Document 2Nqx7oOx48gzrGR2y8pBeYya

906 CHAPTER 60 1965 Guide;And Data Book Fig. 4____ Percentage Running Tune vs. Room. Tem perature and Box Temperature for Typical 8-cu ft and 10-cu ft Conventional Refrigerators .tor whose major functions are cooling the cabinet interior, pro ducing ice cubes, and providing limited frozen food-storage for, very snort periods of time. 2. Combtnaiion Refrigerator-Freezer. In this type the size of the frozen-food storage compartment is increased substantially to where it may in some instances be as large as the normal food storage compartment and additional controls are employed, to maintain temperatures suitable for long time storage of frozen foods. ' -;Characteristic energy .consumption and percent .running performance .of the conventional refrigerator* are shown in Figs. 4 and 5. Performance of. the combination type cannot be represented by such simple curves because of widevariations in the sue of the frozen-food compartments together with the variations in temperature tolerances and means of control.in both the frozen-food and normal food-storage compartments acceptable to different manufacturers. Energy consumption in a 90 F room of from 2 to 8 kwh for 24 hr and running times from 38 to 78 percent have been ob served on different makes of these refrigerators in the 12 to-18 cubic foot total size. Frozen-food compartment sizes varied up to Yt of the total volume and temperatures maintained in this compartment ranged from --2 to +10 F and from 37 to 40 F in normal food storage compartment. Specifications for testing mechanically operated refrigera tors are described in Standard B38.1-1955. Figs. 4 and 5 show performance of typical 8 and 10 cubic foot refrigerators. External and interior refrigerator temperatures may: be measured by liquid in glass thermometers, electric thermo-, couples or electric resistance thermometers. Glass thermometers are relatively inexpensive but the refrigerator door must.be opened in order to read them within the refrigerator interior. While this may not affect the accuracy of the reading, it slows up the testing of the refrigerator because the box temperatures must be stabilized again before initial kilowatt hour readings nr winning tifni> reaHings'ean be taken. Resistance thermometers are accurate and reliable for meas uring cabinet and room air temperatures but they are too bulky to measure surface temperatures on evaporators, tubes, compressors, and so forth. Thermocouples with potentiometer indicators are the most satisfactory means for measuring tem peratures for development work. This is because they.are in- fig. 5 .... Kilowatt Hours Consumption for 24 Hours for Typical 8-cu ft ond 10-cu ft Conventional Refrigerators expensive, small, and have such low thermal mass that they ea&ly follow rapid changes in temperatiire. They can also be lagged after putting them in contact with a mass of metal or fluid to read average rather than momentary, cycling tem peratures. Recorders are available for use with thermocouples or resistance thermometers that will plot as many as 16 records on one chart. During testing, it is important that the temperature gradi ents throughout the test room be kept to a minimum, because of the effect of room temperature on refrigerator perfonn. ance. The temperature at the floor should not be essentially different from that in the rest of the room, or the cold floor.air being drawn through the condenser will give inaccurate' re sults." When testing a thermal-convection-cooled condenser located'on the back of the refrigerator, it is necessary to keep the room air velocity low. enough so that heat dissipation from the condenser will not be affected. The American Standard B3S.1-1955 requires that the room temperature be maintained within plus dr minus'1 F'deg of the specified value, and that the vertical temperature gradient from the floor to a height of 7 ft shall not exceed a half a degree for each foot of vertical distance. The best method for conducting an ice freezing test is to measure ice freezing time by means of thermocouples inserted in the ice cube that will freeze last. As the water cools, the temperature in the trays will go down rapidly to 32 F. During the actual freezing period, the temperature will stay at 32 F and at the conclusion of this period, will'go down rapidly from this point. The ice is considered frozen when tire temperature drops below 28 F. If an ice'tray is placed on the shelf'of a dry evaporator, there will be an entirely different rate of ice freezing than if the contact surfaces between the tray and the evaporator were thoroughly wet before the test. Differences as great as two .to one in ice freezing time can result from this contact variation. Therefore, it is' the usual procedure to wet the evaporator surface before putting the tray in place. Kilowatt hours can be readily measured by an integrating Household Refrigerators and Food Freezers 907 kilowatt meter having a scale multiplier of 0.01-or less so that the data'can be read to 0.01 kwh and estimated to 0.001'kwh. The running time of tho refrigerator unit can be measured by means of self-starting electric clocks. While-there are no standard specifications for testing re frigerators under simulated field operation; such testing-is desirable. - In setting up a laboratory test procedure that would simu late field conditions reasonablywell, there are five variables that should be considered: ' a. Dry-bulb temperature. b. Dew-point temperature. c. Number of refrigerator door openings. d. Length of door openings. . t c. Usage load. To simulate severe field usage,' the following conditions'may serve as a pattern for'a suitable test.procedure. A dry-bulb temperature of 90 F is suggested. This is 2 F deg below the dry- bulb temperature which is not exceeded more than 5 percent of the 12 hr during the middle of the day from June to Septem ber, inclusive, of a normal summer. A dewpoint of 81 F repre sents a condition along the Gulf Coast which-was not ex ceeded-more than 5 percent of the total hours from June to September, inclusive, for a normal summer.