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American Society of Heating and Ventilating Engineers Guide, 1936 The expansion of low pressure steam piping is normally taken as 114 to 1% in. per 100 ft of pipe. With a five story building a double swing connection between the riser and the main will suffice. In buildings between 5 and 10 stories high the riser should be anchored near its center and have double swing connections to the main. For taller buildings expansion loops or riser offsets are used which are capable of handling a length of riser reaching 5 stories in either direction from the joint. The risers are anchored at each alternate 5 stories. All radiators must have double swing connections, and those con nected above where the riser is anchored must be given greater pitch to insure their having proper grade when the riser is heated. 8 Why should all boiler steam supply tappings be used full size? In order to operate at low steam velocities so the water in suspension can separate from the steam and remain in the boiler. 9 What is the Underwriters Loop of the Hartford Connection? An arrangement of piping on the returns to low pressure boilers wherein the return line is raised up nearly to the water line of the boiler and is then dropped back and con nected to the boiler return inlet; the high point is connected by a balance pipe to the steam runout from the boiler on the boiler side of all stop valves. With this loop no check valve is required, and water cannot be backed put of the boiler and into the return at a point lower than the invert of the pipe at the top of the loop. 10 What are the important factors in making radiator connections? Connections to radiators should be made as direct as possible, of proper size, with ample pitch of piping and allowance for expansion. 11 Why should careful attention be given to proper dripping and drainage of steam piping? The steam mains and risers must be quickly drained of condensate and where necessary vented of air in order to obtain a sufficient supply of steam to the radiators. Proper drainage is also necessary to insure a noiseless heating system. 12 What is the limit of pressure drop usually recommended in a vacuum system? Not over lb (2 oz) per 100 ft of equivalent run, and not over 1 lb total drop. 13 When steam and condensation are flowing in the same direction, what is the maximum total pressure drop which should be used? The maximum total pressure drop should not exceed one half of the initial steam pressure. 14 t What does a proper installation of a pressure reducing valve include? A strainer in front of the pressure reducing valve; a gate valve in front of the strainer; a gate valve after the reducing valve; a by-pass around the two gate valves, strainer, and pressure reducing valve; and a globe valve in the by-pass. Sometimes a safety valve on the low pressure side and pressure gages on both sides are installed. The high pressure line should be dripped just before the high pressure steam enters the pressure reducing valve assembly. 15 Will a pressure reducing valve which is reducing the steam pressure from 100 lb gage to SO lb gage pass more or less steam than the same valve when reducing the steam pressure from 100 lb gage to 5 lb gage? The valve will pass practically the same volume of steam in each case as the velocity of steam flowing through an orifice shows no material increase after the reduced absolute pressure has fallen to 58 per cent of the initial absolute pressure. Because of its greater density, the weight of steam passed will be greater in the case of the reduction to 50 lb gage. 586 Chapter 33 HOT WATER HEATING SYSTEMS AND PIPING One- and Two-Pipe Systems, Selecting Pipe Sizes, Forced Circu lation, Effect of Variations in Pipe Sizes, Gravity Circulation, Mechanical Circulation, Expansion Tanks, Installation Details AHOT water heating system is one in which water is the medium by which heat is carried through pipes from the boiler to the heating units. There are two general types, namely, forced circulation and gravity circulation systems. In the former the pressure head maintaining flow is produced mechanically, whereas in the latter the pressure head is pro duced by the differences in weight of the water in the flow and in the return risers. The fundamental nile in the design of a hot water system is that the total friction and resistance head in any circuit must equal the pressure head causing the water to flow in the same circuit. In designing a hot water heating system, it is necessary to determine; 1. The heat losses of the rooms or spaces to be heated. (See Chapter 7.) 2. The size and type of boiler. (See Chapter 25.) 3. The location."type, and size of heating units. (See Chapter 30.) 4. The method of piping. 5. Suitable pipe sizes. 6. The type and size of circulating pump (if forced circulation). 7. The type.and size of expansion tank. The unit, a square foot of equivalent direct radiation, EDR, has been used for many years for rating purposes in both steam and hot water systems, but its use, especially in hot water systems, has always resulted in complications and confusion. It is the plan of The Guide to eventually eliminate this empirical expression and to substitute a logical unit based on the Btu. The Mb, the equivalent of 1000 Btu, and the Mbh, the equivalent of 1000 Btu per hour, which have been approved by the A. S.H.V. E., are used in this chapter on hot water systems to replace the square foot of radiation formerly used. ONE- AND. TWO-PIPE SYSTEMS Pipe systems may be divided into two general types, namely, two-pipe and one-pipe systems. In a two-pipe system the piping is arranged so that the water flows through only one radiator during a circuit through the system, so that all radiators are supplied with water at practically the same temperature as that in the boiler. In a one-pipe system, the water flows through more than one radiator during its circuit. In that case, the 587