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RESEARCH PAPERS

J. Sol. Energy Eng. 1985;107(4):265-272. doi:10.1115/1.3267690.

A performance prediction methodology is developed which is applicable to most commercially available integral collection-storage passive solar domestic hot water systems. A computer model of a general ICS component was created to be compatible with the transient simulation program TRNSYS[3], and was used to develop and verify the simpler monthly performance prediction method. The method uses the system parameters from available test methods, monthly average climatic data, and load size to predict long term performance of ICS systems.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):273-276. doi:10.1115/1.3267691.

For single-pass open-loop solar thermal energy systems, in which the flow rate can vary with radiation but is constrained to have a given annual average, an upper bound is derived for the yearly energy delivery. Compared to the corresponding constant flow rate, single-pass open-loop system, the upper bound for additional yearly delivery is found to be negligible for solar systems with practical design parameters. This implies that the sophistication and expense involved in searching for, and implementing, optimal variable (radiation-dependent) collector flow rate strategies for these systems may not be worth the effort. The sensitivity of this upper bound to climatic and collector characteristics is determined analytically, and is illustrated by several numerical examples. The results derived are general in that they apply to all collector types.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):277-280. doi:10.1115/1.3267692.

A 1.5 × non-evacuated CPC type concentrator is described and tested. The results obtained can be summarized by F ′ ηo = 0.673 ± 0.001 and F ′ U = (2.64 ± 0.041) W/m2 ° C. The early average performance of the concentrator is calculated and compared with the performance of two other collector types at constant operating temperature: a selectively coated regular flat plate and an evacuated tube type collector. It is shown that the concentrator performs better than both the flat plate and the evacuated tube collector for constant operating temperatures for 35° C to 100° C in a climate like the one in Lisbon. The three collectors are also compared operating in two systems: (1) DHW in which they all deliver comparable yearly average amounts of energy, and (2) IPH at 95° C (process return temperature = 65° C) in which the flat plate delivers ∼30 percent less yearly energy on the average in comparison with the other two which behave very much in the same way. The 1.5 × low cost is discussed in comparison with the other two collector types, establishing the concentrator as an excellent choice for hot water heating applications.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):281-285. doi:10.1115/1.3267693.

Spherically curved solar reflectors consist of a thin glass plate elastically bent to form a spherical surface, glued onto a honeycomb backing, and covered with steel plates at the back and with plastic strips on the sides. Nonlinear Von Karman plate equations are used to analyze the induced stresses in the glass plate as its deflections become large. The analysis consists of evaluation of stresses due to bending and membrane forces during the forming of the spherical surface, along with the calculation of edge moments and the transverse loads due to molds. The interaction of the plate with the honeycomb is analyzed assuming that the plate is resting on an elastic foundation (honeycomb), where the edge moments and the transverse forces calculated earlier are released. The results are compared with other available solutions as well as experimental data.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):286-292. doi:10.1115/1.3267694.

Energy conservation and economic potential of large capacity (∼MW th ) solar-assisted water-to-water heat pumps (SAHP) is evaluated for year round low temperature (<100° C) industrial process heating applications at four locations in the United States. The long-term thermal performance of the SAHP system is determined by a recently proposed utilizability method that accounts for the variable coefficient of performance of the SAHP system. The large SAHP system appears to be an attractive energy conservation alternative to fuel oil and electricity for locations with high solar resources and low electricity costs. In all but one location, the SAHP system was clearly superior to the solar only systems, such as flat plate and concentrating collectors, from the point of view of the annualized delivered energy cost. For the ranges of collector area and load temperatures considered in this study, the large SAHP system has clearly superior energy conservation potential at all four locations compared to other alternatives such as fuel oil or electricity. However, the practial suitability of SAHP cycle, as determined by the levelized cost of delivered energy, is unfavorable at all four locations when compared with fuel oil.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):293-296. doi:10.1115/1.3267695.

