Browsing ESL Theses and Dissertations by Title
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Analysis of improved fenestration for code-compliant residential buildings in hot and humid climatesMukhopadhyay, Jaya (Texas A&M University, August 2005)[more][less]
Abstract: This thesis presents an analysis of energy efficient residential windows in hot and humid climates. To accomplish this analysis, the use of accurate simulation tools such as DOE-2.1e is required, which incorporates the results from the WINDOW-5.2 simulation program to assess accurate fenestration performance. The thesis also investigates the use of optimal glazing types, which, for future applications, could be specified in the code to reduce annual net energy consumption to zero. Results show that combinations of low-E and double pane, clear-glazed windows, which are optimally shaded according to orientation are the best solution for lowering both annual energy consumption and peak electricity loads. The study also concludes that the method used to model fenestration in the simulation program plays an important role in accurately determining the effectiveness of the glazing option used. In this particular study, the use of the WINDOW-5.2 program is highly recommended especially for high performance windows (i.e., low-E glazing). Finally, a discussion on the incorporation of super high performance windows (i.e., super low-E, ultra low-E and dynamic / switchable glazing) into the IECC code concludes that these types of glazing strategies can reduce annual net energy use of the window to zero. Future work identified by this thesis includes a more extensive examination of the passive solar potential of high performance fenestration, and an examination of the appropriate methods for specifying these properties in future versions of the IECC code. This implies that future specifications for fenestration in the IECC code could aim for zero net annual energy consumption levels from residential fenestration.
Files in this item: 1etd-tamu-2005B-ARCH-Mukhopa.pdf (5.655Mb)
An Analysis of Low Cost, Energy Efficient, Housing for Low-income Residents of How and Humid ClimatesKootin-Sanwu, Victor (Energy Systems Laboratory, May 2004)[more][less]
Abstract: The purpose of this research is to develop methods that will enable the reduction of owning and operating costs of low-income housing in the hot-humid climates of the U. S. The objectives include investigating various scenarios that will enable the implementation of cost-effective construction of low-income housing using volunteer labor. The research uses a case study approach where a base-line energy use is established using a comparative Princeton Score Keeping Method (PRISM) analysis and measurements from a case study house. A prototype house is then simulated with the DOE-2 building simulation program, and the energy savings calculated by comparing simulated energy and water conservation design measures (E&WCDMs) with the calibrated baseline energy simulation. The cost and maintenance of the house are analyzed with the real cost of construction of a case study house in Bryan/College Station, Texas.
Files in this item: 1ESL-TH-04-05-01.pdf (24.12Mb)
Nutter, Darin Wayne (December 1994)[more][less]
Abstract: The mass flow characteristics of flashing Refrigerant-22 from a small vessel were investigated. A flash boiling apparatus was designed and built. It was modeled after the flashing process encountered by the accumulator of air-source heat pump systems. Three small pyrex glass vessels were used to hold the refrigerant and allow for visualization studies of the flashing process. Baseline experiments were run varying initial pressure, initial refrigerant amount, orifice diameter, and vessel geometry. Three sets of experiments were run using two passive enhancement methods (the addition of steel balls and the addition of small amounts of oil) and one active enhancement method (the addition of an immersion heater). Furthermore, a lumped-parameter analytical model was developed from basic thermodynamic principles that predicted the rate of depressurization for the flashing refrigerant. The study showed that the initial refrigerant amount and the orifice size had the greatest influence on the mass flow and pressure characteristics during each sixty second test. The initial pressure and vessel volume had less of an impact under the conditions tested. Two of the enhancement methods consistently increased the amount of refrigerant flashed during the tests as compared to the baseline data for the same initial conditions. The addition a 1 cm layer of 3.6 mm steel balls to the base of the vessel increased the amount flashed from 21% to 81% and the addition of the 215-watt flat-spiral immersion heater the increased the amount flashed from 47% to 111 %. Foaming at the vapor-liquid interface was observed with the refrigerant-oil mixture experiments as two of the eight test conditions averaged an increase while six averaged a decrease, ranging from a 21% increase to a 27% decrease. The analytical depressurization model predicted general pressure and mass flux trends, and revisions to the model improved pressure predictions to within ±11%.
