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HEATINC VENTILATINC AIR CONDITIONING GUIDE 1941 vapor'pressure which is constant, as long as the total heat loss from the sphere is of the desired rate. If the BET becomes too high for comfort, a greater vapor pressure results from the smaller heat loss from the sphere, acts on a diaphragm, and turns down the supply of heat to the room. With falling BET, the reverse action occurs. For testing work* the globe thermometer is a very 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. The temperature thus recorded is termed the radiation-convection temperature. 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). 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 (Healing, Piping and Air Conditioning, June, July, August, September and October, 1940). Panel Heating' in the British Embassy, by Alfred L. Jaros, Jr. arid Richard K. Wolff (Heating and Ventilating, May and June, 1930). Calculations for Radiant Heating, by T. Napier Adlam (Healing and Ventilating, October, 1931). Notes on Electric Warming with Special Reference to Low Temperature Panel Systems, by R. Grierson (Proceedings of The Institution of Heating and Ventilating Engineers, London, Vol. 28, 1929). Notes on the Theory of Radiant Heating, by C. G. Heys Hallett (Proceedings of The Institution of Heating and Ventilating Engineers, London, Vol. 29, 1930). Radiant Heat, by A. F. Dufton (Proceedings of The Institution of Heating and Ven tilating Engineers, London, Vol. 30, 1931). Panel Heating, by C. M. Oates (Proceedings of The Institution of Heating and Ventila ting Engineers, London, Vol. 30, 1931). Principles of Calculation of Low Temperature Radiant Heating, by A. H. Barker (Proceedings of The Institution of Heating and Ventilating Engineers, London, Vol. 30,` 1931). Radiant Heat, by A. F. Dufton (Proceedings of The Institution of Heating and Ven tilating Engineers, London, Vol. 31, 1932). 768 Chapter 45 WATER SUPPLY PIPING AND WATER HEATING Maximum Probable Flow, Factor of Usage, Kind of Pipe Used, Sizing of Risers, Sizing of Mains, Sizing of Systems, Hot Water Supply, Water Heating, Hot Water Storage DOMESTIC water supply systems present the engineer with a design problem that requires combining the somewhat empirical rules and formulae in use with the more or less exact hydraulic principles involved. Unlike heating and ventilating layouts, there are practically no definite data for estimating the quantity of water likely to be consumed or the probable rate of water flow at any particular moment. Metered results in one building often show two or three times the metered amount in another building of the same size and with the same types of tenants. In hotels, one riser will often have an almost constant flow that may never be reached by another at peak load. In office buildings, the women's toilets show a far greater daily consumption than those of the men, yet at no time will they approach the hourly consump tion of the men's toilet during the first hour of the day. This condition has led to a multiplicity of rules of practice which vary as much as the data used. All must of necessity be based on an assumed rate of con sumption and on an assumed probability of simultaneous use, and while the formulae employed may have been derived on sound technical basis the assumptions are often in error. To arrive at a safe standard,- the approximate rate of flow of each fixture to be supplied must be known and the probable number of fixtures in use at any one time must be assumed.- Obviously, the maximum number of fixtures assumed to be in 'use must be taken at the peak of demand and the lines must be made adequate to supply such a peak regardless of the riser or branch on which the deinand may occur. This' means that all water piping under the usual conditions will be over-sized. In tall buildings it is customary to divide the. water supply systems, both hot and cold, into sections of 10 to 20'stories. Such zoning1 or is impractical to attempt to.size piping so as to produce the proper pressure on fixtures at different levels by employing friction, owing to the fact that this frictionwill be built up to the amount desired only; in times of maximum demand and at all other times the friction will'be'oniy a fraction of the maximum friction so that the fixtures by. this method are subjected to a varying pressure oh the water supply line. A much more practical method is'to-throttle the flow at the fixture, or to use flow regulators, so that the quantity of water delivered will approximate the fixture demands and so that this is accomplished without splashing or noise. !. 769