Air Exfiltration Research Articles

Hygrothermal response of a wood-frame thick-wall assembly to rainwater wetting under future climate scenarios in Canada

Current exterior wall assembly designs for new low-rise residential buildings targeting low-energy demand in heating dominated countries include split-insulation wall and thick-wall assembly designs. Both have been shown to result in thermal efficiency gains compared to building-code minimum assemblies, however long-term hygrothermal performance can vary depending on boundary conditions and the presence of construction deficiencies. Future climate scenarios estimate many heating-dominated climates will experience a reduction in heating-degree day hours and an increase in annual rainfall. Using validated assembly performance data from a Passive House certified facility, a sensitivity analysis is performed to determine the impact of rainwater wetting, air exfiltration and insulation material properties on the hygrothermal response of a thick-wall assembly. Results show that rainwater leakage values of 0.50% and greater of the adhering rainfall on the exterior surface of the assembly results in the greatest risk for failure. The hygrothermal response of the assembly is then examined under a global temperature rise scenario of 3.5°C for five geographic locations across Canada. Results show that an increase in average annual total rainfall does not directly result in an increase in the failure rate of the assembly when a rainwater leak is present. Additional climatic factors, including outdoor air temperature, driving rain and solar radiation received will influence the hygrothermal response of the assembly and need to be considered when modelling the performance under future climate change scenarios.

Application of reference-free natural background–oriented schlieren photography for visualizing leakage sites in building walls

Air leakage in buildings can cause health and comfort concerns for occupants and can contribute to mold growth on building materials, or in extreme conditions, rot of building materials. Unwanted air leakage through the building envelope also contributes to approximately 4 quadrillion Btu (1172 TWh) of energy consumption per year in the building sector in the United States. Locating and sealing leakage sites can improve the energy efficiency, comfort, air quality, and moisture durability of the building stock. Typical methods of finding leakage sites, such as infrared imaging and smoke tracing, rely on concurrent blower door operation, which can also measure the total leakage rate of the building. Smoke tracing can be disruptive to occupants, and infrared imaging and smoke tracing cannot measure the contribution of individual leaks to prioritize sealing efforts. In this work, an optical fluid flow imaging technique, reference-free natural background–oriented schlieren imaging, was adapted to visualize air exfiltration. This is the first step in developing a method to noninvasively locate and measure exfiltration or infiltration sites so that sealing efforts can be prioritized. Experimental results of this technique are presented, demonstrating the method's applicability to visualizing exfiltration through three common building claddings in an outdoor environment. Key variables impacting the performance of this technique when applied to building leakage are also discussed.

Hygrothermal performance of highly insulated external walls subjected to indoor air exfiltration

The study comprises three laboratory tests in which typical Finnish highly insulated (HI) walls were exposed to concentrated leakages of indoor air under steady outdoor temperatures of 1–5°C. Airflows with a relative humidity of 50% and at rates of 1–3 L/min were directed close to the wooden frames inside the walls. The thermal resistance ratios between the exterior sheathing(s) and the whole wall (Γ) were 20%–22% and 1%–10% for the HI and baseline (BL) walls. The HI walls that presented Γ values of at least 20% were observed to be resistant to air exfiltration, and their durability was not affected by the addition of a gypsum sheathing outside the wooden frame or a more permeable vapor retarder. This is related to the negative linear correlation that exists between the moisture accumulation rate in wood-based material and the dew point depression (DPD) value. The developed approach, called the DPD method, shows that a significant degree of moisture accumulation does not occur even for DPD values of as low as −2°C if the exterior sheathing is vapor permeable. The airflow does not penetrate into the rigid mineral wool sheathing, which helps to avoid interstitial condensation. Regardless of thermal transmittance, the HI and BL walls with maximum Γ values of 1% were exposed to a high relative humidity and even interstitial condensation because the DPD values were often below −2°C. For these walls, the mold index analysis and visual observations confirmed the local risk for mold growth on the opposite side of the leakage point. In practice, long-term mold growth may be limited if the seasonal periods during which the outdoor temperature is 1–5°C last for a maximum of about 1 month every year.