Files in this item: 1ESL-TH-94-12-05.pdf (4.956Mb)
Malhotra, Mini (Texas A&M University, December 2005)[more][less]
Abstract: Energy-efficient building design involves minimizing the energy use and optimizing the performance of individual systems and components of the building. The benefits of energyefficient design, in the residential sector, are direct and tangible, provided that design strategies with a substantial combined energy and cost-saving potential are adopted. Many studies have been performed to evaluate the energy-saving potential and the costeffectiveness of various design options, and to identify conditions for optimizing the performance of building systems and components. The results of these studies, published in various resources, were analyzed discretely using different techniques, and were reported using different bases for comparison. Considering the complex interaction of, and energy flows through various building components, it is difficult to directly compare/combine the results from various studies to determine the energy-saving potential of combination of strategies, and to select an appropriate set of strategies for making design decisions. Therefore, this thesis develops a comprehensive survey and analysis of energy-efficient design strategies and their energy-saving potential, in isolation as well as in combination, using a DOE-2 simulation model of a prototype house in the hot and humid climate of Houston, Texas. Optimized strategies that included building configuration, materials/ assembly for building envelop components, and efficient mechanical and electrical systems, equipment and appliances, were applied in combination that could minimize the annual energy use. Application of these strategies is expected to allow downsizing systems and equipment and to confirm their operation at their rated performance, resulting in additional installation and operation cost savings. The study is concluded by outlining the procedures for selecting optimized set of strategies, and by developing guidelines for achieving maximum energy-efficiency in singlefamily detached houses in hot and humid climates. Thus, this study will facilitate the selection of energy-saving measures for their individual or combined application for developing energyefficient residences in hot and humid climates.
Files in this item: 1etd-tamu-2005C-ARCH-Malhotra.pdf (1.937Mb)
Building Design and Operation for Improving Thermal Comfort in Naturally Ventilated Buildings in a Hot-Humid ClimateSreshthaputra, Atch (November 29, 2007)[more][less]
Abstract: The goal of this research was to develop new techniques for designing and operating unconditioned buildings in a hot-humid climate that could contribute to an improvement of thermal performance and comfort condition. The recommendations proposed in this research will also be useful for facility managers on how to maintain unconditioned buildings in this climate. This study investigated two unconditioned Thai Buddhist temples located in the urban area of Bangkok, Thailand. One is a 100-year-old, high-mass temple. The other is a 5-year-old, lower-mass temple. The indoor measurements revealed that the thermal condition inside both temples exceed the ASHRAE-recommended comfort zone. Surprisingly, the older temple maintained a more comfortable indoor condition due to its thermal inertia, shading, and earth contacts. A baseline thermal and airflow model of the old temple was established using a calibrated computer simulation method. To accomplish this, HEATX, a 3-D Computational Fluid Dynamics (CFD) code, was coupled with the DOE-2 thermal simulation program. HEATX was used to calculate the airflow rate and the surface convection coefficients for DOE-2, and DOE-2 was used to provide physical input variables to form the boundary conditions for HEATX. In this way calibrated DOE-2/CFD simulation model was accomplished, and the baseline model was obtained. To investigate an improved design, four design options were studied: 1) a reflective or low-solar absorption roof, 2) R-30 ceiling insulation, 3) shading devices, and 4) attic ventilation. Each was operated using three modes of ventilation. The low-absorption roof and the R-30 ceiling insulation options were found to be the most effective options, whereas the shading devices and attic ventilation were less effective options, regardless of which ventilation mode was applied. All design options performed much better when nighttime-only ventilation was used. Based on this analysis, two prototype temples was proposed (i.e., low-mass and high-mass temples). From the simulation results of the two prototypes, design and operation guidelines are proposed, which consist of: 1) increased wall and ceiling insulation, 2) white-colored, low-absorption roof, 3) slab-on-ground floor, 4) shading devices, 5) nighttime-only ventilation, 6) attic ventilation, and 7) wider openings to increase the natural ventilation air flow windows, wing walls, and vertical fins.
