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430 CHAPTER 29 1960 Guide Another typical application is the control of a low- or medium-pressure steam generator, usually less than 50 psig, using high-temperature water as the source of heat. In this application a proportional pressure controller in the steam generator supply positions a high-temperature water valve located in the return line to maintain the desired steam pres sure. High-temperature water is sometimes used to supply coils in air handling units where heating surfaces are so placed that possibility of personal contact is avoided. Care ful gjing of coil and valve is required to obtain stable con trol. In some cases face and bypass damper control is used, because then the control of water flow through the coil is not as critical. In some cases face and bypass damper control is used in conjunction with valve control. The coil valve, operating in sequence with the damper, must be closed when the face damper is dosed. The coil arrangement should' be such as to minimize air temperature pick-up when the bypass damper is at or near the open position. WATER TREATMENT Water treatment is seldom required where there is con tinual re-use of the water. Where none of the water is lost, except such minor amounts as may accompany venting or be due to occasional leakage at stuffing boms, it is usually suffi cient to mat-o the water slightly alkaline when the system is first filled. Where the make-up water is appreciable, treat ment appropriate to the mineral content and quantity is indicated. See Closed Recirculation Systems in Chapter 55. It is desirfthlp- that systems with steam driven auxiliaries be arranged to conserve the heat in the exhaust. Steam driven auxiliaries can rarely be justified unless the exhaust steam can be used. Usually this is accomplished with a minor ad dition in capital expenditure. Fig. 15 shows an arrangement for boiler feed where exhaust steam is available. STORAGE High-temperature water systems may be operated to even out the peak loads and low loads within 24-hr cycles by storage. Storage is usually accomplished by the bypassing of water from the flow to the return mains and thereby storing heat in the return main for future use, or storing heat in accumulators. Systems which experience normal peaks may obtain as much as 15 percent added capacity through such heat storage. REFERENCES j. G. Frost: High temperature hot water boiler plant at Dartmouth (The Engineering Journal of Canada, June 1953). *0 S Lieberg: High temperature water (Air Conditioning, Heating' and Ventilating, September 1955, p. 83; November 1955, p. 85; January 1956, p. 69). Also published as a separate bulletin. E a Pierce: High pressure hot water systems (The Heat ing and Ventilating Engineer <t Journal of Av. Conditioning, London, 1942). J. R_ Kell: High pressure hot water (Heating, Piping and Air Conditioning, April 1948, p. 93; June 1948, p. 97; August 1948, p. 91; October 1948, p- 85). George Applegate, Jr.: British and European design and construction methods (ASHAE Journal Section, Heating, Ptping and Air Conditioning, March 1958, p. 169). C. A. Carter and B. L. Sturtevant: Design of high tem perature water systems for military installations (ASHAE Journal Section, Heating, Piping and Air Conditioning, Febru ary 1958, p. 109). E. G. Hansen and William Liddy: A flexible high pressure hot water and steam boiler plant (Power, May 1958, p. 109). Centrifugal Pump Section, Standards of the Hydraulic Institute, p. B(Vi)-9 (Hydraulic Institute, New York, 1955). Oscar Faber and J. R. Kell: Heating and Air Conditioning of Buildings (Architectural Press, London). BIBLIOGRAPHY J. H. Keenan and F. G. Keyes: Thermodynamic Properties of Steam (John Wiley & Sons, Inc, New York, 1936, 1st ed.). S. R. Lewis: Hot-water system of advantage in meeting plant heating requirements (Heating, Piping and Air Conditioning, May 1938, p. 319). K. Aschof: Die Calliqua-Heisswasserheisung (Die Warme: Zeitschrift fur Dampfkeasel & Machinenbetrieb, October 1931). F. R. L. White:' Some notes on high-pressure hot-water heat ing (Journal of the Institution of Heating and Ventilating En gineers, 1945). P. L. Geiringer: High pressure hot water (Heating, Piping and Air Conditioning, May 1948, p. 103). T. W. Reynolds: The high temperature water system (Heat ing and Ventilating, September 1951). High Temperature High Pressure Hot Water Heating Man ual No. 2685 (Dunham-Bush, Inc, New York, 1955). Charles Broder: Heating and air-conditioning a civilian air port (ASHAE Jocbnal Ssctzon, Heating, Piping and Air Con ditioning, March 1958, p. 147). 