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A thermosyphon solar water heating system with electric auxiliary heater was simulated using the TRNSYS simulation program. Location of the auxiliary heater, inside the storage tank or connected in series between the system and the user, was studied using the TMY meteorological data for Los Angeles, California. Simulations were performed for two different water load temperatures (60 and 80°C) and for two types of daily hot water volumes (250 and 150 l). Four types of daily hot water consumption profiles were used in the present study, namely; the widely used Rand profile, continuous, evening and morning profiles. Also, the simulation is extended to cover the effects of thermal and optical properties of the flatplate collector and the volume of the storage tank. The results show that if water is drawn on a schedule corresponding to the Rand draw profile, the system operates with higher efficiency when the auxiliary heater is located in the storage tank than when the auxiliary heater is outside the storage tank. When operated with each of the other three draw schedules, however, better performance is achieved by locating the auxiliary heater outside the tank. The increase in solar fraction depends on the load profile and volume, temperature setting, as well as the quality of the collector and the storage tank volume. When the values of the parameters FR(τα)n and FRUL are changed from 0.8 and 16 kJ/h m2°C to 0.6 and 30 kJ/h m2°C, the solar fraction decreases by approximately 40–50%.

Solar space heating with warm air in typical air collectors and rock bed storage systems involves constant air flow rates and varying the temperature of supply to rooms and to storage. This practice results in undesirable fluctuations in comfort levels in the living space, excessive storage size, useful but inaccessible heat in storage, and unnecessarily high energy consumption for air circulation and auxiliary heat. These drawbacks can be avoided by use of a practical controller and variable speed fan to provide heated air from the collector at constant temperature and a continually varying flow rate. Collector manufacturer`s data, confirmed by seasonal tests on a solar air heating system in Solar House II at Colorado State University, have been used in simulations at constant hot air supply temperatures of 40{degree}, 50{degree}, and 60{degree}C, and at one typical constant flow rate of 49 kg/h per m{sup 2} through a 50 m{sup 2} collector and rock bed storage unit, providing approximately half the seasonal heating requirements of a residential building. Auxiliary heat requirements and fan power use in the 40{degree}C and 50{degree}C constant temperature operations were significantly reduced from the levels prevailing under constant flow conditions. Collection efficiency and solar heat supply atmore » constant flow were slightly higher than values at the 60{degree}C constant temperature level. 8 refs., 8 figs., 1 tab.« less

Evaporation rates and total energy loads from an unoccupied, heated, outdoor pool in Fort Collins, Colorado were investigated. Pool and air temperatures, humidity, thermal radiation, wind speed, and water loss due to evaporation were measured over 21 test periods ranging from 1.1 to 16.2 hours during August and September, 1992. Data were analyzed and compared to commonly used evaporation rate equations, most notably that used in the ASHRAE Applications Handbook. Measured evaporation was 72% of the ASHRAE calculated value with near-zero wind velocity, and 82% of the ASHRAE value at 2.2 m/s wind velocity. A modified version of the ASHRAE equation was developed. Two overnight tests showed energy loss of 56% by evaporation, 26% by radiation, and 18% by convection. A correlation between radiation loss and temperatures was also found for the range of test conditions.

A nominal 10.5-kW (3-ton) open-cycle liquid desiccant dehumidification system has been designed, installed, and successfully operated at the Solar Energy Applications Laboratory, Colorado State University. Packed bed units were used to dry the air in the dehumidifier and to concentrate the desiccant in the regenerator. Liquid distribution in the regenerator was studied for two systems: a gravity tray distributor, and a spray nozzle system. Higher capacities (40–50% increase) and lower pressure drop (30–40% reduction) for the air flow were observed with the spray system. Cooling capacities of 3.5–14.0 kW (1.0–4.0 refrigeration tons) were achieved for both the regenerator and dehumidifier. Functional relationships correlating the independent variables to the rate of vaporization in the regenerator and rate of condensation in the dehumidifier were obtained by statistical analysis of the experimental data. These studies thus provide data and correlations useful for design guidance and performance analysis of similar open-cycle liquid desiccant cooling systems, particularly for the liquid/vapor contact units.

The development of parametric performance and cost models for various solar concentrators is discussed. The equations are derived in the context of an optimization scheme which can be applied to many different problems which arise when heat is generated by means of solar concentrators. Thus, while the results presented were developed for finding a minimum cost solar electric energy power plant, the method employed has been found to have general applicability. Sensitivity analysis of the subsytems is also discussed. Finally, numerous illustrative examples are presented.

