Girma Bitsuamlak

Air infiltration through building envelopes: A review:

Air leakage through the building envelope into the building interiors has a considerable impact on the energy loads and consequently energy demand and energy costs of buildings. This phenomenon known as infiltration happens through various openings and venues in the building envelope varying from large openings such as doors and windows to minute cracks and crevices. In addition to impacting building energy loads, infiltration impacts indoor air quality and can result in moisture accumulation problems in the building envelope. A generalized review of infiltration that includes evaluation techniques and models, quantification, and interaction with other heat transfer phenomena is presented in this article.

Application of CFD in Modelling Wind-Induced Natural Ventilation of Buildings - A Review

Abstract This paper reviews the application of CFD for designing and parametric studies of wind-induced natural ventilation. The approaches employed in such applications of CFD are whole-domain and domain-decoupled CFD modelling. The domain-decoupled technique separately analyses the external airflow fields outside and internal flows inside a building. In the whole-domain approach, the outdoor and indoor airflow is modelled simultaneously and within the same computational domain. The review showed that the whole-domain approach has been more popular than the domain-decoupled approach, and with efficient computing algorithms, grid generation techniques and advances in hardware technology, can overcome the computational overhead it incurs during application. CFD has also allowed the concept of stream tube and the local dynamic similarity model (LDSM) to be used in practice. These concepts have helped in the fundamental understanding of wind-driven natural ventilation and in distinguishing flow through large openings from that of “cracks”. An important and practical approach for natural ventilation design and analysis is the integration of CFD with other simulation programs such as Building Simulation (BS) and Geographic Information Systems (GIS). Apparently, CFD is increasing its importance in sustainable building design and it is expected that more complex naturally ventilated buildings will be designed and analysed as CFD techniques continue to improve.

Wind-Induced Pressures on Solar Panels Mounted on Residential Homes

AbstractThis paper presents wind load investigations on solar panel modules mounted on low-rise buildings with gable roofs that have two distinct slopes. Wind loads on the solar panels mounted on several zones of the roofs were systematically investigated in a boundary-layer wind tunnel for different wind directions. The results from the wind-tunnel investigation are compared with ASCE provisions for residential bare roofs. The comparison shows a good agreement with the ASCE standard provisions for the main force resisting system. Nevertheless, the cladding loads on individual modules may be lower or higher than those on the corresponding area of a bare roof (depending on their location and array configuration and the roof’s slope). Avoiding the roof critical zones (zones 3 and 2) is recommended to avoid high net minimum pressures acting on the solar panel modules. Solar panels mounted in zone 1 are locally subjected to higher suction at their outer edges. This is most likely attributed to the effect of a...

Aerodynamic Mitigation of Roof and Wall Corner Suctions Using Simple Architectural Elements

Thispaperpresentstheuseofsimplearchitecturalelementssuchasaerodynamicmitigationdevicesforreducinghighwind-induced suctions occurring at roof and wall corners of low-rise buildings where wind-induced building envelope failures usually initiate. The architectural elements considered in the current study include trellises (pergolas), roof extensions of gable ends (gable end ribs), ridgeline extensions(ridgerib),andsidewaysextensionsofwalls (wallribs). Asmall-scalemodelofresidential villawastestedinaboundarylayer wind tunnel for two different roof geometries (gable and hip). Moreover, selected cases were investigated at the Wall of Wind, a large-scale testing facility, to investigate scale effects. The effectiveness of these architectural elements in reducing high suction (negative pressure) was assessed bycomparingthewind-inducedpressuremeasurementsobtainedbeforeandafterintroducingtheelements.Basedontheresultsobtainedforthe worstwindangleofattacks,thepeaksuctionwasreducedafterintroducingthearchitecturalelementsby65%atgable-endcorners,60%closeto roof ridges, 45% at soffits, 35% at wall corners, and 25% at eaves. These simple architectural elements, which can be retrofitted to the stock of existing homes or incorporated into the design of new buildings, can be used as aerodynamic mitigation devices for reducing peak suction at critical locations of the building envelope. DOI: 10.1061/(ASCE)EM.1943-7889.0000505.

