ESL Theses and Dissertations

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This collection contains theses and dissertations by graduate students affiliated with the Energy Systems Laboratory.

A listing of these documents is found in the catalog on the ESL Community's main page. This list is comprehensive and searchable. It provides a complete view of all documents in the ESL Digital Library except for the proceedings, although a few of them are listed as Published Articles (PAs).

Some of the Master's Theses are not available at this site because of permission constraints. Please email the ESL Librarian at esl_librarian@tees.tamus.edu for more information on the restricted documents.

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The Doctoral Dissertations are located in the Office of Graduate Studies collection.

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Now showing 1 - 20 of 72
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    An Expanded and Updated Framework for Whole-Facility Energy Consumption Statistical Models of Commercial Buildings
    (2022-11-09) Fu, Hongxiang
    A significant portion of energy consumption occurs in buildings today. Accurate and easy-to-implement methods are needed to calculate building energy consumption for a wide range of applications, including efficiency assessment, consumption projection, and measurement and verification, to name a few. There are a number of approaches for building energy estimation but the statistical methods have remained popular. As the availability and quality of building energy data continue to improve, the methodologies behind building energy calculation also require updates. This work proposes three new technologies to bring contemporary mindsets to the application of whole-building energy consumption statistical models. The first is a specialized model formulation for the heating hot water consumption for commercial buildings with constant volume reheat systems. It has been observed that the heating consumption of this system type has an unexpected local increase with an increase in ambient temperature caused by dehumidification and reheat. The proposed new method can improve model fit with statistical significance and remove the local trend in the residuals. The second is the use of domestic cold water use or non-HVAC electricity use as an occupancy proxy for building energy models. It is found that combining domestic cold water use with a clustering technique was able to improve model fit by 2.9 percentage points of the CV-RMSE, on average, on top of 14.2% from the traditional weekday-and-weekend method. In the study it was found that other methods, i.e., the use of electricity use as occupancy proxy and the additional of a linear term, were not able to improve the model fit consistently. Finally, a procedure was proposed to examine all data separation or grouping possibilities automatically and comprehensively with pre-defined elementary day-types through a series of lack-of-fit F-tests. This procedure suggests a best separation that balances between model accuracy and simplicity. It was tested on measured energy consumption data of 76 case study commercial buildings. The proposed method weighed simplicity more heavily than traditional statistical complexity-penalizing metrics. The new method improved the CV-RMSE by 7.6 percentage points, on average, and helped extract information to help better understand the buildings’ energy consumption patterns.
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    A study of occupancy-based smart building controls in commercial buildings
    (2020-12) Kim, Chul
    Occupant behavior has a significant influence on energy consumption in buildings because HVAC, lighting, equipment, and ventilation operations are often tied to occupancy- based controls. However, currently, the traditional methods for the prediction of occupant behavior using a building energy modeling approach has begun to face difficulties due to the complex nature of occupant behavior and the introduction of the new technologies (i.e., occupancy sensors) in new and renovated construction. Research in the previous studies revealed that actual occupancy rates in office buildings were quite different compared to typical simulation schedules used in the analysis of building codes and standards. Therefore, large potential energy use reductions are expected when occupancy-based controls are used in building operations. In addition, many workers are recently encouraged to work more at home, which may cause larger unoccupied periods for a significant portion of time at a commercial office building. This fact further increases the need to better understand various occupancy schedules and usage trends in building energy simulations. However, currently, the U.S. commercial building energy codes and standards (i.e., ASHRAE Standard 90.1) do not fully support building energy modeling for occupancy-based controls for code-compliance. Performance paths (i.e., Appendix G method) in Standard 90.1- 2016 offer only partial credits for occupancy-based lighting controls, which tend to underestimate the potential reduction from the use of occupancy-based controls. Also, the requirements of the ASHRAE Standard 90.1 performance path require the mandatory use of identical schedules for the baseline and the proposed design models, which do not present the calculation of reduction from occupancy-based controls. Therefore, this study seeks to analyze occupancy-based controls to determine how varying factors may impact energy use reduction predictions in commercial office buildings. These factors include: different building types (i.e., lightweight versus heavyweight), with different system types (e.g., variable air volume versus packaged single-zone systems) by orientation (i.e., N,S,E,W) in different climates (e.g., cold and hot climates). To