The amount of solar energy that is intercepted by surfaces of any orientation is estimated from a new model of the clear sky, spatial distribution of solar radiation. The model was developed from measurements made during clear sky conditions and uses direct, isotropic reflected, and anisotropic diffuse radiation. The effects of azimuth, tilt, season, latitude, atmospheric turbidity, and reflectivity of the surroundings were computed using hourly measurements of normal beam and horizontal total radiation at four stations in the United States. A transformation of the co-ordinates of orientation produced a general relationship between orientation and intercepted energy. The general relationship was tested against measurements from six locations in the Northern Hemisphere and was found to be valid. The model is also a better estimator of energy intercepted by a tilted surface than are the more commonly used models.

The long-term performance of a residential solar heating system has been determined for a system which has been operating continuously since 1957 with no maintenance. This residential solar heating system is the Colorado Solar House located in Denver, Colorado, designed and operated by George O. G. Lof. The performance of this system was determined during the 1959–1960 heating season, and the results were publised. The performance of this system was redetermined during the 1974–1975 heating season so that changes in performance occurring over a period of 15 yr could be determined. The collector is an Overlapped-Glass Plate Solar-Air Heater. The system is completely automatic with provision for water heating in addition to space heating. Solar heat is stored in a rock bed of primarily granitic rock approximately 1.3–2.5 cm in diameter. The ratio of useful collected solar heat divided by the total solar radiation on the collector dropped to 71.8 per cent of its original value in 15 yr. For both seasons, the useful collected solar heat was correlated with the ratio of degree days per month divided by the total solar radiation on the collector. For the same value of this ratio, less useful collected solar heat was delivered during the latter season. Additional work that will be published at a later date includes the detailed performance of the hot water heating system.

Reconcentration of a lithium chloride solution in an open-cycle absorption chiller can be accomplished by passing solar heated air through a packed column to which the dilute solution is supplied. Following a theoretical study of heat transfer and water vapor transfer rates in the column, experimental measurement of those rates was made. Heat transfer and mass transfer coefficients are correlated with rates of air and liquid flow, and with temperatures of air and liquid supply. Performance data are presented and commercial design and operating requirements are suggested.

The first integrated system providing heating and cooling to a building by use of solar energy has been designed and installed in a residential-type building at Colorado State University. Solar heated liquid supplies heat to air circulating in the building and to a lithium bromide absorption air conditioner. Service hot water is also provided. Approximately two-thirds of the heating and cooling loads are expected to be met by solar energy, the balance by natural gas. The paper contains details of design and principles of operation. A breakdown of actual costs of the equipment and its installation is also provided.

By surrounding the absorber-heat exchanger component of a solar collector with a glass-enclosed evacuated space and by providing the absorber with a selective surface, solar collectors can operate at efficiencies exceeding 50 per cent under conditions of ΔT H T = 75° C m 2 /kW (ΔT = collector fluid inlet temperature minus ambient temperature, HT = incident solar radiation on a tilted surface). The high performance of these evacuated tubular collectors thus provides the required high temperature inputs (70–88°C) of lithium bromide absorption cooling units, while maintaining high collector efficiency. This paper deals with the performance and analysis of two types of evacuated tubular solar collectors intergrated with the two distinct solar heating and cooling systems installed on CSU Solar Houses I and III.

An extensive analysis of solar heating and dwellings in eight cities in the U.S.A. has been completed by the authors and recently published. The design of the solar heating system was optimized in each location, and the cost of solar heat was determined. The mathematical model of these systems has now been modified to include heat-operated absorption cooling units of the aqueous lithium bromide type. Approximately one hundred analyses of hourly cooling (and heating) performance for a full year in these locations have been made. Designs have been reoptimized to minimize total annual energy costs for house cooling and heating and for hot water supply. The combined system has been found more economical than heating alone in most locations, and some locations unattractive for solar heating have become candidates for the combination. The paper contains a description of the method of computation and the results of the design and cost analyses.

