limn iMHii'j FRIGERATORS & FREEZERS Cs $?.£«"•• CALIFORNIA AGRICULTURAL EXPERIMENT STATION THE COLLEGE OF AGRICULTURE UNIVERSITY OF CALIFORNIA • BERKELEY #<* *)t Practical fo'SuiU fyoun Cam ^efrUy&iatm Vl XL m CONDENSING UNIT U\\\VU\VV^\T] vXxXXXXXXXX ^-STC WWWUW VAWWM ^VV^^VVVVVVV^ CONDENSING UNITS ers, or 20 cylindrical quart containers, or about twice as many pints. Like refrigerators, freezers are divided into two main types, reach-in and walk-in. For farm homes, the reach-in is more practical because the space required for frozen storage on most farms (usually less than 50 cubic feet) is not large enough for a walk-in. There are two kinds of reach-in freezer : Cabinet (side opening). This type is recommended when the freezer is located inside a refrigerator room because it re- quires less floor space than the chest type. The storage space should not be more than 30 inches deep (preferably less) nor more than 6 feet high. It may be as wide as the available space, provided there are enough doors for easy access to all parts of the interior. Chest (top opening). When the freezer is built as an individual unit, the chest type is recommended because it is easier and less expensive to construct than the cabinet. It also has less trouble with air leakage and doors freezing to the jambs, and does not require defrosting so often. The storage space should not be more than 30 inches (preferably less) in depth or width because of the inconvenience in reaching the different parts. The chest it- self may be any length, but it should have enough lids so that all parts may be easily reached. 3. COMBINATIONS A combination walk-in refrigerator and reach-in freezer may be built with the two storage spaces as separate units or with the freezer inside the refrigerator. Two separate units are more convenient because the freezer may be used without having to open two doors and stand in a cold room. There is little difference in initial or operating costs in the two com- binations. The saving on the freezer is offset by the added cost of the refrigera- tor due to the extra space. The two storage spaces, in any combi- [4] Table 1: APPROXIMATE STORAGE SPACE NECESSARY FOR VARIOUS SIZES AND TYPES OF FARM PRODUCE AND CONTAINERS Article Apple box Berry crates — 12-pint 15-pint 24-pint shallow 24-quart 32-quart Cantaloupe crates — Standard Pony Jumbo Standard flat. Pony flat ... Jumbo flat. . Cauliflower crate Celery crate Cherry boxes — Eastern Lambert Orange box Lemon box Grape box Lettuce crate Los Angeles lug Egg crate — 30 dozen Milk cans — 10-gallon 5-gallon Bottle crates — 12-quart 20-pint Beef carcass — 600 pounds Rear quarter of beef — 150 pounds . Front quarter of beef — 150 pounds Hog carcass — 150 pounds Lamb carcass — 50 pounds Veal carcass — 100 pounds Turkey — 12 pounds Chicken — 4 pounds Length Width inches inches inches 20 12 13 20 15 5 23 15 5 24 18 7 24 12 13 24 16 13 24 13 13 24 12 12 24 14 14 24 15 6 24 13 5 24 16 6 25 19 10 25 22 23 20 10 4 20 11 5 26 13 13 27 12 15 18 15 6 25 19 14 18 14 8 27 13 14 15 15 24 12 12 20 20 15 11 20 15 9 48 30 120 20 15 60 48 15 60 18 15 60 12 12 48 18 12 60 12 10 20 8 6 12 Height [5] WHERE TO LOOK FOR CONSTRUCTION DETAILS FRAME CONSTRUCTION SEE PAGES 10 11 WALL DUCTS SEE PAGE 8 COOLING EQUIPMENT SEE PAGE 12 INSULATION SEE PAGE 7 VAPOR BARRIER SEE PAGE 8 REFRIGERANTS SEE PAGE 17 DOORS SEE PAGE 9 PAINT SEE PAGE 9 [6] nation, may be cooled by separate refrig- erating units or by a single unit. Separate units are simpler and are preferable be- cause one unit can still operate in case of trouble with the other. Although two small units are somewhat more expensive than one large unit, the difference is not great when you consider the cost of the extra controls, such as the two-tempera- ture valve, shutoff valves, and check valve, all necessary with a single unit. MATERIALS Wood is the most common material used for home-built refrigerators and freezers because it is easy to work. Any kind of lumber may be used for framing, but it should be of a reasonably good grade, well dried, straight, and milled to a uniform width. Plywood and tongue- and-groove lumber are common materials used for the finish sheathings, but other materials, such as shiplap, fiberboard, and plaster may be used. It is also possible to use concrete, brick, hollow tile, or other types of masonry. These have an advantage over wood be- cause of their resistance to moisture and fire. However, they are more