Files in this item: 1ESL-TH-03-05-01.pdf (18.16Mb)
Development and Application of a Procedure to Estimate Overall Building and Ventilation Parameters from Monitored Commercial Building Energy UseDeng, Song (May 1997)[more][less]
Abstract: This thesis proposes and validates a simplified model appropriate for parameter identification and evaluates several different inverse parameter identification schemes suitable for use when heating and cooling data from a commercial building are available. The validation has been performed using such data generated from a detailed building simulation program for different building geometries and building mass levels in two different climatic locations. Such a synthetic evaluation will validate the model used as well as determine the best parameter identification scheme, i.e., one likely to yield the most accurate set of parameter estimates. A multistep identification scheme has been found to yield very accurate results, and a more careful evaluation has been performed in order to evaluate its accuracy and stability with synthetic data against the effects of solar energy, HVAC system operation, internal load schedule, building thermal mass and geometry, and climatic location. This method is also evaluated using data from different time periods and when utility bill data (i.e. monthly data) only is available. The model is then applied to energy use data from two buildings being monitored under the Texas LoanSTAR Program, which are in different locations and have different HVAC systems. With parameters thus determined, two energy use indices, Energy Delivery Efficiency (EDE) and Multizone Efficiency Index (MEI), are calculated to present some insights into the benefits of retrofit from a constant volume (CV) to a variable air volume (VAV) system and of continuous commissioning (CC) work done to these two buildings, respectively. Uses and limitations of EDE and MEI are also discussed. Based on these findings, it is suggested that the multistep regression approach is an accurate and practical building physical parameter determination method, and the combined use of the EDE and MEI indices calculated from these parameters can provide insights into the HVAC system, and the potential for optimizing its operation.
Files in this item: 1ESL-TH-97-05-02.pdf (23.32Mb)
Development of a Transient Heat and Mass Transfer Model of Residential Attics to Predict Energy Savings Produced by the Use of Radiant BarriersMedina, M. A. (Energy Systems Laboratory (http://esl.tamu.edu), December 1992)[more][less]
Abstract: A transient heat and mass transfer model was developed to predict ceiling heat gain/loss through the attic space in residences and to accurately estimate savings in cooling and heating loads produced by the use of radiant barriers. The model accounted for transient conduction, convection and radiation and incorporated moisture and air transport across the attic. Environmental variables such as solar loads on outer attic surfaces and sky temperatures were also estimated. The model was driven by hourly weather data which included: time, outdoor air temperature, horizontal sun and sky radiation, wind speed and direction, relative humidity (dew point), and cloud cover data. The outputs of the model were ceiling heat fluxes, inner and outer heat fluxes from all surfaces, inner and outer surface temperatures and attic air temperatures. Transient conduction was modeled using response factors. Response factors were calculated for each attic component based on construction type. Convective heat transfer was modeled using “flat plate” correlations found in the literature and radiative heat transfer was modeled using radiation enclosure theory. Moisture was incorporated via a condensation/evaporation model. A new procedure was developed to account for attic air stratification. Both forced and natural attic ventilation patterns were added to the model for three types of louver combination arrangements. An iterative technique was used to solve a set of simultaneous heat balance equations. The model predictions were compared to experimental data gathered throughout a three year experimental effort of side-by-side testing of attics retrofit with radiant barriers. The model was compared to the experimental data for a variety of situations which included: different attic insulation levels, various attic airflow rates, cooling and heating seasons, and different radiant barrier orientations. The model predicted ceiling heat flows within 10% for most cases. The model was used to run simulations and parametric studies under a diversity of climates, insulation levels and attic airflow patterns. Model predictions and results were presented on the basis of savings produced by the use of radiant barriers. Hourly, daily, and seasonal predictions by the model were in excellent agreement with observed experimental data and with literature.
Files in this item: 1ESL-TH-92-12-04.pdf (5.868Mb)
Sung, Yong Hoon (Texas A&M University, August 2004)[more][less]
Abstract: In this dissertation I will present and test a model linking actual applicant-interviewer demographic, human capital, and cultural capital similarity to an interviewer's recommendation to hire. Actual similarity is proposed to influence an interviewer's perceptions of similarity with an applicant. These perceptions, in turn, lead to the interviewer's perceptions of the applicant's Person-Organization (PO) fit and the applicant's Person-Job (PJ) fit. Two main mechanisms are proposed to mediate the relationship between an interviewer's perceptions of similarity and an interviewer's perceptions of an applicant's fit: liking and negative behavioral expectations. Lastly, both an interviewer's PO and PJ fit perceptions of an applicant are posited to influence the interviewer's recommendation to hire. A total of 118 interviewer-applicant dyads contacted through the Career Center Office at a University located in the southwestern United States participated in the study. Results partially support the model. An interviewer's perceptions of similarity with an applicant are positively related to an interviewer's fit evaluations. An interviewer's negative behavioral expectations of an applicant mediate this relationship. Furthermore, perceived similarity is positively related to an interviewer's liking of an applicant. In turn, liking is positively related to an interviewer's PO fit perceptions. However, liking does not function as a mediator between perceived similarity and fit evaluations. Finally, fit evaluations are positively related to hiring recommendations. I discuss the main implications of the study as well as strengths, limitations, and future research.
