Browsing ESL Theses and Dissertations by Issue Date
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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.
URI: http://hdl.handle.net/1969.1/94832 Files in this item: 1
ESL-TH-88-08-01.pdf (29.66Mb) -
Peterson, 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.
URI: http://hdl.handle.net/1969.1/93419 Files in this item: 1
ESL-TH-88-08-02.pdf (26.27Mb) -
Katipamula, Srinivas (December 1989)[more][less]
Abstract: An experimental and analytical study concerned with the transient performance of heat pumps is presented. A series of tests were performed to study and characterize the transient sensible and dehumidification performance of a heat pump in the cooling node. All the tests were conducted according to the ASHRAE Standard (1983). The effects of indoor dry-bulb temperature (72 to 80 F), indoor relative humidity (20 to 67%), outdoor dry-bulb temperature (82 to 100 F), cycling rate (0.8 to 10 cph) and percent ON-time (20 to 95%) on the transient performance (sensible and latent capacity, efficiency and sensible heat ratio) are addressed in this study. The results indicated that part load factor (PLF) can be as low as 0.65 at low percent ON-times and high cycling rates. The combination of low percent ON-times and high cycling rates produced maximum cyclic losses. The dehumidification process usually started between 60 to 150 seconds after start-up depending on the indoor ambient conditions, percent ON-time and cycling rate. The sensible and latent capacity response and part load efficiency of the heat pump increased with an increase in indoor relative humidity. There was a slight increase in PLF with indoor dry-bulb temperature. The outdoor dry-bulb temperature did not have any effect on the transient performance. Based on the functional relationship of PLF and coefficient of degradation (C_D) with the five independent variables a multiple linear regression analysis was performed on the experimental data. The analysis yielded two general equations to predict PLF and C_D. A lumped parameter heat pump transient analysis computer model was developed, which drew upon methodologies from the earlier models by Chi and Didion [1982] and Oak Ridge National Laboratory [1981]. The model was capable of simulating the transient response of a vapor compression air-to-air heat pump commonly used in residential applications. The simulated results were in good agreement with the laboratory results at high percent ON-times (> 20) and high relative humidities (> 45).
URI: http://hdl.handle.net/1969.1/6424 Files in this item: 1
ESL-TH-89-12-02.pdf (4.150Mb) -
Farzad, 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 [1983]. 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.
URI: http://hdl.handle.net/1969.1/6420 Files in this item: 1
ESL-TH-90-08-04.pdf (4.680Mb) -
Noboa, Homero L. (December 1991)[more][less]
Abstract: A model of the radiant heat transfer in attics containing dusty radiant barriers was developed. The geometrical model was a triangular enclosure in which the temperatures of the enclosing surfaces were known. The dust particles were simulated as areas of diameter equal to the mean diameter of the real dust to be analyzed and an emissivity substantially larger than the emissivity of the radiant barrier. Several shape factors were calculated using shape factor algebra, including a procedure to find the shape factor between a small rectangle and a triangular surface perpendicular to the rectangular plane. The thermal model was developed using the "Net Radiation Method" in which the net heat exchange between the surfaces surrounding the enclosure was found by solving a system of equations that has as many equations as the number of surfaces involved in the calculations. This led to the necessity of solving a very large system of equations in order to account for the dust particles in a representative amount. The solution of the system of equations provided the heat flux for each element of the enclosure. Finally, replacing the radiant barrier and the dust particles for an equivalent surface corresponding to the dusty radiant barrier provided the means to calculate the emissivity of this dusty radiant barrier. The theoretical model was tested to assess its validity. The experimentation was carried out using a reflection emissometer to measure the increase of the emissivity of aluminum radiant barrier when known quantities of dust were artificially applied to it. The experimental results showed good agreement with the theoretical model. A linear relationship between the emissivity and the area of dust coverage was found. The simple relation developed can be used in future research which still has to deal with the determination of the area of dust coverage by using the geometrical model of dust superposition or other statistical model to simulate the random location of random size dust particles over the radiant barrier.
URI: http://hdl.handle.net/1969.1/6461 Files in this item: 1
ESL-TH-91-12-01.pdf (18.99Mb) -
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.
URI: http://hdl.handle.net/1969.1/6463 Files in this item: 1
ESL-TH-92-08-06.pdf (9.925Mb) -
Medina, 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.
URI: http://hdl.handle.net/1969.1/94831 Files in this item: 1
ESL-TH-92-12-04.pdf (5.868Mb) -
Robinson, 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.
URI: http://hdl.handle.net/1969.1/93418 Files in this item: 1
ESL-TH-93-08-05.pdf (28.62Mb) -
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.
