Document qkEN5JxxRGVGQNQq90zdnjabM

HEATINC VENTILATING AIR CONDITIONING GUIDE 1941 open. However, the A.S.H.V.E. Code for Heating and Ventilating Garages, adopted in 1929 and revised in 1935, states that natural venti lation may be employed for the ventilation of storage sections where it is practical to maintain open windows or other openings at all times. The code specifies that such openings shall be distributed as uniformly as pos sible in at least two outside walls, and that the total area of such openings shall be equivalent to at least 5 per cent of the floor area. The code further states that where it is impractical to operate such a system of natural ventilation, a mechanical system shall be used which shall provide for either the supply of 1 cu ft of air per minute from out-of-doors for each square foot of floor area, or for removing the same amount and' discharging it to the outside as a means of flushing the garage. Research Research on garage ventilation undertaken by the A.S.H.V.E. Com mittee on Research at Washington University, St. Louis, Mo., and at the University of Kansas, Lawrence, Kans., in cooperation with the A.S.H. V.E. Research Laboratory, and at the A.S.H.V.E. Research Laboratory has resulted in authoritative papers on the subject. Some of the conclusions from work at the Laboratory are listed in the following statements: 1. Upward ventilation results in a lower concentration of carbon monoxide at the breathing line and a lower temperature above the breathing line than does downward ventilation, for the same rate of carbon monoxide production, air change and the same temperature at the 30-in. level. 2. A lower rate of air change and a smaller heating load are required with upward than with downward ventilation. 3. In the average case upward ventilation results in a lower concentration of carbon monoxide in the occupied portion of a garage than is had with complete mixing <jf,the exhaust gases and the air supplied. However, the variations in concentration from point to point, together with the possible failure of the advantages of upward ventilation to accrue, suggest the basing of garage ventilation on complete mixing and an air change sufficient to dilute the exhaust gases to the allowable concentration of carbon monoxide. 4. The rate of carbon monoxide production by an idling car is shown to vary from 25 to 50 cu ft per hour, with an average rate of 35 cu ft per hour. 5. An air change of 350,000 cu ft per hour per idling car is required to keep the carbon monoxide concentration down to one part in 10,000 parts of air. Code for Heating and Ventilating Garages (A.S.H.V.E. Transactions. Vol. 35. 1929, p. 355). (A.S. H.V.E. Reprint, January, 1935). Airation Study of Garages by W. C. Randall and L. W. Leonhard (A.S.H.V.E. Transactions. Vol. 36. 1930, p.233). A.S.H.V.E. Research Report No. 874--Carbon Monoxide Concentration in Garages, by A.S. Langsdorf and R. R. Tucker (A.S.H.V.E. Transactions, Vol. 36. 1930. p. 511). A.S.H.V.E. Research Report No. 935--Carbon Monoxide Distribution in Relation to the Ventilation of an Underground Ramp Garage, by F. C. Houghten and Paul McDermott (A.S.H.V.E. Transactions. Vol. 38. 1932. p. 439). A.S.H.V.E. Research Report No. 934--Carbon Monoxide Distribution in Relation to the Ventilation of a One-Floor Garage, by F. C. Houghten and Paul McDermott (A.S.H.V.E. Transactions, Vol. 38,1932. p. 424). A.S.H.V.E. Research Report No. 967--Carbon Monoxide Distribution in Relation to the Heating and Ventilation of a One-Floor Garage, by F. C. Houghten and Paul McDermott (AJ5.H.V.E. Trans actions. Vol. 39. 1933, p. 395). Carbon Monoxide Surveys of Two Garages, by A. H. SIuss, E. K. Campbell and Louis M. Farber (A.S.H.V.E. Transactions, Vol. 40. 1934, p. 263). 726 Chapter 42 PIPE AND DUCT INSULATION Heat Transmission by Radiation and Convection, Heat Losses from Bare and Insulated Pipes, Heat Losses from Ducts, Low Temperature Insulation, Insulation of Pipes to Prevent Freezing, Economical Thickness of Pipe Insulation, Under ground Pipe Insulation HEAT is transmitted to or from pipes and ducts by radiation and convection. The radiant heat transfer per unit area is independent of the geometrical shape, whereas the convected heat depends to a considerable extent on the shape factor. In many cases, it is desirable to calculate the rate of heat transmission from a surface by radiation and convection, as the total rate of transfer is different, for instance, from a heating installation than from a cooling installation with an equal difference in temperature between the surface and the surrounding atmosphere. HEAT TRANSMISSION BY RADIATION AND CONVECTION The heat transmission by radiation from a surface to the surrounding surfaces can be calculated from the well-known Stefan-Boltzman formula: Sr = 17.4 X 10-10 X P (TV - TV) where Sr = heat transmission by radiation, Btu per square foot per hour. p = effective emissivity of surface and surroundings. Ti = temperature of hotter surface, degrees Fahrenheit absolute. Ti = temperature of cooler surface, degrees Fahrenheit absolute. (1) The heat transmission by free or natural convection can be determined from the formula: -d) (fav.) (2) where qc -- heat transmission by convection, Btu per square foot per hour. C -- a constant depending upon the surface shape. D = diameter of pipe or circular duct or height of vertical wall, inches. (effect of diameter or height becomes constant at 24 in.) . T av. = average wall surface and surrounding air temperature, degrees Fahrenheit absolute. ----- dt -- temperature excess between wall surface and surrounding air, degrees Fahrenheit. 727 vy