John D. Garrison

Estimation of precipitable water over the United States for application to the division of solar radiation into its direct and diffuse components

Abstract Monthly mean atmospheric precipitable water data for eighty-two sites in the continental U.S. and Alaska have been analyzed to develop methods for accurately estimating precipitable water at sites where it has not been measured. Monthly mean precipitable water can be estimated with an rms error of about 12%, using the monthly mean surface temperature and relative humidity. This rms error can be reduced to about seven percent, if the properties of the average atmospheric and surface conditions in the region surrounding the site are used. The amount of sunlight scattered by the atmosphere is a function of the amount of precipitable water and other quantities.

Critical evaluation of precipitable water and atmospheric turbidity in Canada using measured hourly solar irradiance

Abstract Global and diffuse radiation and surface meteorological measurements at Edmonton, Montreal, Port Hardy, Toronto and Winnipeg for the years 1977–1984 are analyzed to yield estimates of atmospheric precipitable water and turbidity. Three methods of estimating the precipitable water and two methods of estimating the turbidy are used and compared. Laboratory measurements of pyranometer response as a function of zenith angle are used to correct the global radiation measurements. Circumsolar radiation is removed from the direct radiation obtained from the difference of measured global and diffuse radiation. The magnitude of this circumsolar correction is discussed in the light of recent measurements and calculations of the circumsolar ratio. Turbidity time series are presented, showing a clearly defined El Chichon eruption signature in 1983–1984. A comparison with earlier results in included.

A study of the division of global irradiance into direct and diffuse irradiance at thirty-three U.S. sites

Abstract Solar irradiance data obtained at 33 U.S. sites during parts or most of the period from January 1978 through December 1980 have been analyzed to study the division of global solar irradiance into its direct and diffuse components. New information concerning the dependence of this division upon the amount of global solar irradiance, solar elevation, surface albedo, atmospheric precipitable water and atmospheric turbidity has been obtained.

Manufacture and cost of vacuum glazing

The vacuum glazing project at the University of Sydney has progressed to the point where the main features of the vacuum glazing design are determined well. Over 500 glazings with areas up to one square meter have been formed. The stresses to which these glazings are or may be exposed have been studied extensively. The durability of the glazing structure and the internal vacuum has been demonstrated. Vacuum glazing of the type designed and formed at the University of Sydney has a center-of-glazing thermal conductance as low as 0.85 and 1.2 Wm−2K−1, for glazings with two and one internal low emittance coatings, respectively. A method for the manufacture of the vacuum glazing is outlined from which the cost to manufacture the glazing can be estimated. A cost at the factory of about

Optimization of a fixed solar thermal collector

40 ± 7 m−2 for vacuum glazing using two sheets of low-e glass and about

A study of solar irradiation data for six sites

32 ± 6 m−2 for glazing using one sheet of low-e glass is obtained, when production volume is approx. 105 m2yr−1 and is partially automated. This is about 25% higher than the estimated manufacturing cost of the high thermal resistance, argon filled, double glazing utilizing low-e glass, which are currently in production and being sold in the United States, Europe and Japan. These glazings typically have center-of-glazing thermal conductances of about 1.1 Wm−2K−1 or more.

An evaluation of the effect of volcanic eruption on the solar radiation at six Canadian stations

Abstract Criteria are presented for optimizing solar thermal energy collection. These criteria are then used in setting the design of a fixed solar thermal energy collector. This design is obtained by proceeding carefully through a series of optimization steps. While seeking near optimum performance, features have been retained which should lead to low cost. Initial optimization steps lead to an all glass vacuum collector tube whose side and lower walls are internally silvered to provide optimal Winston concentration on an interior glass tube coated with a selective absorber. Heat transfer calculations, performed for an array module of these collector tubes, produce values for the radiation, heat conduction and pumping losses and indicate operating conditions which minimize these losses. Near this minimum, heat conduction and pumping losses are small and can usually be neglected. Liquids provide much better heat transfer than gases. For liquid heat transfer fluids, the minimum loss collector tube window width (setting the transverse scale) is ∼3 cm and tube length ∼4 m, depending somewhat upon array area and the weighting used for the various losses. A window width of∼5 cm and tube length∼2 m should provide lower cost fabrication, while still allowing operation near minimum loss. Skills now used in the glass and lighting industry are expected to lead to low cost production of these tubes.

Radiation collection by an optimized fixed collector

Abstract Measurements of hourly direct normal solar radiation and total hemispherical solar radiation on ahorizontal surface for Albuquerque, New Mexico; Fort Hood, Texas; Livermore, Calif.; Marynard, Mass.; and Raleigh, North Carolina and measurements of hourly total hemispherical and diffuse radiation on a horizontal surface for Highett, Australia have been studied. The relationships between total and diffuse radiation and distributions and mean values associated with these quantities are considered.

Estimation of atmospheric precipitable water over Australia for application to the division of solar radiation into its direct and diffuse components

Hourly global and diffuse radiation data from the six Canadian stations at Edmonton, Montreal, Port Hardy, Resolute, Toronto and Winnipeg have been analyzed for evidence of the effect of volcanic eruption on the amount of direct beam radiation and diffuse radiation. A strong reduction of clear hour direct beam radiation is seen during 1983 due to aerosols in the stratosphere following the eruption of El Chichon in southern Mexico on 28 March and 3 and 4 April 1982. A corresponding increase in diffuse radiation and Angstrom turbidity coefficient is also seen during 1983. The effect of the aerosols from El Chichon is much reduced during 1984, but is still seen above levels from other sources. By combining all significant evidence found in these Canadian solar radiation data, the presence of an excess of volcanic aerosols associated with one or more of the series of volcanic eruptions occurring during the periods from about 1963 to 1968, near 1975, and just prior to the eruption of El Chichon is clearly seen. The amplitude of the effect of these series of eruptions on the data selected for examination here is approximately one-third the amplitude of the effect found for El Chichon. This study confirms that global radiation shows little change when volcanic aerosols in the stratosphere increase following an eruption.

Analysis of clear hour solar irradiation for seven Canadian stations

Abstract A model for determining, on the average, the angular distribution and intensity of solar radiation at the site of a solar collector as a function of the irradiance on a horizontal surface and the time of day and year is presented. The model is then used to study radiation collection by a collector whose design has been approximately optimized. The variation of radiation collection by this collector with changes in the clearness index KT, operating temperature, ambient temperature, acceptance angle, tilt angle, selective absorber properties and window reflection is studied. This indicates how to further optimize the collector design. The performance of this optimized collector is then compared with that of other existing fixed collector designs.