A popular retrofit option is to install an exterior insulation finish system to the walls of existing buildings. This study evaluates the thermal and moisture performance of such a system with a vented wall assembly. In addition to being a case study, this field monitoring was intended to verify computation methods of building envelope performance. The long term monitoring was designed to be non-destructive so that the building envelope performance is not affected by the measurements that are made, and to allow easy removal of sensors for recalibration and retrieval at the end of the test period. The field monitoring is planned for two years to capture a wide range of environmental conditions. This paper discusses the instrumentation used in the study and presents interim results of the thermal resistance of the wall and surface moisture.
The diffusion coefficients and permeabilities of CCl3F, CCl 2F2, C2Cl2F4, CHClF 2, and CF4 through thin films of Elvax® 3137 ethylene-vinyl acetate copolymer, Surlyn® 1652 ionomer, Alathon® PE 5753 polyethylene, and Mylar® LBT polyester were determined in the temperature range 0 to 40°C in a typical per meation cell. The degree of crystallinity of each polymer as determined by X-ray scattering was used to aid the interpretation of results. Activation energies for diffu sion and permeation in these systems were calculated. The two most important fac tors in determining diffusivities and permeabilities in these systems are the molecular interaction between polymer and penetrant and the degree of crystallinity of the polymer. The molecular size of the diffusing molecules is a lesser factor in the systems studied.
Trichlorofluoromethane, commonly called CFC-11, is the primary blowing agent used in the production of polyurethane (PUR) or polyisocyanurate (PIR) rigid foams for laminate insulation. CFC-11 is also a member of a class of chlo rofluorocarbons called "hard CFC's," which are believed to contribute to the destruc tion of the earth's protective ozone layer located in the stratosphere above the Antarc tic. Two possible CFC-11 replacements for rigid laminate insulation production with lower ozone depletion potentials than CFC-11 have been identified. They are CF3CHCL2 (HCFC-123) and CCL2FCH3 (HCFH-141b). Many properties of the foam contribute to the overall effectiveness of the laminated insulation product when applied as part of a roof or in a sheathing application Some of these properties in clude foam density, compressive strength, dimensional stability, thermal conductiv ity, and performance in specified flammability tests (ASTM-E84 or UL-723). In order to be a viable replacement for CFC-11, utilizing current laminate chemistry and processing technology, HCFC-123 or HCFC-141b must produce foams that give equivalent or better values than CFC-11 blown foams for the properties listed above. Continuous laminate production evaluations of HCFC-123 abd HCFC-141b were conducted at the North Haven Laboratories of The Dow Chemical Company in a typical rigid laminate formulation to determine the viability of these chemicals as replacement blowing agents of CFC-11. These evaluations included a control run of 100% CFC-11 and blends of HCFC-123 or HCFC-141b with CFC-11. Analyses include reactivity profiles, physical property measurements, initial and aged thermal conductivities, and flammability performance as measured by the UL-723 Tunnel Test.
A multiple regression method for analyzing thermal measurements in order to eliminate the influence of varying outdoor temperature is suggested. It is shown that the method worked extremely well for in situ measurements in a one- family house situated in the south of Sweden, where the thermal resistance of 0.8 m loose fill glass fiber attic insulation was determined during a 60-day winter period and a 14-day summer period.
The water absorption characteristics of eight thermal insulation materials have been determined using three different laboratory test methods. The results from this study have been compared with field results from an 18-month below grade perimeter exposure study. It was concluded that moisture gain in perimeter insulation cannot be predicted accurately by any one laboratory test. A relative assessment of performance is possible from the results of a combina tion of laboratory test methods.
The technology for manufacturing high thermal performance cellular plastic insulations such as polyurethane, polyisocyanurate, phenolics and extruded polystyrene uses gases with low thermal conductivity as captive blowing agents. The gas is captured in the closed cells of the material to achieve higher thermal resistance. But once in contact with the atmosphere, the thermal resistances of these materials gradually decrease. This phenomenon is called aging. The present authors investigated the use of Z-transform for the data analyses and compared it with the method used by Brehn and Glicksman and with an improved version of the finite difference method used by Schwartz et al. This paper compares the three methods of analysis and reports a set of data on O2 and N2 diffusion coefficients for a polyurethane foam, a polyisocyanurate foam and an extruded polystyrene insulation. The aim of the analysis is to derive a relation between the test chamber pressure variation and time. This relation in turn is used to calculate the gas diffusion and storage characteristics from the experimental data.
Water absorption coefficient of a material governs the liquid moisture movement into it. In the case of various components of a building envelope, in particular exterior claddings, this is one of the most important hygrothermal material properties that needs to be assessed to determine the overall moisture management strategy. In different geographical locations, components of the building envelope, in particular the surface of the exterior cladding, are exposed to various temperature regimes. However, the effect of various temperature regimes on the water absorption coefficient of common building materials has not been adequately investigated. This study looks at the water absorption characteristic, determined through water absorption test, of three commonly used building materials (i.e., eastern white pine, red clay brick and concrete) at four temperature levels at the surface of the material, ranging from 3 to 35°C. A clear surface temperature effect on water absorption coefficient and derived liquid diffusivity value is shown in eastern white pine whereas changing the surface temperature shows no effect on the water absorption characteristic of red clay brick and concrete.