8. W. Brown: Marine applications of high-temperature wa ter (ASHAE Journal Section, Heating, Piping and Air Con ditioning, Manti 1958, p. 161). E. M. Thompson: Economic evaluation of high-tempera ture water (ASHAE Journal Section, Heating, Piping and Air Conditioning, April 1958, p. 140). CHAPTER 30 PANEL HEATING Application Methods: Embedded Piping for Ceilings, Walls, or Floors; Worm Air and Electrically Heated Ce/lrngs, Walls, or Floors/ Output from Panel Surfaces: Radiation, Convection and Combined Heat Transfer, Panel Heat Losses,Design of Panel Heating Systems: Warm Water Ponds for Plaster, Metal, and Concrete Ceilings/ Wall Panels and Concrete Floor Panels, Installation Details and Accessories. Controls/ Warm Air and Electric Panels IN this chapter the term. Panel Heating, is used to describe antimony, or capillary brazing alloys, be used. All piping a method of space heating in which heat is supplied by should be subjected to a hydrostatic test of at least three -large heated areas of interior room surfaces operating at times the working pressure, but not less than 150 psig. relatively low surface temperatures (80 to 125 F). The heating The most common forms of panels applied in panel heating elements usually consist of warm water piping, warm air are: (1) embedded piping for ceilings; (2) embedded piping ducts, or low temperature electrical resistance elements for walls; (3) embedded piping for floors; (4) air heated embedded in, or located behind, ceiling, wall, or floor sur faces. ceilings, walls, or floors; (5) electrically heated ceilings, walls, ox floors. Panel heating may be considered as another method of convenient and effective space heating. The heat loss require Embedded Piping for Ceilings ments may be calculated in the conventional manner except that the heat loss through the area occupied by the heated panel need not be included. An assumed or computed reverse heat loss from the panel, however, should be included in determining heating main raze and the boiler load. The heat release from the panel is expressed in terms of hourly heat output per square foot of surface. The room air temperatures to be maintained are approximately the same as those maintained by heating systems employing cast-iron radiators, convectors, or warm air ducts. When piping is embedded in ceilings, the construction used is generally one of the following: a. Pipe or tube is embedded in the lower portion of a con crete slab, generally very close to its lower surface. If plaster is to be applied to the concrete, the piping may be placed directly on the wood forms. If the slab is to be used without plaster finish, then the piping should be installed not less than in. above the undersurface of the slab. Fig. 1 shows thin method of construction. The minimum coverage must be in compliance with the local building code requirements. This chapter does not include a separate discussion of such topics as the influence of radiation on human comfort, the mechanisms by which human beings release heat, and other similar topics that apply to all methods of hating interior spaces for human comfort. The reader is referred to Chapter 6 for a detailed discussion of these subjects. APPLICATION METHODS The great majority of panel mstallatanns of the past 50 years (which is the period of the modem utilisation of this method of heating) have used warm water as the heating medium which is circulated in embedded piping. More recently, the use of warm air ducts, and embedded electrical heating elements, has oome into favor, especially where specific local factors have influenced such use. Steam has been used only occasionally because of the problems which result from its higher temperature. When the heating medium is warm water, both ferrous (steel or wrought iron) or non-ferrous (generally copper or aluminum) pipe or tube are used widely in ceiling, wall, or floor panel construction. Tube sizes used are }4, and H in* OD, while piping is generally %, or 1 in. IPS. Where coils are embedded in concrete or plaster, no threaded joints should be used for either pipe coils or mains. The construction should be of all-welded type. Changes in direc tion should be made by bending the pipe itself, rather than by use of fittings. Solder-joint fittingB are used for non- ferrous heating coils and piping. It is recommended that a medium temperature solder of 95 percent tin--5 percent Fig. 1 .... Coils in Structural Concrete Slab b. Pipe or tube is embedded in a metal lath and plaster ceiling. If the lath is suspended to form a hung ceiling, both the lath and the heating coils are securely wired to the sup porting members in such a way that the lath is below, but in good contact with the coils, as shown in Fig. 2. Plaster is then applied to the metal lath, care being taken to embed the coil, as shown'in Fig. 2. c. Copper tube of the smaller diameters is attached to the underside of wire lath or gypsum lath. Plaster is then applied to the lath to embed the tube, as shown in Fig. 3. d. Other forms of ceiling construction are prefabricated panels of metal, composition board, wood paneling, etc., hav ing warm water piping, tube, or channels built into the panel sections. x Coils are usually of the sinuous type, although some header or grid type coils have been used in ceilings. Coils may be of either ferrous or non-ferrous pipe or tube, with coil pipes spaced from 4) to 9 in. on centers, depending on the re quired output, pipe or tube size, and other factors. Where plastering is applied to pipe coils, a standard threecoat gypsum plastering specification1 is followed, with a minimum of % in. of cover below the tubes when the tubes 431