Files in this item: 1etd-tamu-2004B-ARCH-Sung-2.pdf (8.657Mb)
An Experimental Investigaton of the Effect of Oil on Convective Heat Trasfer and Pressure Drop of a HFC-32/HRC-125 MixtureMcJimsey, Bert Ashford (December 1994)[more][less]
Abstract: The heat transfer coefficients and pressure drops of HCFC-22 and a 50% mass mixture of HFC-32/HFC-125 were experimentally measured under flow boiling conditions in a smooth tube. The refrigerants were flowed through an 8 mm diameter smooth tube at mass fluxes of 277, 434, 520 and 700 kg/sm^2. Heat fluxes were applied at values of 5100, 7100 and 11000 W/m^2. The heat transfer coefficients and pressure drops were measured at refrigerant qualities of 10, 15, 20, 25, 30, 40 and 60 percent. The refrigerants were examined at temperatures near 4°C. Oil was added to the HFC-32/HFC-125 mixture in concentrations of 2.6% and 5.4%. Experiments were repeated with the oil laden refrigerant. The heat transfer coefficients for HCFC-22 increased with quality, mass flux and heat flux. The heat transfer coefficients for HFC-32/HFC-125 often decreased at low qualities and increased with quality at high qualities. The pressure drop increased with quality and mass flux for both refrigerants. The heat transfer had a minimal effect upon pressure drop. HFC-32/HFC-125 had a lower pressure drop than HCFC-22 for all conditions. The addition of oil increased the pressure drop. A pressure drop correlation and heat transfer correlation were developed for HFC-32/HFC-125.
Files in this item: 1ESL-TH-94-12-12.pdf (4.536Mb)
An Improved Procedure for Developing a Calibrated Hourly Simulation Model of an Electrically Heated and Cooled Commercial BuildlingBou-Saada, Tarek Edmond (Energy Systems Laboratory, December 1994)[more][less]
Abstract: With the increased use of building energy simulation programs, calibration of simulated data to measured data has been recognized as an important factor in substantiating how well the model fits a real building. Model calibration to measured monthly utility data has been utilized for many years. Recently, efforts have reported calibrated models at the hourly level. Most of the previous methods have relied on very simple comparisons including bar charts, monthly percent difference time-series graphs, and x-y scatter plots. A few advanced methods have been proposed as well which include carpet plots and comparative 3-D time-series plots. Unfortunately, at hourly levels of calibration, many of the traditional graphical calibration techniques become overwhelmed with data and suffer from data overlap. In order to improve upon previously established techniques, this thesis presents new calibration methods including temperature binned box-whisker-mean analysis to improve x-y scatter plots, 24-hour weather-daytype box-whisker-mean graphs to show hourly temperature-dependent energy use profiles, and 52-week box-whisker-mean plots to display long-term trends. In addition to the graphical calibration techniques, other methods are also used including indoor temperature calibration to improve thermostat schedules and architectural rendering as a means of verifying the building envelope dimensions and shading placement. Several statistical methods are also reviewed for their appropriateness including percent difference, mean bias error (MBE), and the coefficient of variation of the root mean squared error. Results are presented using a case study building located in Washington, D.C. In the case study building, nine months of hourly whole-building electricity data and site-specific weather data were measured and used with the D0E-2.1D building simulation program to test the new techniques. Use of the new calibration procedures were able to produce a MBE of -0.7% and a CV(RMSE) of 23.1% which compare favorably with the most accurate hourly neural network models.
Files in this item: 1ESL-TH-94-12-01.pdf (63.93Mb)
Noboa, Homero L. (August 1993)[more][less]
Abstract: The purpose of this project was to model and quantify the increase of the absorptivity of radiant barriers caused by the accumulation of dust on the surface of radiant barriers. This research was the continuation of a previous work by the author at Texas A&M University in which a radiation energy balance inside the attic enclosure was developed. The particles were considered as flat, circular planes, all having the same radii. That early model showed that there was a linear relationship between the fraction of area of the foil covered by dust and the mean absorptivity of the dusty radiant barrier. In the present work, it was found that the assumption of treating the dust particles as plane circles, underestimated the effective area of the particles by about 20%. Experimental measurements indicated that dust particles achieved the same temperature as the radiant barrier. The new model used the linear relationship just described, and simulated the dust particles as flat circular planes having random radii and laying in random locations within the radiant barrier surface. The new model calculated the fraction of radiant barrier area covered by particles using a digital array in which the clean barrier was represented as zeroes and the dust particles were represented as a set of ones appropriately dimensioned inside the array. The experimentation used natural dust and Arizona Road Test Dust. Using an infrared emissometer, the emissivities (absorptivities) of the clean and dusty barriers were measured and using an electronic scale, the dust loading was measured. An electron microscope was used to experimentally find the fraction of radiant barrier covered by the dust particles to correlate the experimentally found absorptivity with the experimentally found fraction of dust coverage. The limited experimental data available were also used to correlate the absorptivity of the dusty radiant barrier with the time of dust accumulation and the location of the barrier inside the attic. A linear relationship between the absorptivity and the time of dust accumulation was found that can be applied to predict future barrier effectiveness based upon the rate of dust accumulation for a given location.