Assessment of the Effect of Energy Saving and Heat Loss Through External Enclosure Structures with Low Resistance to Air Penetration

The features of heat and mass transfer through external enclosure structures with capillary - porous material, which are not taken into account in the norms of thermal protection of buildings, are considered. Such features more often occur in buildings with a long service life because of the increasing heat loss, caused by the violation of the terms of repair for a long time. For structures, located in the lower part of the building and having little resistance to air penetration, a calculation model is considered to determine the value of the economizer effect and the saving of thermal energy in conditions of cold air infiltration. The developed model clearly demonstrates, that for two - and twelve-story houses the saving of thermal energy, as a result of the economizer effect, is about 3% and 10% respectively. A computational model of exfiltration of warm air through similar structures, located in the upper part of the building, is proposed. An additional value of heat loss during exfiltration of the warm air from the rooms is determined, using an example of old building with a wooden floor of a cold attic and bulk insulation in the absence of layers with high resistance to air penetration. This value is 3.5 times higher, then that determined by the standard method, which does not take into account the redistribution of cold and warm air densities along the height of the building. This leads to a deterioration of the indoor climate and an increase in heat loss. By calculation, the dependence of the value of heat losses on the total thermal resistance of the attic floor and on the number of floors was established. A number of measures, aimed at improving the energy efficiency of existing residential buildings, are proposed, such as laying a vapor barrier layer and an additional layer of effective thermal insulation on top of the bulk insulation as part of the attic floor and installing a cement-sand screed for this insulation.

Modeling and analysis of heat emissions from buildings to ambient air

Heat emissions from buildings is a significant source of anthropogenic heat influencing the urban microclimate; however, they are usually oversimplified in urban climate and microclimate modeling. This study developed a bottom-up physics-based approach to calculate heat emissions from buildings to the ambient air and implemented the approach in EnergyPlus. A simple result verification was conducted by comparing the EnergyPlus simulated results against the spreadsheet calculations. Simulations covering 16 commercial building types, four climates, and two energy efficiency levels were conducted to understand and evaluate the building heat emissions and their temporal patterns as well as three major components: (1) building envelope (convective heat transfer to ambient air), (2) zones (air exfiltration and exhaust air), and (3) HVAC systems (relief air and heat rejection from condensers or cooling towers). The main findings are: (1)heat emissions are usually higher than the site energy use (about 2.5 times), and their dynamics should be considered; (2)building characteristics and their energy systems lead to differences in heat emission contributions from the three components, and their dynamics, for example, in the warehouse models, the envelope component accounts for 90.4%, while it is 12.7% for the large office models; (3) for most building typologies, the climate has a strong impact on heat emissions, for example, buildings with dominant heat emissions from the zone exhaust air and/or the HVAC reject heat, a general decrease in heat emissions in hotter climates is observed, while envelope-dominated buildings show the opposite; and (4)building technologies that reduce energy use in buildings may perform differently in reducing heat emissions. The developed heat emissions calculation method can be adopted in EnergyPlus and most other building energy modeling programs. It can provide dynamic building heat emissions as an input to urban climate computational fluid dynamics (CFD) models at a higher spatial and temporal resolution than is currently available, to improve the simulation accuracy of the urban microclimate and capture the urban heat island effect and urban overheating.

CALCULATION OF THE CONVENIENT NATURE FREQUENCY OF POWER BOILER IN MANAGER BUILDINGS IN THE CONDITIONS OF EXTERNAL AND DOMESTIC ENVIRONMENTAL CHANGES

Taking into account the development of the normative base of Ukraine regarding the assessment of energy efficiency of buildings, aimed at reducing the time intervals of calculation, it is important to calculate the level of energy efficiency taking into account the variability of environmental conditions. It should be noted that air exchange is one of the most influential components in the energy balance of the building. The article deals with the generalized method of calculating the natural component of the multiplicity of air exchange. The calculations used data file IWEC international climate typical year for the city of Kyiv. In this work the building is considered as a system and the air exchange of premises of the 8 storey building is calculated. The natural component of the multiplicity of air exchange is designed to support air permeability of the most typical characteristics of translucent structures. It is established that for modern double-glazed windows the hourly calculation of the natural component of the multiplicity of air exchange at a different location of representative premises showed that the value does not exceed 0, 25 h -1 , triple glazing in wooden twisted weaving – 0,4 h -1 , double -0,65 h -1 . It should be noted that in the first floors, the natural component of the multiplicity of air exchange has a positive value (air infiltration) on the upper floors, the negative value (air exfiltration), which must be taken into account when dynamically modeling the energy characteristics of the building. In order to maintain the normative value of the multiplicity of air exchange during the presence of people in the room, it is necessary to use mechanical ventilation additionally. In further research, it is planned to clarify the conditions of air traffic flooding taking into account the landscape, taking into account mechanical ventilation and recovery.

