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American Society of Heating and Ventilating Engineers Guide, 1936 HEATING EFFECT For several years the heating effect of radiators has been considered by engineers in order to use it for the rating of radiators and in the design of heating systems. Heating effect is the useful output of a radiator, in the comfort zone of a room, as related to the total input of the radiator3. tie/ghi" Above Floor fn Fbeff Fig. 1. Room Temperature Gradients and Steam Condensing Rates for Four Types of Cast-Iron Radiators with a Common Temperature at the 60-In. Level Note that the steam condensations are practically the same for all four radiators when the same air temperature of69 F is maintained at the 60-in. level. Chapter 30--Radiators and Gravity Convectors 1. The heating effect of a radiator cannot be judged solely by the amount of steam condensed within the radiator. 2. Smaller floor-to-ceiling temperature differentials can be maintained with long, low, thin, direct radiators, than is possible with high, direct radiators. 3. The larger portion of the floor-to-ceiling temperature differential in a room of average ceiling height heated with direct radiators occurs between the floor and the breathing level. 4. The comfort level (approximately 2 ft-6 in. above floor) is below the breathing line level (approximately 5 ft-0 in. above floor), and temperatures taken at the breathing line may not be indicative of the actual heating effect of a radiator in the room. The comfort-indicating temperature should be taken below the breathing line level. 5. High column radiators placed at the sides of window openings do not produce as comfortable heating effects as long, low, direct radiators placed beneath window ' openings5. HEATING UP THE RADIATOR " The maximum condensation occurs in a heating unit when the steam " is first turned on. Fig. 3 shows a typical curve for the condensation rate in pounds per hour for the time elapsing after steam is turned into a castiron radiator. The data are from tests on old style column type radiators. O t 2.345*70* fie/ght Above. Floor r? Feref Fig. 2. Room Temperature Gradients and Steam Condensing Rates for Four Types of Cast-Iron Radiators with a Common Temperature at the.30-In. Level Note that the steam condensations are different for all four radiators when the same air temperature of 68 F is maintained at the 80-in. level. The results of tests conducted at the University of Illinois are shown in Figs. 1 and 24. For the four types of radiators shown, the following con clusions are given : The Heating Effect of Radiators, by Dr. Charles Brabbie (A.S.H.V.E. Transactions, Vol. 33. 1927. `Steam Condensation an Inverse Index of Heating Effect, by A. P. Kratz and M. K. Fahnestock (A.S.H.V.E. Transactions, Vol. 37, 1931). 524 Time elapsing after Steam is turned into Radiator (in Minutes) Fig. 3. Chart Showing the Steam Demand Rate for Heating Up a Cast-Iron Radiator with Free Air Venting and Ample Steam Supply In practice the rate of steam supply to the heating unit while heating up is frequently retarded by controlled elimination of air through air valves or traps. Automatic control valves may also retard the supply of steam. ENCLOSED RADIATORS The general effect of an enclosure placed about a direct radiator is to restrict the air flow, diminish the radiation and, when properly designed, improve the heating effect. Recent investigations6 indicate that in the design of the enclosure three things should be considered: Effect of Two Types of Cast Iron Steam Radiators In Room Heating, by A. C. Willard and M. K. Fahnestock {Heating, Piping and Air Conditioning, March, 1930). University of Illinois Engineering Experiment Station Bulletins No. 192 and 223, and Investigation of Heating Rooms with Direct Steam Radiators Equipped with Enclosures and Shields, by A. C. Willard, a. h. Kratz. M. K. Fahnestock and S. Konzo (A.S.H.V.E. Transactions, Vol. 35, .1929). 525