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)
Analysis of Innovative HVAC System Technologies and Their Application for Office Buildings in Hot and Humid ClimatesTanskyi, Oleksandr (Energy Systems Laboratory, December 2010)[more][less]
Abstract: ABSTRACT Analysis of Innovative HVAC System Technologies and Their Application for Office Buildings in Hot and Humid Climates. (December 2010) Oleksandr Tanskyi, B.S., National Technical University of Ukraine; M.S., National Technical University of Ukraine Co-Chairs of Advisory Committee: Dr. David E. Claridge Dr. Michael B. Pate The commercial buildings sector in the United States used 18% (17.93 Quads) of the U.S. primary energy in 2006. Office buildings are the largest single energy consumption category in the commercial buildings sector of the United States with annual energy consumption around 1.1 Quads. Traditional approaches used in commercial building designs are not adequate to save energy in both depth and scale. One of the most effective ways to reduce energy consumption is to improve energy performance of HVAC systems. High-performance HVAC systems and components, as well as application of renewable energy sources, were surveyed for buildings in hot and humid climates. An analysis of performance and energy saving potential estimation for selected HVAC systems in hot and humid climates was developed based on energy consumption simulation models in DOE-2.1E. A calibrated energy consumption model of an existing office building located in the hot and humid climate conditions of Texas was developed. Based on this model, the energy saving potential of the building was estimated. In addition, energy consumption simulation models were developed for a new office building, including simulation of energy saving measures that could be achieved with further improvements of HVAC system above the energy conservation codes requirements. The theoretical minimum energy consumption level for the same office building was estimated for the purpose of evaluating the whole building energy efficiency level. The theoretical minimum energy consumption model of the office building was designed to provide the same level of comfort and services to the building occupants as provided in the actual building simulation model. Finally, the energy efficiency of the building that satisfies valid energy conservation codes and the building with an improved HVAC system was estimated based on theoretically minimum energy consumption level. The analysis provided herein can be used for new building practitioners and existing building owners to evaluate energy reduction potential and the performance of innovative technologies such as dedicated outdoor air system, displacement ventilation, improved cooling system efficiency, air source heat pumps and natural gas heat pumps.
Files in this item: 1ESL-TH-10-12-01.pdf (4.684Mb)
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)
Malhotra, Mini (December 2009)[more][less]
Abstract: This dissertation addresses the issues of climate change and depletion of non-renewable resources of energy and water, and aims at eliminating the use of non-renewable resources of energy and water for the building operation in single-family detached residences in the U.S. With this aim, this study investigated the feasibility of the off-grid, off-pipe design approach in six climate locations across the U.S. to achieve self-sufficiency in a house for building energy, indoor water use, and household wastewater and sewage disposal using only on-site available renewable resources. For the analysis, a 2,500 ft2, 2000/2001 International Energy Conservation Code standard reference house with typical building and usage characteristics was selected as the base case. The six U.S. climate locations included: Minneapolis, MN, Boulder, CO, Atlanta, GA, Houston, TX, Phoenix, AZ, and Los Angeles, CA. The renewable resources considered for this study included: solar radiation, wind, biomass for building energy needs; rainwater for indoor water use. In addition, the building site was considered for the disposal of household wastewater and sewage. The selected climate locations provided different scenarios in terms of base-case building energy needs and availability of renewable resources. Depending on these, energy and water efficiency measures were selected for reducing the building needs. For the reduced building needs, the sizing of systems for self-sufficiency was performed, including: solar thermal system for building’s space heating and water heating needs, photovoltaic and wind power systems for building’s electricity needs; rainwater harvesting system for indoor water needs; and septic system for the on-site disposal of household wastewater and sewage. In this manner, an integrated analysis procedure was developed for the analysis and design of off-grid, off-pipe homes, and was demonstrated for six U.S. climate locations. The results of the analysis indicated that achieving self-sufficiency for energy, water and sewage disposal was possible in all climates provided the systems for the collection and storage of renewable resources were large. On the other hand, the utilization of these systems was small for locations, where the year-to-year and seasonal variations in the weather conditions and availability of climate resources was large. For increased system utilization, minimization of the peak building needs, utilization of harvested energy for secondary purposes, and considering alternative systems for such applications are preferred.