Two configurations of series solar assisted heat pumps were experimentally evaluated in TECH House I on the University of Tennessee campus in Knoxville, Tenn. During the 1979–1980 heating season, a 4.2 m3 (1100 gal) insulated above ground storage tank was utilized. During the 1980–1981 heating season, the storage system consisted of an uninsulated 7.6 m3 (2000 gal) steel tank buried 2.1 m (7 ft) in the ground. For 1979–1980 the heating season system performance factor was 2.42 and the system’s maximum peak electric demand was 11.20 kW. For 1980–1981 the heating season performance factor increased to 3.16 while the maximum peak electric demand decreased to 4.33 kW.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):297-301. doi:10.1115/1.3267696.

A parallel solar augmented heat pump system has been experimentally evaluated in TECH House IV for three heating seasons between fall 1979 and spring 1982. Several changes were made in the operation of the system during the three year period. During 1979–1980, the use of on-peak purchased energy was minimized by charging the pebble bin in the off-peak period with a resistance duct heater. This configuration resulted in 83 percent of the purchased energy occurring in the off-peak period but the seasonal performance factor was only 1.61. During 1980–1981, the system was operated in the normal mode without the use of the off-peak heater. The seasonal performance factor then increased to 2.56. During 1981–1982, the mode of operation was the same as 1980–1981, but new outer cover sheets were installed and the inner cover sheet was eliminated resulting in a single glazed collector. The seasonal performance factor for the 1981–1982 season was measured to be 2.11.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):302-307. doi:10.1115/1.3267697.

This paper discusses the design, construction, and initial operation of the solar pond at Los Alamos National Laboratory. This 232 m2 pond is the third facet of a threefold approach to the study of hydrodynamic effects in double diffusive systems, such as solar ponds. The first two facets are flow visualization experiments and one-dimensional laboratory tank tests [1]. Data from these experiments, in addition to other data from the literature, are used to validate the one-dimensional dynamic performance pond model developed by one of the authors [2]. Our particular interest is the boundary-layer structure at the interfaces between the convecting and nonconvecting zones, interaction between the zones, and surface zone effects including diurnal heating effects and wind-induced turbulence. A pond, such as the one this paper describes, provides possible insight into several pond physical processes that may not occur in smaller-scale laboratory experiments due to edge effects, or may be impossible to simulate.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):308-314. doi:10.1115/1.3267698.

An analytical Integrated Daily Performance Model (IDPM) is developed to predict the long term performance of solar air heating systems. The model is developed for systems using packed-bed energy storage and includes the effects of temperature stratification within the storage. The model makes use of the stratification coefficient approach to integrate the equations describing system performance. This analysis differs from similar previous analyses for water heating systems in that a control scheme more typical of air heating systems is used: collector output may go directly to either storage or the load. The IDPM is compared to simulations using a fully mixed model of storage and a single-phase model of storage. The comparisons show that the IDPM is more accurate than the mixed model and requires considerably less computation time than simulations using the single-phase model. In addition, the IDPM identifies several parameters that are important to system performance, but are not easily identified by non-analytical analyses.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):315-321. doi:10.1115/1.3267699.

A review is presented of the development, performance, and operation of a digital image radiometer (DIR) used to evaluate and enhance heliostat optical and tracking performance at the Solar One 10 MWe pilot plant at Daggett, Calif. The system, termed the beam characterization system (BCS), is based on digitizing, calibrating, and computer-processing video images of heliostat-reflected beams displayed on four 30- by 40-ft targets located on the tower beneath the receiver. Additionally, the radiance distribution of the sun is simultaneously recorded by a separate, specially modified solar-tracking video camera. The basic theory and analytical techniques used to determine beam centroid error (i.e., heliostat pointing errors), the actual incident beam power, spillage power off the receiver, and solar radiance distribution are described. The computer system is presented including the automatic data acquisition mode, the interface with the heliostat array controller (HAC), and the data acquisition system (DAS). Data display for plant operator purposes and additional data acquired and stored for more detailed engineering evaluations are discussed. Advanced applications of the DIR such as determination of total incident flux on a receiver from a field of heliostats, reflectance monitoring, and measurement of atmospheric attenuation are presented.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):322-325. doi:10.1115/1.3267700.