URI: http://hdl.handle.net/1969.1/6425 Files in this item: 1
ESL-TH-93-08-02.pdf (4.280Mb) -
Bou-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.
URI: http://hdl.handle.net/1969.1/86260 Files in this item: 1
ESL-TH-94-12-01.pdf (63.93Mb) -
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%.
URI: http://hdl.handle.net/1969.1/6426 Files in this item: 1
ESL-TH-94-12-05.pdf (4.956Mb) -
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.
URI: http://hdl.handle.net/1969.1/6422 Files in this item: 1
ESL-TH-94-12-13.pdf (5.243Mb) -
McJimsey, 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.
URI: http://hdl.handle.net/1969.1/6423 Files in this item: 1
ESL-TH-94-12-12.pdf (4.536Mb) -
Deng, 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.
URI: http://hdl.handle.net/1969.1/6428 Files in this item: 1
ESL-TH-97-05-02.pdf (23.32Mb) -
Wei, Guanghua (August 1997)[more][less]
Abstract: This thesis presents a broadly useful diagnostic methodology to engineers and plant managers for finding the in-situ operating characteristics of power plant boilers when metered data is either missing or obviously erroneous. The methodology is able to analyze conflicting measurements and utilize analytic redundancy (AR) to deduce the measurement or measurements which are substantially in error without shutting down the plant and recalibrating all instrumentation. It is shown, through the case study power plant, that the methodology is quite robust in identifying faulty instruments in plants which possess a low degree of hardware redundancy. Once the malfunctioning meters are identified and the historical data are corrected, boiler characteristic curves can be generated to guide the daily operation and assist future implementation of on-line optimal load allocation. Finally, suggestions are given for the on-line diagnostics of instrument performance, as well as some operational guidelines useful to plant engineers for improved boiler operation.
URI: http://hdl.handle.net/1969.1/6427 Files in this item: 1
ESL-TH-97-08-01.pdf (23.72Mb) -
Watt, 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.
URI: http://hdl.handle.net/1969.1/94784 Files in this item: 1
ESL-TH-97-12-03.pdf (54.24Mb) -
Munger, Bryce Kirtley (Energy Systems Laboratory, December 1997)[more][less]
Abstract: This thesis describes the development of an improved multipyranometer array (MPA) for the continuous remote measurement of direct and diffuse solar radiation. The MPA described in this thesis is an improvement over previously published MPA studies due to the incorporation of an artificial horizon that prevents reflected ground radiation from striking the tilted sensors, the development of an improved solution scheme for the calculation of the beam and diffuse solar radiation components, and the development of an empirical spectral correction for the photovoltaic-type sensors used in the MPA. In this thesis a description of the NIST-traceable calibration facility is provided and results are presented that compare the MPA predicted beam to beam measurements from a precision normal incidence pyrheliometer.
URI: http://hdl.handle.net/1969.1/6409 Files in this item: 1
ESL-TH-97-12-02.pdf (37.02Mb) -
Wang, 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.
URI: http://hdl.handle.net/1969.1/93388 Files in this item: 1
ESL-TH-98-12-01.pdf (25.40Mb) -
Beasley, R. C. (Energy Systems Laboratory (http://esl.tamu.edu), August 1999)[more][less]
Abstract: The development of the energy services industry and the implementation of energy savings retrofits by energy services companies has increased the focus on the performance of energy saving retrofits. Energy savings measurement, though not an exact science, has been developing as well to ensure the benefit of a retrofit and to provide a level of assurance for the customers of energy services companies. This thesis presents a useful methodology for baselining campus utility usage using regression modeling techniques and measured daily data for the purpose of measuring energy savings. The methodology of this thesis improves upon previous regression modeling of individual buildings by extending commercial building energy usage models to an entire campus, modeling the operation of a central plant, and modeling central plant equipment performance with regression models. By adding equipment production layers, the user can more easily determine the cause of changes in the primary energy usage of a central plant. The case study for the application of the methodology of this thesis was the Texas A&M University main campus central plant. Useful results were obtained by utilizing one portion of the data to develop an energy usage baseline model and using the second portion of the data to validate the performance of the baseline model. Further development of the methodology could include the addition of an economic module and refinement of the model to incorporate the use of hourly data.
URI: http://hdl.handle.net/1969.1/94830 Files in this item: 1
ESL-TH-99-08-01.pdf (59.82Mb) -
Kootin-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.
URI: http://hdl.handle.net/1969.1/85753 Files in this item: 1
ESL-TH-04-05-01.pdf (24.12Mb)
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