Document bBLpZqo660KoZX783Ea6KydXy

American Society of Heating and' Ventilating Engineers Guide water. This will control exactly the temperature and relative humidity of the leaV Two or more tempering sections are required for this method. VlnS 4. The fourth method is desirable where recirculation is used and consists in taining the temperature leaving the washer at about 40 deg. by means of a the? located at this point controlling the admixture of fresh and return air throueh1'0' matically operated dampers. This prevents over-humidification, eliminates riaukor' of freezing, and effects the highest economy in cost, as no steam is required for tempering or humidifying, except after the air has passed the washer. eiteS 5. The fifth method of automatic control is to reheat the air leaving the air w >, to a definite thermostatically controlled temperature, and to control the relative humeri- " of the air by means of a hygrostat which operates either on the tempering section ^ heat the air or which controls a water heater for the spray water. s Steam Requirements Where the spray water is not heated it is necessary that the wet-bulhtemperature of the incoming air be above the freezing point; otherwise' the eliminator plates will coat with ice and stop up, even if the dry-bulb^ temperature of the leaving air is above the freezing point. It is necessary to heat zero air to 48 deg. in order that the wet-bulb temperature may be 35 deg. The temperature of the leaving air may then be expected to be approximately 39 deg. dry bulb and 35 deg. wet bulb, with a dew-point ' of 31 deg. If the humidifying capacity of the washer is 75 per cent the additional heat required to furnish humidification is that indicated by the temperature drop of 9 deg.,, or 162 B.t.u. per 100 cu. ft. of air, or 1 b.hp. for every 3,400 cu. ft. of air. per minute. These are the minimum requirements for humidification, above those required for heating the air. Table 1 gives the heat required, from various outside entering wet-bulb temperatures, to various dew-point tempera tures corresponding with various relative humidities at 70 deg. These values are the total heat required for both heating and humidi fying the air. The amount of heat required for humidifying only, may be found by subtracting from the values given; the heat required to raise the temperature of 1,000 cu. ft. of air pier minute between the limits specified. The heat required for heating the air is given by the formula where H = 1,000 -- ti 55.5 H = B.t.u. required to raise 1,000 cu. ft. of. air from a temperature of h to a temperature of h deg. fahr. VISCOUS CELL FILTERS Viscous-coated air filters are distinguished from air- washers in that they clean the air without the use of water. Thus the temperature and moisture content of the air are not changed by passing through a viscous filter. - v The principle of air cleaning used in these filters is that of adhesive impingement. Dust and dirt in the air, especially soot and carbons, are trapped and retained by successive impingements on oil coated surfaces. While the arrangement of filtering media and the kind of materials used are almost unlimited, there are certain rather definite requirements for a practical commercial filter. 440 AND Chapter 28--Air ..Cleaners See Marks' Engineers Handbook. ,, various Outside Temperatubes Fahr. fef--'In --orde--r--t-o---s--e-cure maximum efficiency it is necessary to divide the air M^anto innumerable fine streams; the more intimately and freely the air is ^Wbrought into contact with the viscous-coated media the better the cleanfe?ing wifi be- As the dirt and dust particles are leached out of the air and W^collected on the adhesive-coated surfaces, additional supplies of viscous iiV tiiquid are required in order to bind further layers of dirt. For this reason ^'^tbe filter medium in unit filters is usually designed to hold, somewhere ?within the cell, additional supplies of viscous liquid, capable of distribu- .. i.#S*iS*.&-tioInnbvyesctaigpailtliaornysaitntrathcitsiocno. untry and abroad demonstrate that the first impingement of dust laden air on a viscous coated surface removes about fX--60 per cent of the dust, the next impingement takes 60 per cent of what V^'then remains--that is, 24 per cent--the next impingement removes 9.6 ,Vv.'per cent, etc. This tendency to eliminate progressively smaller amounts -.1- of dust at each impingement, even though finer dust particles are caught fr-j'.at each successive impingement, has led to progressively packed filter media in practically all unit filters. Such an arrangement provides rela- * {t tively large spaces for the collection of dirt in the front part of the filter, SJ where the bulk of solids is taken out, without undue increase in resistance, while at the back of the filter the openings are smaller and finer dust paTrthicelebsianrdeinregmlioqvueidd. used with viscous filters should have the following ; pro1.peItrstiseusr:face tension should be such as to produce a homogeneous film-like coating on2th. eThfiletevrismcoesdiituyms.hould vary only slightly with normal changes of temperature. - 3. It should be germicidal in its action to prevent the development of mold spores, V bacteria, etc., on the filter media. ,4. The liquid should flow freely at low temperatures. ; 5- Evaporation should not exceed I per cent. . 6. It should be fireproof. -- 7. It should be odorless. 441