Document 06MyZoXGE2NEG3gE0yeVY7MRR

518 CHAPTER 24 1949 Guide The size of a basement-located closed expansion tank should be at least equal to the following: One story buildings: x = 0.10 V Two story buildings: x = 0.13 V where Three story buildings: % * 0.17 V Four story buildings: % -- 0.23 V x = expansion tank size in gallons. V = water volume in heating system in gallons. This condition favors, especially in tall buildings, the placing of the closed expansion tank above the highest heat transmitter. It is common practice to use multiple tank installations on large systems in lieu of one tank the required capacity of which is beyond commercially available sizes. Any closed expansion tank located above the heat transmitters of a hot water heating system should be connected by a direct pipe with the flow main leaving the boiler, in order to enable, the air to pass easily to the ex- Pipe Size. In. iH Table 6. Volume op Water in Standard Pipe Lineal Ft of Pipe . Containing 1 Gal 63.1 36.1 22.2 12.8 9.47 1 Pipb Size, In. 2 2H 3. 4` 5 6 Lineal Ft op Pipe Containing 1 Gal 5.75 4.02 2.60 1.52 0.96 0.67 pansion tank. In a closed hot water heating system the water under pres sure tends to absorb air at a rate increasing with pressure increase and decreasing with temperature increase. . Means must be provided to adjust and to observe the proportion of air within any closed expansion tank. This involves the provision of an air inlet valve, a water gage, and a; relief valve. A source of supply of com pressed. air for renewing the air cushion is highly desirable, especially in 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 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 6. 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 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 radiation by the factor 40 to obtain the required capacity in gallons of the tank. JSIwas!; - --'-- Hot Water Heating Systems and Piping 519 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. When piping must be run around an obstacle such as a beam, it is advisable to drop the piping below the beam. If looped over the beam, it becomes necessary to provide for venting of air from the high point of the pipe. When changing the size of horizontal runs of pipe, eccentric fittings should be used to keep the tops of the pipes in line to permit free passage of air along the pipe. 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 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 and should allow for expansion. 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 circula tion through the risers will start in the right direction. Hence, in a one-pipe system the flow connection must be nearer the heater than the return connection. In a correctly-designed 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 con nections from the heater is not material; but it is generally best to have the two connections about equally distant from the heater. , Generally, connections to risers or radiators are taken out of the top of mains either 45 or 90 deg. Supply connections are usually made at the bottom of radiators so that circulation will not be stopped by accumulation of air, as would be the case with a top supply connection. Short radiators are sometimes connected for top supply and bottom re turn on the same end. When so connected, attention must be given to venting of air * from the top of the radiator somewhat oftener than when bottom connections are used. . Unless used as heating surface, all piping, both flow and return, should be insulated. All large systems should be provided with extra stop and drain valves, suitably located so that parts of the system may be isolated for repairs without making it necessary to drain the water from the entire system. ZONING In large hot water systems improved control and economy can be achieved by separating the systems into sections or zones (vertical or hori zontal) which can be operated independently of each other. Variations in heat requirement of the different zones as influenced by the exposure o(