Large scale field experiments in aquifer thermal energy storage (ATES) were conducted between September, 1976, and November, 1982. Volumes of 7,700 m3 , 54,800 m3 , 58,000 m3 , 24,400 m3 , 58,000 m3 , and 58,680 m3 were injected at average temperatures of 35.0° C, 55.0° C, 55.0° C, 58.5° C, 81.0° C, and 79.0° C, respectively, in an aquifer with ambient temperature of 20.0° C. Based on recovery volumes equal to the injection volumes, the respective energy recovery efficiencies were 69, 65, 74, 56, 45, and 42 percent. Primary factors in reduction of efficiency were aquifer nonhomogeneity and especially convection due to buoyancy of the injection volumes.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):326-334. doi:10.1115/1.3267701.

A discussion of the approaches to, and benefits of, windmill tip-speed ratio (TSR) control is presented. Rotational speed regulation via load-controlled impedance matching is identified as the most efficient control method. An all-mechanical, self-powered windmill TSR controller using this method is presented with a discussion of its operation and wind tunnel test results. The controller, which is applicable to a variety of windmill/load combinations, also provides for rotor start-up and for shutdown in high winds. A design methodology is presented and used to design a controller for a windmill driving an electrical generator and for the same windmill driving a water pump. These designs are verified with a digital computer simulation using real wind data. The TSR controller regulated windmill speed for efficient operation at all wind speeds, limited only by the power rating of the windmill and load machinery. The simulation results also demonstrate the economic feasibility of the system.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):335-342. doi:10.1115/1.3267702.

This paper presents data for convective heat transfer coefficients on the front surface of a free-standing array of solar collectors mounted on the flat roof of a low warehouse-type building and exposed to the wind. The data were obtained by testing a 1:36 scale model in highly turbulent nonuniform flows which simulated the natural wind. For typical full scale conditions, the heat transfer coefficients are substantially lower than those given by a commonly used correlation. The coefficients are only mildly sensitive to wind direction, location of the array on the roof and characteristics of the wind.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):343-351. doi:10.1115/1.3267703.

In this work thermal oscillations at the dryout front in an electrically heated composite tube of inconel and glass have been studied experimentally and analytically. The tube has an inside diameter of 17.2 mm, and a heated length of 1913 mm. The thickness of the inconel half tube is 0.89 mm. In the experiments deionized water and Freon-113 were used as the test liquids while the pressure at the exit of the tube was one atmosphere. The dryout front was established at a predetermined height from the inlet. The frequency and magnitude of the wall temperature oscillations in the vicinity of the dryout front has been obtained from the temperature-time history. The most probable time period obtained from the probability distributions has been correlated with dimensionless groups formed with mass velocity, tube diameter and the physical properties of the test liquid. Normalized probability distributions for the time period have been found to be represented by a modified gamma-distribution. The magnitude and the nature of the temperature oscillations has been predicted by solving the energy equation for the heated tube and the mass conservation equation for the liquid film left on the wall during upward movement of the dryout front. The predictions have been compared with the data.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Sol. Energy Eng. 1985;107(4):352-355. doi:10.1115/1.3267704.
Abstract
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):357-359. doi:10.1115/1.3267706.
Abstract
Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):359-362. doi:10.1115/1.3267707.
Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. Sol. Energy Eng. 1985;107(4):363. doi:10.1115/1.3267708.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 1985;107(4):363-364. doi:10.1115/1.3267709.
FREE TO VIEW
Abstract
Topics: Heat , Design , Solar energy
Commentary by Dr. Valentin Fuster

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