Document DMq27jaEqqaJ9dapYwn9nr3vM

4/8 CHAPTER 45 1962 Guide And Data Book n um muon Rg. 6 .... Warehouse Door protection Vestibules. An effective way to minimize loss of refrigeration through door openings is to provide a vestibule equipped with a ptur of double-acting doors. See Fig. 7. This arrangement drastically reduces the interchange of warm and cold air. A vestibule should be deep enough so that, on entering, the power operated horizontal door should be well on its way to the closed position before the double-acting doors are acti vated. Heat in the floor of the vestibule-contributes strongly to good operation. Very heavy traffic can justify the use of B separate refrigeration unit to control the temperature and humidity of the air in the vestibule. The horizontal sliding door in Fig. 7 is 6 ft wide and the double-acting door is 8 ft wide, based on a 48 in. pallet load. The 8 ft width is selected to minimize truck damage to the double-acting doors. It is strongly recommended that (l) double-acting doors be hung on a steel channel frame, (2)spring steel bumpers be provided on both sides of each Ip^ and (3) heat be supplied at the sides, head, and sill to prevent freezing. Tracking platforms. Increasing regulations on temperature control during all steps of product handling has led to the refrigerated trucking platform designed as an anteroom to the cold storage space. With the platform space maintained at about 45 F or lower, frozen product can be handled with out exposure to warm humid ambient conditions, thus holding more favorable product temperatures and avoiding damage to the product packaging because they can be kept essentially dry. The platform doorways are equipped in many awes with special devices, such as a polyurethane bumper around the sides and head on the outside of the opening, to reduce the intake of ambient air to a minimum. RRE PROTECTION Ordinary sprinkler systems cannot be applied to refrig erated space without modification. Two types of modify systems are in use, the brine system, and the dry pipe system. The brine system (Fig. 8) employs the ordinary sprinkler scheme, but the pipes in the refrigerated spaces are filM with calcium chloride brine. The brine is maint-ninod under greater pressure than the city water, and is sealed off from it by special check valves A and B. The individual distributing headers are sealed off by similar valves C. The distributing header pressure is maintained above the brine stand pipe pressure by a brine pump.-The booster pump can be used to pump city water to the plant at increased pressure through valve B, by manually opening the normally closed valves C, on this line. Additional special check valves are installs! in the city water supply line before it enters the plant to insure against brine flowing into the city water mains. Refrigerate'1 Warehouse Practice 479 A checker's office should be in view of the platform and traffic arrangement. Personnel warm-up rooms should be in view of the superintendent's office. Rented space should be isolated from warehouse operations. The machine room should include ample space for refrig erating equipment and its maintenance. It should be wellventilated and have stand-by capacity for emergency ven tilation. It should be segregated from other areas and have separate exists as required by most building codes. A main tenance shop and space for parking, charging and servicing . warehouse equipment should be located adjacent to the , maehinft room. In the dry pipe system, the sprinkler pipes in the refrigaited spaces are filled with dry compressed air. The water is F"lpd off from the compressed air by a special dry pipe valve. The air pressure, which is carefully controlled, keeps this valve closed as long as no sprinkler failure occurs. When the air pressure is relieved the water pressure forces the valve open and feeds water into the sprinkler system. -The air in tire sprinkler system must be dehydrated to avoid frost buildup in the pipes. This is sometimes accom plished by taking the suction to the air compressor, assigned to tins duty, from the refrigerated space. An alternate is- to nse bottled nitrogen gas instead of air for filling and sustain ing the pressure in the sprinkler system. If the building is not aprinklered, a number of central re porting or wanting systems (such as American DistrictTelegraph) are available for installation in more hazardous areas to give an alarm outside the plant. UTILITY SPACE Shipping platform, corridors and elevator vestibules should provide liberal space for movement of goods to and from storage, pallet storage, battery charging, sorting, in specting and checking and also for idle equipment. The ship ping platform should be not less than 15 ft wide and prefer ably 20 ft or wider. Floor heights of refrigerated cars and trucks vary widely, but average higher than for unrefrig erated. A shipping platform, height of 54 in..above the rail is recommended for reefer railroad cars. For trucks, a shipping platform height of 50 in. above the pavement is recom mended. Local delivery trucks may be much lower. Some reefer truck beds are up to 58 in. above grade. Adjustable' ramps at some of the truck spots will partly compensate for bright variation. Five to seven railroad car spots per million cu ft are rnmiTM=nHri. It is difficult to include sufficient buck spots in the smaller dimensions of the multi-story building, but the one story design gives ample length. Twelve to fifteen truck spots per million cu ft for the public ware house should be provided if the building dimensions permit. For multi-story buildings, the elevators must be of ample size and weight capacity to promptly and efficiently handle Hft truck operation. It is preferable to have air conditioned 1 vestibules of adequate size at elevator floor levels to avoid frost in the elevator shafts and other inherent problems. Space must be provided for plant general office, locker room *od machine room. A superintendent's and warehouse records office should be located near the center of operations. LOAD DETERMINATION , The refrigeration loads of warehouses of thesame capacity will vary widely. Many factors, including building design. Inside and outside temperatures, and most important, the type and the flow of the goods expected plus the duly freez ing capacity, contribute to this load. Therefore, no rule of thumb can be applied. Experience of comparable buildings .nH operations is valuable, but an analysis of any projected operation should be made. Compressor and room cooling equipment should be designed for maximum daily require ments, which will be well above any monthly average. The factors to be considered include: 1. Heat transmission through insulated enclosures. 2. Heat infiltration load from warm air passing into and cold air passing out of refrigerated space. 3. Heat from pumps or circulating refrigerated brine or. air, power equipment, working in refrigerated space, and ' heat from lights. 4. Heat removed from goods in reducing them from receiving to storage temperatures. 5. Heat produced by goods in storage. 6. Heat to be removed in freezing goods received unfrozen. 7. Other loads such as office air conditioning, car preceding, or special operations inside the building. Heat leakage or transmission load can be calculated closely using'the known overall heat transfer coefficient of various portions of the insulating envelope, the area of each portion, and the temperature difference between the lowest design cold room temperature and the highest average air tempera ture for 3 to 5 consecutive days at the building location. For floors on ground, the average yearly temperature should be. U&d instead of the mari/niim Heat infiltration load varies greatly, with these variables: size of room; number of openings to warm.areas; protection on openings; traffic through openings; cold and warm air temperatures and humidities. Basis for calculation should be on experience remembering that most of the load occurs dur ing the day operations. See Chapter 27 of the 1961 Guide And Data Boos for a complete analysis of load calculations. Heat from pumps and fans can also be computed, being close to % ton per hp. The useful load of a motor circulating refrigerated air or brine b reflected as'heat to the refrigerating system, even though the motor b outside refrigerated space. The daily load of motors will vary with plant requirements, which normally allow shut down of part of the units except with near maximum loads/Heat due to men working, lights, etc., will vary from day to day with activity of movement' and operating control. Hus load b subject to estimates from experience, except for that from total lights which should be in the range of 10 to 20 tons per million cu ft. One watt of lighting per sq ft requires one ton of refrigeration for each 3500 sq ft of floor area.