Evaluation of thermal properties of insulation systems in pitched roofs

The article outlines the basic requirements for pitched roof insulation systems. The analysis of the properties of thermal insulation materials used in insulation systems was conducted. It is substantiated that the thermal resistance of such structures on the surface of the roof is formed taking into account the thermal conductivity of thermal insulation, thermal conductivity of wooden rafters and heat loss through the leakiness of joints and mounting devices. An assessment was made of the effect of loads of various types on the heat-insulating layer, namely: the effect of the air flow in the ventilated gap; the movement of the vapor-air mixture in the material; condensation of water vapor and penetration of drip liquid; exfiltration of air at the joints of the plates and on the surfaces of contact with the supporting structures. The expediency of using products on the basis of unstitched polyethylene foam in the construction of pitched roofs with a wooden roof system, taking into account the advantages and features of this material, as well as taking into account the possibility of creating a seamless insulating shell, is substantiated.

Wooden beam ends in combination with interior insulation: An experimental study on the impact of convective moisture transport

The risk free applicability of interior insulation in the presence of wooden beam ends is still a point of discussion. Two phenomena enlarge the risk on wood decay when interior insulation is applied: (1) a higher moisture load in the masonry due to a reduced drying potential and (2) a lower temperature in the masonry resulting in a higher risk on condensation if exfiltration of moist indoor air occurs. This paper studies - based on a hot box-cold box experiment - the impact of convective moisture transport and this for two vapour tight and one capillary active vapour open interior insulation system applied to a masonry wall with an embedded wooden beam. A comparison is made to a non-insulated wall. No wind-driven rain is included, making a pure analysis of convective moisture transport possible. For non-sealed beam junctions, a significant increase in relative humidity due to moist indoor air reaching the colder beam surface was clearly visible. The impact of air exfiltration was most pronounced for the capillary active system and was influenced by the way of sealing the airgap between the beam end and the wall. It is recommended to avoid air exfiltration as well as air circulation near the beam end. For mineral wool, the importance of an airtight sealing was less pronounced. An overpressure was found to influence the hygrothermal conditions near the beam ends of the poorly sealed test setups. Additionally, the convective air flow near the beam ends was analysed based on the measured temperatures.

Modeling air leakage in buildings caused by the cyclic variation of the atmospheric pressure

This article considers a new type of air infiltration through building envelopes caused by the barometric pressure variation. This process is independent from wind action or stack effect. A new building–atmosphere differential equation of air exchange is established. Based on the solution of the differential equation of air exchange, we propose the notion of pressure equilibration time [Formula: see text] that characterizes the dynamic response of the building. Furthermore, experimental climatic data were processed using Fourier analysis methods in order to build an identification model based on the regular harmonics of external pressure oscillation. The barometric pressure reconstructed in its parameterized form was introduced in the differential equation of air exchange as a term that models the dynamics of the external action. The analytic solution of the differential equation of air exchange demonstrates that the indoor–outdoor pressure difference is insignificant at less than 10−3 Pa for any harmonic of the external pressure variation. At the same time, it is concluded that the airtightness of the envelope has little influence on the process, as the indoor–outdoor pressure equilibration is almost instantaneous in a continuous regime of variation. The described mechanism of air infiltration explains the alternation of infiltration and exfiltration of air in buildings. For this, a mass balance of air exchange for the specific ranges of time is performed. We prove that the barometric pressure variation has an effect that accounts for 3.19% of the total quantity of air exchanged. The advances provided by this paper constitute a useful instrument for further studies concerning the stack effect in thermal dynamic conditions. Practical application: The paper proposes a novel methodology of determining the air exchange building–environment by considering a new component of infiltration and its cyclic variation: the barometric pressure. A new mechanism of natural air infiltration is determined and modeled and it should be added to the existing ones: wind action and stack effect. A complete methodology of analysis and extraction of the cyclic processes hidden in an envelope of stochastic variations is defined and applied with the support of signal processing techniques and spectral analysis. The refinement of the mathematical instrument was able to distinguish through a deterministic approach an influence of 3.19% of the new barometric component. Furthermore, with few adaptations, the methodology constructed in this study can be applied for investigation of the stack effect by considering the cyclic variation of the atmospheric temperature. Currently, the stack effect is analyzed only for average conditions of temperature, a simplistic approach that suggests a large potential for further improvement.