A new test method for water absorption proposed for inclusion in the ASTM Book of Standards has been subjected to test series by seven laboratories using four rigid thermal insulating materials. This note presents a statistical analysis and addresses general questions concerning evaluation of the test method uncertainities. Une novelle méthode de mesure de l'absorption de l'eau à paraître dans l'ASTM Book of Standards a éte soumise à une série d'essais par sept laboratoires. Les essais ont porté sur des isolants thermiques rigides. La présente communication renferme une analyse statistique et aborde des quesions générales concernant l'évaluation des incertitudes inhérentes à la méthode. RES
For isotropic materials with a significant fraction of micro-pores, the cumulative water intake per unit of inflow surface area typically yields a linear function of the square root of time elapse. The authors postulate that this dependence has a limited range of validity. The validity of this approximation starts from an initial period that is inversely proportional to the rate of water intake and ends much before the material reaches the capillary moisture content.
Experimental investigation presented here uses a differential presentation of the cumulative water inflow and clearly indicates that material such as calcium silicate or brick belong to a broad class of materials characterized by a constant water absorption coefficient (A-coefficient). Initial period varies from ½ to 4 minutes. On the other hand, materials with a multiple pore-system such as an Aerated Autoclaved Concrete (AAC) may display a systematically varying A-coefficient. Authors propose a test procedure limited to 1-hour duration that can be used to derive a practical and reproducible value of A-coefficient.
Moisture diffusivity is a transport property that is frequently used in the hygrothermal analysis of building envelope components. This property is dependent on the local moisture content. The experiments that lead to the detailed information on the dependence of diffusivity on moisture content are often very sophisticated. However, two recent exercises, as a part of the activities of an International Energy Agency Annex, have shown that a correct estimate of the magnitude of the moisture diffusivity can provide useful information with regard to its application in hygrothermal analysis. This technical note presents results from a simple moisture absorption measurement that led to a good estimate of the moisture diffusivity of building materials. Results from measurements on a sample of spruce are presented.
It is well recognised that the accuracy of numerical solutions for coupled heat and moisture transport problems are highly dependent upon the space discretization regime adopted. While a range of possible space discretization methods are outlined in the literature, most of the commonly available simulation models for heat and moisture transfer through building constructions adopt the oneway expansion method. As part of the process of developing a new simulation model based on the Control Volume technique, the Authors have conducted a range of computer simulations to study the influence of space discretization on modelling results. Comparisons between different space discretization methods are presented which show that the two-way expansion method generally produces the best solution. This method has now been adopted by the Authors and has the advantage of avoiding the need to use extremely fine grids even when modelling complex building structures.
The purpose of this article is to analyze the effects of thermal mass on heating and cooling energy in Nordic climate and for modern, well-insulated Nordic buildings. The effect of thermal mass is analyzed by calculations made by seven researchers and by seven different calculation programs. Six of these programs are simulation programs (Consolis Energy, IDA-ICE, SciaQPro, TASE, VIP, VTT House model) and one monthly energy balance method (maxit energy) based on the standard EN 832, which is the predecessor of ISO DIS 13790. It is purpose to evaluate the reliability of the monthly energy calculation method and especially its gain utilization factor compared with the simulation programs. In addition some sensitivity analysis concerning e.g., the effects of the size and the orientation of windows and the weather data on the energy consumption are made.The results show that the simplified standard methods of EN 832 and of ISO DIS 13790 generally give accurate results in calculating the annual heating energy, e.g., in the context of energy design and energy certification. However, the gain utilization factor of these standards is too low for very light buildings having no massive surfaces resulting in a too high energy consumption. The study shows, that the differences in input data cause often greater differences in calculation results than the differences between various calculation and simulation methods.
Experiments were carried out to study the moisture transport across bonded or natural contact interface between autoclaved aerated concrete (AAC) and mortar. Bonded contact, in the present study, refers to the contact between two building materials involving penetration of pore structure with a bonding agent, while natural contact refers to the good physical contact between two building materials without penetration of pore structure. The moisture content profiles were measured using gamma ray spectrometer. The experimental results showed that, for both types of contact, the assumption of imperfect hydraulic contact is more appropriate than the widely used assumption, perfect hydraulic contact. Furthermore, the latter assumption may result in significant error in predicting moisture transport. The mismatching resistance was assumed in the study to explain the impact of imperfect hydraulic contact on the moisture transport. In addition, a numerical model was developed to calculate the moisture transport in multilayered materials and was applied to estimate either the mismatching resistance of the interface or the resistance of air films. For a specimen without an interface, the agreement between model prediction and experimental results was good. It was found that mismatching resistance of the interface varied with moisture content, the type of source material, and the interface with the sink material. This study indicates that the bonded interface can be approximately treated as the natural contact interface, while the presence of an air gap between AAC and AAC could significantly increase the resistance to moisture transport from one material to another.
