Rock Glazer

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.

Performance Testing of a Residential Motorless Air Exchanger System

Abstract A heat recovery ventilator (HRV) is used to create a balanced ventilation system in residential buildings and as an energy-saving measure. HRVs bring in outside air which is tempered with outgoing stale air, with only the small energy penalty of the blower power to overcome the pressure drop in the HRV. HRVs have been used in cold climates and have often performed poorly due to frosting failure. HRVs require de-icing in cold climate application, where the exhaust warm air is periodically recirculated during defrost cycles, interrupting the flow of the exhausting air and redirecting the stale warm air back into the house, to defrost the HRV core. This study was performed to assess the performance of a motorless air exchanger (MAE), in comparison to a conventional motorized HRV, and determine if it could perform in winter without frosting failure. The parameters that were compared for this study include sensible effectiveness, defrost occurrence and energy consumption. The air exchanger system showed higher sensible effectiveness and no “defrost cycles” were required. Operation of the air exchanger system resulted in a slight increase (~2.8%) in whole house energy consumption in winter and showed savings of ~11.2% in summer.