difficult to work with and are usually more expen- sive. Special lightweight types of ma- sonry have more insulating value than the heavier types, but not enough to fur- nish all the insulation necessary. Regular insulating materials must also be used, as with any other masonry. INSULATION Insulation helps keep outside heat from getting into the storage space. Factors to consider when selecting materials are: Heat conductivity Odor Moisture resistance Availability Ease of installing Possibility of settling Resistance to vermin Cost Table 2: CONDUCTIVITY OF SOME INSU- LATING AND STRUCTURAL MATERIALS Material Conduc- tivity * Thickness to equal 1 in. of corkboard Balsam wool .27 .35 5.00 .30 .31 .33 8.00 .27 .33 .42 .27 .33 .27 .27 .34 .26 .41 .41 .28 .75 .90 Balsa wood 1.17 Brick . 16.67 Corkboard 1.00 Cork (granulated) Celotex 1.03 1.10 Concrete 26.67 Cotton .90 Firtex 1.10 Foamglass 1.40 Fiberglass .90 Insulite 1.10 Mineral wool .90 Rock wool .90 Rock cork 1.13 Redwood bark fiber Sawdust .87 1.37 Shavings 1.37 VermicuUte (expanded) . Wood .93 2.50 * B.T.U. per square foot per hour per inch of thick- ness per °F temperature difference. There are a number of materials avail- able in board, batt, and shredded or gran- ulated forms which make a satisfactory insulator when properly installed and protected from moisture. Some of these materials and their heat-transfer factors are listed in table 2. Corkboard is generally used as a stand- ard for comparing the insulating value of various materials. The thickness of insulation is usually expressed as the equivalent thickness of corkboard. Each increase in the thickness of insulation decreases the heat conducted through it and reduces the operating cost. But there is an economic limit beyond which the added cost of the insulation is more than the saving in operating cost. There is also a practical limit because of the space oc- cupied by the walls. The following thick- [7] nesses of corkboard or its equivalent are considered satisfactory : Reach-in refrigerator . 3 to 4 inches Walk-in refrigerator. . 4 to 6 inches Reach-in freezer 6 to 8 inches Walk-in freezer 8 to TO inches Follow the manufacturer's instructions as to proper methods of installing a particular type of insulation. It is very important, with loose or granulated ma- terial, that the proper density be used so that it will not settle and leave air spaces. VAPOR BARRIER The protection of the insulation from moisture by a suitable vapor barrier is one of the most important features in the con- struction of a refrigerator or freezer. Air contains a certain amount of moisture in the form of vapor. The amount of vapor which air will hold depends on its tem- perature—the higher the temperature, the larger the holding capacity, and vice versa. When the air becomes saturated (filled with all the moisture it can hold), the vapor condenses into liquid and forms dew or fog. If the vapor is allowed to penetrate into the walls, it cools and con- denses in the insulation. This reduces insulating value, and may also cause rotting. There are two ways that vapor may enter the walls. First, it exerts a pressure in all directions and moves by diffusion from areas of high vapor pressure to those of lower pressure. Because the air in a refrigerator or freezer is cold, and the moisture is condensed or frozen on the cooling coil, the vapor pressure is lower than outside and the vapor tends to pene- trate the walls, floor, and ceiling. It will easily pass through ordinary building ma- terials and even some paints. The second way in which vapor may enter the insulation is by "breathing" of the walls. Since the temperature sur- rounding the refrigerator or freezer changes between day and night and be- tween seasons, there is a corresponding change inside the walls. When the tem- perature rises, the air expands and some air is forced out. When the temperature falls, the air contracts and some air is drawn in. If outside air is drawn in, it carries vapor with it. The air cools as it moves inside, and the vapor condenses. Some board and batt types of insula- tion are available which are already sealed against moisture or which may be sealed by coating with asphalt. But com- mon practice is to construct a vapor bar- rier around the entire storage space outside the insulation. The barrier should be made of vapor-proof, odorless build- ing paper lapped at least 4 inches and sealed with odorless asphalt at the joints. Use