Behavioural, physiological and psychological adaptive processes are presumed reasons for the discrepancies between predicted mean vote and observed comfort votes during field studies. However, few are known about the individual portions of these processes. An experimental design was developed, which aims at identifying those portions and is meant for climate chambers with operable windows facing the exterior. This article looks in detail at behavioural and physiological reactions together with their effect on the perceived level of comfort. By means of multivariate regression analyses, these reactions are analysed in order to assess differences due to variations in indoor/outdoor conditions as well as the number of interactive opportunities. One of the results shows that the restriction to keep the window closed is counterbalanced by an increased amount of physiological reactions, such as an increased level of skin temperature, together with an increase of still permitted actions such as drinking. The results highlight the importance of detailed insights into single aspect of adaptive processes for a better understanding of the phenomenon called ‘adaptive comfort’. Such approach is novel and important because a detailed knowledge and quantification of the occupant’s comfort perception in naturally ventilated buildings permits a planning with less uncertainty.
The relationship between the content of boron- containing additives in loose fill cellulose fiber insulation and various performance characteristics was studied. The relative tox icity of the off-gases appeared to decrease with increasing additive content, but the change was not significant at the lower additive levels. The yield of carbon monoxide tended to decrease with increasing additive. The weight of residue generally increased with increasing additive, but the difference between the weight of ini tial additive and the weight of residue varied with the additive content and with the boron compound.
Insulating house basements is becoming a popular method of reducing space heating energy consumption and improving the basement environment. With a reduced heat flow to the surrounding soil, the soil temperatures are lowered and the depth of the frost penetration increases. Insulation strategies must be considered carefully, otherwise foundations bearing on soils that experience volume changes upon freezing can be shifted and building damage may occur.
This study reports on frost penetration measurements adjacent to nine dif ferent house basement configurations. The maximum depth of frost penetra tion against the exterior wall and 1.5 m (5 ft.) from the wall are reported for a number of winters with a range of freezing indices from 1249°C days to 2409°C days (2248°F days to 4336°F days).
Initial observations show that only shallow, highly insulated basements with both wall and floor insulation have frost depths extending below the footings.
Methods for predicting frost penetrations are necessary when foundations are placed on frost susceptible soils if problems with frost heave are to be avoided. Graphical methods exist for predicting frost penetration for unheated foundations, however, design information for heated foundations is very limited Insulation levels on heated foundations will affect the heat loss to the surrounding soil and hence the depth of frost penetration.
The paper presents long term measured frost penetration and soil conductivity data for four typical heated residential foundations. Graphical relationships (modified design curves) between frost depths and freezing indices are presented and compared with open field (unheated) conditions.
The storage of solar thermal energy has been a subject of extensive study for many years. Various storage concepts have been extensively investigated. However, little research has been done on energy storage in the heat-of- adsorption of chemical compounds. Zeolite is, perhaps, the only substance that has been studied for its heat-of- adsorption properties (1).
A recent proposal utilizes the hygroscopic properties of sodium sulfide for thermal storage (2). Sodium sulfide has a storage capacity of 3600 kJ per kilogram. The system is economically desirable as sodium sulfide costs a mere $0.27 per kilogram (3).
Experimental research has been continuing for a year on the feasibility of the system. The performance of the model has been reasonably close to the expected level. It is believed that further work can raise the storage temperatures to levels suitable for space heating and other low temperature ap plications. This system has two problems: 1) the salt has to be under vacuum, 2) the chemical odor in the vacuum pump exhaust.
A new conceptual design has been developed that eliminates the problem of odor and the need for a vacuum pump.
Thermal insulation with thermal resistivities of at least 20 (h ft ² F/ Btu in.) have been shown to have the potential for significant energy conservation if employed in residential and commercial refrigerator/freezers Many materials and systems have been proposed which may be incorporated into refrigerator/freezers to achieve this potential.
The current state of the art for advanced evacuated insulations which may achieve resistivities of 20 was established by reviewing data on many materials available in the open literature on the dependence of the thermal performance on internal pressure. The costs for the powdered, fiber, foam and multilayer materials were then obtained from the manufacturer of the products Possible candidate materials for m- clusion into refrigerator/freezers are described and ranked based upon their thermal properties and costs.
Several materials were found that may be used to make super-insulation panels with material costs of less than $1.00 per board foot, if a plastic laminate is used for the container required to maintain the necessary vacuum. Materials falling in this category included. Beverly silica dust, open-cell polyurethane foam, fine perlite, 2.7 lb/ft ³ fiberglass and 3.6 lb/ft ³ fiberglass opacified with vapor-deposited alu minum, precipitated silica, and mixtures of precipitated silica and fly ash. Mate rial costs approaching $3.00 per board foot will result if metallic contamment is required.
New plastic foam insulation manufacturers or products encounter the problem that long age thermal performance data cannot be available, such as 5 years old. A method for estimating long-term thermal performance of extruded polystyrene foams based on computer curve fitting against a menu of classic techmcal equations is presented and compared with actual measurements at 5 years after insu lation manufacture. The effect of closed cell content, deviation of the foam from ideal uniformity, and foam density is discussed. The method permits estimation of long age thermal performance using relatively short age measurements without detailed and accurate knowledge of gas permeabilities, foam cell morphology, and deviations from ideal foam uniformity.