Files in this item: 1ESL-TH-09-12-02.pdf (5.970Mb)
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 an Automated Methodology for Calibration of Simplified Air-Side HVAC System Models and Estimation of Potential Savings from Retrofit/Commissioning MeasuresBaltazar-Cervantes, Juan-Carlos (December 2006)[more][less]
Abstract: This dissertation provides one methodology to determine potential energy savings of buildings with limited information. This methodology is based upon the simplified energy analysis procedure of HVAC systems and the control of the comfort conditions. Numerically, the algorithm is a tailored exhaustive search over all the independent variables that are commonly controlled for a specific type of HVAC system. The potential energy savings methodology has been applied in several buildings that have been retrofitted and/or commissioned previously. Results from the determined savings for the Zachry building at Texas A&M after being commissioned show a close agreement to the calculated potential energy savings (about 85%). Differences are mainly attributed to the use of simplified models. Due to the restriction of limited information about the building characteristics and operational control, the potential energy savings method requires the determination of parameters that characterize its thermal performance. Thus, a calibrated building is needed. A general procedure has been developed to carry out automated calibration of building energy use simulations. The methodology has been tested successfully on building simulations based on the simplified energy analysis procedure. The automated calibration is the minimization of the RMSE of the energy use over daily conditions. The minimization procedure is fulfilled with a non-canonical optimization algorithm, the Simulated Annealing, which mimics the Statistical Thermodynamic performance of the annealing process. That is to say, starting at a specified temperature the algorithm searches variable-space states that are steadier, while heuristically, by the Boltzmann distribution, the local minima is avoided. The process is repeated at a new lower temperature that is determined by a specific schedule until the global minimum is found. This methodology was applied to the most common air-handler units producing excellent results for ideal cases or for samples modified with a 1% white noise.
Files in this item: 1ESL-TH-06-12-01.pdf (3.649Mb)
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)
Development of Empirical Temperature and Humidity-Based Degraded-Condition Indicators for Low-Tonnage Air ConditionersWatt, J. B. (Energy Systems Laboratory (http://esl.tamu.edu), December 1997)[more][less]
Abstract: A split-system direct-expansion air conditioner was used to empirically determine temperature and return-air humidity indicators that could detect performance degradation resulting from degraded conditions. The air conditioner test bench was equipped with the ability to use either a short-tube orifice (STO) or a thermal expansion valve (TXV). The degraded conditions studied include low evaporator airflow, highand low-charge, and a blocked condenser coil. The work presented in this thesis is experimentally based which could identify degraded effects that fall outside of a simulation-based approach. It sought to utilize only low-cost temperature sensing means, although return-air humidity was an important factor for obtaining early detection over a wide range of operating conditions. It was empirically based rather than model based to reduce computation time with a real-time processor. Further, the current work differentiated between a system that uses a shorttube orifice (STO), or fixed-orifice expansion, and a system that uses a thermal expansion valve (TXV), or variable-orifice expansion. This thesis shows that low-cost temperature sensors could be used to detect the degraded conditions studied. However, it is also shown that indicators of low evaporator airflow depend on three loading factors; outdoor-air temperature, return-air temperature, and return-air humidity. In the literature, the humidity sensing point has been neglected by automated detection systems for failures and degraded conditions of low-tonnage air conditioners. The effects of the loading factors on the indicators relative to improper charge and a blocked condenser coil were not studied. Finally, while there were differences in the performance of a STO system and a TXV system relative to the degradations studied, a common set of indicators was identified that could detect degraded conditions without regard to the expansion device.