Files in this item: 1ESL-TH-93-08-02.pdf (4.280Mb)
An investigation of methods for reducing the use of non-renewable energy resources for housing in ThailandRasisuttha, Sakkara (Texas A&M University, May 2003)[more][less]
Abstract: The purpose of this research is to develop methods that reduce energy consumption in a residential building in a hot and humid climate region (Thailand) using efficient architectural building components and renewable energy (solar energy) to produce electricity, domestic hot water, and supplemental cooling by night sky radiation. Improving the architectural building components, including building materials, is an option to reduce energy consumption in a building. Using renewable energy sources is another option to reduce the consumption of non-renewable energy. In residential buildings, solar energy has been utilized for space heating and domestic hot water using active solar collector systems and for generating electricity using photovoltaic (PV) systems. One photovoltaic system, the hybrid photovoltaic-thermal (PV-T) collector system, has been developed by several researchers over the last 20 years. The hybrid photovoltaic-thermal (PV-T) collector system is a combination photovoltaic (for producing electricity) and solar thermal collector (for producing hot water). Theoretical and experimental studies of this collector have highlighted the advantages of the hybrid PV-T collector system over separate systems of PV and solar collector in term of system efficiency and economics. Unfortunately, very little experimental data exists that demonstrates the advantages of a combined system. Therefore, one of the objectives of this study conducted was an experimental study of this system as an auxiliary energy source for a residential building. Night sky radiation has also been studied as a cooling strategy. However, no attempt so far could be found to integrate it to a hybrid PV-T collector system. The night sky radiation strategy could be operated with the hybrid PV/T collector system by using existing resources that are already present in the solar system. The integration of the night sky radiation into the hybrid PV-T collector system should yield more productivity of the system than the operation of the Hybrid PVT system alone. The research methods used in this work included instrumentation of a case-study house in Thailand, an experimental PV-T collector system, and a calibrated building thermal simulation. A typical contemporary Thai residential building was selected as a case-study house. Its energy use and local weather data were measured and analyzed. Published energy use of Thai residential buildings was also analyzed as well to determine average energy consumption. A calibrated computer model of the case-study building was constructed using the DOE-2 program. A field experiment of the thermal PV system was constructed to test its ability to simultaneously produce electricity and hot water in the daytime, and shed heat at night as a cooling strategy (i.e., night sky radiation). The resultant electricity and hot water produced by the hybrid PV-T collector system helped to reduce the use of non-renewable energy. The cooling produced by the night sky radiation also has to potential to reduce the cooling load. The evaluation of the case-study house and results of the field experiment helped to quantify the potential reduction of energy use in Thai residential buildings. This research provided the following benefits: 1) experimental results of a hybrid PV-T solar collector system that demonstrates its performance compared to typical system of separate photovoltaic and solar collector, 2) results of night sky radiation experiments using a photovoltaic panel as a radiator to demonstrate the performance of this new space cooling strategy, and 3) useful data from the case-study house simulation results and guidelines to assist others in transferring the results to other projects.
Files in this item: 1etd-tamu-2005A-ARCH-Rasisut.pdf (7.261Mb)
A Methodology to Develop Monthly Energy Use Models From Utility Billing Data For Seasonally Scheduled Buildings: Application to SchoolsWang, W. (Energy Systems Laboratory (http://esl.tamu.edu), December 1998)[more][less]
Abstract: The measured energy savings from retrofits in buildings in the Texas LoanSTAR program are determined as the difference between the energy consumption predicted by a baseline model and the measured energy consumption during the post-retrofit period. Savings measurement for buildings such as primary and secondary schools is very difficult due to the special operating schedules of these buildings. Currently, savings are often determined by simple pre-post utility bill comparison; they may also be determined with two separate models for the baseline: a 3-P model for non-summer months, and a mean model for the summer months. (Landman 1996). This thesis proposes a methodology for developing baseline models of energy use for buildings such as schools which have important daily and seasonal variations in occupancy. The method utilizes utility billing data, but also explicitly incorporates occupancy rate, permitting a generalized model which retains the distinction between energy use levels during occupied and unoccupied days of the year. The proposed methodology has been evaluated against the one proposed by Landman for 10 schools in Texas.