Trichlorofluoromethane, CFC-11, has been the predommant blow ing agent used in spray formulations for polyurethane systems. The low thermal con ductivity of this gas has provided polyurethane foam with its excellent msulation properties. However, due to environmental concerns over depletion of ozone in the upper atmosphere, regulations have been proposed limiting the production of CFC's in 1989, with further reductions in the 1990's. This limited supply situation will re quire a great deal of reformulation and testing by suppliers of polyurethane systems as they seek alternative blowing agents. This paper provides data on the performance of two hydrochlorofluorocarbons, HCFC-123 and HCFC-141b, which are currently being promoted as alternatives to CFC-11. The alternate materials differ from CFC- 11 in molecular weight, boiling point, latent heat of vaporization, flammability and thermal conductivity. Therefore, formulations must be modified to determine the total blowing agent required for foam density, catalyst levels required to achieve the proper reactivity and flame retardant loading needed to meet flammabihty require ments. In addition, the use of mcreased water levels, which reduces the total quantity of CFC required is discussed. The use of increased water levels will be required for the following two reasons. First, although using increased water levels has its limita tions, it is the most viable alternate method of blowing available for the short term since alternate materials are not currently in large scale production. Second, even when the alternative materials are readily available, the relatively high costs for these materials will certainly motivate the formulator to mimmize usage and therefore maximize the formulation economics. This paper presents data on the required quan tity of various blowing agent combinations, formulation modifications required, the physical properties and flammability test performance in sprayfoam applications.
An experimental procedure for the determination of temperature dependence of thermal conductivity of foam insulations blown with condensable gases is presented. The procedure is used to investigate the effect of the blowing agent on thermal conductivty of a polyurethane system blown with CFC-11 or HCFC-123, at various stages of its aging. A method to calculate the partial pressure of the blowing agent in the cell gas mixture of the test specimens, from the data on thermal conductivity, is also presented. Ce document décrit une technique expérimentale permettant de déterminer l'influence de la température sur la conductivité thermique des isolants en mousse formés par soufflage au moyen de gaz condensables. Cette technique sert à étudier l'effet de l'agent porogène sur la conductivité thermique d'un système polyuréthane formé par soufflage à l'aide de CFC-11 ou de HCFC-123, à divers stades de son vieillissement. On présente aussi une méthode permettant de calculer, à partir des données concernant la conductivité thermique, la pression partielle de l'agent porogène dans le mélange gazeux des échantillons. RES
Trichlorofluoromethane, CFC-11, is the predominant blowing agent used for rigid PUR and PUR/PIR insulation foams. The low thermal conductivity of CFC-11 provides these products with excellent insulation properties. But, it is now known that future supplies of CFC-11 may be limited and possibly eliminated as a consequence of international regulation. New, hydro-chloro-fluorocarbons (HCFCs) are under development and evaluation, with HCFC-141b and HCFC-123 emerging as the front runners to replace CFC-11. However, neither product is ex pected to be commercially available for several years. In the meantime, it is expected that regulation, in combmation with industry growth, will cause a real shortage of CFC blowing agent available for foam blowing.
Water blowing of polyurethane foams has been used to a limited extent for a num ber of applications. Therefore, it was concluded that increasing the level of water blowing in PUR and PUR/PIR foams offered the most promising short term solution to extending future supplies of CFC-11. This paper discusses the use of water blow ing for a number of rigid foam applications including appliances and lamination boardstock. Information obtained from both laboratory and commercial production experience is presented. It is shown how careful optimization of all formulating ele ments involved can, in some cases, result in no loss in the foam insulation efficiency even with up to 40% reduction of CFC-11 usage.
A non-destructive technique, involving specimen encapsulation and determination of the dependence of thermal resistance on temperature, to measure the blowing agent pressure in cellular plastic insulation was recently presented. This technique was applied to a polyurethane foam manufactured with different blowing agents and the results were compared with those obtained from model calculations. The results indicate that the long-term solubility of the gas in the polymer matrix may differ from that determined from short-term experiments. The paper presents results for HCFC-123 and HCFC-141b as well as CFC-11 and discusses their implication for long-term thermal resistance of polyurethane foams.
