Document V80db8J4g3MRbVk7Qy0y3B7p

American Society of Heating and Ventilating Engineers Guide, 1930 In industrial ventilation, where specific contaminants are to be con tended with, a knowledge of the concentration and character of the contaminating substances is essential for best results. Ozone is not a cure-all for industrial odors in general, for instance, allyl alcohol vapors, which possess an annoying odor, when subjected to action with ozone, produce the aldehyde acrolein, which is exceedingly irritating, even in very small concentrations. Here harm rather than good will be done. It is best to submit problems of this character to engineers experienced in the use of ozone for definite recommendations. It has been recommended (Hill & Aeberly, Heating and Ventilating Magazine, March, 1922) that sufficient ozone capacity be provided to permit of building up comparatively high concentrations when the building is not occupied. In schools, for example, the ozone equipment should be operated at a capacity to give perhaps 0.01 ppm of ozone when the building is occupied, and after the pupils have left the building, the full capacity of the machine should be used, closing all openings, recircu lating the entire amount of air, and building up a sufficient concentration to exert the maximum deodorizing effect throughout the building, the duct work and mechanical equipment. For general ventilation, under average conditions (85 per cent ventila tion), the ozonizer should be of sufficient capacity to provide a concen tration of 0.05 ppm of ozone in the fan volume. For 100 per cent ventilat- ing systems a lesser quantity can be made to suffice. A generalization, cannot be made broad enough to cover the many special conditions, ' particularly problems of specific deodorization. Capacity of Ozonizers - Having chosen the maximum required concentration of ozone, for the purpose in hand, it becomes necessary to calculate the capacity of the ozonizer. There seems to be no agreement, among makers of ozone ' equipment, regarding the unit of rating for ventilating ozonizers. There are three methods in common use, as follows: . Parts per Million: Wherein the ozonizer is rated in parts per million (generally by . volume) in some specific air volume. At first this may seem a very desirable method for rating ozonizers, as it is simply necessary to state the ppm of ozone, required for the specific CFM of air. Ozonizers so rated, have their ozone meter calibrated in ppm for v + . the specified CFM, and should the fan volume be varied, the meter is liable to become 1 misleading, as the original CFM may not always be considered when reading it. Con sideration of the original CFM, and proportioning to any new CFM; is essential with an ozonizer so rated, if accurate knowledge of the concentration employed at any other CFM is desired. Ozone is generally applied on the basis of ppm by volume, and as there is no existing agreement concerning a standard temperature and pressure at which the ozonizer should be calibrated, this method of rating leaves the actual capacity of the unit open to question, unless the temperature and pressure employed for calibrating is stated. Since weight is unaffected by temperature and pressure, and as ozone is determined chemically, directly in the terms of weight, weight forms a better basis for the rating of ozonizers, and eliminates a number of qualifying factors, together with tedious calculations in ozonizer design. Milligrams per Minute: Ozonizers so rated have their ozone meter calibrated directly in the terms of milligrams per minute, and leave no questions concerning the actual capacity of the unit. Errors of omission are further circumvented by forcing:.a con sideration of all factors, when determining the concentration of ozone in the air of the ventilating system. . 496 Chapter 30--Ozone and Ventilation The expression ppm, generally means parts per million by volume at room temperature and average barometric pressure, when referred to ozone in ventilation. One litre of ozone at 25 deg. cent, and 740 mm Hg, weighs 1.9127 grams. Taking these conditions as a basis, the weight of 1 cc. of ozone may be taken as 2 milligrams, yielding a very convenient figure for use, easily remembered, and sufficiently accurate for all practical purposes. The metric system is best employed here, for convenience of analysis and calculations of design, with final conversion into English units for purpose of application. It is on this basis that the following formulae have been derived: Formulae for Application: CFM = fan capacity, cubic feet per minute of air. mpm = milligrams of ozone per minute, ppm = parts of ozone per million parts of air, by volume, at 25 deg. cent, and 740 mm. Hg. 28,320 = cc per cubic foot. 2 = weight of 1 cc of Oa at 25 deg. cent, and 740 mm. Hg. Given: CFM and ppm; Find, mpm: ppl? x 28,320 X 2 = mpm which reduces to: -C--F--M-- yX ppm X 56..6.4 .=.m_p_m_ ,,................................ -.......... m(1; Given: mpm and ppm; Find, CFM: mp"1 * 10* X --= CFM.................. ......................... (2) 56.64 ppm Given: mpm and CFM; Find, ppm: SB**- ppm -.......................... (3) Ventilating Unit: The Ventilating Unit (VU) has been created by the author, for the. purpose of simplifying the calculations for applying ozone to ventilating systems. It is a compound unit, taking into consideration quantity and time. It is analagous to the horsepower, wherein 33,000 lb. are lifted one foot in one minute. It represents that quantity of ozone necessary to produce a concentration of 0.1 ppm in 1,000 CFM, at 25 deg. cent, and 740 mm Hg. 1 VU = 5.7 milligram of 03 per minute 340 milligrams of 0 per hour The formulae for its application are very simple: Given: CFM and ppm; Find, VU: which reduces to pointing off two places in the'CFM and multiplying by the ppm. Given: VU and CFM; Find, ppm: M|^x 1.000 = ppm.:................ ............................ (5) which reduces to pointing off three places in the CFM, one place in the VU, and dividing the former into the latter. Given: VU and ppm; Find, CFM: 1,0?P-.n X VU = CFM.............................................. (6) ppm X 10 As the VU represents a definite weight of ozone, in "a definite period of time, ozonizers so rated leave no question as to their actual capacity. The decimal character of the unit admits of much facility in calculations. 497