achieve the goal of this study, a reference office building was analyzed based on the prototype office building model that was developed by the U.S. DOE and PNNL for small office building for Standard 90.1-2016. Using this model, different thermal zoning models were developed for single-zone and five-zone models to evaluate the impact of occupancy-based controls in the prototype office building. The impact of occupancy-based controls was then evaluated using simulation to study the influence of occupant behavior on HVAC, lighting, equipment, and ventilation system energy use. A sensitivity analysis of each occupancy control schedule (i.e., occupancy, lighting, equipment) was performed in 100%-0% variations to determine interactions between occupancy variables. In addition, simulations for a set of specific occupancy control schedules (i.e., occupancy, lighting, equipment) were conducted in hot-humid and cold-humid climate zones with different building designs (i.e., a raised floor lightweight building and a heavyweight building with varying window-to-wall ratios) and different HVAC system types (i.e., packaged variable air volume versus packaged single-zone systems) to identify potential energy use reduction of occupancy-based building controls on annual energy consumption. The results showed substantial energy reduction potential from varying factors related to occupancy-based controls in commercial office buildings. The evaluation in two climate zones showed a range of energy reduction in Houston and Chicago due to the weather-dependent loads (i.e., heating, cooling, ventilation). Heavyweight material models showed higher percent energy use reduction potential ratios and less energy use compared to the reference building and lightweight models. Also, smaller window-to-wall models represented less total energy use than higher window-to-wall models, which led to higher energy use reduction ratios for smaller window-to-wall ratios. The PVAV systems had higher total load reduction ratios and less total energy use than PSZ systems in Houston and Chicago, especially for heating loads. Whole-building occupancy-based controls revealed more energy use reduction potential ratios in Houston compared to Chicago. The impact of orientation was different depending on thermal zone locations. However, the impact was not fully analyzed because this study did not evaluate combined occupancy sensor controls, daylight controls, and daylighting-based schedules. The largest energy use reduction contributors to occupancy modeling were the internal load factors (e.g., lighting, equipment). The outcome of this study should help guide the development of a guideline for evaluating how occupancy-based building controls can be better incorporated in different building types for different climate zones to reach compliance with ASHRAE Standard 90.1- 2016.
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    Analysis of Residential Building Energy Code Compliance for New and Existing Buildings Based on Building Energy
    (2020-12) Jung, Sungkyun
    Currently, the International Energy Conservation Code (IECC) is the most widely-used residential building energy code in the United States. Either the IECC or IECC with amendments has been adopted by 33 states. The latest version of the IECC contains three compliance requirements, including: mandatory, prescriptive, and performance paths for compliance. The performance path includes specifications for the standard house design and the proposed design to be analyzed using whole-building energy simulations. In the performance path, the annual simulated energy cost of the proposed house must be less than the annual energy cost (or source energy usage) of the standard reference house. Unfortunately, most of the whole-building energy simulation programs are too complicated to be used by building energy code officials or homeowners without special training. To resolve this problem, simplified simulation tools have been developed that require fewer user input parameters. Such simplified software tools have had a significant impact on the increased use of the performance-based code compliance path for residential analysis. However, many of the simplified features may not represent the energy efficient features found in an existing residence. This may mis-represent the potential energy saving when/if a house owner decides to invest in a retrofit to reduce their annual energy costs. Currently, there are building energy simulation validation methods developed by ASHRAE, and RESNET including: ASHRAE Standard-140, IEA BESTEST, HVAC BESTEST, and BESTEST-EX. These tests have been developed to test the algorithms of building energy performance simulation, which require complex inputs and outputs to view the test results. Unfortunately, even though two different building simulation validation programs may produce the necessary inputs/outputs for certification, they are rarely tested side-by-side or on actual residences. Furthermore, results from a simplified analysis of a building is rarely compared against a detailed simulation of an existing building. Therefore, there is a need to compare the results of a simplified simulation versus a detailed simulation of an existing residence to better determine which parameters best represent the existing house so more accurate code-compliant simulations can be performed on existing structures. The purpose of this study is to develop an accurate, detailed simulation model of an existing single-family residence that is compared with a simplified building energy simulation of the same residence to help determine which on-site measurements can be made to help tune the simplified model so it better represents the existing residence. Such an improved building energy simulation can be used to better represent annual energy cost savings from retrofits to an existing building.