The NSF/CSU Solar House I solar heating and cooling system became operational on 1 July 1974. During the first months of operation the emphasis was placed on adjustment, “tuning”, and fault correction in the solar collection and the solar/fuel/cooling subsystems. Following this initial check out period, analysis and testing of the system utilizing a full year of data was begun. This paper discusses the preliminary performance of the heating and cooling system. During the period 1 August 1974–31 January 1975, approximately 40 per cent of the cooling load was provided by solar energy. Solar heating over the same period of time provided 86 per cent of the space heating load and 68 per cent of the domestic hot water heating load. These percentages represent a total solar contribution of 33,996 MJ delivered to load (8061 MJ to the cooling unit; 20,687 MJ to heating; 5248 MJ to hot water). Natural gas accounted for 22,442 MJ, total. In addition, preliminary analysis has provided several significant results associated with the operating characteristics of the solar system and the individual components.

The use of cool storage in conjunction with residential lithium bromide absorption chillers allows for improved operating conditions of the cooling subsystem. Significant performance degradation in the absorption cooling capacity is evident whenever the chiller cycles on and off during periods of low cooling demand. The capability of providing storage for the chiller out-put prevents short-term cycling of the absorption machine and significantly improves the seasonal average coefficient of performance of the cooling system. Cool storage can also be utilized to allow for a lower cooling capacity of the absorption unit (lower tonnage), without decreasing the ability of the subsystem to meet the cooling demands of the building. The size of cool storage can, in fact, be optimized by evaluating the ability of the cool storage component to minimize cycling of the absorption machine and in meeting the cooling demands on a smaller tonnage chiller.

Results of an experimental study of a full-scale passive solar hot water heating system utilizing a boiling collector are presented. The self-pumping system alternates between two modes of operation. During the run cycle, vapor pressure drives the evaporated refrigerant downward from the collector to the condenser. Once a preset quantity of refrigerant is condensed, vapor pressure is again used to force the return of the condensate to the collector during the pump cycle. In order to assess the thermal penalty of self-pumping operation, the system is also operated with a mechanical pump. Daily operating characteristics and seasonal performance are discussed. Performance of the self-pumping system is strongly influenced by the duration of the pump cycle. The average thermal loss attributed to self-pumping during one heating season in Fort Collins, Colo. is approximately nine percent of the solar energy incident on the collector. Refinement of the system design, including individual components, is required to reduce losses and improve performance.

A solar desiccant cooling system was operated at the Solar Energy Applications Laboratory, Colorado State University, throughout the 1986 summer. The system comprises an American Solar King fresh air heating/desiccant evaporative cooling unit, a Sunmaster evacuated tube solar collector, hot water solar storage tank, auxiliary electric boiler, controls, and accessories. The cooling unit is operated in the ventilation mode, fresh air being dried in a rotating desiccant matrix, and cooled by heat exchange and evaporative cooling. Return air is used as a cooling medium in a rotating heat exchange matrix, heated by solar energy in a heat exchange coil, and discarded through the rotating desiccant bed. The solar-driven system provided over 90 percent of the seasonal cooling requirements in an experimental, residence type building at average COP levels of 1.0 and solar collection efficiencies of 50 percent when supplied with solar heated water at temperatures of 50 to 65° C. Detailed operating results, including total and average solar cooling provided, coefficients of performance, and overall solar cooling performance ratios are presented.

This paper describes the design of a solar air heating and night/day exchange cooling system with emphasis on the operational modes. In this type of system the collector absorbs solar energy and converts it to heat for space heating and domestic water heating. Cooling is accomplished by using the cool night air available in dry climates) to cool a pebble-bed storage unit and subsequently using the cool pebbles to lower the air temperature in the building during the day. Circulation is from the solar system to the building in the same manner as most modern heating and air conditioning units but uses air as the medium for heat transfer. The air system is particularly suited for climatic regions where heating loads are high and cooling requirements are moderate. The system utilized in Solar House II operates in either the heating or cooling mode as selected through a seasonable change-over switch. Solar preheated hot water is furnished for domestic use in either mode.

There has long been a need for a practical method of predicting the true cost of heating a house with solar energy and designing the heating system (solar and auxiliary) to achieve the minimum total annual heating cost possible under the particular climatic, geographic, and residential characteristics involved. Rough approximations based on various types of averaged values of weather and seasonal variables have previously been developed, but the reliability of such methods and results is open to question. The authors have therefore made a rigorous analysis of projected solar heating costs in eight U.S. cities and have optimized the heating system design in each location. The analysis involved the use of a high speed computer and approximately 400,000 hourly observations in eight cities of radiation, temperature, wind, solar altitude, cloud cover, and humidity. Equations for performance of flat plate solar collectors and sensible heat storage systems were developed and programmed with the above weather variables and with eight design parameters comprising house size, collector size, storage size, collector tilt, number of transparent surfaces in collector, hot water demand, insulation on storage unit, and thermal capacity of collector. Capital and operating costs were quantitatively related to heating system design parameters, and the values of all design variables which yielded lowest annual heating cost in each city were then selected. The findings are presented in the form of two tables and ten graphs, showing heating costs as functions of various design and location factors. The relative importance of each factor is discussed, and the overall costs of solar heating are compared with the costs of conventional heat supply in each location. The method for designing the least-cost combination of solar and conventional heat supplies is also shown, and an example of the use of the method is presented.

