Fitsum Tariku

Heat, Air, and Moisture Transport Properties of Several North American Bricks and Mortar Mixes

Hygrothermal models are emerging as practical building design tools. These models require a set of reliable inputs to provide results that are meaningful to the designers. One of these inputs is the set of heat, air and moisture transport properties of materials. For any given class of building materials the properties may vary within a broad range. This paper reports the porosity, density, matrix density, thermal conductivity, equilibrium moisture content, water vapor permeability, water absorption coefficient, liquid diffusivity and air permeability of six types of bricks and four mortar mixes that are commonly used in North America. The experimental and analytical procedures follow either international standards or well-established methodologies.

Application of a Whole-Building Hygrothermal model in energy, durability, and indoor humidity retrofit design

A building shall be classified as high performance building if it is energy efficient and durable and at the same time provides comfortable and healthy indoor environment for occupants. To achieve this objective, the hygrothermal performance of alternative building designs should be evaluated based on the simultaneous analysis of these three functional requirements rather than separately. In this article, a Whole-Building Hygrothermal model is used for evaluation of various retrofit design parameters that potentially enhance the overall performance of an existing residential house. The retrofit options considered in this study include changes to the reference house’s ventilation rate and operation, windows, insulation level, and various combinations of these options. Energy efficiency, building envelope and moisture management potential, indoor humidity control, and window condensation potentials are considered to be the four performance indicators in searching for a retrofit option that delivers an optimal performance. The hygrothermal simulation results indicate that changing a design parameter to improve one of the design goals may result in less optimal results in the other one or both goals, or even in some cases result in severe negative consequences.

Numerical analysis of convective heat transfer coefficient for building facades

The latest architectural trends demand an extensive use of glazed curtain walls running from building floor to ceiling. While glazing poorly controls the heat flow, it is important for viewing, daylighting, and solar design features. In order to evaluate building energy consumption accurately, knowledge of convective heat transfer coefficient (CHTC) distribution over the façade of the building is important. In this article, high-resolution numerical simulations that use three-dimensional steady Reynolds-averaged Navier–Stokes and energy equations are performed. Convective heat transfer coefficient values at the windward facade of five buildings, with rectangular floor plans, and heights of 3, 10, 15, 20–30 stories, have been produced. The influence of building height on CHTC distribution is investigated at Reynolds numbers ranging from 0.7 × 106 to 33 × 106, and a correlation equation as a function of building height and a reference wind velocity is developed. For example, as the height increases from 10.1 to 101 m in the study cases, the surface-averaged convective heat transfer coefficient on the windward façade increases by 55%. The high-resolution spatial distribution of convective heat transfer coefficient over façade of the tallest building indicates that the top-corner zone convective heat transfer coefficient values are higher by 24% and the base-center zone values are lower by 27% compared to the average CHTC value, implying the necessity for zonal treatment.

HYGROTHERMAL PERFORMANCE ASSESSMENT OF ICF WALLS WITH DIFFERENT MOISTURE CONTROL STRATEGIES AND WALL DESIGNS

ABSTRACT The initial high moisture content of concrete and the low vapor permeability of insulation layers on both sides of the concrete complicate the drying process of Insulated Concrete Forms (ICF). In order to facilitate the moisture transport and enhance the drying process, different moisture control strategies and wall designs can be implemented. The application of an air and vapor barrier is one of the most common moisture control strategies. In this paper, the impact of vapor permeance of an air and vapor barriers on the hygrothermal performance of an ICF wall in three different cold and wet climates is examined using a validated Heat-Air-Moisture transfer model. The hygrothermal performance of an ICF wall assembly with different types of barriers and locations in the wall system for several wall designs is investigated. Results indicate that a smaller thickness of insulation on the outside facilitates removing the moisture towards the outside and installing low permeance air/vapor barrier systems...

Temperature and Air Flow Patterns in Attic Roofs

Understanding temperature and airflow patterns in an attic roof helps to identify the sections of the roof where moisture damage and roofing material durability problems can be expected. In this paper, the temperature distribution and the airflow patterns inside an attic space in a climate that can be characterized with cold winter and hot summer periods are discussed. In the study, transient boundary conditions were applied, and the dynamic responses of a typical attic roof, including the flow patterns, attic air and roof sheathing temperatures, ventilation rates, and heating and cooling loads, are presented. These findings can be used to understand the airflow pattern and how it can be affected by an incoming wind speed and solar gain.

Experimental Investigation of Moisture Transfer between Concrete Foundation and Sill Plate

AbstractPrecipitation is one of the most common moisture sources on which building designers focus. Water comes from both top down and bottom up. Although foundations are sometimes constructed out of pressure-treated lumber, generally they are constructed from poured concrete. In a wet climate zone, the foundation of a house is often under continuous contact with moisture, which is mainly caused by rundown rainwater, wet soil, a high water table, or a combination of all these factors. This causes rot growth and decay of the wood-frame structure as it sits constantly on the damp foundation concrete. In this research, moisture transfer between concrete and wood is investigated under three different scenarios: a case with direct wood and concrete contact and two cases with different moisture barriers between the two materials. The moisture barrier materials considered in this study are the damp-proofing layer and sill plate gasket. The moisture transfer processes in these three cases are investigated in a fi...

Seasonal Indoor Humidity Levels of Apartment Suites in a Mild Coastal Climate

AbstractIt is essential to design and operate buildings with good indoor air quality because people spend most of their time indoors, and their productivity, comfort, and health depend on the quality of the indoor air. In addition to other indoor-air-quality parameters, the indoor humidity and temperature need to be controlled and maintained within acceptable ranges. Elevated indoor humidity creates favorable conditions for mold growth and building-envelope damage. To minimize such problems, it is important that designers have insight into the level of indoor humidity that will be expected in a building operating under a set of conditions and weather variation. In this paper, the results of monitoring the indoor temperature and humidity of four apartment suites with different occupancy levels are reported. Along with the indoor-air conditions, the local outdoor temperature and relative humidity were continuously measured for 17 months. The indoor humidities in the suites were correlated with the outdoor a...

Heat, Air and Moisture Transport Properties of Three North American Stuccos

Heat, air, and moisture transfer models that are used as practical building design tools require reliable inputs to provide meaningful results. One of these inputs is the set of heat, air, and moisture transport properties of materials. For any given class of building materials the properties may vary within a broad range. This paper reports the porosity, density, matrix density, thermal conductivity, equilibrium moisture content, water vapor permeability, water absorption coefficient, liquid diffusivity, and air permeability of regular lime stucco, regular portland cement stucco, and acrylic stucco which are commonly used in North America. The experimental and analytical procedures follow either international standards or well established methodologies.