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    An Improved Method for the Estimation of the Energy Consumption and Savings of Code-Compliant office Buildings in Different Climates
    (2020-12) Kheiri, Farshad
    Degree day methods are used in the estimation of building energy consumption and climate classification for buildings (e.g. in ASHRAE Standard 169-2013, which is adopted in ASHRAE Standard 90.1-2016). This study, first assessed the effectiveness of the conventional degree days in estimating building energy consumption in different moisture regimes. The analysis was done by comparing the energy performance of the DOE/PNNL medium office prototype building models in the 801 locations in the U.S. The results revealed large variations in the annual energy consumption of the models in the different moisture regimes within each climate zone. Furthermore, large differences in the estimated energy savings by utilization of daylight were shown in different locations. In addition, detailed pairwise analyses were performed to analyze the large variation in the cooling or heating energy consumption in sites with similar Cooling Degree Days (CDD) or Heating Degree Days (HDD), respectively. The analysis revealed that the influential weather parameters that affected the building energy consumption were not fully accounted for in a conventional degree day method. In other words, the level of aggregation of the data in the conventional degree day method masks some of the informative characteristics of the outdoor dry-bulb temperature. To resolve these discrepancies, a split-degree day method was proposed to calculate the split-Cooling Degree Days (sCDD) and the split-Heating Degree Days (sHDD). The results show that in the regression models using the split degree days compared to the conventional degree days, the coefficient of determination of the estimations of the energy consumption increased for the total annual energy use (from 0.913 to 0.965), the heating energy use (from 0.891 to 0.981), the cooling energy use (from 0.979 to 0.982), and the fan energy use (from 0.383 to 0.722). Similar results were shown for the models with higher thermal mass. The proposed method can be used for building energy consumption estimation, weather-normalized building energy savings calculation, and climate classification. Moreover, a new adjustment method was developed using the proposed split-degree day method that reduces the variations in the above code values in the performance compliance path in different locations from 14% to 2%.
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    Analysis of Support Vector Machine Regression for Building Energy Use Prediction
    (2020-08) Lee, Shinwoo; Baltazar, Juan-Carlos
    There are many inverse modeling methods to model the whole building energy use. Multiple linear regression (MLR) and change-point liner regression (CPLR) have been some of the most common methods due to their direct interpretation concerning building energy modeling and their fair accuracy. Recently, as machine-learning techniques have become more accessible, there have been many attempts to apply these techniques to building energy modeling. However, no studies have conducted an in-depth comparison with the conventional inverse model methods using large buildings sample size. This study conducted a comprehensive comparative study based on Support Vector Machine (SVM), one of the most widely used machine-learning methods for flexibility and accuracy, with enough cases to draw a reasonable conclusion between models generated from conventional methods such as MLR and CPLR, and those from SVM. This work, besides the comparative analysis, included a thorough SVM performance analysis for building energy modeling. It described in detail its implementation, and showed its performance as a regression technique for building energy modeling under the influence of different variables. The comparative study focused on modeling whole building chilled water use (CHW) and heating hot water use (HHW), and analyzed the influence of such variables as the outdoor dry-bulb temperature (OAT), the outdoor dew-point temperature (DPT), the outdoor air enthalpy (OAE), and the operational effective enthalpy (OEE). The numerical experiments were based on a sample of 41 whole year daily and hourly building energy use datasets that were converted from hourly data. According to the comparative analysis between SVM and MLR, based on CHW data, SVM consistently showed higher performances by an average of 6.8% on daily and 2.0% on monthly models, respectively. For the SVM and CPLR performance analysis, four pairs of dependent and independent variables were considered: CHW-OAT, CHW- OAE, CHW-OEE, and HHW-OAT. On daily modeling, SVM demonstrated consistently higher performance, although most of the cases resulted in a marginal advantage by less than 1% for all variables utilized. Despite such marginal gains in mean performance, SVM showed advantages by up to 3% for some datasets. On the monthly model, however, SVM did not exhibit better results for any dependent-independent variable pair.