Abundance, cleanliness and widespread distri bution are great incentives for the application of solar energy to man's energy requirements. Recent and impend ing fuel shortages, cost increases of energy and environ mental degradation have provided strong incentives for the development of solar energy for wide practical use. However, its low intensity and high variability impose severe econo mic problems in converting it to useful forms. Conversion of solar radiation to thermal, electrical and mechanical energy has been well demonstrated in numerous experi mental systems. Of these methods, those of greatest current interest are the production of heat for the heating and cooling of buildings and the direct, or indirect, conversion to elec tricity. In favorable locations, the costs of solar heating and cooling equipment under development appear to be nearly competitive with fuels; hence, this application is ex pected to be widespread within a very few years. Electric power from solar energy is not now competitive with conventional supply and is, therefore, a longer term possibility.

Solar energy applications are examined from the point of view of their profit-making potential. The study is based on a consideration of the availability and characteristics of solar energy, the sources of profit in conventional energy sources, and the type of industry which could participate in the commercialization of solar energy. Solar equipment now being manufactured is of four types—water heaters, batteries, cookers, and toys and novelties. Three types of solar energy equipment now in the development stage are seen to have early commercialization prospects. The largest market during the present century will likely be residential heating and cooling systems. Technical or economic considerations will limit several applications such as commercial electricity from solar energy and capture and storage by photochemical means.

The use of plastics in fabrication of reflectors for focusing collectors offers possibilities for reduction of material and fabrication costs. Fiber-glass-rein-forced polyesters, cellulose acetate butyrate, and polystyrene have been considered for reflector shell fabrication, and vacuum-metallized films for reflecting surfaces. Polystyrene shells with aluminized Mylar reflective lining have been the most promising of the materials considered. Flexible laminates of aluminized Mylar to vinyl or vinyl-cloth combinations are considered for flexible reflectors. Application of plastic reflectors to solar cookers is noted.

A basin-type solar still has been developed that is practical and economical to use in some parts of the world. Materials of construction and performance characteristics, as determined from extensive field testing and from analytical and laboratory investigations, are discussed. These studies indicate that the primary factor affecting still productivity, in addition to solar radiation, is basin depth. Of the many still designs and materials evaluated, one basic design and combination of materials appears most promising. An Office of Saline Water report giving details on the construction of such a still has been published. This paper describes that still briefly. An economic comparison of vapor-compression, flash-distillation, and basin-type solar stills shows that the solar still produces water at the lowest cost when plant capacity is below 50,000 gallons per day.

Photovoltaic cells presently used in satellites and other applications are, for the most part, silicon cells which have a power output of about 12 milliwatts per square centimeter at a radiation level of 90 milliwatts per square centimeter. Using special close-gridded cells, a solar concentrator to obtain radiation intensities of 28 watts per square centimeter and an auxiliary cell cooling system, the power output can be raised to over 1.5 watts per square centimeter. At these high fluxes, the customary equivalent circuit of a photovoltaic device is not adequate. An equivalent circuit, which includes a distributed diode, a distributed series resistance, a single shunted series diode and series resistance, was used with experimentally determined constants to predict the cell voltage-current characteristics as a function of grid spacing at high fluxes. The additional problem of cell cooling at high radiation levels has been solved by using water in a forced circulation, closed-loop cooling system. A theoretical analysis shows that the cells can be maintained below 200 deg F by mounting them on water-cooled, pinned heat-transfer surfaces. The thermal energy of the water can then be dissipated to the ambient atmosphere by a natural convection air-to-water heat exchanger. From experimental cell data, a system design is presented that will produce 50 watts of electrical energy from 36 square centimeters of cell area.

