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American Society of Heating and Ventilating Engineers Guide, 1932 Sectional Insulation Type (Tile or Concrete Trench) : A type ohconstruction frequently used in city streets, where service connections are required at frequent intervals, the pipes are insulated as described in the preceding paragraph, and are enclosed in a box or trench made either entirely of concrete, or with concrete bottom and specially con structed tile sides and tops. The pipes are supported on roller frames secured in the concrete. At C and E, Fig. 1, are shown two tile conduits using sectional insulation. Ii> these particular designs the space surrounding the pipe is filled partially or wholly with a loose insulating material. The use of loose material in addition to the sectional insula tion is, of course, optional and is only justifiable where high pressure steam is used. The conduit shown at F is of a similar type and has the advantage of being made entirely of concrete and other common materials. Sectional Insulation Type (Bituminized Fibre Conduit): Each pipe is individually insulated and encased in a bituminized fibre conduit.. The insulating material is 85 per cent carbonate of magnesia sectional pipe covering, applied in the usual manner as on overhead pipes, except that bands are omitted. After every fifth section of magnesia covering there is applied a short, hollow section of very hard asbestos material in the Fig. 1. Construction Details of Conduits Commonly Used bottom portion of which rests a grooved-iron plate carrying ball-bearings upon which the pipe rides when expanding or contracting. This short expansion section is of the same outside diameter as the adjacent 85 per cent magnesia covering. Over the pipe covering and expansion device there are placed two layers of bituminized fibre conduit with all joints staggered and the surface of each conduit, finished with , liquid cement: Conduits are placed on a bed of crushed rock or gravel, approximately 6 in. deep, and this is extended upward to about the center line of the conduit when trench is backfilled.- Underdrains leading, to points of free discharge are placed in the gravel or crushed rock beds. Special Water Tight Designs. It is occasionally necessary to install pipes in a very wet ground, which calls for special construction. The ordinary tile or concrete conduit is not absolutely water tight even when laid with the utmost care. The conduit shown at G, Fig. 1, is of cast-iron with lead-calked joints and is water tight if properly laid. It is obviously expensive and is justified only in exceptional cases. A reasonably satisfactory construction in wet ground is the concrete or tile conduit: with a waterproof jacket enclosing the pipe and its insulation, and with the interior of the conduit carefully drained to a manhole or sump having an automatic pump. It is useless to install external drain tile when the conduit is actually submerged. , 316 Chapter 22--District Heating PIPE TUNNELS Where steam heating lines are installed in tunnels large enough to provide walking space, the pipes are supported by means of hangers or roller frames on brackets or frame racks at the side or sides of the tunnel. The pipes aire insulated with sectional pipe insulation over which is placed a sewed-on painted canvas jacket or a jacket of asphalt saturated asbestos water-proofing felt. The tunnel itself is usually built of concrete or brick and water-proofed on the outside with membrane water-proofing. On account of their relatively high first cost as compared with smaller conduits, walking tunnels are sometimes not installed where provision for the heating lines is the only consideration, but only where required Table 3. Capacity of Returns for Underground Distribution Systems in Pounds of Condensate per Hour Sizes 0,In. 1 im 2 3 4 5 6 8 10 12 6' 448 1740 2700 4980 13900 30900 54800 90000 190000 344000 555000 i' 998 2490 4190 7380 22500 44800 79800 138000 277000 498000 798000 . Pitch of Pipe per 100 Ft. V 1890 3990 5740 10700 30900 64800 120000 187000 404000 724000 1148000 3' 2240 4880 7480 13900 ; 37400 79700 144800 237000 508000 900000 1499000 S' 3490 6480 9480 16900 50400 105000 195000 312000 660000 1190000 1990000 to' 5490 9480 14500 24900 . 74800 154000 294000 449000 938000 __________ -- 20' 7490 13500 20900 36900 105000 229000 418000 .......... ____........ __________ ------** aSize of pipe should be increased if same carries any steam. to accommodate miscellaneous other services, such as for underground passage between buildings. SERVICE CONNECTIONS Most district heating companies enforce certain regulations regarding the consumer's installation, partly to safeguard their own interests but principally to insure satisfactory and economical service to the consumer. There are certain fundamental principles that should be followed in the design of a building heating system which is to be supplied from street mains. Although some of these apply to any building, they have been demonstrated to be especially important when steam is purchased. 1. Provision should be madefor conveniently shutting off the steam supply at night and at other times when heat is not needed. It "has been thoroughly demonstrated that a considerable, amount of heat can be saved by shutting off steam at night. Although there is, in some cases, an increased consumption of heat when steam is again turned on in the morning, there is a large net saving which may be explained by the fact that the lower inside temperature maintained during the night obviously results in lower heat loss from the building, and less heat need therefore be supplied. 317