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    Development of a Prototype for Integrating Building Information Model (BIM) with Daylighting Simulation Tools for Designing High-Performance Buildings
    (2020-09-13) Kota, Sandeep
    The outcome of this study is the development of a prototype REVIT2RADIANCE add-in program for a Building Information Modeling (BIM) authoring tool Autodesk Revit to perform daylighting studies with ease by architects and simulation experts alike for designing High-Performance Buildings. To achieve this, first, a literature survey of several different daylighting calculation methods and tools was conducted to identify their capabilities and limitations, which include a comparative analysis of tools that are widely used and comparative analysis of daylighting simulation tools was ascertained from the comparative analysis. The results of the comparative analysis revealed that the state-of-the-art daylighting simulation tool RADIANCE has the most advanced capabilities to perform daylighting simulation, followed by RADIANCE based tool DAYSIM. Second, a survey of the previous methodologies that explored the integration of CAD (e.g., AutoCAD) or BIM authoring tools (e.g., Revit) with daylighting simulation tools was conducted. The survey provided: an overview of different aspects involved in the integration process; the shortcomings of each method; the necessity for a better integration process; and finally, the need for integration of Revit, a BIM-authoring tool with RADIANCE and DAYSIM. Third, for integrating Revit with RADIANCE and DAYSIM, different methods were explored. First, the conventional method that uses Radiance utilities that facilitate the translation of geometry created by various CAD-based tools into RADIANCE geometry and material information. Several significant limitations were observed in these methods, one of which is the partial translation involving only geometry but not the material information from Revit to RADIANCE. To address these limitations, a second method using a custom prototype REVIT2RADIANCE comprising of several Revit add-in programs was developed using the Revit API and C# programing language. The new prototype provides seamless integration of Revit with RADIANCE and DAYSIM, not only translating both geometry and material information but also simultaneously performing a daylighting simulation using RADIANCE and DAYSIM that generates results in a widely-used format. Finally, the prototype was tested using two different test cases, one with simple geometry and a second comprising of complex geometry. Validation of the prototype REVIT2RADIANCE was performed to check the accuracy in translating the Revit geometry and material in to RADIANCE and DAYSIM geometry and translating the material information necessary to perform the daylighting simulation. The first validation test was performed by visually comparing the Revit model with the rendered RADIANCE model, generated using the RVIEW program of the input file created by the prototype. In the second validation test, the parameter values of the RADIANCE Materials written by the prototype were compared with the parameter values obtained using hand calculations. Both the validation tests confirmed the accuracy in the translation of geometry and material information contained in Revit into the proper RADIANCE and DAYSIM formats.
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    TCEQ Annual Report Volume I: Technical Report
    (2018-02-06) Haberl, Jeff; Yazdani, Bahman; Baltazar, Juan-Carlos; Ellis, Shirley; Parker, Patrick; Zilbertshtein, Gali; Claridge, David
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    TCEQ Annual Preliminary Report: Integrated NOx Emissions Savings from EE/RE Programs Statewide
    (2018-02-06) Haberl, Jeff; Baltazar, Juan-Carlos; Yazdani, Bahman; Parker, Patrick; Ellis, Shirley; Zilbertshtein, Gali; Claridge, David
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    An Expert System for the Analysis of Building Energy Consumption, Doctoral Disseration
    (University of Colorado, 1986-07) Haberl, Jeff
    This work concludes six years of energy conservation studies performed for the University of Colorado Student Recreation Center. The studies began late in 1980 when the University of Colorado Student Administrators asked Dr. John Dow to perform a solar feasibility study. Since such a feasibility study had previously been performed by Dr. Dow, as well as other studies (Numark and Bartlett, 1981), a comprehensive energy conservation project was recommended, funded, performed and delivered (Dow, 1981). The second phase of the study began in November 1983, when Dr. Judith Bryant asked that additional energy conservation studies be performed. The building has been under continuous study since. The third phase of the study, beginning in the summer of 1985, represents the prelude to this work. It originally focused on providing monthly forecasts of energy consumption. Early attempts to deliver such an administrative tool failed because of an insufficient understanding of the inter-related energy consuming subsystems. This work, beginning in September 1985, finally presented a satisfactory predictor of energy consumption; the results are the regression work described herein. The expert system portion of the work was developed to electronically capture and deliver the expertise of maintenance personnel at Facilities Management as well as the six years of knowledge gained by the author. The work serves as an administrative warning "beacon" that identifies potential problems, and hence the name BEACON.
