Document OEym6E61nr6JzJ8XDem2V8GYQ

1 HEATINC VENTILATING AIR CONDITIONING GUIDE 1944 CHAPTER 16. HOT WATER HEATING SYSTEMS AND PIPING large, high pressure hot water heating systems where it is inconvenient, if not impracticable, to drain down the water in the system so as to permit introduction of atmospheric pressure air. For every hot water heating system the designer should calculate the connection must be nearer the heater than the return connection. In a correctlydesigned two-pipe system, the pressure in the flow main is higher than that in the return main, and a slight variation in the distances of the flow and return connections from the heater is not material; but it is generally best to have the two connections about equally distant from the heater. volume of water contained in the radiators, piping system, boiler, etc., in order to select the proper size of expansion tank. The water content of the piping can be obtained from Table 5. For a rough selection of size, however, it is sometimes assumed that 50 per cent of the volume of water is contained in the radiators, and that the water content per square foot Generally connections to risers or radiators are taken out of the top of mains either 45 or 90 deg. In some cases it may be advisable to take the flow connection off the top of the main and the return connection from the side. With forced circulation and high velocities, it is advisable to let the water enter at the top of the radiator and leave at the bottom of the opposite end. With gravity circulation 1 of radiator heating surface is 0.2 gal for column radiators and 0.13 gal for tube type radiators. } Another rough method for determining the size of an expansion tank to be located above the highest radiator is to divide the square feet of . Table 5. Volume of Water in Standard Pipe Pipe Size, In. H % 1 1H m 2 2H 3 4 5 6 Lineal Ft of Pipe Containing 1 Gal 63.1 36.1 22.2 12.8 9.47 5.75 4.02 2.60. 1.52 0.96 0.67 radiation by the factor 40 to obtain the required capacity in gallons of the expansion tank. INSTALLATION DETAILS Items that should be considered in the design of this type of system are: All piping must be so pitched that all air in the system can'be vented either through an open expansion tank, radiators or automatic relief valves. All piping must be arranged so that the entire system can be drained. Sections of piping'individually valved shall have corresponding drain valves. In large buildings, the piping may be zoned according to exposure of building, usage of building, or method of control. All piping must be installed so that it is free to expand and contract with changes of temperature without producing undue stresses in the pipes or connections. For this purpose it is generally sufficient to allow for a variation in length of 1 in. for 100 ft of pipe. The pipe system should be designed so that each circuit has its correct friction head for balanced water distribution. This may be done by change of pipe size or change in piping detail. The connections from the boiler to the mains should be short and direct, to reduce the friction head and allow for expansion. It is frequently possible to avoid an elbow and to.reduce the length of the pipe by running the pipe in a diagonal direction, either in a horizontal or in a vertical plane. The mains and branches should pitch up and away from the heater, generally not less than 1 in. in 10 ft. The connections from mains to branches and to risers should be such that circulation through the risers will start in the right direction. Hence, iri a one-pipe system the flow 312 the flow connection may be either at the top or at the bottom of the radiator. With short radiators both flow and return may be at same end, but top and bottom. Unless used as heating surface, all piping, both flow and return, should be insulated. EXAMPLES OF PIPING DESIGN The following graded series of examples of the design of hot water piping systems will illustrate the fundamental principles and methods. The differences between reversed return and direct return systems are shown, and the methods of balancing the several radiators or circuits are illustrated. A simple gravity system is shown in Fig. 7 and an elementary forced circulation system is diagrammed in Fig. 8. Elementary Gravity System Example 1. A simple gravity-circulation system is illustrated in Fig. 7 with one radiator that is giving off heat at the rate of 20,000 Btu per hour or 20 Mbh. The boiler imparts heat to the water at the same rate, and the water circulates at a uniform velocity. The thermal or gravity pressure head which produces the circulation is equal to the friction head which resists the circulation. The circuit consists of 1 boiler, 1 radiator, 2 ells, 1 radiator valve and a total of 24 feet of pipe. Solution. With the average water temperatures of 200 and 180 F in the supply and return risers, respectively, the pressure head will be 90 milinches per foot of water 313