Document o9dm7nBRG9pK2ymBq67xgm2pE

564 CHAPTER 24 1954 Guide 15 are marked Part 1 to Part 4 and, as will be evident by following the dashed line on Pthaertch1.artS, taarertiunsgedfraosmfotlhloewdse:pth of cover (2.5 in.), proceed vertically to the line representing pipe spacing on centers (12 in.), and then horizontally to the first ordi natPeaorft P8.arMt 2o.ve parallel to the nearest upward sloping line, indicating "2 in. & over" cover, to intersect the ordinate representing ) in. pipe, and then proceed hori zonPtaarlltySt.oPthroecefiersdt poardrainllaetletoof Panadrt a3l.ong the nearest downward sloping line to an intersection with the ordinate representing the panel output (34 Btu per sq ft), and then move horizontally to the right hand scale of Part 3 and read a required average waPtearrtie4m.peFrraotumrethine twheatceorilteomf 1p0e6raFt.ure 106 F just found in Part 3, proceed hori zontally into Part 4 to intersect the line representing insulation between the slab and fill. Directly below this intersection read 1.09 (on the bottom scale) as the muTlthipelireerqtuoirebed upsaende.l. input is, therefore, 1.09 x panel output, or 1.09 x 34 = 37.1 BtuThpeerto(tsaql rfet)qu(irherd). panel input is 37.1 x panel area = 37.1 x 480 = 17800 Btuh. CEILING AND WALL PANEL DESIGN Where coils are embedded in plaster on ceilings or walls, design pro cedure is simplified considerably by the physical limitations of the space available. For tube fastened to the underside of lath, the largest practical size is | in. O.D., while for ferrous pipes above the lath, it is 1 in. .I.P-STherefore, the actual tube or pipe size selected is usually determined by the length of coil circuit and its flow resistance in consideration of the . avaInilaobrldeecrirtcouloabtitnaginhaearde.asonably even heat distribution over the finished Panel Heating 565 plaster heating surface, pipes or tubes should be spaced on about 6 in. centers, and not over 9 in. centers. Within these limitations it is found in practice that heat output rates do not vary too seriously with variations in pipe and tube size and tube spacing. In general, for plaster ceiling panels with tubes or pipes spaced on 4^ to 9 in. centers, the temperature of the circulating water is about 10 to25 deg above the desired surface temperature. The hourly heat output per square foot of panel surface may be found by means of Figs. 11, 12, and 13, and the calculations for room heat loss and UMRT, as previously illustrated in the example of floor panel design. HOT WATER PIPING When water is used as the heating medium, the piping layout and ar rangement should be based on the design principles outlined in Chapter 22 for Two-Pipe Forced Circulation Systems. The pressure drops through the coils should be carefully calculated, and it is recommended that all branch circuits and coils be balanced to provide for uniform distribution by means of regulating valves or tees. Generally, a 15 to 20 deg total temperature drop is used in determining water flow rates, and a total'pump head of more than-30.ft js undesirable due to noise caused by high water velocity. . Panel systems involving several rooms and panels comprising a single zone, require that all coils be selected for the same inlet water tempera tures. Panel areas and pipe spacing must be selected to make this pos sible. INSTALLATION DETAILS, ACCESSORIES, AND CONTROLS Installation details, as given in Chapter 22, Hot Water Systems, also apply to piping systems for panel heating. Control problems of panel heating systems are discussed in Chapter 39, Automatic Control. Efficient venting of air from the coils may be obtained by arranging the circulation so that the air moves in the direction of water flow to a high point in the system where an automatic float-type vent or connection to expansion tank should be provided for its release. Coils should be installed as nearly level as possible or, if they are on sloping surfaces due to structural conditions, they should be arranged to vent air at their high points. Arrangements of pumps, expansion tanks, drainage, and flow and return mains may be generally the same as for conventional hot water heating systems. SNOW MELTING The practicability of melting snow by means of heated coils has been demonstrated in a large number of installations in sidewalks, roadways, ramps, and runways. In addition to eliminating the heed for snow removal, other advantages gained are greater safety to pedestrians and vehicles, and reduction of labor in removal of slush from floors. The design of a snow-melting system involves primarily (1) a determina tion of the heat requirement which depends on snow fall and atmospheric conditions, (2) the coil and piping design which depends on heat transfer from a panel and on friction loss in piping due to the circulating medium Used, and (3) the selection or design of a heat exchanger for heating the cir culating medium.