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    The Effects of Frost Growth on Finned Tube Heat Exchangers under Laminar Flow
    (Texas A&M University, 1988-12) Kondepudi, Sekhar
    A study on the effects of frost growth on the performance of finned tube heat exchangers under laminar flow has been conducted. The study was both experimental and analytical. The experimental part of the investigation dealt with different fin geometries: louvered, corrugated, wavy, flat plate fins and also spine fin types. The parameters which were varied include the air humidity, air and refrigerant temperature, air flow rate and fin density. A new term called the energy transfer coefficient has been defined to account for the combined heat and mass transfer processes occurring during frosting. The variables measured were the amount of frost growth, the energy transfer coefficient, the pressure drop across the coils, the enthalpy drop, and the effectiveness of the coils. The general trends were found to be consistent with the literature. It was found that the frost growth increases with humidity, air temperature, velocity and fin density due to an increase in the mass transfer. The dominant factor was the humidity content of the air. When the relative humidity was increased from 74% to 80 % at an air temperature of 32 degrees F, the frost growth increased by approximately 22 %. The energy transfer coefficient initially increases by 10 to 15% with the onset of frost formation due to increased surface area and surface roughness but then drops off due to the insulating layer of frost. The louvered fin type had the highest energy transfer coefficient in the neighborhood of 50 Btu/hr-F-sq. ft. as compared to the flat fin type which was in the neighborhood of 38 Btu/hr-sq. ft. • However, when these results were normalized with respect to dry co.1ditions, it was found that the flat fin type performed better than the louvered fin type. A mathematical model was developed to simulate the experiments, based on fundamental heat and mass transfer principles. Due to the complexity of the problem, the model in its present form can handle flat plate fin types only. In addition to being able to predict energy transfer and frost growth, the model also performs a non-dimensional analysis on the heat exchanger performance in terms of NTU - Effectiveness, and Fin Performance. Comparisons were made between the experimental results and those predicted by the model for the frost growth, energy transfer coefficient, pressure drop and heat exchanger effectiveness. The results from the model were within 15 to 20% of the experimental values
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    The Measured Energy Impact of Air Leakage on Frame Wall Systems
    (Texas A&M University, 1991-05) Bhattacharyya, Souvik
    Infiltration is customarily assumed to increase the heating and cooling load of a building by an amount equal to the mass flow rate of the infiltration times the enthalpy difference between the inside and outside air - with the latent portion of the enthalpy difference sometimes neglected. An experimental and analytical investigation has been conducted on the actual energy impact of air leakage on frame wall systems. Calorimetric measurements conducted on a small test cell and on a well characterized stud-cavity wall specimen with measured amounts of air leakage introduced under a variety of controlled conditions and configurations show convincingly that infiltration can lead to a much smaller change in the energy load than is customarily calculated. The data also suggest that the phenomenon occurs in full-sized houses as well. Infiltration Heat Exchange Effectiveness {IHEE), €, is introduced as a mea­ sure of the effectiveness of a building in 'recovering' heat otherwise lost {or gained) because of infiltration. Measurements show that € increases as: a) flow rate decreases; b) flow path length increases; c) hole/crack size decreases. € also generally increases as the pressurization exponent, n, increases; so fan - pressurization results may be useful in predicting E for buildings. An analytical • model based on fundamental heat and mass transfer principles has been developed and all the predicted values of E as a function of air flow rates and effective path length for the different stud-cavity wall specimen test configurations were remarkably consistent with the experimental results. Significant experimental results include: a) E values as high as 0.9 and as low as 0.05 for the test cell configurations tested indicate an energy impact of the air leakage as low as 10% of customary values; b) E values in the 0.16-0.7 range in the stud-cavity (vs. theoretical maximum of 0.5); and • c) E values of 0.16 to 0.34 for air exiting the stud-cavity directly across from the entry. •
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    Monitoring the Performance of a Residential Central Air Conditioner under Reduced Evaporator Air Flow on a Test Bench
    (Texas A&M University, 1992-11) Palani, Manivannan
    This report presents results from degraded performance measurements of a residential air conditioning system operating under reduced evaporator air flow. Experiments were conducted using a R-22 three-ton split-type cooling system with a short-tube orifice expansion device. Results are presented here for a series of tests in which the air flow across evaporator was reduced by 25%, 50%, 75%, and 90% of normal amount of air flow as specified by ARI. Return air temperature was maintained at 80 F dry bulb for all the standard and degraded experiments. Experiments were conducted for three different return humidity conditions of20% RH, 45% RH, and 65% RH and three outdoor conditions of70°F, 85°F, and 100°F dry bulb temperature. At present, very little information has been published which quantifies the degraded performance of a residential cooling system operating under reduced evaporator air flow. Degraded performance measurements can provide information which could help electric utilities evaluate the potential impact of system-wide maintenance programs.
