The renewed interest in the utilization of solar radiation has been precipitated by pollution problems and the energy crisis which currently face the world. The direct use of the energy contained in the sun's rays is one of the f~w methods of obta~ning power which will not deplete the available supply of fuels currently at the disposal of the world's population. Since the energy available in the form of fossil fuels, nuclear sources, etc. is finite, it follows that the length of time required for the total depletion of these reserves is a function of the rate of usage. It is therefore evident that the wise course of action is to use, as much as possible, a power source that is constant and inexhaustable, thereby conserving the fossil fuels and other energy sources which have only fixed amounts available. These fuels and other energy sources may then be saved for other uses by the world's population.

A recognition of this fact has caused ASHRAE to reactivate and reorganize Technical Committee 6.7, "Solar Energy Utilization," to promote research and development in this vital field. This paper has been developed at the request of that committee and written under its leadership, with its purpose being to acquaint members of the society with data which will be presented in the 1974 ASHRAE, HANDBOOK & Product Iarectory, Applications Volume.

The inclusion of these data in the ASHRAE HANDBOOK is necessary since its users will have need for reliable information concerning the irradiation of surfaces at angles other than horizontal and vertical and at various locations in the northern hemisphe're. The data currently available in the guide are for horizontal and vertical surfaces, and the information is available in the form of heat gain factors in which the insolation value is reduced by the transmittance of 1/8 in. double strength plate glass. It is, therefore, necessary to develop data which considers the solar insolation of a surface at an angle to the horizontal at various times of the day and year.