Chapter VII. Cast-iron pipes are either socketed or flanged. In (Part 3)

Drop System. To alleviate the disadvantage of the system just described, each of the drop pipes is stopped at the lowest radiator in the tier, while a ‘‘return” is started at the outlet of the top radiator, connecting up with each of the radiator outlets on the way down and finally connecting to the main return back to the boiler. The method is shown in one tier of radiators in Fig. 118. Otherwise Fig. 117 remains unaltered. In this way, every radiator gets its own supply from the boiler and all cooled water goes straight back to be reheated instead of hot and cold mixing in the radiators. Dips in Pipe Line. It is sometimes necessary to dip the pipes to pass under doorways and similar features, rising again on the far side of the obstruction. Such dips form traps and obstruct the circulation; they should therefore be avoided wherever possible, but, if unavoidable, an air cock should be inserted at the top of the loop produced, so that any steam or air collecting there may be released. Dips of this type do least harm on the return pipe near the boiler, but they always slow down the circulation and, as the convection currents have far less power than the force of gravity, everything possible should be done to avoid friction or hindrance to flow. | THE BUILDING—ITS WARMING AND LIGHTING 1838 Cold Supply to Boiler. The cold supply should be taken either direct into the boiler or connected to the return pipe just before the boiler is reached, the supply pipe having a dip or trap at the point of connection, to prevent the hot water circulating up it to the feed cistern. An expansion pipe should be carried up as nearly over the boiler as possible, in the form of a continuation of the vertical flow pipe, and should have its upper end bent over the feed cistern. This allows for the expansion of the water in heating, and also for any discharge that may occur from it to occur in a place of safety. Two-pipe System. Fig. 119 illustrates the ordinary two-pipe system. It is far more adaptable to irregularly designed buildings than the one-pipe systems, and it is easier to control the temperature, as each radiator has its inlet from the main flow pipe, while the branch return goes back, via the main return pipe, to the boiler, and there can be no question of one radiator being fed with the leavings of its predecessors. In the two-pipe system the pipes are arranged to flow and return as before, but in a different way, the flow and return following the same course. Figs. 120 and 121 show this, and should be com. pared with Fig. 119. An inspection of Figs. 120 and 121 will show that they give different positions for the inlet in the two cases. The top inlet shown in Fig. 120 is the more efficient, but the bottom inlet shown in Fig. 121 is the neater in appearance, being only a little above the floor. The difference, however, is apparent rather than real, for when the inlet is taken in low down, the bottom connecting nipple between the first and second radiator sections is blocked up, and the first section then acts as an inlet pipe as well as being part of the radiator. When this is done the inlet control valve is often of a different pattern, being placed with its working parts in the connecting nipple between sections 1 and 2 at the top, and the handle is then placed horizontally beside the top of the first section and right opposite the air-cock, Two Pipe with Vertical Risers. The two-pipe system with vertical risers is shown in Fig. 126. Its chief advantage is seen in office or factory blocks in which the floor plans are more or less stereotyped, so that the radiators can be arranged in tiers one above the other. It is not so easy to hide the pipes unless the walls are panelled, enabling the pipes to be hidden behind the panelling. Pipes in Ducts or Chases. If the pipes are run in chases left or cut in the walls, care must be taken to insulate the heat and to permit free expansion and contraction. Pipes embedded in this way are often wrapped first in canvas-backed asbestos fibre or in 184 THE BUILDING—ITS WARMING AND LIGHTING ee : Pet STEAM TRAP 122 STEAM CALORIFIER COLD FRESH AIR DUCT 123 HER. CAN BE CONNECTED HERE TO EXPANSION CHAMBER . OR AIR RELIEF PIPE RE. roo <9 CEILING PANEL REALLY ae RAT CONTROL —- CONTROL VALVE FIRE BOX BRANCH Fi FLOW ee TO OTHER stovereyen| vVVVVVTVY BRANCH "RETURN INSULATING JACKET 74 INSULATING JACKET ASH PIT “ONE~PIPE” HEATER DIAGRAM OF PART OF 124 PANEL SYSTEM 125 THE BUILDING—ITS WARMING AND LIGHTING 185 Zw» Sw LL ilbbibe Ke GGL BSG RET A 1 Main YN CIRCUIT OR iM BASEMENT DIAGRAM OF “TWO-PIPE" SYSTEM WITH RISERS, (AIR coors NEEDED ON TOP RADIATORS ONLY.) LE FOR LOFTY BUILDINGS Win OSYMMETRICAL PLANNING LOW- PRESSURE STEAM SYSTEM, “ONE-PIPE” CIRCULATION WITH STEAM AND CONDENSATION WATER IN SAME PIPES 130 136 THE BUILDING—ITS WARMING AND LIGHTING hair felt. A closely fitting metal collar is often placed round the pipes where they emerge from the plaster of ceilings and walls, or from the timber of floors, so that a neat but non-rigid joint is possible. Too tight a joint will damage the plaster and result in all sorts of weird noises in the dead of night, or in the early morn- ing, as the pipes contract or expand with changes in temperature. Each system of arranging the pipes has its advantages and dis- advantages, and those of the one-pipe system are as follows: The advantages are economy, and the fact that there is no liability to short-cireuiting; i.e. no radiator can escape being supplied. On the other hand, it is not so suitable as other systems for a building of several