The state of the art in testing solar collectors to determine their thermal performance is reviewed here. A brief history of the significant work done to establish the procedures for testing is given, including the current proposed and adopted worldwide procedures. In the second section, the basic mathematical equations describing the thermal performance of solar collectors are given as the basis for showing what information can be obtained from such tests. In the third section, a detailed description is given of the testing techniques used to determine collector thermal performance under clear-sky, full-irradiance conditions, as typically called for in most of the currently adopted standards. This section will also include a discussion of typical instrumentation, its accuracies and limitations, the results of major round-robin programs conducted to date showing the comparability of data between laboratories when the tests are conducted outside under real-sun conditions, and special techniques required to test concentrating collectors. In the fourth section, a technique for obtaining collector efficiency indoors under zero-irradiance will be discussed. In the fifth section, special considerations when testing air collectors will be discussed. In the final section, concepts for using test data to calculate all-day collector performance will be presented.

Testing Solar Collectors

: This report presents design criteria and cost analysis for methods for the sizing and justification of solar heat collectors for potable water heaters and space heaters. Sufficient information is presented to enable engineers to design solar space and water heating systems or conduct basic feasibility studies preparatory to design of large installations. Both retrofit and new installations are considered. This report has been substantially revised from the previous edition (Beck and Field, 1977). However, most of the revision is in Section 2.0, where more material of an exploratory nature has been added. Section 3.0, which contains the calculation method and worksheets, is largely the same, except that the economic analysis has been revised and new tables have been added to provide a self-contained source of meteorological data and collector test data.

Solar Heating of Buildings and Domestic Hot Water. Revision.

This paper gives the testing apparatus, instrumentation, and testing procedure which can be used to determine a design flow rate through the manifold for any particular system of identical flat-plate solar collectors. The use of two identical collectors in a side-by-side arrangement is employed. A least-squares mathematical model is developed to fit the data to the commonly accepted collector performance equation, FR = [CG/Ut ] [1 —exp (-F' UL/GC}]. A variation of this model is solved by trial-and-err or on a computer. Pressure drop data are correlated by a least-squares parabola curve, and an economic model is developed to find the optimum flow rate for the particular type of collector. Nomenclature A — constant to be found by a least-squares data fit B = constant to be found by a least-squares data fit C = specific heat of circulating fluid, cal/kg-°C CL = lifetime cost, $/m2 CP = lifetime pumping cost, $/m2 CC = initial collector cost, $/m2 E = cost of electricity, $/kWh FR = actual energy collection rate for a flat-plate collector divided by the collection rate attainable if the entire plate temperature were equal to the inlet fluid temperature, dimensionless F' = actual energy collection rate divided by the rate attainable if the entire plate temperature were equal to the average of inlet fluid and exit fluid temperature, dimensionless F" = collector performance factor FK /F', dimensionless G = mass flow rate per unit area, kg/h-m2 K = dimensional conversion constant AP — pressure drop across the collector, mm Hg Qu = useful rate of energy collection, cal/h-m2 Te = fluid exit temperature, °C Tf = fluid inlet temperature, °C / = lifetime of operation, h UL = total energy loss rate for the collector, cal/m2-h-°C 77 = pump-motor overall efficiency, dimensionless p = fluid density, kg/m

A Test for Determining a Best Flow Rate through Solar Collectors

A simple test for determining a best flow rate through solar collectors

A testing procedure using identical side-by-side, flat-plate, solar air collectors has been developed and used to evaluate collectors. This procedure was shown to provide a simple method for determining some of the most important parameters in collector performance. The performance data collected were fitted to the equation F" =AQ{ 1-exp (-B/Q)}. Then this equation, along with pressure drop data, were used in an economic model to find the optimal flow rate for the particular collector. Nomenclature A,B = parameters to be found by a least-squares data fit C = specific heat of circulating fluid, J/kg-K CL = lifetime cost, $/m2 Cp = lifetime pumping cost, $/m2 CC = initial collector cost, $/m2 E = cost of electricity, $/kW-h FR = collector performance factor F' = collector performance factor F" = collector performance factor AP = pressure drop across the collector, N/m2 Q = volume flow rate per unit collector area, m3 /Min-m2 Qu = useful rate of energy collection per unit collector area, J/h-m2 Te = fluid exit temperature, K Tf = fluid inlet temperature, K t = lifetime of operation, h UL -overall energy loss coefficient for the collector, J/hm2-K r? = blower-motor-duct overall efficiency p = fluid density, kg/m3

T. Kusuda

Papers

Method of testing for rating solar collectors based on thermal performance. Interim report