. The case study buildings are located in Ottawa and Gatineau, Canada (ASHRAE climate zone 6). The buildings formed part of a new sustainable development neighbourhood project (One Planned Community), including the adaptive reuse of industrial buildings into new mix-use buildings (commercial, retail and office). For these buildings, the developer was concerned about long-term durability and wished to explore the risks and benefits of improving thermal comfort and energy efficiency through an interior insulation retrofit.
Field investigation combined with lab testing of brick samples informed hygrothermal analysis, 3D thermal, and building energy analysis to evaluate feasible levels of insulation where energy savings and thermal comfort objectives could be met without increasing the risk of freeze-thaw damage and compromising the structural integrity of the existing buildings.
Author: Ivan Lee, M.A.Sc. Patrick Roppel, P.Eng., M.A.Sc., Randy Van Straaten, P.Eng., M.A.Sc. Jamie McKay, P.Eng., LEED Fellow