- Some data avail able indicate that not more than 2 percent of the refrigerator users open the refrigerator door more than 80 times per 24 hr. There is some deviation from this figure, 'depending upon the season of the year and the size of the refrigerator. A value of 10 door openings per (24 hr) (cu ft) of refrigerator volume may be reasonable. A door opening period .of from 10 to.15 sec i3 suggested. Laboratory tests indicated that at 60 F dew point and 90 F dry-bulb temperature door openings of greater than 10 sec duration have little effect on the amount of mois ture pickup on the' evaporator. Over a 12-hr interval,'80 door openings 'of approximately 13-sec duration' can be .worked into a schedule of six approxunately one-hour periods of door openings. It is suggested that to duplicate the food load in the refrigerator, an equivalent' weight of 78 F water in glass jars be substituted for the food in a fully loaded refrigerator. A schedule of twice a week shopping and the preparation of three meals a day can be assumed, with simulated food added to or taken from the refrigerator accordingly. In addition, one tray of ice cubes should be frozen for each of the threemeals.' Much can be learned from'the standpoint of development by operating the compressor unit with.a calorimeter of some kind. One type of calorimeter consists of a relatively ishort copper tube surrounding a tubular electric heater. Refrigerant is admitted in one end of the tube through a constant pressure expansion valve, and the heat input adjusted until the desired degree of superheat is obtained at the output. A modification of this particular idea has been used' in ' connection with flooded evaporators. One feature of a good calorimeter'is a small thermal mass so that its response to a .change is rapid, thus reducing testing time. . A calorimeter achieving these characteristics particularly well employs a heater immersed in the liquid of a secondary refrigerant circuit, while the evapored tor of the compressor under test functions as a condenser for this secondary circuit. The control on the calorimeter turns the beater on and off in response to the pressure of the second ly system while the total heater input over' a period of time is measured by a kilowatt-hour meter. ' Cabinet heat-leakage tests can be run in several ways, as follows: ' '' 1. The cabinet may be placed in a hot room and the refrigerant Phased to the evaporator at a rate necessary to maintain a con stant cabinet temperature. The heat leakage per degree may then be determined from the quantity of refrigerant circulated; the condition-of:the refrigerant entering and'Ieavingrandithe interior and exterior cabinet temperature. . . .... . .,;r. 2. The cabinet may be placed in a cool room (about 50 F) and the cabinet interior heatea withelectric heaters to apbint' where the mean temperature of the insulation is about 75 F. The over all heat loss may then be determined from the heater input and the interior and exterior cabinet temperatures.. , 3. The cabinet may be operated in a hot room with a calibrated refrigerating unit of the type normally installed in the cabinet. This method takes into account the localized hcating'of cabinet surfaces from the condenser and compressor, and gives the most accurate overall results under operating conditions approaching normal..' ............ 4. ,Ice may be placed in the cabinet and its rate'of malting measured. OPERATING CYCLE OF. THE HEAT-OPERATED . - ABSORPTION REFRIGERATORS ..- "Absorption refrigerating machines based'`on. the Platen- Muntere system have been the most successful of the heat^ operated refrigerating cycles so far applied to household re frigerators. It is a three-fluid system and all locations in the hermetically'sealed unit are at the same total pressure, aside from minor variations which arise from the presence of fluid columns'and which are used to circulate the fluids. . ' The charge includes an aqua-ammonia solutionofa strength of1about 28 percent concentration (ammonia by weight)Kand hydrogen. The charge for a typical unit is approximately^.!) Ib ammonia, 5.2 lb water and 0.03 lb hydrogen. 'The elements of the system include a generator (sometimes called.boiler or still), a condenser, an evaporator and an.ab* sorber. (See Fig. 6.) There are three distinct fluid circuits in the system: an ammonia circuit including the generator, condenser, evaporator and absorber; a hydrogen circuit in cluding the'evaporator and absorber;'and a solution circuit including the generator and absorber. ' Heat is applied to the generator by a gas burner or other source of heat to expel ammonia from solution. The ammonia vapor thus generated'flows to the condenser! In the'path,of