at least one layer for refrigerators and two for freezers. The paper's weight should be at least 35 pounds per 500- square-foot roll. Tarred and asphalted felts are not satisfactory^ It is very important that the asphalt be of a type suitable for refrigerator con- struction, otherwise odors may result which cannot be eliminated. Be careful not to have any holes or cracks in the barrier. Do not place a vapor barrier inside the insulation so that moisture in the insula- tion may pass into the storage space. (This tends to dry the insulation.) WALL DUCTS The tubing connecting the condensing unit to the cooling coil, and the electric wiring (if a light is desired) must pass PIPE SCREWED INTO EXTERIOR SHEATHING ASPHALT SEAL TO VAPOR BARRIER PIPE SET IN CONCRETE [8 GASKET I" TO VA" TRIM HINGE- Vz" CLEARANCE' Va" PLYWOOD VAPORPROOF PAPER Vl" PLYWOOD HINGE %" CLEARANCE GASKET DOOR AND SILL CONSTRUCTION JAMBS HORIZONTAL SECTION 2" STUDS HIGH SILL - VERTICAL SECTION FLUSH WOOD SILL FLUSH CONCRETE SILL through the walls of the storage space, not make the rough wall opening until Drilling holes through the walls is not you have measured the jamb and sill of satisfactory because the vapor barrier is the door you buy. Stock walk-in doors broken and moisture may get into the 2 to 5 feet wide and 6 to 7 feet high are insulation. A satisfactory duct may be available. For ordinary use, a 2V2-by-6 made of ordinary pipe which is sealed to foot door is recommended. the vapor barrier. The ducts should be The high sill is used where the floor of placed near the top of the walls and close the refrigerator and outside floors are on to the location of the cooling coil or the different levels. The flush sill is used when light. The following sizes of pipe for the refrigerator and outside floors are on ducts are recommended for the tubing the same level. Flush concrete sills are connections: recommended for wet locations. condensing unit size of pipe For a home-constructed door, all lum- Up to Vz H.P 1 inch ber should be clean, dry, well seasoned, Va to 1 Vz H.P 1 to 1 Va inch and of the best grade available. The hard- 2 to 3 H.P 1 Vz inch ware should be heavy duty, galvanized, A Vi-inch duct is sufficient for the wiring, refrigerator type. The plywood should be held in place with rust-resistant screws. DOORS For safety and convenience, locks on wr n . n ! . , , walk-ins should open from both sides. Walk-in type doors are heavy and have hard usage. If not well made of good ma- DAI NT terials, they will warp, sag, or come apart. This makes them difficult to open and Paint for the outside may be of any close and allows air leakage. It is usually type or color desired. For the inside, how- better to buy commercially made walk-in ever, only special odorless refrigerator doors than to build them. Jambs and sills paint should be used. Shellac or a good are included with ready-made doors. Do spar varnish are also satisfactory. [9] TOP PLATE CEILING JOISTS Above: solid stud and joist fram- ing. This is the simplest and com- monest type framing for insulation up to 6 inches thick. TYPES OF CO zz FURRING T CEILING JOISTS f STUDS VERTICAL SECTION FURRING FLOOR JOISTS Staggered stud and crossed joist framing, commonly used for insulation that is over 6 inches thick. With this type, prac- tically all the wall, floor, and ceiling spaces have some insulating material between their sides. HORIZONTAL SECTION Below: wall construction with dou- ble sheathing on both exterior and interior. EXTERIOR FINISH PLYWOOD T. & G. OR PLASTER SHIPLAP 1" ROUGH SHEATHING INSULATION VAPORPROOF PAPER The spacing of the studs and joists in the framing will vary according to the type of insulating material used. For loose-fill insulation, a spacing of 24 inches or less is satisfactory. For the batt and board insulations, the spacing should be such that the insulating material will fit between the studs with a minimum of cut- ting and fitting. Single sheathing is less expensive, but with this construction it is more difficult to erect the vapor barrier because there is no backing to press against in sealing the joints. When loose-fill insulation is used, the side from which it is installed (usually the interior) must be tongued- and-grooved lumber so that the sheathing may be put on as the insulation is put in place. With board and batt insulating ma- terials which will stay in place, plywood may be used on both sides. With single 10] STRUCTI VAPORPROOF PAPER