Document DrKNpdrpOwjeo5jk62RevMLQ

398 CHAPTER 21 1946 Guide - /--"> --i fIt/Mfefacl./.sj/hield ex tending id beyond casing. ......... ' oJrc,ix:fcs ,s --1 sr space- open'- Insulated with airspace or cov ered with magne sia. asbestos. or sand. Inner finer-from -top casing ring to grate level /,ietof casing Fig. 5. Details of Furnace Bonnet, Casing, and Foundation (From Gravity Code and Manual) Masonry wall, fleia! thimble. Collar z` or les ,Sonnet K, iped with asbestos paper rig'righ't collar Insulated with 3 layers of air cellasbestos paper whenpipe passes thru unheaTed space. Fig. 6. Details of Bonnet and Leader of Gravity Warm-Air Furnace (From Gravity Code and Manual) Figs. 5 and 6 show recommended practice as given in the N.W.A.H. &A.C.` Assn. Gravity Code and Manual. For construction,, design features, and ratings of gravity furnaces see Chapter 18. REFERENCES The engineering data were obtained from University of Illinois, Engineering Experiment Station Bulletins Nos. 141, 188, 189 and 246; Warm Air Furnaces and Heating Systems, by A. C. Willard, A. P. Kratz, V.-S: Day, and'S. Konzo. See also Gravity Code and Manual for Gravity Warm Air Heating Systems, published by the National Warm Air Heating and Air Conditioning Association. 2--Simplified Procedure for Selecting Capacities of Duct Systems for Gravity Warm-Air Heating Plants, by'A. P. Kratz and S. Konzo (University of lUinois. Engineering Experiment Station Circular 45. Dec.. 1942). .. . / *--Gravity Code and Manual for Gravity Warm Air Heating Systems, Second Edition. 1945; National Warm Air Heating and Air Conditioning Association. , CHAPTER 22 nuctnicai 'lAJarm. _^Air temi Air Distribution, Standard Combinations of Parts, Automatic Controls, Simplified Design, of Heating System, Cooling Methods, Cooling System Design IN mechanical warm air or fan. furnace heating systems', the air circu lation is effected by motor-driven fans instead of by the difference in weight between the heated air leaving the top of the casing and the cooled air entering the bottom, as in gravity systems described in Chapter 21. The advantages of mechanical systems, as compared with gravity systems, are: 1. The furnace need not be centrally located but may be placed in any part of the . basement. 2. Basement distribution piping can be made smaller and can be so installed as to give full head room in all parts of the. average basement, or be completely concealed from view .where desired. 3. Circulation of air is positive, and in a properly designed system can be balanced in. such a way as to give a greater uniformity of temperature distribution. 4. Humidity control is more readily attained. 5. The air may be cleaned by sprays or biters, or both. 6. The fan and duct-equipment may be utilized for a complete cooling and dehumidifying system for summer, using either ice, mechanical refrigeration, or low temperature water for cooling and dehumidifying, or adsorbers for dehumidifying. 7. The use of the fan increases, the volume of air which can be handled, thereby', increasing the rate of heat extraction from a given amount of heating .surface and insuring sufficient air volume to obtain proper distribution in a large room. 8. Ventilation air may be positively introduced and heated. The construction features of mechanical warm air furnace, units and discussions of the function and selection of the various parts, such as the furnace, casings, motors, filters and controls are included in.Chapter 18. AIR DISTRIBUTION The conditions of comfort obtained in a room are' greatly influenced by the type of register used and the locations of the supply registers and return grilles. In general it has been found that changes in the type, air velocity, and location of the supply register affect the room conditions much more than the changes in the location of the return grilles.' One method is to locate the supply register near the floor so that the warm air from the register blankets a cold wall, and mixes with the cold air dropping off from the exposed walls and glass.- Another method is to locate the supply openings near the floor on the inside wall and the return openings near the greatest, outside exposure. In any case-the warm air registers should be located so that the air stream never discharges directly into space that will normally be occupied by people at rest. Tests in the Warm Air Research Residence2 have indicated that continuous fan operation provided better results than intermittent fan operation. Register and GriUe - Openings Supply registers located in the floor require attention .to keep them clean and are-usually avoided. Tests conducted in the Warm Air Research 399