Document KGDMk0QM87dgDm6mRaQ3en92K

850 CHAPTER 77 1962 Guide And Data fig. 11 ... Evaporative Cooling System for Conventional Stall-Type Bam the roof with vertical ducts dropped down to the ceiling. In the case of high ceiling barns, the ducts should terminate ap proximately 10 ft above the floor as there is no advantage in cooling the upper air space of the bam. Evaporative cooling may also be applied to the other types of farm animal buildings and to poultry bouses. A recent de velopment is the blackout poultry house to improve egg production of layers by- delaying their age of maturity. These bouses are tightly closed to exclude all light from en tering. Packaged air coolers are used to keep temperature below 90 F and to provide ventilation. The evaporative cool ing system also keeps the birds calm and less flighty. The pullets are maintained on 8 hr of artificial light per 24 hr period until they are 12 weeks of age. From 12 to 20 weeks, the birds are maintained on 6 hr of artificial light per 24 hr period. After 20 weeks they are placed on the usual 14 hr daylight.** Another new use for evaporative cooling is the cooling of farrowing houses. It is now possible to farrow sows throughout the year. In the past, pig production Hp~linp^ dur ing the summer because it was not possible to keep the sows cool. If a sow becomes over-heated she becomes nervous, restless and, in turn, tramples her litter.*1 PRODUCE COOUNG15 Farm storages for fruits and vegetables may be rlarifiH as common storage and refrigerated storage. Common storages can be improved considerably through the use of evaporative cooling. High humidity, lower temperature and fresh air to provide adequate oxygen for respiration and for carrying away the waste products of the living processes can be achieved. Potato Storage Evaporative cooling systems for potato storage houses should be designed for through-cooling with the air directly through and in contact with the potato pile. Capacity of the cooling system should be based on a 3 min air change to give quick and even cooling. The total volume of the storage should be considered in calculating the size of the system so as to provide sufficient cooling if the depth of storage is in creased at a future time. Above floor ducts can be used but under floor ducts are to be preferred as they can also be used for the handling of the potatoes with bin unloaders. The ducts should be 20 in. wide and at least 14 in. deep to allow room for the insertion of the bin unloader conveyors. Duet tor* must be removable and should be 3 X 8 in. lumber to of port a loaded track. Boards should be spaced to provide u' in. slots. Distributing and delivery ducts act as extended plenums so it is not necessary to reduce duct depth as tfaef*. end of the ducts is approached. Delivery ducts should extend to within 6 ft of the walls to provide uniform air flow through the storage. Since friction loss in the duct system is nofrij^j the resistance of the potato pile is the principal load on the fan in the evaporative cooler. The resistance is approximate!? 0.25 in. static pressure (potato storage should not ft in depth). The additional resistance of the ducts, mWfa dampers and evaporative cooler will add another 0 9-5 ^ for a total of 0.50 in. that the fan must overcome. In large storages it may be advisable to divide the house into two sections to keep the cooling system within practical limits. A single system should not handle over 12,000 cfm of air if main and distributing ducts are to be of reasonable Fig. 12 shows the floor plan of a typical potato storage house. Ducts have been sued by the velocity reduction method using 1000 fpm for trunk duct, 750 fpm for distribut ing ducts, and 500 fpm for delivery ducts. Duct system is laid out so that all delivery ducts are of equal length and spared on 12 ft centers. Ail outdoor air is normally used during the cooling period. As an example, maanw that the desired tem perature within the storage is to be 40 F. The system should operate on 100 percent outdoor air if the temperature of the air discharged from the evaporative cooler is as cool or cooler than the inside of the storage and the storage temperature is not lower than 40 F. Should the temperature of the air dis charged from the cooler become warmer than the inside of the storage, the air within the house should be recirculated. If the outdoor air drops below 40 F, some outdoor air and some storage air should be circulated. During the winter nvmtKa tiie air should be recirculated. Continuous recirculation is not necessary, and the evaporative cooler may be put on time switch operation to ran intermittently 10 to 15 rnm out of every hour. Apple Storages Evaporative cooling systems for apple storages should be designed to distribute the cool air to all parts of the storage. The evaporative cooler may be floor mounted or located near tiie ceiling in a fan room. The system should be designed to discharge the air horizontally at the wiling level Since the degree of cooling possible is limited by the prevailing wet-bulb temperature, the maximum practicable size system should be installed to bring down the storage temperature rapidly and as close to the wet-bulb temperature as possible. In general fig. 12 .... Evaporative Cooling System for Potato Storage House Evaporative Air Cooling . n .... Three-year Average Hourly Solar Radiation tToble horizontal Surface during Peak Summer Month Btu/ Sq ft N. M....... Fla........... D. 170 132 158 140 H3L Ma------ Boise, Idaho............. Boston, Brownsville, Texas.. Caribou, Maine........ 128 155 125 175 115 Charleston, S. C............. QeveUnd, Ohio.............. Columbia, Mo................ Columbus, Ohio............. Pavia, Calif...................... 152 152 153 127 184 Dodge City, Kan...... East Lansing, Mich----East Wareham, Mass.. El Paso, Texas............. By, Nev........................ Fort Worth, Texas. Fresno, Calif........... Gainesville, Fla.... Glasgow, Mont.. . . Grandby, Colo........ 176 188 156 152 149 Grand Junction, Cob... Great Falls, Mont.......... Greensboro, N. C........... Griffin, Ga........................ Hatteras, N. C................ 173 150 155 164 177 Indianapolis, Ind.......... Inyokern, Calif............ Ithaca, N. Y.................. Talrp Charles, La......... Lander, Wyo................. Ins Vegas, Nev... *... 