floors. In the overhead or drop system the flow pipe is taken to the highest point straight away, and then split up into several vertical returns, which are collected together at the bottom into one main return. The system is particularly suitable for a high building, if the radiators are-arranged one over the other on the various floors. The advantages beyond this are that the large amount of vertical piping ensures a rapid circulation and permits the use of smaller pipes, and no air valves are needed. Choice of Circuit. The two-pipe systems should be considered the most satisfactory, especially for large or irregularly planned buildings—the two-pipe system with risers being chosen when all floors are much alike. The system is rather more expensive to install, but it gives much better control, as the cooled water from radiators is taken straight back to the boiler to be reheated and does not cool the water in the main circuit. Accelerated Heating Schemes. These are conventional high- or low-pressure heating circulations of the ordinary one-pipe, drop, two-pipe and similar design in which the design of the building or the long horizontal travel makes it difficult or impossible to obtain a sufficient circulation by gravity. It then becomes necessary to instal an accelerating pump. This is usually on the return pipe just before returning to the boiler, where the water is coolest and the working parts least likely to be affected by excessive expansion and contraction. Such pump is generally worked by electric motor (as least troublesome), the pump being of centrifugal type as being most free from valves. The inclusion of such a pump, in speeding up the circulation tends to increase the efficiency of the boiler, as the transfer of heat from the boiler plates to the water is more rapid. . Pipe Sizing. The size of pipes needs to be worked out with extreme care if the heating capacity of the radiators is to be in THE BUILDING—ITS WARMING AND LIGHTING 187 any way controlled by them. This control, as has been shown, is contrived mainly by the size of the radiator, the hand valve on the inlet and (sometimes) the key valve on the outlet, so that exact pipe sizes are not necessary, provided they are large enough to carry the volume of water needed. In an efficient low-pressure hot-water system, with a mean temperature of 180° F., branch pipes ? inch in diameter will be sufficient for inlets and outlets, and the mains leading to them can be made of a sectional area large enough to equal that of the sum of the inlet branches, worked out by the rule of similar figures. Thus, if D is the diameter in inches of main supply pipe and d the diameter of twelve 2-inch inlets to radiators to be served thereby, the main supply should be worked out so: D2 @ ‘ities 8\2 Lee ed Ma D ( i) x 12, D = ht 24 in. (approximately). 4x4 In the same manner, and ignoring any alteration in friction, we might assume that, if one main supply pipe has to provide two loop mains with hot water, each loop being of 24 inches diameter, the trunk main should be such that: D2 @ + an D2 =2 x 24 x 2, —— D = Sei he 34 in. approximately, 2x2 Lagging. Where pipes pass through rooms not requiring to be warmed, or where the warmth would be wasted, a non-conducting covering or lagging should be used, the materials suitable for boilers usually being suitable also for pipes. High-pressure Systems. The high-pressure system of hot-water heating was introduced early in the nineteenth century by Perkins and is still often referred to as the Perkins’ system. The method of installing the system has varied but little since it was first intro- duced. Whereas the low-pressure system is open to the atmos- phere, through the medium of the expansion and air pipes, the high-pressure system is hermetically sealed. Broadly speaking, 138 THE BUILDING—ITS WARMING AND LIGHTING it consists of an endless pipe nearly filled with water, a coil of the pipe being placed in a furnace to act as a boiler. There should be about 10 feet run of pipe in the boiler coil for every 50 feet around the building. It is a well-known fact that water boils at different temperatures when subjected to different pressures. Thus, at sea level, it boils at about 212° F., but at the top of a high mountain, where the pressure of the atmosphere is less, it would boil at a lower tempera- ture. Similarly, at the bottom of a very deep mine, it would not boil until it reached a much higher temperature than 212°, because the pressure is greater. This phenomenon is utilised in the de- termination of heights, the science of determining heights by the relative boiling-point of water being termed hypsometry. By eliminating the expansion pipe (or other means of maintain- ing atmospheric pressure), and strengthening the pipes and fittings to correspond, it is possible to heat the water to a much higher temperature without the water boiling. In the ordinary forms of high-pressure apparatus the pipes reach a temperature of about 250° to 300° F., and in any good installation valves are used to prevent a higher temperature being reached, since as high as 600° F. is quite a possibility. The pressure referred to above is obtained entirely by natural means, the expansion of the relatively incompressible water compressing the air. The component units are the coil or coils forming the boiler, the pipes and joints, the expansion chamber and the filling pipe. No stop valves are needed in this system, neither are air valves used, as the air is dislodged when the apparatus is first charged with water, while that which is given out from the water during the heating accumulates in the expansion