NA test methodology that uses thermal resistance-time curves determined on thin slices of the foam and the scaling technique to relate aging time to the specimen thickness, was applied to evaluate long-term thermal performance of six polyurethane foams manufactured with the same polymer but different blowing agents. The blowing agents employed were: CFC-11 with 0, 0.5, 1.0 or 1.5% water and HCFC-123 or HCFC-14 lb. Except for foams manufactured with CFC-11 and 1.0% or 1.5% of water, for which material inhomogeneity was higher than can be tolerated by the proposed test methodology, polyurethane foams manufactured with CFC-11 and 0.5% water, HCFC-123 and HCFC-14 lb showed long-term thermal performance similar to that of CFC-11 blown materials. Afin d'évaluer la performance thermique à long terme de six mousses de polyuréthane fabriquées avec le même polymère mais des agents de glonflage différents, on s'est servi d'une méthodologie d'essais utilisant des courbes résistance thermique-temps établies à partir de minces tranches de mousse, ainsi que la technique de mise à échelle visant à déterminer le temps de vieillissement en fonction de l'épaisseur de l'échantillon. Les agents de gonflage qui ont été employés sont : CFC-11 avec 0, 0,5, 1,0 ou 1,5 % d'eau et HCFC-123 ou HCFC-141b. Sauf dans le cas des mousses fabriqué es avec CFC-11 et 1,0 ou 1,5 % d'eau, pour lesquelles le manque d'homogénéité du matériau était plus grand que ne peut le tolérer la méthodologie d'essais proposée, les mousses de polyuréthane fabriquées avec CFC-11 et 0,5 % d' eau, HCFC-123 ou HCFC-141b ont affiché une performance thermique à long terme semblable à celle des matériaux gonflé s au CFC-11. RES
One of the techniques used to determine aging of gas-filled cellular plastics (GFCP) is to correlate the thermal resistance of thin material layers with that of full thickness boards. Either models of aging or scaling factors may be used for this purpose. This paper discusses the concept of scaling factors relating aging of thin and thick layers of GFCP, and points out their limitations. Une des techniques utilisées pour déterminer le vieillissement des plastiques à alvéoles remplies de gaz (PARG) consiste à établir une corrélation entre la résistance thermique de couches minces de ce matériau et celle de panneaux pleine épaisseur. On peut utiliser à cette fin les modèles de vieillissement ou la méthode des coefficients de changement d'échelle. L'auteur étudie ici cette dernière en comparant le vieillissement de couches minces et celui de couches épaisses de PARG, et il souligne ses limites. RES
By employing the fuzzy control theory and dynamic matrix control method, the controllers for temperature control of a room cooled by a displacement ventilation system are developed. The fluid flow and heat transfer inside the room are calculated by solving the Reynolds-averaged Navier–Stokes equations, including the effects of buoyancy in conjunction with a two-equation realizable k–ε turbulence model. Thus, the physical environment is represented by a nonlinear system of partial differential equations. The system also has a large time delay because of the slowness of the heat exchange. Additionally, the temperature of the exterior wall of the room first increases and then decreases with time during a 24-h period, which acts as a strong disturbance in changing the temperature of the room. The goal of this article is to develop controllers that will maintain the temperature in the room within the specified upper and lower bounds by deploying the displacement ventilation system. In order to solve this temperature control problem, we develop a special fuzzy control method. At the same time, we analyze the peak value of the error and employ the dynamic matrix control method to replace the fuzzy control method with success. The results show that the fuzzy controller is effective in saving energy, and the dynamic matrix control method can contain the error within the specified bounds in the worst situation (when the temperature of the exterior wall is highest). These kinds of fuzzy control and dynamic matrix control methods can also be employed for other heating, ventilating, and air-conditioning systems such as overhead variable air volume system and radiant cooling hydronic system.
Simplified ventilation system designs suitable for houses that do not have the ducted air delivery system of forced-air heating are examined. Five ventilation systems were considered, four were exhaust-only systems and one was a balanced system. The single tracer gas technique used seemed to be an effective method for determining the amount of fresh air supplied to the rooms in a house. However, it tends to underestimate the ventilation rate somewhat in rooms where the majority of inflow is from other rooms in the house. The multiple gas technique, while unable to quantitatively identify all the interzonal flow rates among all the rooms, was useful to complement the single tracer gas measurements of fresh air supply rates with measurements of the total air supply rates to the master bedroom as an illustrative example.
This note describes a test method for determination of air flow resistance of exterior membranes and sheathings. The test specimen is placed between two chambers with different air pressures and the volumetric air flow rate through it at a steady state is determined. The relevant experimental quantities can presently be measured with precision better than 0.5% and with an accuracy of 2 to 3%, using commercial instruments. However, the instrumental precision does not mean much, due to the uncertainty introduced by material variability normally occurring in commerical products. This aspect of the test method is studied and a practical test procedure is suggested. Ce document fait état d'une méthode d'essai en vue de déterminer la résistance à l'écoulement de l'air des membranes et parements extérieurs. Il s'agit d'installer un échantillon d'essai entre deux chambres dont les pressions de l'air sont différentes, puis de déterminer le coefficient d'écoulement volumétrique de l'air dans des conditions stabilisées. Il est possible de mesurer les quantités expérimentales pertinentes au moyen d'instruments commerciaux et avec un degré de précision inférieure à 0,5 % et une exactitude de 2 à 3 %. La précision des instruments n'est toutefois pas déterminante compte tenu de l'incertitude créée par la variabilité matérielle de la plupart des instruments commerciaux. Cet aspect de la méthode d'essai est à l'étude ainsi qu'une méthode d'essai pratique. RES
The standardised Glaser method for calculation, prediction and evaluation of moisture performance is considered as rarely applicable. The present state of knowledge, analytical as well as experimental, concerning heat, air and moisture demands updating of standards. This paper presents five numerical benchmark cases for the quality assessment of simulation models for one-dimensional heat, air and moisture (HAM) transfer. In one case, the analytical solution is known and excellent agreement between several solutions from different universities and institutes is obtained. In the remaining four cases, consensus solutions have been found, with good agreement between different HAM models. The work presented here is an outcome of the EU-initiated project for standardisation of HAM calculation methods (HAMSTAD WP2).