Files in this item: 1ESL-TH-97-12-03.pdf (54.24Mb)
Song, Suwon (September 25, 2007)[more][less]
Abstract: During the past decade, utility companies and others have offered new construction programs to promote energy savings based on energy-efficient design, which maximize design flexibility as well as energy savings. For such programs, the concept of Measurement and Verification (M&V) of a new building continues to become more important because efficient design alone is often not sufficient to deliver an efficient building. Simulation models that are calibrated to measured data can be used to evaluate the energy performance of new buildings if it is compared to energy baselines such as similar buildings, energy codes, and design standards (IPMVP 2003; Torcellini et. 2004). Unfortunately, there is a lack of detailed M&V methods and analysis methods to measure energy savings from new buildings that would have hypothetical energy baselines. In addition, many important questions remain, for example: how to simulate and calibrate a simulation with measured data, how to develop energy baselines for comparison to the new building, and how to calculate energy savings compared to energy baselines. Therefore, this study developed and demonstrated several methodologies for evaluating the energy performance of new commercial buildings using a case-study building in Austin, Texas, in terms of: 1) Whole-building energy metering with in-situ measurements, 2) Simulation and calibration methods applicable to new buildings, and 3) Building energy baselines and savings assessments. Consequently, three new M&V methods were developed in this study to enhance the generic M&V framework (IPMVP 2003) for new buildings, including: 1) The development of a procedure to synthesize weather-normalized cooling energy use (i.e., Btu cooling production) from a correlation of MCC electricity use when chilled water use is unavailable, 2) The development of an improved method to analyze measured solar transmittance against incidence angle for sample glazing using different solar sensor types, including an Eppley PSP and Li-Cor sensor, and 3) The development of an improved method to analyze chiller efficiency and operation at part-load conditions. Second, three new methods were also developed and analyzed in the process of the as-built model simulation and calibration, including: 1) A new percentile analysis to the previous signature method (Wei et al. 1998) for use with a DOE-2 calibration, 2) A new analysis to account for undocumented exhaust air in DOE-2 calibration, and 3) An analysis of the impact of synthesized direct normal solar radiation using the Erbs correlation (Duffie and Beckman 1991) on DOE-2 simulation. Third, an analysis of the actual energy savings compared to three different energy baselines was performed, including: 1) Energy Use Index (EUI) comparisons with sub-metered data, 2) New comparisons against Standards 90.1-1989 and 90.1-2001, and 3) A new evaluation of the performance of selected ECDMs. Finally, potential energy savings were also simulated from selected improvements, including minimum supply air flow, undocumented exhaust air, and daylighting. As a result, the calibrated models were determined to have an overall 20.38% CV(RMSE) and a 0.63% MBE for the 2001 model and an overall 23.82% CV(RMSE) and a 0.61% MBE for the 2004 model, which compares well with the previous research (Kreider and Haberl 1994; Bou-Saada 1994; ASHRAE 2002). It was found that the end-use EUIs, such as cooling, heating, and Motor Control Center (MCC) electricity use can begin to provide information about the building’s heating and cooling efficiencies compared to similar buildings in a control groups. It was also determined that the REJ building is 20.79% more efficient than the Standard 90.1-1989 and approximately equal to the Standard 90.1-2001. Using an ECDM-subtraction method, the REJ building was shown to use approximately 67% less energy than the base-case building without the ECDMs. Potential savings were simulated to be 7,053.3 MMBtu (19.26%) from the combined improvements when compared to the 2004 as-built simulation.
Files in this item: 1ESL-TH-06-08-01.pdf (15.67Mb)
Landman, David Shea (October 23, 2007)[more][less]
Abstract: Indices are an important tool used to increase the accuracy and efficiency of the energy audit process. This thesis describes methods for using annual, monthly, daily, and hourly indices to improve current energy auditing processes. Eleven schools in different regions in Texas were identified for the case studies. The results show that certain indices match what is recommended by on-site visits and actually provide additional information that is sometimes not identified by a site visit. The indices developed provide a useful means by which energy audit firms and building owners/administrators can identify those areas of a building that have the most potential for energy cost reduction measures and operation and maintenance measures prior to a site visit. These indices assist the energy auditor in performing more efficient energy analyses on buildings. Each school in this thesis was audited prior to this study as part of the Texas LoanSTAR program. The indices were then developed using data from the period between September 1991 and December 1993. Retrofits to the case study buildings were completed during this period also. The sites were then reaudited to confirm the results from the previous audits, the usefulness of the indices, and/or discover new areas for energy savings. Two important new findings from this thesis are: 1) that schools are better modeled by grouping data into separate occupancy profiles consisting of school year months and summer months; and 2) the school year base-level electricity consumption can be calculated by taking the 25th percentiles of all twelve months of data reported. This approximately matches the base-level determined when running a 3-parameter cooling models on monthly energy consumption data and has the advantage that it does not require coincident weather data.
