Document 0vrVEG76BEyBwwKyG7BXvGGm

American Society of Heating and Ventilating Engineers Air-pass velocity = 1200 = 400 fpra. Air-pass area -- 1600 = 4 sq ft = 576 sq in. 5 # In Question 2 what would be the gap between the chamber and th when the chamber is centered in the casing? ne Area of combustion chamber (30-in. diam) . 706.9 'sq in... Area of air pass 576.0 sq in. Total area 1282.9 sq in. The diameter of a circle with an area of 1282:9 sq in. is'40.4"in. One half of the diff between the diameters is the amount of gap. , nei Gap 40.4 - 30.0 = 5.2 in. = approximately 5J4 in. 1 Why should secondary surface be designed for easy cleaning? If the combustion is not perfect, soot is formed immediately above, the fire and is a to form a deposit on the secondary surface from which it should be removed' if secondary surface is so designed that there are horizontal passages, fine gray-ash settle out in these to form an insulation between the hot gases of combustion and th metal of the,furnace; consequently, these should be readily cleaned. If the passages are vertical they are largely self-cleaning of ash, but provision should be.made for easy and thorough cleaning of the collection chamber below them. " 5 Why is baffling inside the casing necessary'on fan systems? Because :the movement of-air is independent of. its temperature, air must be guided bv baffles of one form or another to: bring jt j,, contact with the hot surfaces so it will not PMS through the.casing unheated.. .Dn the other hand, if. the air is held against a hot surface too long it' might become overheated, for the average register temperature on a fan system should not exceed 120 F. fifiJFhy do buildings. which are intermittently used require more heating capacity than buildings constantly used? Between heating periods the intermittently used building is allowed to cool down. All ofthe material in the building'loses heat:-, and before.the building can belreheated toa comfortablertemperature this material must also:beteKeated. .. 7 WHat practical points should be observed in designing a fan system in onlfr to eliminate noise? a. Use a large fan so it can be run at slow speed. b. Set the fan and motor on a solid foundation. ......... c. Insulate the fan and'motor from the foundation with rubber, cork, or other springy material according to the principles given in Chapter 18, provided, of course, that such insulation:is of value. _ .- d. See that the air velocity is not too high in the ducts. Properly designed splitters in the eJbows will avoid high .velocities at the turns in'Cases where the velocity through the ducts themselves is not too high.; ,: 'Use!carivas connections between the ducts arid any running'eqUipment. /. Be,sure the ducts have.a relatively smooth interior and are rigid. 388 Chapter 24 gravity warm air furnace " SYSTEMS Procedure for Design, Estimating Heating Requirements, Sizes of reader Pipes, Proportioning Wall Stacks, Register Sizes; RecirculaHng Ducts and Grilles, Return Connection to Furnace, Furnace Capacity, Examples, Booster Fans WARM air heating systems of the gravity type are described in this chapter1, and those of the mechanical type are described in Chapter 23 In the gravity type, the motive head producing flow depends upon dhe difference in weight between the heated air leaving the top of the "sing and the cooled air entering the bottom of the casing, while in the mechanical type a fan may supply all or part of the motive head. Booster fans are often used in conjunction with gravity-designed systems to increase air circulation. ............................... In general, a warm-air furnace heating plant consists of a fuel-burning furnace or heater, enclosed in a casing of sheet metal or brick, which is placed in the basement of the building. The heated air, taken from the top or sides near the top of the furnace casing, is distributed to the various rooms of the building through sheet metal warm-air pipes. The warm-air pipes in the basement are known as leaders, and the vertical warm-air pipes which are run in the inside partitions of the building are called stacks. The heated air is finally discharged into the rooms through registers which are set in register boxes placed either in the floor or in the side wall, usually at or near the baseboard. The air supply to the furnace may be taken (1) entirely from inside the building through one or more recirculating-ducts, (2) entirely from outside the building, in which case no air is recirculated, or (3) through a combination of the inside and the outside air supply systems. PROCEDURE FOR DESIGN The design of a furnace heating system involves the determination of the following items: 1. Heat loss in Btu from each room in the building. 2. Area and diameter in inches of warm-air pipes in basement (known as leaders). 3.. Area and dimensions in inches, of vertical pipes (known as wall stacks). 4. Free and gross area and dimensions in inches of warm-air registers. 5.. Area and dimensions of recirculating or outside air ducts, in inches. 6.; Free and gross area and dimensions in inches of recirculating registers. All figures and much of the engineering data which follow are from Bulletins No. 141, 188 and 189. Warm Air Furnaces and Heating Systems, Part II. by Professor A. C. Willard. A. P. Kratz. and V. S. Day, Engineering Experiment Station, University of Illinois. 389