Selecting and Installing Energy-Efficient Windows to Improve Dwelling Sustainability

<p>Windows play a significant role in achieving comfort in buildings by letting in natural light, solar warmth, fresh air and permitting outdoor views. On the other hand, poor quality windows can be the source of overheating or unwanted infiltration or exfiltration of air. Quality windows, therefore, influence the dwelling’s energy consumption and consequently its sustainability. Heat losses through the building envelope can occur in any of three mechanisms: conduction, convection and radiation. In all cases, windows are the “weakest link”. As such, windows represent the most important investment in the construction or renovation of any dwelling. They are also highly variable in price, appearance and performance, making their selection an ambiguous and sometimes difficult process. This paper examines a window unit’s energy performance and provides guidelines for its selection, installation and integration into the home’s design.</p>

Numerical Analysis of Elevator Piston Effect on Building Airflow for an Air-Conditioned High-Rise Building in Winter

A model of a 24-storey building (94.5m high) with air-conditioning system was developed to analyze the elevator piston effect on building airflow by dynamic mesh technique of computational fluid dynamics (CFD). The results of the pressure distribution and airflow paths show that with the upward movement of elevator cabs, due to the elevator piston effect, changes in the pressure distribution and airflow paths occur in all the building; the pressure difference across the elevator door is enlarged, which is likely to cause some security issues; but the air exfiltration rate is hardly affected.

Wind effects on atria fires

A series of unsteady atria fire calculations are performed using a finite-volume CFD program on two and three dimensional generic buildings immersed in simulated atmospheric boundary layers. The model results reveal that external winds can modify the infiltration and exfiltration of air through external doors and windows, distort thermal and smoke columns rising above test fires in the atria, cause the plumes to impact directly against atria walls, and modify the resultant filling of elevated atria spaces. In some cases aggressive fire “whirls” form, which can enhance fire strength, enclosure mixing, and exposure. Results are compared qualitatively with similar physical model experiments.

A model for freeze–thaw cycling of the South Pole Station exterior sheathing

An infrared survey [Phetteplace, G. 2006. An Infrared Survey of the South Pole Station Modernization Project, Final Project Report to National Science Foundation, US Army Cold Regions Research and Engineering Laboratory, Hanover, NH.] of the new South Pole Elevated Station revealed evidence of excessive air exfiltration in some locations. Despite the relatively low indoor humidity normal in the South Pole Station, typically less than 10% relative humidity (RH), there was concern that excessive exfiltration could result in moisture accumulation within the building walls. While the accumulation and freezing of moisture at any point in the wall section could be problematic, what was felt to be of greater concern was the potential for repeated freeze-thaw cycling near the exterior oriented strand board (OSB) sheathing due to the significant diurnal temperature cycling of the siding during the Antarctic summers. The intense solar radiation conditions on vertical surfaces at the low Antarctic summer sun angles results in very high solar fluxes, and surface temperatures can rise well above freezing even in ambient temperatures that are -20 °C or lower. Typical building energy analysis methods are not suited to analysis of this problem for a variety of reasons. Thus we constructed a finite difference heat transfer model of the wall section with a full compliment of realistic boundary conditions for the South Pole application. The base case of the planned wall section and various potential retrofits were evaluated with the model using actual weather data for six summer seasons. The results show that under the worse case summer season the base case wall section would see approximately 44 freeze-thaw cycles. That number would be reduced to only 12 with the addition of either 25 mm of extruded polystyrene foam insulation, or 19 mm of plywood and 13 mm of the same insulation. Over a 25 year period these same additions to the exterior of the building would reduce the number of freeze-thaw cycles by over a factor of six.

Improving Energy Efficiency Improves Smoke Safety and Occupant Comfort

ABSTRACT Energy efficiency, smoke safety, and occupant comfort are important building management issues. One pervasive problem connects them all: the challenge of controlling air infiltration, exfiltration, and air movement within the building. Four key factors affect building air movement: overall envelope tightness, climatic conditions, the HVAC system, and the orientation and exposure of the building. This article details the effects of controlling air movement on achieving improved energy performance, better smoke control during a fire, and benefits of improved comfort for building occupants. Energy efficiency improvements are reported using examples of actual buildings. Details are given of how increased air tightness, combined with properly designed and controlled ventilation, can improve thermal performance, reduce short-circuiting of conditioned air, and improve humidity control. A recent report by The National Institute of Science and Technology confirming the energy efficiency contribution of ai...

Experimental Evaluation of Thermal Response and Condensation Performance of Metal Curtain Walls Subjected to Air Leakage

The condensation resistance of fenestration products is typically determined in standard tests with air leakage eliminated by sealing the cracks and balancing the pressure difference across the test specimen. In reality, however, the fenestration system does experience varying pressure differentials. The infiltration and exfiltration of air can affect the temperature distribution on the fenestration system and, thus, the condensation resistance. In this paper the effect of air leakage on the condensation resistance of a large-scale metal curtain wall subjected to a pressure differential of 150 Pa is studied experimentally. By examining the temperature response profiles and the magnitudes of the temperature variations, likely air leakage paths are identified and the impact of air leakage on condensation resistance is quantified. Since the airtightness of the curtain wall tested is relatively high, the effect of air infiltration is relatively small on the average condensation resistance but is significant locally.