A series of 12 monthly world maps of the daily means of total solar radiation incident on a horizontal surface has been prepared. Isolines of constant radiation have been drawn at intervals of 50 langleys per day (cal/sq cm, day). Data for the computation of mean radiation levels were compiled from many sources, including weather reports and summaries, personal communications from weather and research organizations, and IGY and IGC reports. For areas in which few or no radiation data were available, such information was synthesized by use of sunshine-hours data and approximation formulae applicable to the particular climate type. Radiation data were obtained for 668 stations, whereas sunshine-hours values were used in estimating radiation from 233 additional locations. The maps are recommended for general use in appraising the collector area requirements for solar applications in broad regions. They do not, of course, reveal the influence of microclimatic factors on local solar-radiation levels. In addition to the maps, the paper contains an explanation of the various radiation instruments, the methods for data handling, the estimation of radiation values from sunshine-hours data, and the limitations and utility of the radiation maps.

It is surprising that a process used as commonly as solar drying has received so little technical development. With the enormous tonnage of materials being processed by this method, greater effort in its development and improvement would seem in order. It is not unreasonable to believe that annual saving in the millions of dollars might be realized through lowering the costs of drying, improving the quality of the products, and reducing losses by spoilage, deterioration, transport delays, and other factors. The substitution of solar drying for fuel drying or simply the reduction in fuel demand by a cheap supplementary solar heat supply would appear of considerable benefit in many areas. Solar drying development appears to warrant increased effort.

A nominal 3 ton (10.5 kW) open-cycle liquid desiccant cooling system has been designed, installed and operated at the Solar Energy Applications Laboratory, Colorado State University. Performance data for the regenerator, operated in a decoupled mode, were obtained for a variety of inlet conditions. Depending on the operating conditions, capacities of 1.4 – 3.0 refrigeration tons (4.9 –10.3 kW) were obtained in the regenerator. Liquid distribution in the regenerator was studied for two systems: a gravity tray liquid distributor and a spray nozzle manifold. Higher capacities (40–50% increase) in the regenerator were obtained with the spray nozzle system. Another advantage of the spray nozzle arrangement, as compared to the tray liquid distributor, was a reduction in pressure drop (by 30–40%) for the air flow across the regenerator. The independent variables affecting the capacity were correlated by statistical analysis of the data.

A solar heating system comprising a 25 m 2 evacuated tube solar collector, 4 m 3 stratified hot water storage tank, liquid-to-air heat exchange coil in a commercial fresh air heating-cooling unit in which heat recovery in a regenerative air-to-air exchanger is employed, and an electric auxiliary heater was operated and monitored continuously through four months of the 1985–86 winter in a residential style building of 200 m 2 floor area. Design improvements over a previously tested system included the control system which provided higher solar collection efficiency, better temperature stratification in storage, higher reflectivity of evacuated tube reflectors, and the supply of fresh air rather than recirculated air without significant thermal and economic penalty. Average daily solar collection efficiency during four months of operation, January through April, was 42% based on collector aperture area. The portion of the heating requirements met by solar was 53%, and 61% of the hot water was supplied by solar. An improved reflector increased energy collection 6.8%, and use of a solar intensity sensor resulted in a 16% increase in energy collection compared with conventional delta T control.

By surrounding the absorber-heat exchanger component of a solar collector with a glass-enclosed evacuated space and by providing the absorber with a selective surface, solar collectors can operate at efficiencies exceeding 50% under conditions of δT/HT = 75°C·m2/Kw (δT = collector fluid outlet temperature minus ambient temperature, HT = incident solar radiation on a tilted surface). The high performance of these evacuated tubular collectors thus provides the required high temperature inputs (70–88°C) of lithium bromide absorption cooling units, while maintaining high collector efficiency. This paper deals with the performance and analysis of two types of evacuated tubular solar collectors integrated with the two distinct solar heating and cooling systems installed on CSU Solar Houses I and III.

The manufacturer of pulp and paper results in the generation of residuals in gaseous, liquid, and solid forms. The major sources of each type of residual are identified and quantities generated in the production of a typical product are tabulated. The influence of raw material, pulping and bleaching processes, product characteristics, and other production factors is indicated. Methods for reducing discharge of residuals are classified and described, including by-product production, process changes involving partially offsetting cost advantages, and end-of-pipe waste treatment. Application of these methods to change the quantity or form of one residual usually affects one or more other residuals. Examples of the extent of modification required to meet discharge standards for residuals are included for a 500-ton-per-day integrated mill producing tissue paper.