Files in this item: 1ESL-TH-98-12-01.pdf (25.40Mb)
A methodology to evaluate energy savings and NOx emissions reductions from the adoption of the 2000 International Energy Conservation Code (IECC) to new residences in non-attainment and affected counties in TexasIm, Piljae (Texas A&M University, December 2003)[more][less]
Abstract: Currently, four areas of Texas have been designated by the United States Environmental Protection Agency (EPA) as non-attainment areas because they exceeded the national one-hour ground-level ozone standard of 0.12 parts-per-million (ppm). Ozone is formed in the atmosphere by the reaction of Volatile Organic Compounds (VOCs) and Nitrogen Oxides (NOx) in the presence of heat and sunlight. In May 2002, The Texas State Legislature passed Senate Bill 5, the Texas Emissions Reduction Plan (TERP), to reduce the emissions of NOx by several sources. As part of the 2001 building energy performance standards program which is one of the programs in the TERP, the Texas Legislature established the 2000 International Energy Conservation Code (IECC) as the state energy code. Since September 1, 2001, the 2000 IECC has been required for newly constructed single and multifamily houses in Texas. Therefore, this study develops and applies portions of a methodology to calculate the energy savings and NOx emissions reductions from the adoption of the 2000 IECC to new single family houses in non-attainment and affected counties in Texas. To accomplish the objectives of the research, six major tasks were developed: 1) baseline data collection, 2) development of the 2000 IECC standard building simulation, 3) projection of the number of building permits in 2002, 4) comparison of energy simulations, 5) validation and, 6) NOx emissions reduction calculations. To begin, the 1999 standard residential building characteristics which are the baseline construction data were collected, and the 2000 IECC standard building characteristics were reviewed. Next, the annual and peak-day energy savings were calculated using the DOE-2 building energy simulation program. The building characteristics and the energy savings were then crosschecked using the data from previous studies, a site visit survey, and utility billing analysis. In this thesis, several case study houses are used to demonstrate the validation procedure. Finally, the calculated electricity savings (MWh/yr) were then converted into the NOx emissions reductions (tons/yr) using the EPA's eGRID database. The results of the peak-day electricity savings and NOx emissions reductions using this procedure are approximately twice the average day electricity savings and NOx emissions reductions.
Files in this item: 1etd-tamu-2003C-ARCH-Im-1.pdf (11.38Mb)
Kissock, John Kelly (January 16, 2008)[more][less]
Abstract: Measured energy savings promote and sustain energy conservation retrofits by verifying the success of retrofits, determining pay-back schedules, guiding the selection of future retrofits and identifying opportunities for further savings. This dissertation develops a methodology to measure retrofit energy savings and the uncertainty of the savings in commercial buildings. The functional forms of empirical models of cooling and heating energy use in commercial buildings are derived from an engineering analysis of constant-air-volume and variable-air-volume HVAC systems. One, two, three and four parameter, temperature-dependent regression models are proposed to model baseline energy use. Retrofit savings are measured as the difference between the baseline energy use project by the models and the measured post-retrofit energy use. A hybrid ordinary least squares/autoregressive method is developed to determine the uncertainty of the predicated energy use and savings. The annual predictive ability of models based on pre-retrofit data sets of less than a full year is investigated. The energy delivery efficiency is introduced to measure the efficiency of air-side systems at meeting the net building load. A preliminary investigation of the use of artificial neural network models to measure savings is presented. The methodology is demonstrated on case study examples using software specifically developed for the analysis of commercial building energy use.