The aim of this study was to collect long-term in-service energy efficiency data from older-generation energy-efficient houses built in Canada in the past decades. Six houses with highly insulated building envelope assemblies built (or retrofitted) from 1979 to 1992 in the Saskatoon area were inspected during March 2012. As typical energy-efficient houses for this area, all were built with double 2 × 4 stud walls with the gap between walls ranging from 4 to about 12 in and with nominal wall insulation varying from RSI* 6.34 (R* 36) to RSI 10.57 (R 60). The roof insulation ranged from RSI 10.57 (R 60) to RSI 14.09 (R 80). The below-grade walls were also well insulated, and these were mainly permanent wood foundations. Polyethylene was used as a combined air barrier and vapour barrier for the building envelopes. The major results included the following: the airtightness values based on blower-door tests ranged from 0.78 to 2.55 air changes per hour at 50 Pa measured under normal operation conditions, with four houses below 1.50 air changes per hour at 50 Pa after 20–30 years. The No. 2 house had an original airtightness of 0.29 air changes per hour at 50 Pa and 0.22 air changes per hour when the windows were sealed with masking tape after the energy retrofit in 1982. The airtightness was measured to be 1.23 air changes per hour at 50 Pa in this survey after the owner installed new windows without properly sealing the interior air barrier. The No. 4 house had an airtightness of 0.78 air changes per hour, while the original airtightness test was 0.47 air changes per hour when the house was built over 20 years ago. All the six houses had EnerGuide Rating System of over 80, and one had a remarkable EnerGuide Rating System of 87. Windows and ventilation air were identified to be the largest heat loss components, followed by basement and exterior walls.
By measuring the pressure decline in a pressurized air volume from which air is leaking it is possible to determine the air leakage rate as a function of the pressure difference. The leakage rate is proportional to the time derivative of the pressure. The formula, which is quite simple, accounts for temperature change of the air and volume change of the chamber. The derivation of the equation relating air leakage to pressure drop is described. Initial tests of the method have been performed and the derived equation shows good agreement with air leakage rates obtained by theoretical as well as standard steady-state methods.
Occupants of low-humidity environments often complain of a sensation of dryness. According to the results of a questionnaire administered to 1000 Japanese office workers, 70% of that population experiences dryness during dry seasons. It is therefore important to clarify the environmental conditions that cause discomfort due to dryness and control the indoor environmental conditions to avoid such discomfort. For the purpose, this study aims at creating a numerical model to predict the sensation of dryness under certain environmental conditions. Since one of the causes of dryness would be the high evaporation rates from the body part where dryness is perceived, the modeling of moisture evaporation from the surface of skin, eyes, and airway was studied in this article, using the thermal model of human body. At the same time, the evaporation rates from the skin surface, eyes, and airway of a human were calculated for various air temperatures and humidity levels. It was shown quantitatively from the calculated results that the air temperature as well as the vapor pressure influences the evaporation rate because the air temperature thermally influences the temperature of the surface where evaporation occurs (skin, eyes, and throat).
Although vacuum insulation panels (VIPs) are thermal insulators with very low center-of-panel thermal conductivity, their effective thermal conductivity is raised significantly due to large edge heat fluxes caused by a continuously enveloping high barrier laminate, especially if metal based foils are applied. This study therefore presents and validates two analytical approximating models for calculating this thermal edge effect for thin high barrier laminates around VIPs. A comparison of these models with numerical simulations shows that they can be applied with an inaccuracy of <5% for idealized barrier laminates, considering the limitations specified. These models also demonstrate that the linear thermal transmittance, representing this edge effect, amongst others depends on envelope thickness and thermal conductivity, panel thickness, and center-of-panel thermal conductivity. Moreover, this study shows that these models are able to estimate the linear thermal transmittance resulting from more realistic VIPs with seams near their edges, as well. For these realistic panels, deviations between numerical data and prediction model maximally amount to about 9%. Using the presented models then, enables VIP designers, architects, and building engineers to estimate the overall thermal performance of a VIP.