Files in this item: 1ESL-TH-98-05-01.pdf (51.05Mb)
Schliesing, J. S. (Energy Systems Laboratory (http://esl.tamu.edu), August 1988)[more][less]
Abstract: The effect of alternate defrost strategies on the transient performance of the air-source heat pump during the reverse-cycle defrost was investigated. Tests of a base-case heat pump configuration and defrost strategy were completed to provide a basis for performance evaluations of the alternate defrost strategies. The compressor and indoor coil fan operated continuously in the base-case defrost strategy, and the outdoor coil fan was stopped. Alternate defrost strategies utilized variations in fan and compressor operation during and after the defrost. Pre-starting of the outdoor coil fan prior to termination of the reverse-cycle defrost reduced pressure spikes commonly seen at defrost termination in the base-case defrost strategy. A strategy in which the compressor was stopped and the outdoor coil was allowed to drain of melted frost during the last three minutes of the defrost improved overall cyclic performance. Strategies which involved stopping of the indoor fan during defrost or delaying the start of the outdoor fan following defrost termination had a negative impact on defrost performance. A final strategy involved down-sizing of the heat pump compressor from 3.0 tons (36,000 btu/hr) capacity to 2.5 tons capacity. This alternate configuration had a comparable overall performance with the base-case while having a reduced frequency of required defrost periods.
Files in this item: 1ESL-TH-88-08-01.pdf (29.66Mb)
Effect of Refrigerant Charge, Duct Leakage, and Evaporator Air Flow on the High Temperature Performance of Air Conditioners and Heat PumpsRodriguez, Angel Gerardo (November 29, 2007)[more][less]
Abstract: <p>An experimental study was conducted to quantify the effect of several installation items on the high outdoor ambient temperature performance of air conditioners. These installation items were: improper amount of refrigerant charge, reduced evaporator airflow, and return air leakage from hot attic spaces. There were five sets of tests used for this research: two of them for the charging tests, two for the reduced evaporator airflow, and one for the return air leakage tests. </p> <p> For the charging tests, the indoor room conditions were 80°F (27.8°C) dry-bulb and 50% relative humidity. The outdoor conditions ranged from 95°F (35°C) all the way up to 120°F (48.9°C). Charge levels ranged from 30% undercharged to 40% overcharged for the short-tube orifice unit. For the thermal expansion valve (TXV) unit, charge levels ranged from -36% charging to +27% charging. Performance was quantified with the following variables: total capacity, energy efficiency ratio (EER), and power. The performance of the orifice unit was more sensitive to charge than it was for the TXV unit. For the TXV unit on the -27% to +27% charging range, the capacity and EER changed little with charge. A TXV unit and a short-tube orifice unit were also tested for reduced evaporator airflow. As evaporator airflow decreased, the capacity and EER both decreased as expected. However, the drop was not as significant as with the charging tests. For the extreme case of 50% reduced evaporator airflow, neither unit's capacity or EER dropped more than 25%. </p> <p> Return air leakage from hot attic spaces was simulated by assuming adiabatic mixing of the indoor air at normal conditions with the attic air at high temperatures. Effective capacity and EER both decreased with increased return air leakage. However, power consumption was relatively constant for all variables except outdoor temperature, which meant that for the same power consumption, the unit delivered much lower performance when there was return air leakage. The increase in sensible heat ratio (SHR) with increasing leakage showed perhaps the most detrimental effect of return air leakage on performance, which was the inability of the unit to absorb moisture from the environment. </p>
Files in this item: 1ESL-TH-95-08-01.pdf (28.21Mb)
The Effects of Expansion Devices on the Transient Response Characteristics of the Air-Source Heat Pump During the Reverse Cycle DefrostPeterson, K. T. (Energy Systems Laboratory (http://esl.tamu.edu), August 1988)[more][less]
Abstract: The effects of the defrost expansion device on the transient performance of the air-source heat pump during the reverse cycle defrost was investigated. A base case test was established using an average response thermal expansion valve in the experimental setup. The base case test was compared to tests using fast and slow response TXVs and different diameter orifices. The overall performance of each test was analyzed as well as a detailed investigation of the refrigerant dynamics. The results of the investigation for TXVs indicated bulb/suction line contact was more critical to the response of the TXV than the internal bulb charge. The orifice investigation showed a general trend of faster defrost times with larger orifices, although the largest orifices allowed liquid refrigerant to enter the compressor intake. The investigation also described the different refrigerant flow control of the TXV and the orifice.
