Hakim Elmahdy

3D heat and air transport model for predicting the thermal resistances of insulated wall assemblies

A wall energy rating (WER) system has been proposed to account for simultaneous thermal conduction and air leakage heat losses through a full-scale insulated wall system. Determining WER requires performing two standard tests on a full-scale wall specimen: a thermal resistance test and an air leakage test. A 3D model representation of the wall specimen is developed to combine the results of these tests to obtain an accurate prediction of the wall thermal resistance (apparent R-value) under the influence of air leakage. Two types of wall configurations were tested and simulated. The first one was a standard 2” × 6” wood stud frame construction, made of spruce, spaced at 16” (406 mm) o/c in 2.4 m × 2.4 m full-scale wall specimens. The second wall configuration was similar to the first one except that it included through-wall penetrations. The cavities of the two types of wall configurations were filled with different types of insulation, namely glass fibre batts and two different types of open cell spray polyurethane foams (light density, 6.8 and 12 kg/m3 nominal), a total of six walls. The present 3D model was used to predict the R-values of different types of wall assemblies (with and without air leakage). This model is a new hygrothermal tool that was recently developed and benchmarked against hygIRC-2D that was previously developed at the National Research Council of Canada, Institute for Research in Construction. The 3D version of this model was benchmarked by comparing its predictions of R-values for different types of wall assemblies against the measured R-values in the guarded hot box at no air leakage. Results showed that the present model predicted R-values of six walls to within ±5%. The 3D model was then used to investigate the effect of air leakage rate on the apparent R-values for these same walls. The results showed that the apparent R-values decreases linearly with air leakage rate less than ∼0.1 L/(m2 · s). At air leakage rate greater than ∼0.1 L/(m2 · s), the apparent R-values decrease asymptotically.

Condensation risk assessment on box windows: the effect of the window-wall interface

Windows generally have the lowest temperature index in current building types, and will consequently be the primary location for interior surface condensation. Surface temperatures can easily be calculated using thermal finite-element models, but these generally omit the effect of convection in the windows and the window–wall interface. Hence, there is a need to determine if specific interface details provide potential for condensation on the window components in which air leakage paths may be prominent. The article reports on a laboratory evaluation of condensation risk assessment in a hotbox with varying pressure differences and the introduction of deficiencies. It was concluded that the effect of the type of insulation in the window–wall interface was very low for isobaric boundary conditions, whereas it has a significant effect when pressure differences are applied.

Assessment of Energy Rating of Polyurethane Spray Foam Walls: Procedure and Interim Results

The application of polyurethane spray foam (SPF) insulation in buildings provides a durable and efficient thermal barrier. The industry is also promoting the SPF as an effective air barrier system in addition to its thermal insulation characteristics. In an effort to address these issues, a consortium of SPF manufacturers and contractors, jointly with the National Research Council of Canada’s Institute for Research in Construction conducted an extensive research project to assess the thermal and air leakage characteristics of SPF walls as well as conventional wall assemblies. The objective is to develop analytical and experimental procedures to determine a wall energy rating (WER) that captures both the thermal and airleakage performance of a wall assembly. The experimental part included two streams of testing: (1) To determine the wall air leakage rate at different conditions and (2) their thermal resistance, R-value, at different temperature differences. An analytical procedure was also developed to calculate WER by combining the heat loss due to thermal transmission and that due to air leakage with the aim of arriving at WER. Six conventional full-scale wood frame wall assemblies were built, two with glass fiber batts and of four with medium density SPF. Some walls were constructed without penetrations and others were built with penetrations. The testing regime included: (i) Initial testing of air leakage and thermal resistance; (ii) conditioning in the dynamic wall test facility according to an established routine; and (iii) retesting for air leakage and thermal resistance. This paper presents the results of six walls included in this project. The focus of this paper will be on presenting a brief summary of the project objective, testing protocol, and the theoretical approach to determine the WER number for the six walls.

Thermal characteristics of fenestration systems A global look at harmonization of standards

The recent changes in trade barriers between countries are permitting more exchange of goods across borders with reduced difficulties. Fenestration products (windows, doors and skylights or roof-mounted windows) are among the popular construction products to cross boundaries. In many cases, fenestration manufacturers have to demonstrate that their products meet certain performance criteria wherever the products are sold.