EXTERIOR FINISH SHEATHING EXTERIOR SHEATHING OF PLYWOOD OR T & G VAPORPROOF PAPER Wall construction with solid studs and single sheathing on both sides. ASPHALT COATING CONCRETE, BRICK OR TILE VAPORPROOF PAPER INSULATION STUDS Wall and floor construction using solid studs with double exterior sheathing and single interior sheathing. MASONRY WALL CEMENT PLASTER 3" CONCRETE FLOOR JOISTS 4" CONCRETE BASE ASPHALT COATING ASPHALT COATING OVER INSULATION EXTENDING 6" UP WALL Left: wall and floor construction using concrete exterior and wood interior. Right: wall and floor construction using concrete and board type insulation. With both types of construction, the inside surface of the concrete should be sealed with asphalt before the vapor barrier is installed. sheathing, 1-inch tongue-and-groove or at least %-inch (preferably %-inch) ply- wood should be used. Double sheathing is more expensive but the vapor barrier is easier to install, and the finish may be of almost any desired material since the rough sheathing furnishes all the neces- sary structural strength. The rough sheathing should be 1-inch material but may be of any grade available. [ii] COOLING EQUIPMENT EXPANSION VALVE CONDENSING UNIT Above: refrigerating equipment for cooling two storage spaces held at different temperatures with a single con- densing unit. Below: refrigerating equipment for cooling single storage space. Parts marked (*) are not a necessity. \ \\\\\\\\\\\\\\\\\\\\\\\\\.\ S EXPANSION VALVE l a^p ^ (c COOLING COIL HEAT EXCHANGER* LIQUID LINE SUCTION LINE M^ww wwwwww^ CONDENSING UNIT [12] The equipment to cool a refrigerator or freezer consists of two main parts, the condensing unit and the cooling coil (sometimes called an evaporator) . These two units are connected by tubing or pipes to form a closed system containing a sub- stance known as the refrigerant. During operation, the refrigerant enters the con- densing unit as a gas. It is compressed under high pressure, cooled, and con- densed to a liquid. The liquid refrigerant is released into the cooling coil through an expansion valve. There it absorbs heat which converts it to a gas and it is then drawn back to the compressor. Auxiliary equipment, such as special valves, pres- sure switches, thermostats, etc., is needed for operation of the main equipment. The condensing unit consists of the following parts: 1 . A motor, which drives the compres- sor. 2. A compressor, which draws the gas out of the evaporator and com- presses it to high pressure. 3. A condenser where the gas is cooled and liquified. 4. A receiver where the liquid refrig- erant is stored. Table 3: APPROXIMATE CAPACITIES OF CONDENSING UNITS AND SIZES OF COOLING COILS 1 Horsepower of condensing unit l 5 l 1 Type of condensing unit air air air. . . water. air. . . water. air. . . water. air. . . water. air water. air. . . water. air water. B.T.U. per hour capacity of condensing unit Freezer 0°F 700 950 1400 1600 2000 2400 3000 3700 4100 5000 6200 7400 8200 10,000 10,500 13,000 Refrigerator 36° F 1500 2000 2900 3400 4400 5300 6500 8000 8500 10,500 12,800 16,300 17,000 22,000 22,000 29,000 Square feet of surface area for plate or plain tube coils 2 Freezer 0°F 23 32 47 53 67 80 100 123 137 167 207 247 273 333 350 433 Refrigerator 36° F 40 53 77 91 117 141 173 213 226 280 344 435 453 586 586 772 1 Based on 90° F air and 70° F water temperatures, and 15° F temperature differential between cooling coil and storage temperature. . .. 2 Finned-tube coils should have a rated capacity equal to the condensing unit. [13] The condenser is cooled by either air or water. The air-cooled type is less expen- sive and easier to install, but has less ca- pacity per horsepower. The water-cooled type requires a continuous flow of water when operating, as well as some means of disposing of waste water. The sizes of condensing units are commonly desig- nated by the horsepower of the motor used. Their refrigerating capacities are rated by the amount of heat (B.T.U.) 1 they will extract per hour. The capacity is greatly affected by the temperature of the refrigerant in the cooling coil because the temperature determines the pressure. The lower the pressure, the less the amount of gas taken into the compressor on each stroke. The temperature of the cooling medium also affects the capacity because the higher the temperature, the greater the pressure required for condensing the refrigerant. The approximate capacities for various