Files in this item: 1ESL-TH-88-08-02.pdf (26.27Mb)
An Evaluation of the Bioclimatic Chart for Choosing Design Strategies for a Thermostatically-controlled Residence in Selected ClimatesVisitsak, Sopa (Energy Systems Laboratory, December 2007)[more][less]
Abstract: To be successful in sustainable building design, architects must consider energy efficient design strategies in the early design stage. Unfortunately, many architects still rely on simplified analysis, synthesis techniques, and historical examples. Although, building energy simulations are becoming more common in the design of buildings, architects rarely use simulation in the early design stage. The “Bioclimatic” charts have been used in the early design stage to define potential building design strategies to achieve indoor thermal comfort. Currently, many architects use the Givoni-Milne bioclimatic design chart (Milne and Givoni, 1979), which was developed based on principle reasoning and heuristics. There have been many attempts to develop computerized programs to further the bioclimatic analysis; however, there have been very limited efforts to test and evaluate the design strategies of the chart using simulations of a thermostatically-controlled building. Therefore, the purpose of this research is to promote comfortable buildings that reduce energy use through appropriate building design strategies. The objectives of the research are to develop a more accurate bioclimatic chart for a thermostaticallycontrolled residence by testing and evaluating the Givoni-Milne bioclimatic chart. The analysis is performed with DOE-2.1e program (Winkelmann, 1993) and TMY2 weather data (Marion and Urban, 1995) for several climates. To achieve these objectives, four main tasks were accomplished: 1) investigate the Givoni-Milne Bioclimatic Chart using representative weather data from several climates, 2) analyze and modify the design strategy boundaries using DOE-2 program and TMY2 weather data to simulate the effects of varied conditions of a thermostatically-controlled residence in different climates, 3) compare these new design strategy boundaries to the original Givoni-Milne design strategy boundaries, and 4) develop general guidelines for the new bioclimatic chart. In summary, there were some differences in the results from the Givoni-Milne bioclimatic chart and the DOE-2 simulation results. These results imply that without further modification, the G-M Chart may have only a limited use for a thermostaticallycontrolled residence. Therefore, to improve the usefulness of the bioclimatic chart the new bio-climatic chart for choosing design strategies for a thermostatically-controlled residence in the hot-humid climate of Houston, Texas, was developed. This new bioclimatic chart for a thermostatically-controlled residence will be a useful tool for architects and engineers in the early design stage. Similar versions of the new bioclimatic for other climates could then be developed.
Files in this item: 1ESL-TH-07-08-01.pdf (35.15Mb)
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)
The Impact of Charge on Performance of an Air-to-Air Heat Pump for R22 and Three Binary Blends of Refrigerants 32 and 134aRobinson, J. H. (Energy Systems Laboratory (http://esl.tamu.edu), August 1993)[more][less]
Abstract: An experimental study was conducted in which the performance of three blends of R134a and R32 were compared to R22. The effect of refrigerant charge and the size of expansion device on the performance of these refrigerants in an air-to-air heat pump operating in the air-conditioning mode was quantified. All tests were conducted according to ASHRAE Standard 116 (1983). The mixtures consisted of 60%/40%, 70%/30% and 80%/20% ratios by mass of R134a and R32. Charge levels of 5, 5.45, 5.90 and 6.00 kilograms (11, 12, 13 and 14 pounds) were tested. At each charge level, outdoor room conditions of 27.8°C, 35.0°C and 40.6°C (82°F, 95°F and 105°F) were tested. For each combination of charge level and outdoor room temperature, orifice diameters of 1.64, 1.78, 1.96 and 2.07 millimeters (0.0645, 0.0700, 0.0770 and 0.0815 inches) were tested. Three variables were used to quantify refrigerant performance: total capacity, total electrical power consumption and coefficient of performance (COP). Several other variables such as mass flow rate, compressor suction pressures and differential pressures were also used to determine system characteristics. The performance of the three mixtures was not as good as the R22. The capacities were between 7 and 17% lower than R22. The energy efficiency ratios were IV within three percent in some cases but the corresponding capacities at these EERs were more than 12% lower than the R22 base case. The best results for a mixture was the 60/40 blend. The capacity was 7.3% lower than the base case and the EER was 8.5% lower.
Files in this item: 1ESL-TH-93-08-05.pdf (28.62Mb)