W. Maref

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.

Thermal response of basement wall systems with low-emissivity material and furred airspace

In basement wall systems, airspaces can contribute in obtaining a higher thermal resistance, if a low-emissivity material such as reflective foil is installed within a furred-airspace. In this study, numerical simulations were conducted using the hygrothermal model ‘hygIRC-C’ that was developed at the National Research Council of Canada’s Institute for Research in Construction to investigate the steady-state and transient thermal performance of basement wall systems. This model solves simultaneously the energy equation in the various material layers, surface-to-surface radiation equation in the furred-airspace assembly, Navier–Stokes equation for the airspace, and Darcy and Brinkman equations for the porous material layers. The wall systems used in the simulations incorporate a low-emissivity material (foil with emissivity = 0.04) bonded to a moulded/expanded polystyrene foam that is installed in a furred-airspace assembly. The furring is installed horizontally and covered with a gypsum board. The structural element of the wall (external layer) is a poured-in-place concrete. Walls with and without furred-airspace assembly were considered in this study. Also, consideration was given to investigate the effect of the above-grade and below-grade portions of the wall on the thermal performance when these walls are subjected to two different Canadian climates. Results showed that at steady-state condition, the effective thermal resistance (R-value) of the wall with a furred-airspace assembly depends on the soil, outdoor, and indoor temperatures. Additionally, these wall configurations resulted in an energy savings of ~17% compared to walls without furred-airspace assembly when these walls are subjected to two different climate conditions.

Numerical modeling and experimental investigations of thermal performance of reflective insulations

Reflective insulations are being used in attics, flat roof, and wall systems. Numerical modeling and experimental investigations were conducted to assess the thermal performance of assemblies with reflective insulations. In this article, the present model was used to verify the use of the ASTM C-518 test method for measuring the effective thermal resistances (R-values) of sample stacks comprising reflective insulations. Two tests were conducted on sample stacks using heat flow meter apparatus. The sample stack consists of two expanded polystyrene layers and a reflective insulation installed in between. The model predictions agreed with the measured heat fluxes within ±1%. The article also discusses the combined effect of heat transfer by convection and radiation in the airspace facing the reflective insulation, showing that the derived R-value from the test data resulted in underestimation of the effective R-value of the sample stack.

Three-dimensional analysis of thermal resistance of exterior basement insulation systems (EIBS)

Abstract A consortium 1 research project was initiated to determine the field performance of various thermal insulation products as applied in the exterior insulation basement system (EIBS). Initially a two-dimensional (2-D) analytical tool was used to derive the thermal transmission characteristics from an array of temperature measurements performed over a period of two years. Results immediately showed the influence of lateral heat flux between various products that differed in thermal transmission properties. Therefore, development of a three-dimensional (3-D) model became imperative. This paper gives the theoretical and numerical approaches adopted to develop a 3-D computer model of heat transfer. The implicit Spline Method was selected for the problem solver. The applicability of the model was verified using measured data on temperature distributions at several material interfaces. Then the model was used to estimate the effect of lateral heat flows. The paper also briefly reports the experimental details and presents results on model verification.

Experimental assessment of hygrothermal properties of wood-frame wall assemblies - moisture content calibration curve for OSB using moisture pins.

As part of a research program to establish the hygrothermal response of wood-frame wall assemblies to varying climate conditions, a series of drying experiments was performed in a programmable environmental chamber used to replicate exterior climatic conditions. In these experiments, bulk moisture content of the assembly was measured using a weighing system, and as well, measurements of local moisture content of oriented strand board (OSB) sheathing were taken with the use of electrical resistance moisture pin pairs. The local moisture content of the OSB was based on the relationship between moisture content and electrical resistance determined from a series of controlled laboratory experiments on OSB specimens of the same type and thickness. This paper reports on the results from experimental tests on seven small-size OSB specimens to establish the correlation between electrical resistance and the moisture content of the OSB. The process required the installation of several moisture pin pairs at different locations on and depths in the OSB. The weights of specimens together with resistance measurements taken across each pair of moisture pins were continuously monitored and results captured on a data acquisition unit. Details are provided in regard to electrical resistance measurements, the data acquisition unit, and method of weighing specimens. The results of the tests provided a simple equation to correlate moisture content of OSB to electrical resistance measurements using moisture pins pairs and as well correlation to moisture measurements using commercially available moisture metre. Given that moisture reading results obtained from commercially available moisture metres typically correlate to a specific wood species, the work completed in these experimental tests can be used to determine moisture contents in OSB from moisture metre readings.

