Document byy2237MjVrYXQ0Qo3pjeNYjy

HEATINC VENTILATING AIR CONDITIONING CUIDE 1944 center of a sphere from 6 to 9 in. in diameter, usually made of thin copper and painted black and sometimes covered with cloth. The temperature 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 Fig. 10. Typical Radiant Heat Control System 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 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 or off control system is 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 798 CHAPTER 45. RADIANT HEATING 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 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 equivalent temperature 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 an equivalent temperature 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 resistence to give uniform con ditions throughout all rooms. Owing to unforseen 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. REFERENCES Trend Curves for Estimating Performance of Panel Heating Systems, by B. F. Raber and F. W. Hutchinson (A.S.H.V.E. Transactions, Vol. 48, 1942, p. 425). A.S.H.V.E. Research Report No. 1192--Panel Heating and Cooling Performance Studies, by B. F. Raber and F. W. Hutchinson (A.S.H.V.E. Transactions, Vol. 48, 1942, p. 35). A.S.H.V.E. Research Report No. 1193--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. Transactions, Vol. 48, 1942, p. 55). Panel Heating and Cooling Analysis, by B. F. Raber and F. W. Hutchinson (A.S.H.V.E. Transactions, Vol. 47, 1941, p. 285). Operating Results of a Residence Radiant Wall Heating System, by E. J. Rodee (A.S.H.V.E. Transactions, Vol. 47, 1941, p. 123). Performance of a Residential Panel Heating System, by H. F. Randolph and J. B Wallace (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, August, 1943, p. 424). Radiant Heating (Heating and Ventilating, March, 1941, p. 35). Radiant Heating and Cooling, by F. E. Giesecke (Heating, Piping and Air Condi tioning, June, July, August, September and October,-1940). American Practice in Panel Heating, by L. L. Munier (Heating, Piping and Air Conditioning, June, 1937, p. 424). What Will be the Future Development of Heating and Air Conditioning, by W. H. Carrier (Heating, Piping and Air Conditioning, January, 1933, p. 16). Radiant Heat, by A. F. Dufton (Proceedings of The Institution of Healing and Ven tilating Engineers, London, Vol. 31, 1932). Room Warming by Radiation, by A. H. Barker (A.S.H.V.E. Transactions, Vol. 38, 1932, p.331). Calculations for Radiant Heating, by T. Napier Adlam (Heating and Ventilating October, 1931). 799