sizes of condensing units are given in table 4. These capacities should be used for estimating only. The actual ca- pacity of the units varies with different manufacturers and models. The size of condensing unit for a given job should be 1 British Thermal Unit. Amount of heat re- quired to increase the temperature of one pound of water one degree Fahrenheit. Table 4: HEAT LEAKAGE FACTORS FOR DETERMINING CAPACITIES OF CON- DENSING UNITS AND COILS* Thickness of insulation equivalent to cork, Heat leakage factor per square foot of exterior surface, B.T.U. per hour inches Freezer 0°F Refrigerator 36° F 1 60 38.4 2 30 19.2 3 20 12.8 4 15 9.6 5 12 7.7 6 10 6.4 8 7.5 4.8 10 6 3.8 * Based on 100° F air temperature around storage box and operating time of 12 hours per day for the re- frigerating unit. determined on a basis of a maximum of 12 hours' operation per day, to cool the storage space only, during the warmest part of the year. This will allow sufficient capacity for cooling or freezing the prod- ucts and for losses in door openings with average farm use. Table 3 gives the heat leak factors for various insulation thick- nesses. These may be used to determine the condensing unit capacity necessary. Here is how to find the necessary con- densing unit capacity for your refrigera- tor. First, find out the total number of square feet in the outside surface: For example, a refrigerator 6 feet high, 8 feet deep, and 10 feet wide would have an outside surface of 376 square feet. Multiply: Width by height-6 x 1 0' = 60 sq. ft. Depth by height-6' - 8 48 sq. ft. Width by depth-! 0x8= 80 sq. ft. 188 Multiply by 2 2 Total 376 sq. ft. This refrigerator has the equivalent of 6 inches of cork insulation. Turn to table 4, where you will find that a refrigerator with 6-inch insulation has a heat leakage factor of 6.4 (B.T.U.) per square foot per hour. Multiply 376 by 6.4 = 2406 B.T.U. per hour. This is the capacity necessary for the condensing unit and cooling coil. Now turn to table 4, column 4. Check back to column 1, where you will find that a one-third H.P. air-cooled unit would be the smallest size with this capacity. The cooling coil (sometimes called an evaporator) is the part of the refriger- ating unit located inside the storage space. It acts as a container for the refrigerant which absorbs the heat from the storage space and transfers it to the condensing [14 PLACEMENT OF COILS Location of the cooling coil: A, overhead, single, gravity type coil with L type baffle; B, overhead, double, gravity coils with V baffle; C, forced-draft coil with no baffling. Ar- rows show direction of air currents. \\\\\\\\\\\^^^ \\NS\\\\\\\\\\ \\\\\\\\S\Vl Rs SSSSSSSWSS SSSSSSSSSSS^ r ^wwww^ vvvww^ unit. Commercially made coils are avail- able in various types, sizes, and shapes, and the choice among them depends on the conditions under which they are to be used. A gravity type finned-tube coil depends upon natural convection currents to cir- culate the air over it. It consists of tubing through which the refrigerant flows, and sheet metal fins to increase the surface area. A forced draft finned-tube coil is equipped with a fan driven by an electric motor to circulate the air over it. This type is the most common for walk-in and large reach-in refrigerators because it has greater capacity for a given size and usu- ally requires no baffling for proper air circulation in the storage space. The finned-tube coils are designed for maintaining temperatures above 35° F where they can be operated on a defrost- ing cycle. (The frost melts each time the condensing unit stops.) This is desirable because their capacities are greatly af- fected if the frost decreases the space between the fins and cuts down the air circulation. Finned-tube coils can be used in freezers if an easy, convenient method of defrosting is provided. Usually, they must be defrosted at least once a week, and sometimes oftener. A common method of defrosting is to run water over [15 TYPES OF COOLING COILS 1 Jllplll \ ! Finned tube, forced-draft coil. Gravity finned tube coils. ^NNSSSSSSSSSSSS^ ^ S<^\V\\\\\\^^^ Cabinet type freezer with plate colls as shelves* the coils. Or you may have a special ar- rangement of the refrigerating equipment so that hot gaseous refrigerant from the compressor can be run through the coils. Plate type coils may be used for main- taining temperatures both above and be- low freezing since their capacity is not greatly affected by frost. They