Condensation de l'acide sulfurique dans un conduit d'evacuation des gaz de combustion

Abstract A method for computing the condensation of water vapour and sulphuric acid in a removal gas conduct is proposed. It utilizes a theoretical approach to determine the condensate production during the phase change from the numerically computed thermal and dynamic properties of the steam in the conduct. The temperature and velocity distributions are given from a k — e model in one-phase incompressible flow, taking into account the initial temperature and flow rate in the conduct. The quality of the model is tested on a full-scale experimentation pilot equipped with thermocouples and collectors of liquid condensate. The deposit production is obtained for different conditions of temperature and concentration, and the model proves to be satisfactory in domestic boiler conditions.

Energy retrofit using vacuum insulation panels: An alternative solution for enhancing the thermal performance of wood-frame walls

Field monitorings of thermal performance of residential 2 x 6 wood-frame wall systems that had been retrofitted using vacuum insulation panels (VIPs) and extruded polystyrene foam (XPS) panels were undertaken in May 2011 – May 2012 at the Field Exposure of Walls Facility (FEWF) of NRC-Construction. The main objective of this research was to measure the steady-state and transient thermal performance of three wall assemblies (4 ft x 6 ft), two of which incorporated VIPs within an XPS Tongue and Groove (T&G) configuration and VIPs within an XPS Clip-On (C-O) configuration, and a third assembly incorporating only XPS. The three wall assemblies were installed in the FEWF for 1-year cycle of exposure to outdoor natural weather conditions. The hygIRC-C model was used in this study. The results of the model calculations were in good agreement with the experimental data. Given that the VIPs could be punctured during the installation process or could fail during normal operating conditions, additional model calculations were used to predict the thermal resistance in cases where one or more VIPs failed. The model was also used to predict the yearly cumulative heat losses across these wall systems. It is important to point out that the aging effect and the effect of the thermal bridging due to envelope (i.e. skin) of the VIPs are not accounted for in this study. However, sensitivity analysis of the thickness and thermal conductivity of the VIP envelope was conducted to investigate the effect of these parameters on the effective thermal resistance of VIP.

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.

In situ performance of expanded molded polystyrene in the Exterior Basement Insulation Systems (EIBS)

Several different Exterior Basement Insulation Systems (EIBS) were built and instrumented as part of the basement consortium2 research project. These EIBS specimens were instrumented prior to back filling with soil, and their in situ thermal performance was monitored over two years. Soil temperatures and moisture content were monitored concurrently. Weather data were recorded on a daily basis. Through analysis of the measured surface temperature records, the presence of water was detected at the outer surface during various periods of heavy rain and major thaws throughout the two-year period. During these periods, the surface of the concrete showed no evidence of water penetration through the insulation layer over most of the height of the basement wall. Since the test setup involved different thermal insulating materials placed next to each other, the presence of lateral heat flow was inevitable. Both 2-D and 3-D models were used to quantify the lateral heat flow across the edges of different in sulating materials. The measured spatial and temporal temperature profiles were used as boundary conditions. The thermal performance of each insulation specimen was found to remain sta ble over the two-year period and was not significantly affected by episodes of wa ter movement at the exterior face of the specimens. The thermal resistance of

Heat transfer in the turbulent flow through a conduit for removal of combustion products

Abstract A numerical model was presented to calculate the velocity and thermal fields of turbulent flow through a conduit for removal of combustion products. This study originated in response to an industrial concern to study dynamic behaviour of a smoke conduit connected to a high-efficiency gas boiler working in permanent running mode (steady state), or cyclical non-static running mode (unsteady state). The momentum and temperature fields were calculated via a finite-volume CFD code using the k−e turbulence model. The validation of this calculation was conducted employing a full-scale experimentation. Comparisons of temperature fields were made, and the model was shown to give an acceptable quantitative approach for design within the framework of the coarse approximations adopted.