Document n9gqaw2BgpJZzeRRqDDryR8V8

772 Chapter 45___________________ ____ '____ 1945-Guide- A radiant heating system for an. open-air school may be designed as -described for the opep-air hospital. The heating panel in such a case should be almost as large as the ceiling and, in order to keep the heat loss by radiation at a minimum, should.be placed so that a maximum portion of the heat radiated by the panel will be directed toward the pupils and a minimum toward the outside walls and particularly the windows. MEASUREMENT OF RADIANT HEATING Radiant heating is intended to control the rate of radiant heat loss from the human body and should be measured by calorimetric methods. The apparatus, for this purpose consists essentially of a cylinder, maintained at the accepted mean surface temperature of the human body, together with an accurate (usually electrical) measuring of the varying rate of heat supply required to maintain this exact temperature. This instrument, the eupatheoscope, is readily adapted to function like a thermostat so as to turn heat on or off, when the desired temperature of 80 F, or any other predetermined surface temperature of the cylinder, decreases or increases as a result of changes in the Operative Temperature. For testing work, the globe thermometer is a useful instrument. It consists of an ordinary mercury thermometer, with its bulb placed in the 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 34. CONTROL OF PANEL AND RADIANT HEATING The effectiveness of any type of control will depend largely 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 a thermo stat 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 conditions. The heat emitted by hot water pipes imbedded 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 panel heating. A typical control system operated from an outside thermostat and supplemented with a room heat control instrument is illustrated in Fig. 12. The outside thermostat modulates the temperature of the circulating water in the coils by mixing 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 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 Operative 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 Panel Heating aml Radiant Heating : 773 Fig. 12. Typical Panel and Radiant Heat Control System the room. With too Jow an Operative Temperature the reverse action occurs. A similar instrument which has an electric heating element for ' warming the air inside the sphere and the 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 advantageous 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 factor, and exposures, it as an advantage to be able to regulate permanently 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. Transactions, Vol. 49, 1943, p.'235). 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). Calculations for Radiant Heating, by T. Napier Adlam (Heating and Ventilating, October, 1931). Radiant Heating and Cooling, Part I, by C. O. Mackey, L: T. Wright, Jr., R. E. Clark, and N. R. Gay (Cornell University Engineering Experiment Station, Bulletin No. 32, 1943).