Document G61qNO81dDvKZkDvajG7ey76r

712 CHAPTER 34 1950 Guide' State Table 1. City Average Maximum Water Main .Temperatures* Pm i State -H City fa ol 1 State City fa' 1 Ala. Aris. Calif. Conn. Fla. Ga. Tdohn m. lad. Iowa Kans. KV. La. Md. 84 80 83 80 69 80 75 80 82 78 84 San Francisco......... 71 73 72 83 82 85 60 76 83 88 84 78 77 62 Kansas City........... 86 88 Baltimore................ 75 76 68 Mich. Duluth..].......... 68 76 77 70 84 :77 56 53 64 82 55 so Mo.- - Jefferson-City......... 82 84 84 85 74 70 N.H. . N. J. N. Y. N. C. N. M. Ohio * Okla. 70 76 63 75 78 79 68 78 56 74 75 -72 70 '60 74 69 70 74 85 92 82 65 76 Canton...................; 50 84 77 84 60 82 72 83 Oklahoma City ...'. 82 Pa. R. I. S. C. S. D. Tenn. Utah Va. W.Va. Wls. 86 60 65 74 75 74 82 85 86 68 83 8178 65 84 90 85 90 70 .Austin...................... 90 86 86 85 85 90 83 83 78 85 44 6575 73 80 85 58 62 51 57 65' 78 78' 54 58 75 68 Alta: B. C. PJU. Que. Quebec..................... 64 60 50 63 48 78 68 * These averages taken from various city, water main locations, with some actual values slightly.higher ,. and some lower than values shown. Some Values were supplied oy H. E. Degler, Marley Company. Some were obtained from City Water Department records. The highest values given by the various authorities are usually those listed. bulb temperature, but the same humidity, ratio, more water can be ab sorbed per pound of dry air in passing through the washer, assuming that the humidifying effectiveness of the washer is not adversely affected by operation .at the higher' wet-bulb temperature. The analysis of the process occurring in the washer itself is the same as that explained under. Method 1. The final desired conditions are secured by adjusting the amount of preheating to give the required wet-bulb temperature at entrance to the washer. ... . Method 3. Even if heat is added to the spray , water, the mixing occur ring in the washer itself may still be regarded as adiabatic. The state Spray Apparatus 713 point of the mixture should move in a direction determined by the specific enthalpy of the heated spray as explained in Chapter 3. It is possible, by elevating the water temperature, to raise the air temperature, both dry-bulb and wet-bulb, above the dry-bulb temperature of the entering air. In each of the methods, 1, 2 or 3, the air leaving the air washer may require reheating to produce in the conditioned' space the required drybulb temperature and relative humidity. DEHUMIDIFICATION AND COOLING WITH AIR WASHERS Cooling of the wet-bulb temperature of an air vapor mixture can be accomplished by an air washer if the temperature of the spray water is lower than the wet-bulb temperature of the air. Moisture removal is obtained when the spray water temperature is lower than the dew-point of the entering air. In these cases the final dry-bulb temperature and relative humidity of the leaving air are dependent upon the design factors of the air washer. Both sensible and latent heat are removed in the process-of dehumidi-. fication by cold spray water. Abstraction of sensible heat occurs during the entire time that the air is in contact with the spray medium. Latent heat refnoval takes place as condensation occurs. Therefore, the lower the spray temperature, the greater the amount of moisture removal per pound of dry air, all other conditions remaining the same. Washers with two or more banks of spray are usually selected for dehumidifying installations, whether for comfort or industrial instal lations. Generally such air washers cool the air to within one or two degrees (Fahrenheit) of the leaving spray water temperature; this dif ferential will increase somewhat when the difference between the entering wet-bulb and leaving dew-point is relatively large. Where a limited supply of cold water is available, multiple stage washers may be used to great advantage. In such washers.the cool water is pumped through the multiple spray systems in series and counterflow to the air flow. Such an arrangement brings the delivery air in contact with the coldest water, securing a maximum amount of cooling and saving water. When using cold well water or water from city water mains, care should, be used to secure accurate data on the water temperatures. Table 1 lists some approximate water main averages which may be used as a guide, but they should be verified from local records. This is particularly true with city water main temperatures. In the case of well water temperatures, Fig. 3 shows the approximate temperatures of water to be expected from wells at depths of 30. to 60 ft. Air washers for dehumidifying and cooling usually have separate recircu lating pumps. These pumps deliver a mixture of cold and recirculated water under the control of a three-way valve. The valve may be actuated' either by a thermostat in the washer outlet, or by a humidity or other con troller in the space being conditioned. Air washers for dehumidifying are very often furnished with direct1 expansion or water cooling coils within the washer space, in which case water for the washer sprays is entirely recirculated. APPARATUS FOR DIRECT HUMIDIFICATION Humidifiers may be divided into two general types which are, according to the method of operation: (1) indirect, such as the air washer, which.;