In this paper, a model of the liquid moisture movement in clothing under gravity is developed and applied, based on a diffusion model. Firstly, the moisture diffusivity is determined from the investigation of the moisture absorption process in the horizontal direction where gravity has no influence on the moisture movement. Secondly with the use of the moisture diffusivity thus determined, a moisture absorption process in the upward direction against gravity is investigated. The validity of the parameter related to the gravity effect is examined by comparing the results of numerical calculations with the experimental results obtained from the gamma-ray method. Since the two agree generally well, the parameters viz. liquid moisture diffusivity and sorption isotherm derived here for a sample of broadcloth are considered reliable. Dans le cadre de ce document, un modèle du mouvement de gravité de l'humidité liquide dans les vêtements est mis au point et appliqué, sur la base d'un modèle de dispersion. En premier lieu, le coefficient de diffusion de l'humidité est déterminé à partir de l'investigation du processus d'absorption de l'humidité dans la direction horizontale, où la gravité n?exerce aucune influence sur le mouvement de l'humidité. En second lieu, l'usage du coefficient de diffusion de l'humidité étant ainsi déterminé, un processus d'absorption de l'humidité dans la direction verticale, soit contre la force de gravité, fait l'objet également d'une investigation. On examine la validité du paramètre relié à l'effet gravitationnel en comparant les résultats de calculs numériques aux résultats expérimentaux obtenus par la méthode au rayon gamma. Étant donné que les résultats des premiers concordent généralement bien avec ceux de la seconde, on estime fiables les paramètres, notamment le coefficient de diffusion de l'humidité à l'état liquide et l'isotherme de sorption qui est dérivé ici pour un échantillon de drap. RES
Glass fiber insulation is one of the most commonly used building materials in residential wall cavities. In the normal conditions under which buildings operate, the moisture content in this insulation may locally vary from that of a very dry to a fully saturated state. This gives rise to many mechanisms for moisture transport in the insulation. This article looks at all the possible mechanisms through which moisture is transported. This is done through two series of experiments and detailed numerical analysis. The experiments include investigations on water vapour transport in the presence of thermal gradients and drying of fully saturated specimens through evaporation. Physical quantities measured include history of heat flux, boundary temperatures and relative humidities and transient moisture distributions. The simultaneous heat and moisture transport processes are mathematically described through a pair of conservation equations. In a finite difference method, these equations are used for detailed numerical analysis of the processes. The numerical analysis makes use of the experimental data to derive consistent values for a set of moisture transport properties, representative of a sample of medium density glass fiber insulation. The properties include thermal conductivity as a function of moisture content, vapour permeability as a function of temperature, heat capacity and hydraulic conductivity as functions of moisture content and sorption isotherm. A sensivity analysis and an independent experiment on the drying of a randomly wet specimen support the results obtained from the numerical analysis. RES
Thin specimens of cellular plastic insulations are used in thermal resistance and gas diffusion property measurements. It is known that several cells on the surfaces of the test specimens are destroyed during specimen preparation. Hence the effective thickness of the test specimen differs from the geometrical thickness and proper corrections are to be made for the thickness of the destroyed surface layers before other properties are calculated. This note presents an apparatus, its operating principles and an experimental procedure to determine the thickness of destroyed surface layers of cellular plastic insulation test specimens.
A series of calibration measurements was done on a 600 mm × 600 mm heat flow meter apparatus. Several specimens of medium density glass fiber in sulation and expanded polystyrene insulation were used as transfer standards. The thickness of these transfer standards varied from 25 to 160 mm. The mean tempera ture varied from 0 to 40°C and the temperature difference across the insulation spec imens varied from 10 to 40 K. Measurements included cases in which the ambient temperature of the test assembly was either maintained within 1 K of the mean tem perature, or those with only edge insulation, and an enclosure for the whole test assembly in order to reduce the edge heat losses. A total of 91 sets of measurements were made. Each set of measurements included two sub-sets, one for the warmer(hot) plate and the other for the colder(cold) plate and each sub-set included a heat flow transducer output and the temperatures on either side of the transducer assembly. For 90 out of the 91 sets of measurements, the steady state heat flux across the specimen was correlated, with a standard deviation of 2%, to a simple linear rela tion between the average transducer output and the average of the surface tempera tures of the two transducer assemblies.
This paper describes the procedure, results, and error analysis from a study which characterizes a product lot of low-density, glass-fiber insulation material in terms of apparent thermal conductivity. The uncertainty of the measured values for each of the 75 specimens is estimated to be ± 1.4 percent. The data were taken at a mean temperature of 24°C (75°F), and the specimen thickness was 25.4 mm (1 in.). It is recommended that this lot be made available for distribution as a Standard Reference Material from the Office of Standard Reference Materials of the National Bureau of Standards.
An unguarded longitudinal heat flow apparatus for measuring the apparent thermal conductivity (λ a) of insulations was tested with mean specimen temper atures from 300 to 330°K on samples up to 0.91 m wide, 1.52 m long, and 0.15 m thick. Heat flow is provided by a horizontal electrically heated Nichrome screen that is sandwiched between test samples that are bounded by tempera ture controlled copper plates and 9 cm of mineral fiber insulation. A deter minate error analysis shows λ a measurement uncertainty to be less than ±1.7% for insulating materials as thin as 3 cm. Three-dimensional thermal modeling indicates negligible error in λ a due to edge loss for insulations up to 7.62 cm thick when the temperature difference across the sample is measured at the screen center. System repeatability and reproducibility were determined to be ±0.2%.
This paper deals with the thermal characterization of fiberglass insu lation used in baking oven applications. The apparent thermal conductivities of fiber glass bats were measured with a commercially available guarded hot plate k-tester as a function of density, thickness, hot and cold surface emissivities and mean tempera ture levels applicable to range operation and self cleaning conditions. An axisym metnc conduction analysis was performed to estimate the k-tester accuracy, and a few calibration measurements were executed with a fiberglass mat provided by the k-tester manufacturer. The apparent thermal conductivities, measured within the specific ranges of the parameters listed above, were correlated with a model which in cludes the gas and solid conduction, as well as radiation transport.