140 218 145 160 177 195 atr Btu/ SqO Lemont, 111........................ Lexington, Ky.................. Lincoln, Neb..................... little Rock, Ark.............. Los Angeles, Calif........... 142 170 150 148 162 Madison, Wis................... Medford, Ore.................... Miami, Fla....................... Midland, Texas............... Nashville, Tenn............... 138 170 153 177 154 Newport, R. I................... New York, N. Y.............. Oak Ridge, Tenn............ Oklahoma City, Okie-- Phoenix, Ariz................... 138 140 148 165 200 Portland, Maine........ Prosser, Wash............ Rapid City, S.D.... Richland, Wash......... Riverside, Calif.............. 176 152 137 176 St. Cloud, Minn............... San Antonio, Texas........ Santa Maria, Calif.......... Sault Ste. Marie, Mich.. Sayville, N. Y................... 132 176 188 138 148 Schenectady, N. Y.......... Seabrook, N. J.................. Seattle, Wash.................... Spokane, Wash................ State College, Pa............ 117 135 117 139 141 Stillwater, Okla.............. Tallahassee, Fla............. Tampa, Fla..................... Upton, N. Y................... Washington, D. C......... 167 134 167 148 142 a system having a 3 min air change capacity is the largest practicable system that can be installed. (This will actually result in a 1 to 1)4 min movement of air when the storage is loaded.) Evaporative cooling improves conditions in apple storages so that the length of time in storage can be increased considerably. Operation of the system is imiUr to that for potato houses. For further information on apple storage, see Chapter 47. Gtrus Storages The chief purpose of evaporative air cooling as it is ap plied to fruits and vegetables is to provide an effective yet inexpensive means of improving common storages. How ever, it also serves a special and important function in the case of oranges, grapefruit, and lemons. It is not uncommon for citrus fruit, although mature and ready for harvest, not to have undergone the natural change in color from green. The consumer, however, expects fruit of characteristic color. The color change is achieved through coloring or sweating process.*1 Special rooms equipped with evaporative cooling are used to degreen the fruit. Air with a high relative humidity and at a Moderate temperature is circulated continuously during the sweating operation. Ethylene gas, the concentration depend ing upon the variety and the intensity of green pigment in tiie 851 rind, is discharged into the sweat rooms. The effect of ethylene is mainly to destroy the chlorophyl in the rind, and allow the yellow or orange color to become evident. A temperature of 70 F is maintAinAH in the sweat room during the degreening operation with a relative humidity of 88 to 90 percent. (In the Gulf states 82 to 85Fwith 90 to 92 percent relative humid ity is recommended.) The evaporative cooling system is de signed to deliver 4 cfm per field box of fruit. Another use for evaporative cooling is as a supplement to refrigeration in the storage of citrus fruit. Although oranges have a long harvesting season and are considered a fresh fruit crop, marketing conditions and other factors may make it advisable to bold them in temporary storage at the packing house for as long as 1 month, and in the case of lemons and grapefruit these crops are usually stored for some time. A large portion of the former crop is picked during the period of least consumption. While citrus storage requires refrigeration in the summer, conditions can often be met with evaporative cooling during the fall, winter and spring when tiie outdoor wet-bulb temperature is low. For further information, see Chapter 48. GREENHOUSE COOLING*-* Proper regulation of greenhouse temperatures during the summer is essential for developing high quality crops. Tem perature affects plant growth because it influences the processes which occur within the plant. Temperature and relative humidity can be controlled in tiie presence of strong radiation with evaporative cooling. The most important prob lem to be solved in the design of evaporative cooling systems for greenhouses is the calculation of solar heat which is tiie principal load on a greenhouse. At the edge of the earth's atmosphere there are about 430 Btu per (hr) (sq ft) of sun energy, and when it reaches sea level at about noon in the temperate zone this will be roughly 200 Btu per (hr) (sq ft). In places where much smoke, dust, or heavy clouds exist, the actual incidence of solar radiation will differ from what might otherwise be expected. Table 2 gives solar radiation loads for representative cities. The values cited are average solar heat gft.ing and not peak loads. Temporary rises in temperature inside a greenhouse nan be tolerated. An occasional rise above daaign conditions is not likely to cause damage. Not all of the solar radiation which reaches the inside of the greenhouse becomes a cooling load. Solar radiation is trans formed into: (1) heat of evaporation, (2) chemical energy, and (3) sensible heat. Process 2 (photosynthesis) does not amount to more than about 2 percent of the total radiation. Process 1 will vary from crop to crop, but might tentatively be set at 48 percent of the radiation.*7 This leaves 50 percent which has to be removed by tiie cooling system. The specific heat of air is 0.24 Btu per lb or roughly 0.018 Btu per cu ft. Therefore, each cu ft per min of air delivered by the cooling system will handle approximately 1 Btu per hr of heat at a temperature rise of l deg. Since 50 percent of the solar radia tion is used up in Processes 1 and 2, I cfm will handle 2 Btu per hr of solar heat at a temperature rise of 1 deg. Example 2 shows how t-hi* information can be used to calculate tiie size of greenhouse evaporative cooling systems. Example t: An evaporative cooling system is to be installed in a 50 X 100 ft greenhouse. Design conditions are assumed to bp 92 F dry bulb and 73 F wet bulb, and solar radiation is 138 Btu per sq ft. Ao indoor temperature of 90 F dry bulb is not to be exceeded at design conditions. _ - Solution.' The evaporative air cooler is assumed to have a saturation effectiveness of 80 percent. For the conditions of this problem Equation 2 becomes: t, - 92 - 08 (92-73) tt - 77 F