Document 109q8VeYBN2yqM8ob8NyRm8BE

Heating Ventilating Air Conditioning Guide 1938 dust-counter, using a microscope, the impinger12, using chemical changes in water, and the Lewis sampling tube13, involving the analytical weighing of a porous crucible, are accepted. All test results should be accompanied by the name of the instrument used as great variation in counts with the different instruments will be obtained. The Society has developed a code14 for the testing and rating of air cleaning devices used in general ventilation work. FLUE GAS ANALYSIS The analysis of flue gases by chemical means is made with the Orsat apparatus. A solution of KOH is used to absorb the COt- Free oxygen is absorbed by a mixture of pyrogallic acid and KOH. The solution for absorbing the CO is cuprous chloride. The apparatus consists of a burette surrounded by a water jacket, to receive and measure the volume Fig. 1. Ringelmann Smoke Chart of gas. The burette is connected by a manifold of glass to pipettes con taining liquids for absorbing CO2, Ot and CO. Various forms of automatic indicating and recording gas analysis devices are available, operating on either chemical or physical principles. Such devices are convenient for plant operation. MEASUREMENT OF SMOKE DENSITY Relative smoke density is usually measured by comparison with the Ringelmann Chart (Fig. 1). In making observations of the smoke issuing from a chimney, four cards'ruled like those in Fig. 1, together with a card printed in solid black and another left entirely white, are placed in a horizontal row and hung at a point 50 ft from the observer and con veniently in line with the chimney. At this distance, the lines become invisible, and the cards appear to be of different shades of gray, ranging from very light gray to almost black. The observer glances from the smoke coming from the chimney to the cards, which are numbered from 0 to 5, determines which card most nearly corresponds with the color of "Public Health Bulletin. No. 144. 1925, V. S. Public Health Service. "Testing and Rating of Air Cleaning Devices Used for General Ventilation Work, by Samuel R. Lewis (A.S.H.V.E. Transactions, Vol. 39, 1933. p. 270). "A.S.H.V.E. Standard Code for Testing and Rating Air Cleaning Devices Used in General Ventilation Work (A.S.H.V.E. Transactions, Vol. 39. 1933, p. 225). 816 Chapter 44. Test Methods and Instruments the smoke, and makes a record accordingly, noting the time. Observa tions are made continuously during one minute, and the estimated average density during that minute recorded. The average of all the records made during a boiler test is taken as the average figure for the smoke density during the test, and the entire record is plotted on cross-section paper in order to show how the smoke varied in density from time to time. Smoke recorders are available which give a much more accurate in dication of the amount of smoke being produced than does the Ringel mann Chart. They all depend upon projecting a beam of light through the smoke flue or through a separate compartment from which a sample of the flue gas is drawn continuously. The light of the beam which passes through without being absorbed by the smoke is measured to determine the smoke density. Most of these instruments make use of a photo electric cell or a thermopile to measure the relative amount of light which has not been absorbed. Standard electrical instruments serve for in dicating or recording. MEASUREMENT OF RATE OF HEAT TRANSMISSION The standard methods of testing built-up wall sections are by means of the guarded hot-box15 and the guarded hot-platel6. The Nicholls heat-flow meter may be used for testing actual walls of buildings. It would be obviously impossible to determine the air-to-air heat trans mission coefficients of every type of wall construction in use with the heat-flow meter, the guarded hot-box or the guarded hot-plate on account of the great amount of time involved. Hence, the method of computing the coefficients from the fundamental constants must be resorted to in most cases. The guarded hot-plate is used to determine the fundamental constants. The heat-flow meter, guarded hot-box and guarded hot-plate tests can be used to good advantage in checking the accuracy of the computed values. If the hot-box or hot-pl^te methods are used, tests are usually run under still air conditions, which means there is no wind movement over the surfaces of the wall during the test. In the hot-plate method of test the inside surface coefficient is eliminated by the plates being in direct contact with the wall. In practice, some wind movement over the exterior surface of the wall should always be allowed for; hence, still-air coefficients cannot be used over the outside of the building during the heating season. Moreover, still-air transmission coefficients cannot be corrected to provide for moving-air conditions by applying a single constant factor. Computed coefficients of transmission for various types of construction are given in Chapter 5. EUPATHEOSCOPE The eupatheoscope affords a means of evaluating the combined effect of radiation and convection in a given environment in terms of a standard environment and in some terms related to human comfort. See Chapter 41. "Standard Code for Heat Transmission through Walls (A.S.H.V.E. Transactions, Vol. 34,1928, p. 253) and Report of the Committee on Heat Transmission, National Research Council. "Measuring Heat Transmission in Building Structures and a Heat Transmission Meter, by P. Nicholls (A.S.H.V.E. Transactions, VoL 30, 1924, p. 65). 817