Files in this item: 1ESL-TH-93-12-03.pdf (7.376Mb)
A methodology to pre-screen commercial buildings for potential energy savings using limited informationZhu, Yiwen (Texas A&M University, December 2005)[more][less]
Abstract: Typical energy audits are sufficiently expensive and time-consuming that many owners and managers of buildings are not willing to invest the time and money required for a full audit. This dissertation provides a methodology to identify buildings with large potential energy savings using limited information, specifically, utility bills, total area and weather data. The methodology is developed based on the hypothesis: if a commercial building is properly designed, constructed, operated, and maintained, the measured energy consumption should approximately match the simulated value for a typical building of the same size with the most efficient HVAC system; otherwise, there may be potential for energy savings. There are four steps in the methodology: 1) testing to determine whether the utility bills include both weather-dependent and weatherindependent loads; 2) separating weather-dependent and weather-independent loads when both are present in the same data; 3) determining the main type of HVAC system; 4) estimating potential energy savings and recommending an energy audit if appropriate. The Flatness Index is selected to test whether the utility bills include both weatherdependent and weather-independent loads. An approach to separate the utility bills based on thermal balance is developed to separate utility bills into weather-dependent and weather-independent loads for facilities in hot and humid climates. The average relative error in estimated cooling consumption is only 1.1% for 40 buildings in Texas, whereas it is -54.8% using the traditional 3P method. An application of fuzzy logic is used to identify the main type of HVAC system in buildings from their 12-month weatherdependent energy consumption. When 40 buildings were tested, 18 systems were identified correctly, seven were incorrect and the HVAC system type cannot be identified in 15 cases. The estimated potential savings by the screening methodology in eight large commercial buildings were compared with audit estimated savings for the same buildings. The audit estimated savings are between 25% - 150% of the potential energy savings estimated by the screening procedure in seven cases. The other two cases are less accurate, indicating that further refinement of the method would be valuable. The data required are easily obtained; the procedure can be carried out automatically, so no experience is required. If the actual type of HVAC system, measured weather-dependent, and weather-independent energy consumption are known, the methodology should work better.
Files in this item: 1etd-tamu-2005C-MEEN-Zhu.pdf (7.856Mb)
Modeling the effects of Refrigerant Charging on Air Conditioner Performance Characteristics For Three Expansion DevicesFarzad, Mohsen (August 1990)[more][less]
Abstract: An experimental and analytical study concerned with the off-design refrigerant charging of air conditioners is presented. A series of experiments were conducted to characterize the effects of refrigerant charge and type of expansion device on the system performance (capacity, EER, SEER, etc.) of an air conditioner. All experiments were performed according to the ASHRAE Standard . The effects of off-design refrigerant charge in the system, type of expansion device (capillary tube, TXV, and short-tube orifice), and outdoor dry-bulb temperature (82° to l00°F) on the wet and dry steady state and cyclic tests are addressed in this study. The fully charged condition was established as a base case for all the expansion device systems. A full charge was obtained by charging the unit to the superheat or subcooled condition specified by the manufacturer charging chan. Once the full charge was determined, refrigerant was then added in 5% increments from -20% of full charge to +20% of full charge to cover the full range of charging conditions for a particular expansion device being tested. The investigation of off-design charging indicated that the system performance variables (total capacity, EER, and SEER) of the unit with capillary tube were more sensitive to off-design charging than the systems with TXV and short-tube orifice. From -20% to +20% charging, the capacity and EER showed a strong dependence on the outdoor temperature, but varied little with charge for the TXV and short-tube orifice expansion systems. A -20% charging resulted in a 21% reduction in SEER while a +20% charging produced an 11% reduction in SEER for the unit with capillary tube. For the TXV, SEER dropped 2% and 8% for -20% and +20% refrigerant charging, respectively. The SEER was constant at 9.4 for all the charging condition except for -5% charging where it peaked to 9.9 for the short-tube orifice expansion system. This trend would suggest that the range of sensitivity of a short-tube orifice system is confined within a small refrigerant charge. A new heat exchanger model based on tube-by-tube simulation was developed and integrated into the ORNL heat pump model. The model was capable of simulating the steady state response of a vapor compression air-to-air heat pump and air conditioner commonly used in residential applications. The simulated results were compared with laboratory tests at two outdoor temperatures. It was found that the ORNL model estimates were within an average of 3% of the experimental results from - 10% to +10% charging conditions. The model predicted the system performance up to 8% higher than measured results at +/-20% and +/-15% charging conditions. Among the eight void fraction models studied, the Hughmark model showed the best agreement between superheat and subcooled temperatures, refrigerant flow rate and capacity and the measured results.