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    Energy Conservation Opportunities in Commercial and Industrial Facilities: Energy Utilization Indices (EUI) in Texas LoanSTAR Buildings
    (Texas A&M University, 1993-08) Phillips, Michael
    The work described in this report was performed under the direction of the Energy Analysis and Diagnostic Center (EADC) at Texas A&M University. The EADC program is managed by University City Science Center under agreement with the U.S. Department of Energy, which financially supports the program. The objective of the EADC is to identify, evaluate, and recommend--through analyses of an industrial plant's operations--opportunities to conserve energy and reduce its cost. Our recommendations are based upon observations and measurements we made in your plant; because our time was limited, we do not claim to have complete detail on every aspect of the plant's operations. At all times we try to offer specific and quantitative recommendations of cost savings and energy conservation to the plants we serve. We do not attempt, however, to prepare engineering designs or otherwise perform services you would expect from an engineering firm, a vendor, or a manufacturer's representative. When the need for that kind of assistance arises, we urge you to consult them directly. If, however, you would like to discuss the content of the report or if you have another question about energy use, please feel welcome to contact us at the EADC at (409) 845-5019.
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    An Analysis of Grocery Store Energy Use
    (Texas A&M University, 1993-12) Cox, Raplh Luther, III
    Approximately 3% of the United States' commercial building energy consumption is attributable to food sales facilities. Although this is one of the smallest consumption percentages, it is still significant, amounting to about 151 trillion Btu, or $2.17 billion per year. Food sales facilities ranging from 10,000 to 100,000 sq. ft. use 3 to 5.5 W/ sq. ft. (32 to 60 W/ sq. m.) of electricity two to three times what typical office buildings of the same size use (EIA 1986). Identifying potentials for energy savings in food sales facilities is therefore a worth-while pursuit. Why do people study energy consumption? According to Haberl et al. (1990), there are five different groups of people who can benefit from building energy monitoring and at least seven basic applications of energy monitoring projects. The five groups of beneficiaries are: the energy analyst; the energy consumer; governmental agencies; engineers, manufacturers, and contractors; and, utility and fuel suppliers. The seven basic applications are: energy consumption and load forecasting, evaluation of end-use energy data, the monitoring of energy savings from retrofits, determining system .efficiencies, environmental quality issues, analyzing the human factor, and diagnosing operational and maintenance problems. This thesis is a study of the energy use in supermarkets, which fall into the category of the energy consumer. This study is of interest to the energy analyst and the manufacturers of grocery store equipment, and to utilities which can use the results of energy consumption modeling procedures developed herein as inputs to load-predicting models. Many papers and reports have been written about the energy use in grocery stores. In general, they addressed three major issues: energy use surveys and market analyses, refrigeration and HVAC system improvements, and energy use modeling methods. This thesis extends the foregoing work by first performing a general energy use survey of over 90 grocery stores, and presenting statistics regarding their energy use characteristics. Then, several of the previous methods of energy consumption modeling are adapted and applied to the whole- building and sub-metered component load data from two case study grocery stores. Two methods of modeling, multiple linear regression and principal component analysis are evaluated. Finally, a new method is developed and tested that allows for the accurate estimation of sub-metered loads without incurring the expense of collecting many months of hourly, sub-metered data.
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    Aerosol Deposition in Transport Lines
    (Texas A&M University, 1995-12) Muyshondt, Arnoldo
    Particle deposition in contraction fittings with half-angles of 12 degrees, 45 degrees, and 90 degrees; expansion fittings with half-angles of 3 degrees, 6 degrees, 12 degrees, 45 degrees, and 90 degrees; and large-diameter transport lines (up to 102 mm diameter) was measured experimentally. Aerosol losses in the transition fittings were found to be a function of three parameters; namely, Stokes number, area ratio, and half-angle. Based on experimental data, correlations were developed that allow prediction of particle losses in contraction and expansion fittings as a function of Stokes number, area ratio, and half-angle. A correlation was also developed for large transport tubes that allows prediction of non-dimensional dep0sition velocity as a function of non-dimensional relaxation time and flow Reynolds number. For a given half-angle, losses in a contraction fitting correlate well with the parameter Stkc(1-Ao, Ae) Aerosol particle deposition in the contraction fittings was also modelled numerically and the numerical results show good agreement with experimental data. In general, losses in a contraction fitting decrease with decreasing half-angle and area ratio. Losses in expansion fittings increase with decreasing half-angle down to an angle of approximately 12 degrees thereafter, losses decrease with decreasing half-angle. Losses decrease with decreasing area ratio. A 90 degree expansion half-angle fitting produced the lowest aerosol losses. The correlation for large-diameter transport tubes shows good agreement with previous correlations for deposition in small diameter tubes as well for the full range of tube sizes (13 mm to 102 mm diameter) and Reynolds numbers (up to 55,000) tested. For large tubes, the correlation shows improved prediction characteristics as compared to earlier models. For example, penetration of 20 um aerodynamic diameter aerosol particles through a I 02 mm diameter tube at a flow rate of 2260 L/min was measured to be 59%. The present model predicts a penetration of 62%, while two previously reported models that do not include Reynolds number effects, predict 80% and 82%. The correlations presented in this study should be useful sub-models for predicting aerosol losses in transition fittings and large-diameter transport system; in general, models that are used to evaluate overall losses in aerosol transport systems.