This article presents results for the average convective moisture transfer coefficients of several porous building material samples exposed to airflow. The experimental measurements explore the effect of the various air velocities, air temperatures and local positions on the average convective moisture transfer coefficients. Selected building materials were soaked in distilled water at least 2 weeks before the measurements. A thin building specimen with moisture content close to the saturation point was mounted in level with the bottom wind tunnel surface. A stable airflow regime was measured over the thin samples placed in the specimen holder. Water from the sample holder was absorbed from the bottom side of the building materials and evaporated from the upper side of the specimen during the airflow exposure. Two different membranes were fixed over the water cup as reference materials for comparison. The measurements were carried out at a relative humidity of 50% ± 3%, air temperatures of 23.6°C ± 0.5°C, 26.5°C ± 0.5°C and 30.0°C ± 0.5°C, and air velocities of 1.1, 3.0 and 5.5 m/s. The experimental data show that the convective moisture transfer coefficient is a function of velocity, temperature difference between the ambient air and material surface, local position as well as of the material type. The experimental results from water surfaces were compared to the expressions for the convective moisture transfer coefficients from the literature.
Predicted heat losses through building walls are typically based on measurements of the wall system clear wall area using test methods such as ASTM C 236 or are calculated by one of the procedures recommended in the ASHRAE Handbook of Fundamentals that often are carried out for the clear wall area exclu sively. In this paper, the phrase "clear wall area" is defined as the part of the wall system that is free of thermal anomalies due to building envelope subsystems, or thermally unaffected by intersections with other surfaces of the building envelope. These experiments or calculations normally do not include the effects of building en velope subsystems such as corners, window and door openings, and structural joints with roofs, floors, ceilings, and other walls. These details represent completely different constructions; it is apparent that the thermal properties measured or calculated for the clear wall area may not adequately represent the total wall system thermal performance. Factors that would impact the ability of today's standard prac tice to accurately predict the total wall system thermal performance are the accuracy of the calculation methods, the amount of the total wall area that is clear wall, and the quantity and thermal performance of the various wall system details.
Based on 3-D finite difference computer modelling, the thermal performance of several typical wall systems including various system details have been analyzed, and the overall wall system thermal performance for a typical single-story ranch house has been determined. These data are compared to typical experimental and analytical techniques to ascertain their precision in predicting the overall wall system perfor mance.
Sustainable energy system design offers credible and innovative strategies to overcome environmental energy crises. Solar walls offer feasible technique for the exploitation of directional flow of heat in buildings. This article reviewed state-of-the-art concepts, applications and significance of solar walls for energy savings in buildings. Detailed operational framework of various solar-wall configurations, technology and efficiency as building component was discussed. Need for this sustainable energy design in buildings and constraints associated with their realisation were reported to aid proposed future research work.
Cell size and shape and closed or open configurations were found to greatly influence the compressive strength, density, water absorption, and insulative properties of two sintered fly ash/acid materials. In one case, finely ground fly ash, mixed with a water/phosphoric acid solution and alumina, is sintered to produce an open microstructure consisting of a large number of small pores dispersed relatively uniformly throughout the material. The material has a density of 0.8 gm/cm3 (800 kg/m3), very low bending strength, a compressive strength of under 800 psi (5000 KPa), and thermal conductivity of .17 W/mK. In the second case, the material had a lower density of 0.52 gm/cm3 (520 kg/m3) a higher compressive strength of 800-1000 psi (5000-7000 KPa), and thermal conductivity of .11 W/mK. This con sisted of larger closed spherical cells mixed within the other material. In a third case, theoretical studies lead us to predict values of density (696 kg/m3), improved com pressive strength (6500-9100 KPa), thermal conductivity (.099 W/mK), and less water absorption for a material consisting of closed cell/close packing structure ob tained by a different sintering process, one using a vacuum to expand the spheres to close pack them. These materials are for use as exterior applied insulation on build ings.
In this article a commercial computational fluid dynamic program is used to study the effect of the horizontal aspect ratio on heat flow through cavities with a high vertical aspect ratio (cavities typically found in vertical window frames with internal cavities). The cavities studied have two opposite isothermal vertical walls separated by four adiabatic walls. The vertical aspect ratios are 20, 40, and 80 and the horizontal aspect ratios range from 0.2 to 5. Simulations of two-dimensional cavities are also included. The simulations show that three-dimensional cavities with a horizontal aspect ratio larger than five can be considered as being two-dimensional cavities to within 4% when considering heat transfer rates. Nusselt number correlations for the different horizontal aspect ratios are included. Complex multicellular flow is presented for one of the three-dimensional cavities.
In wall systems, airspaces can increase thermal resistance if a reflective material such as foil with low emissivity is installed in a furred-airspace assembly. In this article, the present model, hygIRC-C, was used to investigate the steady-state thermal resistance of wall assemblies that incorporate foil adhered to expanded polystyrene foam in a furred assembly. To investigate the effect of the furring orientation, the furring was installed horizontally and vertically and compared to walls with no furring. For wall with vertical furring, the three-dimensional version of the present model was used to capture the three-dimensional effect of the thermal bridges. Because the foil emissivity can be affected by dust accumulation and/or water vapor condensation on the foil surface, consideration was given to investigate the effect of both varying foil emissivity and outdoor temperature on the thermal performance of the various wall specimens. The results showed that the thermal resistance (R-value) of the reference wall (no furring) is greater than the wall specimens with furring. Also, the results showed that the contribution of the furred-airspace assembly to the R-value of wall specimen with vertical furring is higher than that for wall specimen with horizontal furring.