Document n9VqnyG90boD3gVKM7kjzVn6z

American Society of Heating and Ventilating Engineers Guide, 19302. Draw line 2 vertically downward from the intersection located as per paragraph 1, 3. Locate on scale D the temperature difference of 95 deg. between the ceiling tem perature of 85 deg. arid the lowest outside temperature of --10 deg., and draw a line horizontally until it intersects with line 2. 4. From the point of intersection of lines 2 and S, draw a line to the point P. 5. From the intersection of lines 4 and AB, draw a line horizontally until it intersects with the diagonal line corresponding to a coefficient of transmission of the roof of 0.485, located on scale F. 6. From the intersection found as per paragraph 5, draw line 6 vertically downward. 7. Locate the conductivity of 0.30 B.t.u. per hour per square foot per degree fahrenheit of the insulation on scale G and draw a line to point Q. Fig. 12. Saturation Curves showing Relationship between Relative Humidity and Temperature Difference for Single, Double and Triple Windows' 8. From the intersection of lines 6 and 7, draw a line horizontally to scale H, on which the thickness of insulation of this coriductivity is indicated, which is 1.3 in. The nearest commercial thickness above 1.3 in. would, of course, be selected. Condensation on Windows Fundamentally, the problem of preventing condensation on windows is no different than that of preventing condensation on walls and windows. However, it is not economical to decrease, the inside surface resistance by blowing air against the window, as this increases the overall transmission. Hence, if it is necessary that a high relative humidity be maintained; the only practical method by which condensation can be prevented or 're duced on windows is to increase the overall resistance by using two'or, more air spaces. 82 , Chapter 2--Heat Losses from Buildings yyifidow Condensation Chart The chart (Fig. 12) is intended to be used for determining the number of panes of glass required to prevent condensation for certain temperature and humidity conditions, or for determining the outside temperature at which condensation will take place on the inside surface of single, double or triple glass for the humidity and temperature conditions involved. To determine the type of glass required to prevent condensation, locate the relative humidity on scale A` and then locate the difference in tem perature between the air on the two sides of the glass on scale B. The curve corresponding to the inside temperature conditions immediately above the intersection of the lines drawn from these two scales indicates the type of glass required. For example: If the relative humidity is 60 per cent (scale A) and the inside and outside temperatures are 70 deg. and 0 deg. respectively, the temperature difference (scale B) will be 70 deg. and triple-pane glass will be required to prevent condensation, as indicated by the curve immediately above the intersection of the lines drawn from scales A and B. Because the transmission of even triple glass, with two air spaces, is relatively high as compared with a well-insulated wall or roof, and con sequently the resistance small, the relative humidity that can exist in a building without condensation taking place on the glass is low. For this reason, and also because window condensation in many cases is not objectionable, no effort is made to prevent the condensation, the only precaution taken being to provide gutters under the windows to drain the water. REFERENCES Mechanical Equipment of Buildings, Vol. I, second edition. 1929, By Harding and Willard. Bulletin No. lOt, Engineering Experiment Station, University of Illinois. Report of /nsuiofton Committee, A. S. R. E. Annual Meeting, 1922, Revised to 1924. Measuring Heat Emission in Building Structures, By P. Nicholls (Transactions, A. S. H. V. E., Vol. 30. 1924, No. 685). Air Leakage, By Houghten and Schraeder (Transactions, A. S. H. V. E., Vol. 30, 1924, No. 686). Air Leakage Around Window Panes, By C. C. Schraeder (Transactions, A. S. H. V. E., Vol. 30, 1924. No. 704). Data on Infiltration of Air Through Building Openings, By C. C. Schraeder (Transactions, A. S. H. V. E.t Vol. 31. 1925. No. 716). Some Results of Heat Transmission Research, By F. B. Rowley (Transactions, A. S. H. V. E., Vol. 32, 1926, No. 748). Standard Test Code for Heat Transmission Through Walls, By A. P. Kratz (Journal, A. S. H. V. E., Vol. 34, No. 1. January. 1928). Economic Thickness of Building Insulation, By "M. S. Wunderlich (Journal, A. S. H. V. E., Vol. 34, No. 3. March, 1928). Value of Building Insulation to Reduce Heat Losses, By E. N. Sanbern (Journal, A. S. H. V. E., Vol. 34. No. 3. March, 1928). Weathertightness of Rolled Section Steel Windows, By Emswiler and Randall (Journal, A. S. H. V. E., Vol. 34. No. 6. June. 1928). Heat Transmission Research, By Rowley; Morris and Algren (Journal, A. S. H. V. E., Vol. 34, No. 7, July, 1928). Air Leakage Through a Pivoted Metal Window, By Houghten and O'Connell (Journal, A. S. H. V. E., Vol. 34. No. 7. July. 1928). Heat Transfer Through Roofs Under Summer Conditions, By Houghten and Zobel (Journal, A.S.H.V.E., Vol. 34. No. 8. August. 1928). Effect of Frame Calking and Storm Windows on Infiltration Around and Through Windows, By Richtmann and Braatz (Journal, A. S. H..V. E.. Vol. 34, No. 9. September, 1928). Frost and Condensation on Windows, By Leonhard and Grant, (Journal, A. S. H. V. E., Vol. 35. No. 1, January. 1929). 83