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    Development of Fourier Series and Artificial Neural Network Approaches to Model Hourly Energy Use in Commercial Buildings
    (Texas A&M University, 1995-05) Dhar, Amitava
    This dissertation develops Fourier series and Artificial Neural Network (ANN) approaches to model hourly energy use in commercial buildings and illustrates application to data-screening. The procedure for modeling hourly energy use has two steps: (i) Day-typing and (ii) Model development. The mean diurnal energy use and the diurnal profile may be different during working weekdays, weekends, holidays and Christmas due to major changes in mode of operation. The first step, known as day-typing, is important for removing such effects. The second step is to develop models for each day-type. Fourier series analysis is eminently suitable for modeling strongly periodic data. Energy use in commercial buildings being strongly periodic, is appropriate for Fourier series treatment. Generalized Fourier Series (GFS) model equations, developed for both weather independent and weather dependent energy use, give a set of parameters involving time and/or weather variables. Stepwise regression is performed to select the important parameters and a final model for each day-type is developed using the selected parameters. There are situations when only temperature data is available. A Temperature based Fourier Series (TFS) equation for modeling heating and cooling energy use has been developed to deal with such cases. Two important advantages of TFS are that it (i) represents nonlinear variation of energy use in a linearized functional form and (ii) can indirectly account for humidity and solar effect in the cooling energy use. ANNs with back propagation algorithms give high prediction accuracy and has been applied by many researchers to model hourly energy use in commercial buildings. However, the training of Back Propagation Network (BPN) algorithms is a long, uncertain process. ANNs with local basis functions require significantly shorter training times than conventional BPNs. A methodology has been developed to model heating and cooling energy use in commercial buildings using a one-hidden-layer ANN with two dimensional wavelet basis functions derived from cubic splines. A suitable prediction interval can be generated and used to perform data­ screening. Application of the TFS approach to data-screening is illustrated with monitored data.
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    Performance of Energy Management Control Systems (EMCS) in Selected Texas LoanSTAR Buildings
    (Texas A&M University, 1995-08) Schmode, Michele
    This report describes an investigation of energy use at various LoanSTAR sites. The effects of installing Energy Management Control Systems (EMCS) on electricity consumption was studied at four LoanSTAR sites: Stroman High School, Victoria High school, Sims Elementary School, and Zachry Engineering Center. In the course of this study, LoanSTAR monitoring data was used to analyze the changes in energy consumption based only on EMCS retrofits. The results will show that the installation ofEMCS was successful in reducing energy consumption and/or changing the hourly energy consumption pattern.
