Document Z8popvxbGkdyJO13LDMZXnqVY

HEATINC VENTILATINC AIR CONDITIONING CUIDE 1943 . The variation in radiation intensity on differently oriented surfaces is given in Fig. 1, and in Tables 2, 3, 4 and 5. The greater part of the radi ation intensity is always direct radiation from the sun. However, during the time when the sun is shining, any surface receives radiation of a lower intensity coming from all parts of the sky due to reflection and refraction. This scattered radiation intensity was found to vary from a very low value to values as high as 20 per cent of the total radiation observed on certain days in Pittsburgh. The curves and tables are for combined direct solar and scattered sky radiation, and are given to represent expected design radiation intensity for August 1. They were prepared by the A.S.H.V.E. Laboratory fr.om data1 obtained by pyrheliometer observations. A study of these curves discloses the periodic relationship and wide variation in solar intensity on various surfaces. It will be observed that CHAPTER 7. COOLING LOAD convection and conduction. A mathematical solution for the determina tion of solar heat transmission has been developed but the equations involved are too complex for practical application2. The heat flow in summer through various types of roofs and walls has been measured by the AiS.H.V.E. Laboratory. The curves in Fig. 2, give the heat flow through the inside surface of roofs3 with details of the construction of the roofs tested. The condition for which these results are given are: solar radiation for 40 deg north latitude on August 1 as given in Fig. 1 and Table 4; outdoor design temperature reaching a maximum- of 95 F as shown by the temperature curve in Fig. 2 and an indoor temperature of 75 F. ' Curves in Fig. 3 were prepared by the A.S.H.V.E. Laboratory from Fig. 1. Solar Intensity Normal to Sun on Horizontal Surface and on Walls for August 1 at 40 Deg North Latitude both the roof (horizontal surface) and south wall radiation curves are in exact phase relationship with each other, while those for the east and west walls overlap each other due to scattered sky radiation on the west wall during the forenoon and on the east wall during the afternoon. This phase relationship has an important bearing on the cooling load. Failure to consider the periodic character of heat flow resulting from diurnal movement of the sun and the lag due to heat capacity of the structure, which determine the timing and magnitude of the he.at wave flowing through the wall, may result in a large error in load calculations. The values of solar intensity appearing in Fig. 1 must not be confused with the actual heat transmission through the wall for much of the solar radiation impinging against the outer surface fails to pass through the walk Instead it is delivered to the outside air by reflection, radiation, A.S.H.V.E. Research Repost No. 1147--Heat Gain Through Glass Blocks by Solar Radiation and Transmittance, by F. C. Houghten, David Shore, H. T. Olson and Burt-Gunst (A.S.H.V.E. Transactions. VoL 46, 1940, p. 83). 152 Fig. 2. Relation Between Time and Heat Flow Through Inside Surface of Horizontal Roofs Corrected to Design Day of August 1 recent tests made there and show the heat flow through the inside surface of three types of walls for various orientations4. The results are given for the following conditions: 90 per cent of the solar radiation given in Fig. 1 and Table 4 for 40 deg north latitude on August 1; outdoor design tem- ^A.S.H.V.E. Research Report No. 923--Heat Transmission as Influenced by Heat Capacity .and Solar Radiation, by F. C. Houghten. J. L. Blackshaw, E. M. Pugh and Paul McDermott (A.S.H.V.E. Transactions, Vol. 38, 1932, p. 231). Effect of Heat Storage and Variation in Outdoor Temperature and Solar Intensity on Heat Transfer Through Walls, by J. S. Alford. J. E. Ryan and F. O. Urban (A.S.H.V.E. Transactions, Vol. 45, 1939, p. 369). Periodic Heat Flow in Building Walls Determined by Electrical Analogy Method, by Victor Paschkis (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning; February, 1942, p. 133). Summer Comfort Factors as Influenced by the Thermal Properties of Building Materials, by C. O. Mackey and L. T. Wright, Jr. (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, December/1942, p. 750). A.S.H.V.E. Research Report No. 1157--Summer Cooling Load as Affected by Heat Gain Through Dry, Sprinkled Water Covered Roofs, by F. C. Houghten, H. T. Olson and Carl Gutberlet (A.S.H.V.E. Transactions, Vol. 46. 1940. p. 231). A S.H.V.E. Research Paper--Heat Gain Through Walls and Roofs as Affected by Solar Radiation, by F. C. Houghten. E. C. Hach. S. I. Taimuty and Carl Gutberlet (A.S.H.V.E. Journal Section, Heating. Piping and Air Conditioning, May, 1942, p. 306). 153