Document 1519BJEJ2Ya96LoEjJ0Q6ZmYZ

American Society of Heating and Ventilating Engineers Guide, 1936 PIPE SIZING FOR INDIRECT HEATING UNITS Pipe connections and mains for indirect heating units are sized in a manner similar to radiators, but the equivalent direct radiation must be ascertained for each row of heating unit stacks and then must be divided into the number of stacks constituting that row and into the number of connections to each stack. EDR QX 60 X ft - ie) 55.2 X 240 Q X i - <e) 220.8 (3) where EDR = equivalent direct radiation, square feet. Q = volume of air, cubic feet per minute. It = the temperature of the air entering the row of heating units under con sideration, degrees Fahrenheit. fl = the temperature of the air leaving the row of heating units under considera tion, degrees Fahrenheit. 60 = the number of minutes in one hour. 55.2 = the number of cubic feet of air heated 1 F by 1 Btu. 240 = the number of Btu in 1 sq ft of EDR. Example 5. Assume that the heating units shown in Fig. 25 are handling 50,000 cfm of air and that the rise in the first row is from 0 to 40 F, in the second row from 40 to 65 F, and in the third row from 65 to 80 F. What is the load in EDR on each supply and return connection? Solution. For row 1, R 50,000 X (40 - 0) 220.8 9058 sq ft. For row 2, R 50,000 X (65 - 40) 220.8 5661 sq ft. For row 3, _ 50,000 X (80 - 65) 220.8 3397 sq ft. Each row of heating units consists of four stacks and each stack has two connections so that the load on each stack and each connection of the stack is as follows: - Row Total Load (EDR) Stack Load* (EDR) ComrecnoN Load** (EDR) i 9058 2265 2265 or 1132 2 5661 1415 1415 or 708 3 3397 \849 849 or 425 One quarter of total row load. ;' bOne half of stack load if two steam connections are made; otherwise, same as stack load. DRIPPING Any steam main in any type of steam heating system may be dropped to a lower level without dripping if the pitch is downward with the steam flow. Any steam main in any heating system can be elevated if dripped (Fig. 27). Steam mains also may be run over obstructions without a change in level if a small pipe is carried below the obstruction to care for the condensation (Fig. 28). Return mains may be carried past doorways or other obstructions by using the scheme illustrated in Fig. 29; in vacuum systems it is well to have a gate valve in the air line. 582 32Chapter --Piping for Steam Heating Systems TeOr foVoOuUsiHwGfimFCoa- a.MULTBLV A anqle Fig. 30. Constants for Determining Proper Length of Offset Pipe One Pipe Air Vent System with Dry Return Note.--If connection can be made to a wet return, no 5 ft loop is required. Fig. 31. Acceptable and Preferred Methods of Taking Branch from Main of Dripping Main Where It Rises toHigher Level Note.--Suitable for vapor and atmospheric. systems. Fig. 28. Looping Main Around Beam. Fig. 32. Dirt Pocket Connection t-oer BETUGM LsuPtvr MAIn Fig. 29. Looping Dry ' Return Main Around Opening retura hnecuairtray'?inkgfairr.any dry return line and a: QEDUCWG C0UPUNG-O' Fig. 33. Dripping End of Main into Wet Return W.TEB LINE Note.--Suitable for vapor systems. 583