Wind Effects on Roofs with High-Profile Tiles: Experimental Study

AbstractHurricane wind–induced damage to the roofs of residential buildings has raised concerns regarding design provisions and construction practices. Current code provisions on wind loads on roofs are mainly based on testing of building models that do not include the architectural details of roofing materials. Past research has indicated that net pressures on roof tiles can differ significantly from external pressures on bare roofs and depend on wind direction, the location of the tile, and whether the eaves are sealed. This study presents experimental pressure measurements that confirm existing findings and provide more extensive results on wind loads on high-profile roof tiles. Four different roof models with bare and tiled roof decks were tested. Pressures on the external surfaces of the tiles, within the cavity space, and in the joint space between two overlapping tiles were measured to evaluate their effects on the net peak pressures on the tiles. Area-averaged peak pressure coefficients obtained f...

Study on roof vents subjected to simulated hurricane effects

Most residential buildings use a natural ventilation process by which overheated air inside buildings is vented out and fresh air is pulled in to replace it. Proper ventilation helps maintain a comfortable temperature inside buildings, maintain indoor air quality, increase energy efficiency, and prevent moisture damage. Vents are necessary to prevent heat and moisture buildup and contribute to the longevity of building components. However, the vents are subjected to wind loading and can be the path for water infiltration during hurricane events. Limited research has been performed on water intrusion through various types of vents in residential buildings to relate such water intrusion to the vent mechanism and the differential pressures that the vents are subjected to during hurricanes. The objectives of this research were to perform full-scale holistic testing of vents subjected to simulated hurricane-level wind and wind-driven rain to evaluate such relations and vent performance under hurricane conditions. Two building models incorporating a variety of vents were tested using the wall-of-wind facility. It was found that the extent to which water intrusion increased with higher positive differential pressure across the vent for various angles of attack can be affected significantly by the vent mechanism.

Large-Scale Experimentation Using the 12-Fan Wall of Wind to Assess and Mitigate Hurricane Wind and Rain Impacts on Buildings and Infrastructure Systems

AbstractEngineering research is undergoing dramatic changes with novel, large-scale research facilities being developed to help reduce the growing economic losses associated with natural disasters....

Collective contextual anomaly detection framework for smart buildings

Buildings are responsible for a significant amount of total global energy consumption and as a result account for a substantial portion of overall carbon emissions. Moreover, buildings have a great potential for helping to meet energy efficiency targets. Hence, energy saving goals that target buildings can have a significant contribution in reducing environmental impact. Todays smart buildings achieve energy efficiency by monitoring energy usage with the aim of detecting and diagnosing abnormal energy consumption behaviour. This research proposes a generic collective contextual anomaly detection (CCAD) framework that uses sliding window approach and integrates historic sensor data along with generated and contextual features to train an autoencoder to recognize normal consumption patterns. Subsequently, by determining a threshold that optimizes sensitivity and specificity, the framework identifies abnormal consumption behaviour. The research compares two models trained with different features using real-world data provided by Powersmiths, located in Brampton, Ontario, Canada.

Asynchronous Parallelization of a CFD Solver

A Navier-Stokes equations solver is parallelized to run on a cluster of computers using the domain decomposition method. Two approaches of communication and computation are investigated, namely, synchronous and asynchronous methods. Asynchronous communication between subdomains is not commonly used in CFD codes; however, it has a potential to alleviate scaling bottlenecks incurred due to processors having to wait for each other at designated synchronization points. A common way to avoid this idle time is to overlap asynchronous communication with computation. For this to work, however, there must be something useful and independent a processor can do while waiting for messages to arrive. We investigate an alternative approach of computation, namely, conducting asynchronous iterations to improve local subdomain solution while communication is in progress. An in-house CFD code is parallelized using message passing interface (MPI), and scalability tests are conducted that suggest asynchronous iterations are a viable way of parallelizing CFD code.

Testing of Residential Homes under Wind Loads

Aerodynamic testing of low-rise structures is fraught with difficulties that can be the cause of large measurement errors, resulting in the underestimation of aerodynamic pressures by a factor of as much as two. The errors are primarily attributable to the inadequate knowledge and simulation of wind flows affecting low-rise buildings, especially residential homes in suburban environments. A type of aerodynamic testing of sufficiently small low-rise structures is explored that does not entail the simulation of the turbulence intensity and integral turbulence scales. That type of testing would offer several advantages: eliminating a major cause of discrepancies among measurements conducted in different laboratories, allowing the use of larger model scales, and allowing testing in both typical commercial wind tunnels and in open jet facilities of the Wall of Wind (WoW) type. Preliminary tests based on data obtained at the University of Western Ontario wind tunnel and the Florida International University large-scale six-fan WoW facility suggest that the proposed type of testing yields systematically conservative results for the specialized type of measurements considered herein. In most cases, but not all, the degree of conservatism is modest. The results appear to be of sufficient interest to warrant additional research.