are par- ticularly adaptable for freezers as they can be used as shelves or partitions and Table 5: LENGTHS OF VARIOUS SIZES OF TUBING AND PIPE FOR ONE SQUARE FOOT OF SURFACE AREA Tubing Standard pipe Size, O.D. Length for 1 sq. ft. of surface Size Length for 1 sq. ft. of surface inches V2 Vs 1 feet 7.6 6.1 5.1 3.8 3.1 inches M H l iy 2 feet 4.5 3.6 2.9 2.3 2.0 can be easily defrosted by scraping. Some contain a solution in the jacket which freezes and furnishes a certain amount of holdover refrigeration in case the refrig- erating unit is off for a limited length of time. If you are planning on homemade coils, the bare tube type is the most practical. This type may also be used for maintain- ing temperatures both above and below freezing. These coils are more difficult to defrost than are the plate type, but are less expensive. Copper tubing is the most common material used, but steel, brass, or aluminum tubing or pipe are also suit- able. The heat absorbing capacity of a coil depends on its surface area, the rate of air movement over it, and the difference in temperature between it and the air. It is essential, for proper operation, that the correct size be installed. The capaci- ties of finned-tube coils are rated by the manufacturers in B.T.U. per hour, and when the operating conditions are known, [16 Left: flat plate type cool- ing coil consisting of tub- ing enclosed in sheet- metal casing. Bare tube coil* the proper size may be selected. The ca- pacities of plate and plain tube coils are in direct proportion to their surface area and they are chosen on that basis. When you have determined the size of your con- densing unit (see page 14), turn to table 4 to find the correct coil capacity. REFRIGERANTS The purpose of the refrigerant is to transfer heat. It absorbs the heat in the cooling coil and gives up the heat in the condensing unit. A number of different chemical compounds have been used for refrigerants, but the most common are ammonia, freon 12, methyl chloride, and sulfur dioxide. Ammonia (NH 3 ) is a colorless sub- stance with a strong, offensive odor. When mixed with water, it attacks copper and copper alloys but has no effect on iron or steel. Leaks are easy to find by the odor, or by burning sulfur, which forms a white smoke in the presence of ammonia. It is used mainly in large units (2 horsepower and larger). Freon 12 (C C1 2 F 2 ), a relatively new substance, is the most common refriger- ant in small units, but is also used in units up to 25 horsepower. It is colorless, odor- less, noninflammable, nontoxic, and does not attack copper, copper alloys, iron, or steel. Leaks are relatively difficult to de- tect because of the lack of odor, but can be located by an alcohol flame which turns green if freon is present. Methyl chloride (CH 3 C1) is colorless and has a sweet odor resembling chloro- form. It does not attack copper, copper alloys, iron, or steel but is inflammable at certain concentrations. Leaks may be detected by a special type of alcohol torch. Sulfur dioxide (S0 2 ), which is pro- duced by burning sulfur, has a strong, suffocating odor. When mixed with water, it forms sulfurous acid which attacks iron, copper, and zinc. Leaks are easy to detect by the odor and by ammonia vapor which forms a white smoke in its pres- ence. At one time, it was quite popular as a refrigerant in small units, but it has been largely replaced by freon. Although one refrigerant may have ad- vantages over others for certain jobs be- cause of the pressures in the system and consequent danger of leaks, any one will operate satisfactorily if the equipment is properly designed and engineered for it. If the equipment is designed for a certain refrigerant, do not use another kind. While some of the refrigerants may be interchanged, it is usually necessary to make adjustments in the control valves, speed of the compressor, or other changes for proper operation. [17] AUXILIARY EQUIPMENT A pressure switch or a thermostat, or a combination of both, is necessary for automatic operation of the refrigerating equipment. A pressure switch is operated by the pressure in the cooling coil which in turn is dependent on the temperature of the coil. A thermostat is operated by the temperature of the air in the storage space. An expansion valve is necessary on each cooling coil to control the amount of liquid refrigerant going into the coil. A dehydrator is desirable to remove any moisture which may be in the