Document 829NZpqrZwLY7rO2M4kMwObgB

HEATING VENTILATING AIR CONDITIONING GUIDE 1943 recorded by thermometer with its bulb in the center of the sphere is termed the radiation-convection temperature: See Chapter 35. ' CONTROL OF RADIANT HEATING The effectiveness of any type of control will largely depend on the time lag of the system. With warm air passing through floor ducts the time lag is usually too long for any kind of room thermostat, in fact this type of-thermostat will not prove suitable with any system if the building is constructed with massive brickwork and masonry, unless it operates in conjunction with a time control responsive to changes in outside con ditions. , The heat emitted by hot water pipes embedded in the plaster of the Fig. 10. Typical Radiant Heat Control System ceiling and walls or in the concrete base of a floor can.be effectively con trolled by an instrument designed to modulate the temperature of the water circulating in the system according to the outside conditions. Metal , panels which can .be installed in the ceiling or side walls may be either, controlled, by. an instrument-responsive to outside weather con ditions or by a .specially designed instrument, responsive to both air temperature and radiation. Any purely on dr off control system js not recommended for radiant heating. ' A typical control system operated from an outside thermostat, and supplemented with a room heat control instrument is illustrated in Fig. 10. The outside thermostat modulates the temperature of the circulating water,in the coils by introducing some of the hot water leaving the boiler with, a proportionate amount of return water which is diverted to the -three-.way valve. One type of room instrument consists of a blackened copper, sphere of 816 CHAPTER 45. RADIANT HEATING 6 or 8: in; in'diameter, in which a cylindrical sump contains a volatile liquid. A small electric heating coil creates in the sphere a vapor pressure which remains constant as long as the total heat loss from the sphere is at the desired rate. If the BET becomes too high for comfort, a greater vapor, pressure results from the smaller heat loss from the sphere. This acts on a diaphragm and reduces the supply of heat to the' room. With too low a BET the reverse action occurs. A similar instrument which has an electric heating element for warming the air inside the sphere and thermostat operated switch is also used for controlling room conditions. In addition to a thermostatically controlled device for modulating the temperature of the circulating water, it is an advantage to insert in each coil a locked flow control or adjustable resistance to give uniform, con ditions throughout all rooms. Owing to unforeseen difficulties with varying frictional losses in pipes, emission factors and exposures it is an advantage to be able to permanently regulate the flow through each circuit by means of a key operated valve as indicated in Fig. 4. FUEL CONSUMPTION Because of the lower air temperature desired with radiant heating, there is a possible saving in fuel consumption. This saving depends very largely on the method employed to heat the surfaces and the provision made to prevent heat passing from the coils to the earth or outside air. REFERENCES Panel Warming, by L. J. Fowler (A.S.H.V.E. Transactions, Vol. 36, 1930, p. 287). Room Warming by Radiation, by A. H. Barker (A.S.H.V.E. Transactions, Vol. 38, 1932, p. 331). Operating Results of a Residence Radiant Wall Heating System, by E. J. Rodee (A.S.H.V.E. Transactions, Vol. 47, 1941, p. 123). Panel Heating and Cooling Analysis, by B. F. Raber and F. W. Hutchinson (A.S.H.V.E. Transactions, Vol. 47, 1941, p. 285). A.S.H.V.E. Research Paper--Radiation as a Factor in the Feeling of Warmth in Convection, Radiator and Panel Heated Rooms, by F. C. Houghten, Carl Gutberlet and E. C. Hach-(A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, December,"1941y p. 778). A.S.H.V.E. Research Paper--Panel Heating and Cooling Performance Studies, by B. F. Raber and F.. W. Hutchinson (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, February, 1942, p. 125). Trend Curves for Estimating Performance of Panel Heating Systems, by B. F. Raber and F. W. Hutchinson (A.S.H.V.E. Journal Section, Heating, Piping and Air Con ditioning, July, 1942, p. 432). What Will be the Future Development of Heating and Air Conditioning, by W. H. Carrier (Heating, Piping and Air Conditioning, January, 1933, p. 16). American Practice in Panel Heating, by L. L. Munier (Heating, Piping and Air Conditioning, June, 1937, p. 424). Radiant Heating and Cooling, by F. E. Giesecke (Heating, Piping and Air Condi tioning, June, July, August, September and October, 1940). Panel Heating in the British Embassy, by Alfred L. Jaros, Jr. and Richard A. Wolff (Heating and Ventilating, May and June, .1930). Calculations for Radiant Heating, by T. Napier Adlam (Heating and Ventilating, October, 1931). - Radiant Heating (Healing and Ventilating, March, 1941, p. 35). -817