Files in this item: 1ESL-TH-90-08-04.pdf (4.680Mb)
Muraya, Norman K. (December 1994)[more][less]
Abstract: Non-linear finite element models were developed to simulate transient heat and mass transfer in the soil surrounding the ground heat exchangers of ground-coupled heat pumps (GCHPs) operating in the cooling mode. Parametric studies were performed with two dimensional horizontal cross sectional models. The heat transfer and temperature distributions yielded excess errors less than 6% and 3%, respectively, when compared to analytical solutions. Two constant temperature sources performed equivalent heating as one constant temperature source having twice the radius. For constant heat flux sources, the equivalent radius was found to be increased by √2. A heat flux equivalent radius (tau_h,eqv) was developed and shown to be more consistent than the geometric radius (tau_g,eqv). All equivalent radii varied with time and source separation. A heat exchanger effectiveness for two sources, (epsilon_A), was introduced based on an earlier definition for one source. Effectiveness was found to be independent of a dimensionless temperature variable that included temperatures of the tubes and soil, and varied only with separation distance at steady state. Thermal short circuiting was defined as 1 – epsilon_A and ranged from 38% to 47% in the reasonable installation separation range. Non-homogenous media were modeled by varying backfill thermal conductivity. Maximum heat transfer was achieved with a fictitious backfill thermal conductivity of 1,000 W/m-K, while measured bentonite backfill conductivities were less than 2 W/m-K. The overall heat transfer increased with backfill thermal conductivity but epsilon_A decreased. Therefore, the backfill effectiveness of Couvillion was used to rank backfill performance. The range of the backfill effectiveness was from 45% for touching bentonite backfill tubes to 60% for the fictitious backfill at a separation of seven l/Do. Moisture migration was incorporated into the numerical finite element model by formulating coupled partial differential equations for non-linear heat and mass transfer. Simulations with decreasing soil moisture contents resulted in lower thermal conductivity and performance degradation. Increasing the bore hole size improved the efficiency (decreased thermal short circuiting) by as much as 20%. In addition, higher conductivity fictitious backfills improved efficiency by up to an additional 20%. However, cost savings in both cases had a negligible effect compared to the bore hole cost.
Files in this item: 1ESL-TH-94-12-13.pdf (5.243Mb)
Cho, Sool Yeon (June 10, 2008)[more][less]
Abstract: The objective of this study is to investigate the reasons why the performance of mechanical systems degrades over time after commissioning and to recommend intervals at which testing should be performed to maintain the integrity of the commissioning process. The initial phase of this study investigated the energy savings in ten buildings commissioned between 1996 and 1997. The results of this study show that hot water, chilled water and electric savings have all degraded. Aggregate annual cost savings for the ten buildings decreased by 17% from 1998 to 2000 from $1,192,884 to $985,626. The investigation has found that the decreased savings are due to numerous changes in control settings since the commissioning and to significant control malfunctions in two buildings.
Files in this item: 1ESL-TH-02-05-01.pdf (77.98Mb)
Liu, Mingsheng (August 1992)[more][less]
Abstract: The influence of heat recovery on the energy impact of air infiltration, and the systematic error due to the steady-state method were studied both experimentally and theoretically. Two methodologies suitable for measurement of the overall heat loss factors in full-size houses have been developed and validated. Dynamic measurements of Infiltration Heat Exchange effectiveness (IHEE), which expresses the air infiltration heat recovery as a fraction of the classical value of air infiltration energy consumption, showed that results from earlier steady-state measurements can be approximately applied to dynamic conditions when solar radiation is not present. However, this study has shown for the first time that IHEE is strongly dependent on air flow direction due to the impacts of air flow on the recovery or rejection of solar radiation energy. IHEE values greater than one and less than zero have been measured. These values are impossible in the absence of solar radiation. The results highlight the necessity of considering the air infiltration heat recovery and improving the current design methods for calculating the heating and cooling loads in buildings. The experimental and theoretical investigation show that steady-state methodology can: *be used without systematic error in the case of constant air flow *result in IHEE prediction error in a range of 1% to 8% when one-way dynamic air f1ow is present *cause significantly larger error when balanced dynamic air flow is present. The SSP (Single input and Single output data Pair) method can identify UAo of an enclosure using short term measurement data, typically a few hours long. It has overcome most of the typical problems in UA0 identification, such as errors due to thermal storage, ground heat transfer, inter-correlated multi-inputs, and solar radiation. The STAM (Short Term Average Method) has also been developed which makes it possible for the first time to determine both the UA and the solar aperture precisely under outdoor conditions from a two-day or a three-day test. These methods were developed and used to measure heat loss factors needed to determine IHEE values in this study.
Files in this item: 1ESL-TH-92-08-06.pdf (9.925Mb)