Document LJNzr2wv4Xzwe4jVvOQ8dbqxb

American Society of Heating and Ventilating Engineers Guide, 1930 Figs. 36 and 37 show typical connections to indirect cast iron convectorheaters, and apply to vapor and vacuum systems especially. Fig's. 35 and 38 show duct connections to such heaters. Pipe Coil Connections Fig. 39 shows practicable piping connections to pipe coils. It is important that the supply valves for all radiators which come below the supply mains shall be above these mains, or that there shall- be a drainage connection consisting of a trap or of a pipe-leading to the wet return, depending on the type of system, above these supply valves. Without such provision water will condense above the valves when they are closed, and this may cause objectionable noise or damage when the valves are opened. Blast Heater Connections Fig. 40 shows vacuum system returns for fan-blast heaters with the auxiliary air vent piping and air-line valves usually required with these heaters, especially when they are of cast iron. Fig. 41 illustrates another typical blast heater piping hook-up frequently encountered, but with which only the return ends have auxiliary air vents. It is to be noted that while the two super-imposed heaters may drain to a trap common to both, the successive layers of heaters with reference to the air flow from the fan should each have a separate trap, since the condensation rate varies in each successive layer after its predecessor has warmed the entering air. Unit Heater Connections When unit heaters are used with steam heating systems the designer must always take into consideration the great condensing capacity of these devices. They must be placed high enough above the boiler water line to compensate for the pressure drop or must be used with systems having pumps or other positive return devices, and must always have pipe connections proportional to their maximum heat emission. Some typical details of unit heater connections are shown in Chapter 9, Unit Heaters and Air Conditioners. .. 366 / CHAPTER 21 PIPING FOR HOT WATER HEATING SYSTEMS Determination of Pipe Sizes for Gravity and Forced Circulation Systems; Heat Emission of Hot Water Radiators; Various Arrangements of Piping; Recommended Temperatures; Elbow Equivalents. IN order to insure satisfactory operation of gravity flow or forced circu lation hot water heating systems, careful attention must be paid to design. This is particularly true of gravity systems which must depend for operation upon the small motive forces created by the difference in weight of columns of water of different temperatures. The principal factors to be considered in the design of the piping system are: 1. The heat losses of the rooms or spaces to be heated. 2. The location and type of radiators. 3. Arrangement of the circuits of the system, including length of pipe and number and type of fittings. 4. The temperature of the water in the flow and return risers. Several different piping systems may be designed for any given com bination of heater and radiator. The general rule to apply to the design of a pipe system is that the friction head leading from the heater to a radiator and back again must equal the pressure head causing the water to flow for that particular circuit. This rule is based on the condition that the water in the system is circulating with a uniform velocity as is the case when the radiators (and piping) dissipate exactly the same quantity of heat in a given period of time as is delivered to the water in the heater. The pressure head maintaining circulation through the system may be produced by the difference in the weights of the water in the flow and return risers, in which case the system is a gravity-flow system; or it may be produced by a circulating pump, in which case the system is a forced circulation system. GRAVITY-FLOW SYSTEM Before undertaking the design of a pipe system, it is necessary to assume: 1. The maximum temperature of the water leaving the heater lyhen the outside temperature is the minimum for which the system is to be designed. 2. The drop in the-temperature of the water while it is flowing through the radiator. 3. The arrangement of the pipe connecting the heater with the several radiators. 367