refrig- erant. A strainer or scale trap is sometimes desirable, particularly when steel pipe is used, to remove particles, such as scale or rust, in the system, which may cause trouble. A heat exchanger is not necessary, but when used, it increases the efficiency and capacity of the condensing unit. Its purpose is to cool the liquid refrigerant going into the cooling coil by transferring heat to the gaseous refrigerant coming out of the coil. Two temperature valves are neces- sary when you have two or more storage spaces, at different temperatures, but cooled by a single condensing unit. These valves control the operation of the cool- ing coils in the warmer storage space. Shutoff valves are desirable and some- times necessary for convenience in repair work. They close the liquid and suction lines to the cooling coil. A sight glass, which is placed in the liquid line, is not necessary, but is a con- venience for determining when the system needs more refrigerant. Check valves are necessary when two or more storage spaces are maintained at different temperatures by a single con- densing unit. These valves prevent refrig- erant from one cooling coil flowing back into the other coils. COSTS The initial costs for constructing re- frigerators and freezers vary with size, type, materials, and methods of construc- tion, so that it is not possible to give defi- nite figures. However, under present prices, the materials (labor excluded) for constructing the storage space will usu- ally cost from 50 cents to $1.00 per square foot of exterior surface. The cost of the refrigerating equipment, including the cooling coil, will vary from about the same cost as the storage space for large walk-in rooms to three to four times the cost of the storage space for small reach- in boxes. The exact cost of the refrigerat- ing equipment may be obtained from dealers who sell it. The operating costs also vary according to size, location, tem- peratures, thickness of insulation, use, and electric rates. Observations of well constructed, reach-in refrigerators and freezers, and walk-in refrigerators up to 300 cubic feet, indicate that the operat- ing cost usually averages less than $5.00 per month, and most often is between $1.00 and $3.00 per month. The electrical energy used by these units varies from 50 to 200 kilowatt hours per month. [18] UNIVERSITY PLANS FOR REFRIGERATORS AND FREEZERS The Agricultural Engineering Division of the College of Agriculture has designed four different sizes of refrigerators and three sizes of freezers. De- tailed plans and specifications for these units may be obtained for a small cost from the Agricultural Extension Service, University of California, Berkeley. The following is a list of these plans. Cubic feet of Exterior Cost Plan No. Type storage space dimensions of plan C-152-Reach-in refrigerator* ... 35 2'10" x 4'9" x 7'5" 51^ C-153-Reach-in refrigerator .... 40 2'10" x 4'9" x 7'5" 51tf C-154-Semiwalk-in refrigerator . 30 3'10" x 5'6" x 8'9" 51tf C-155-Walk-in refrigerator 125 4'10" x 5'9" x 9'3" 51^ C-103-Chest type freezer 12 4'x4'x 2'9" 26^ C-104-Chest type freezer 21 4' x 6' x 2'9" 26^ C-105-Chest type freezer 30 4'x8'x 2'9" 260 * Same as C-153 except has ice-making coil. In order that the information in our publications may be more intelligible, it is sometimes necessary to use trade names of products or equipment rather than complicated descriptive or chemical iden- tifications. In so doing it is unavoidable in some cases that similar products which are on the market under other trade names may not be cited. No endorsement of named products is intended nor is criticism implied of similar products which are not mentioned. 25m-9,'48(A9323) m «rfgS^&to f *du a&fi&iuici AGRICULTURE • • • Contains brief, easy-to-read progress reports of agricultural research, and is published monthly by the University of California College of Agricul- ture, Agricultural Experiment Station. FIELD CROPS ORCHARDS TRUCK CROPS LIVESTOCK CALIFORNIA AGRICULTURE offers information useful to the farmer and food processor, together with announce- ments of other publications dealing with farm subjects as they are issued by the College of Agriculture. Upon your request, your name will be added to the mailing list to receive CALIFORNIA AGRICULTURE with- out cost. Send your name and address to: California Agriculture, Publications Office, College of Agriculture, University of California, Berkeley 4, California