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    Effect of Backfill on the Performance of a Vertical U-Tube Ground Coupled Heat Pump
    (Texas A&M University, 1995-08) Gu, Yian
    The present work is concerned with developing a discretized analytical model to investigate the effect of a backfill on the performance of a vertical U-tube ground-coupled heat pump. This work involves the development of an analytical solution and an expression for the equivalent diameter, and the experimental verification of their applications in the system model. The approximate analytical solution was developed to the transient heat­ conduction problem in an infinite composite medium composed of a backfill and the soil with an internal cylindrical heat source. This was intended to improve the prediction of the performance of a U-tube ground heat exchanger. The generalized orthogonal expansion technique was utilized in deriving this solution. Solutions are presented in a wide range of the Fourier number for the non-dimensional temperature as a function of the ratios of thermal conductivities and diffusivities of the backfill and soil Sensitivities of the results to assumptions about the sizes of the backfilling region and the far-field boundary were also examined. To verify the correctness of the solution, comparisons were made between this solution, and the classical homogeneous cylindrical solution and a finite difference solution.. To improve the equivalent diameter approach to the thermal interference problem between the legs of the U-tube, a general expression for the equivalent diameter was derived under steady state. The transient analytical solution, developed earlier combined with the superposition method and the conformal mapping technique were used to justify this expression. A small-scale U-tube test facility was constructed for the experimental validation of the system model of the U-tube heat exchanger using the analytical solution and the equivalent diameter expression. Two types of backfill materials: bentonite/masonry sand and bentonite/copper powder were chosen for the tests. Finally, the parametric studies were conducted to characterize the effects of the thermal properties of the backfill, the leg spacing as well as the size of the backfill region. A backfill effectiveness was proposed and discussed. These studies provide a number of insights into the heat transfer behavior of the U-tube heat exchanger buried in a non­ homogeneous medium.
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    Effects of Hydrophobic Surface Treatments on Dropwise Condensation and Freezing of Water
    (Texas A&M University, 1995-12) Bryant, John
    The effects of hydrophobic coatings on the dropwise condensation process for a flat horizontal copper plate held at a temperature much lower than the surrounding air was investigated. Extensive qualitative and quantitative data were taken to describe these effects in terms of dropsize distributions, heat and mass transfer coefficients, and digital imaging of the microscopic condensing droplets in terms of various extensive properties. Conditions of the tests were laminar flow (Reynolds numbers of 600 to 1600), condensing surface temperature of -10.0°C, air temperatures of 1.5 to 7.5°C, and relative humidities of 50 to 90%. Digital imaging of the condensation process was done using a medium power microscope coupled to a solid-state camera and a computer-based image capture system. Three different treatments were used on the polished copper condensing surface; no coating, a silicone conformal coating, and a long-chain sulfur based coating. Results for the heat transfer data showed an increase of approximately 33% for condensation over a dry surface for the conditions of the study. The mechanism of condensation appeared consistently to be dropwise. A method to predict the Nusselt number, nucleation time, mean cluster size and the droplet surface density in terms of extensive properties that are known a priori was also developed based on the experimental data. A condensation model was developed based on heat transfer relationships for the condensation process and the psychometric qualities of the ambient air. The inputs to the model were the surface temperature of the condensing system, the contact angle of the liquid phase in contact with the surface, the moisture content and temperature of the air stream, and the velocity of the air flowing over the condensing surface. Comparisons were made between the experimental results and those predicted by the model for dropsize distributions and mass of condensate on the surface. The results from the mode! were within ±25% of the experimental values. It was found that the application of a hydrophobic coating on a surface that is to be operated at a temperature below the freezing point of water will delay the onset of ice nucleation by 15 to 35% over an uncoated surface.
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    An Investigation on Heat Transfer During the Freezing of Condensate Droplets
    (Texas A&M University, 1996-05) Gong, Ying
    The heat transfer and the freezing process of condensate droplets resting on a cold metal plate have been studied both experimentally and numerically. The experimental part of the investigation dealt with the measurements of the thermal and flow parameters and the visualization of the freezing process. The parameters which were varied include the ambient air velocity, air-to-plate temperature difference, and the droplet size. The tests performed were the steady-state temperature distribution, transient cooling curve at a location within a droplet, freezing time, average air-side convection coefficient on a cold metal plate covered with droplets, and freezing front motion on the freezing of droplets. Two new dimensionless numbers have been introduced to account for the freezing time and the air-side convection coefficient. Two empirical correlations, one for freezing time and the other for the average air-side convection coefficient, were developed. A mathematical model based on control volume method was developed to calculate the temperature distributions, heat transfer rates, and phase-change region position during the freezing of hemispherical droplets on a cold metal plate. The model predictions of the freezing of a hemispherical droplet showed that the narrow ring around the droplet perimeter was a good place for continued ice nucleation. The basic structure of a frost layer was composed of two zones: the ice sublayer and the dendritic layer. The results predicted by the mathematical model have been compared with available analytical solutions, previously published results, and experimental data. The good agreements indicated that the model could be used to predict steady-state and transient temperature distribution, temperature history, freezing front velocity, and freezing time. Combined with other softwares, the mathematical model could also be used to graphically simulate the freezing process.
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