Zinc roofs: an evaluation based on test house measurements

In cool and cold climates, interstitial condensation in flat and low-sloped roofs is eliminated by the application of two separate measures: (1) avoiding water vapor from entering the roof from inside; (2) facilitating the evacuation of water vapor that entered by providing a ventilated air space below the roof cover. For decades, manufacturers of metallic sheeting defended the second option as the only one acceptable for metallic roofs. Concerns about costs, however, intensified the interest in new solutions such as compact roofs. The article describes a long-term test building research on compact and ventilated metallic roofs. The outcome after 4 years of testing is both logic and remarkable. Air exfiltration, if any, dominates the moisture response of the compact roofs and increases the risk of moisture attack in ventilated roofs. Also no clear correlation was found between the presence of ventilation, the severity of interstitial condensation and the degree of underside corrosion of the zinc sheeting.

An evaluation of highly insulated cold zinc roofs in a moderate humid region—part I: hygrothermal performance

In order to investigate the hygrothermal performance and durability of well-insulated cold zinc roofs, a total of four cold zinc roofs with a low U-factor [ U<0.25 W/(m 2·K)] were constructed in a test building at the KU Leuven, Belgium. This paper presents the hygrothermal performances measured in the four roofs during an exposure period of 28 months. The zinc roofs with a specific design and careful workmanship exhibited a satisfactory thermal performance. The moisture content in the wood deck generally stayed below 20% by weight. However, the moisture situation at the underside of zinc sheeting was bad in all four roofs studied. We found that the strong undercooling of the zinc sheeting was the main cause for the bad moisture situation observed. Even a combination of a low air exfiltration and a good roof cavity ventilation rate did not eliminate or reduce the condensation at the underside of zinc sheeting.

An evaluation of highly insulated cold zinc roofs in a moderate humid region—part II: corrosion behavior of zinc sheeting

In a previous paper [Zheng et al., Hygrothermal Performance, Part I; Const Building Mater, Vol. 18, Issue 1, pp. 49–59], the hygrothermal performances of four well-insulated cold zinc roofs were evaluated. This paper investigates the corrosion behavior of the zinc sheeting used in the roofs. The main corrosion products identified are Zn 5(CO 3) 2(OH) 6 and ZnO. Little corrosion occurred at the upside of the zinc sheeting. However, serious pitting corrosion developed at the underside. The maximum pit depths measured in the collected samples with an area of 0.35 m 2 were between 167 and 273 μm. The traditional measures to minimize condensation deposit, i.e. low air exfiltration and good roof cavity ventilation, clearly did not work effectively in reducing the underside corrosion of the zinc sheeting. The results show that new techniques and roofing systems should be developed and implemented.

Mapping of Air Leakage in Exterior Wall Assemblies

A full-scale wood frame test hut with nine wall specimens, typical of low-rise residential construction in the province of Quebec, was built inside an environmental chamber. This test hut was subjected to 66 days of simulated winter and 47 days of late spring climatic conditions to verify the feasibility of different methods of mapping and representing graphically air exfiltration. Through a better understanding of the movement of air through the envelope, the risks related to moisture condensation within the envelope for different wall compositions can be better ascertained. The air leakage pattern characterization methods implemented were two-dimensional grid moisture content monitoring and three-dimensional grid temperature monitoring. The moisture content and temperature data were presented in a graphic form, using isohygrons and isotherms. Temperatures without the impact of air leakage were also calculated using a three-dimensional conductive heat transfer model. The air leakage pattern characterization methods and the resulting moisture and temperature maps are presented and discussed herein.

Large-Scale Testing of Two Flat Roof Assemblies Insulated with Cellulose

A laboratory test using a large-scale environmental chamber has been carried out on two flat roof models fully insulated with cellulose fiber. These two models represent the most representative single-cavity flat roofs, built in Montreal between 1930 and 1970, being insulated as part of an energy conservation program. The insulating strategy consists of packing cellulose fiber in the cavity. The goal of the test program was to determine the risk of rotting of the wood structure and moisture accumulation in the roof assembly. The test was performed using real-scale huts that were exposed to 6 months of winter and summer conditions. Two roof assemblies were each divided into five roof cavities. The main variables were the mode of moisture transfer (diffusion only and diffusion combined with air exfiltration), type of vapor barrier, and air leakage paths. The construction of the huts and the monitoring plan are described. The results of the 6-month test program using seven simulated climatic conditions are presented. Wetting and drying curves for different parts of the assemblies as well as the levels of exposure to moisture are presented and analyzed.