chamber. In the original ‘‘ Perkins”? system, no branch services were used, separate loops and boiler coils being employed, when extra tiers of radiators or radiating coils were needed, but in modern high pressure a more conventional type of boiler is employed and branch sections with welded joints are used where needed. Boiler in Perkins System. The boiler is usually formed of a coil or coils of the same pipe as is used for radiation of the heat into the rooms. This method of arranging the coils gives several distinct pairs of flows and returns, each loop having its own expansion chamber, and so ensures a high temperature throughout. Pipe Joints in H.P. System. Radiators are usually formed of the tubes themselves, sometimes just as they are, but more often em- bedded in semi-insulating plaster or concrete of walls, floor or ceiling, when the system is known as the “ Panel” system. THE BUILDING—ITS WARMING AND LIGHTING 189 The pipes are of strong welded wrought iron, § inch in internal diameter and about } inch thick. They are tested to a high pressure and temperature before leaving the factory. These tubes may be threaded at both ends with right- and left-handed threads respectively, the joint being made by means of loose collars, as shown in Fig. 127. No jointing material is used, but one end of each pipe is shaped as shown, so as to give a tight “metal to metal” joint when the socket is fully screwed up. Another method, especially suitable for the panel system, when the tubes are inaccessible, once they are embedded, is to use welded joints. Expansion Chamber. The expansion chamber usually takes the form of a pipe 3 or 4 inches in diameter, fixed vertically or nearly so, with a screw cap at the top. It may, however, take the form of a coil. Charging Plug. The apparatus is charged, in the first instance, through a plug near the boiler, but a recharging plug is provided just below the expansion chamber, for adding water as from time to time required. The flow pipe should go to its highest point by the most direct route, in order to ensure a good circulation. Dips or traps in the pipes are not so difficult to deal with in this system, as the circula- tion is much more rapid than in the low-pressure method. The pipes should be fixed at least 3 inches from any woodwork. They can. be exposed in the room, or, if this is objected to on the ara of appearance, they can be put behind a grating where the skirting of the room would ordinarily be. If radiators of the conventional type are desired in this system, they are most conveniently heated indirectly by small calorifiers in the manner shown in Fig. 128. Below each radiator a large pipe or cylinder is put, of say 3 to 4 inches diameter, to the ends of which the ordinary small pipe is connected. From the larger pipe a flow is taken to the radiator, a return being taken from the opposite end. The method of connecting the flow and return has already been described and should be again noted in Fig. 109, the flow going from the top of the pipe and the return being connected to its side. The Stainton Valve. Instead of the expansion chamber a valve may be used, fixed in a water tank. This valve can be adjusted to limit the pressure and the temperature to any desired figure. Fig. 129 shows a section through one form of such a valve, known as the Stainton valve. At the top, shown by hatched lines, is a weight, connected to a vertical spindle which has a conical lower end. The cone rests on a seating and when the pressure gets beyond the predetermined figure it automatically rises and lets 140 THE BUILDING—ITS WARMING AND LIGHTING the water out into the tank. On the pressure falling below its normal amount, another small valve, at the bottom of the illustra- tion, automatically rises and lets more water in. The spindle of this valve is not of circular but of cruciform section, so that a very slight rise of the spindle will let water in. Water systems are liable to be interfered with by frost, if the furnace is allowed to go out in frosty weather. Anti-freezing liquids are obtainable which can be added to the water to prevent freezing, but a much better method is to take care that the boiler is not allowed to go out at such times. Advantages of H.P. System. In concluding the description of the high-pressure system, its advantages and disadvantages may be briefly set forth. Its first cost is not great, unless the pipes are embedded (panel system); the pipes may be quickly raised to the desired temperature; a high temperature may be obtained, which is particularly desirable for some purposes, such as the drying- rooms of laundries and other businesses; and only a small quantity of water is used. On the other hand, there is danger of explosion if the system is not well designed; the temperature may become too high if a valve is not used, with the result that the adjacent air will be scorched. Panel Heating. This is a system in which flat “grid-iron” shaped coils of heating pipes, generally with welded joints, are buried in the plaster of a wall or ceiling or in the concrete of fire- proof floor, these being invisible to the occupants and leaving the whole of the floor or wall area free for furniture, work-benches or such other usage as may be desired. The boiler is usually operated at high pressure, so the radiating pipes can be of small diameter— as small as } inch—and the spacing between the tubes can be about 6 inches so that the concrete or plaster in which they are embedded lowers down the final radiating surface to a temperature of 90° to 100° F, This lowering of the surface temperature of the panel reduces the amount of heat given