Things that Work! tests conducted by the Home Power Crew Many of you have written for information about efficient, 12 VDC powered, refrigeration. Well, here's a test of Sun Frost's super-efficient RF-12, a 12 cubic foot refrigerator/freezer. It can be powered with only two 48 Watt PV modules. Shipping Container & Documentation The Sun Frost unit arrived from Arcata, California via motor freight in fine shape. It was well packaged, and the actual refrigerator was screwed to a wooden pallet. Complete, written, uncrating instruction were provided by Sun Frost. According to the shipping company, the refrigerator/freezer, its packing and pallet weighed 230 pounds. The installation and operating manual is complete, with sections on food storage techniques, defrosting, door adjustment and troubleshooting. We had no trouble installing and operating the unit from the info provided in its manual. Sun Frost also provides a form for our feedback, complete with stamped envelope. It's nice to see they care about how we feel about their products. Physical Examination First of all, this is the biggest 12 cubic foot refrigerator/freezer we've ever seen. Outside dimensions of the entire unit are 34.5 inches wide by 27.75 inches deep by 49.25 inches high. The inside dimensions of refrigerator compartment are 28 inches wide by 20.5 inches deep by 24 inches high. The inside dimensions of freezer compartment are 26 inches wide by 21 inches deep by 6.5 inches high. If you compare the outside dimensions of the unit to its inside dimensions, then the amount of insulation provided in the Sun Frost is obvious. There is about 3 inches of polyurethane foam insulation surrounding the refrigerator section and about 4.5 inches around the freezer. According to Sun Frost, there are no metal supports between the inside and the outside of the unit. This further insulates the compartments by eliminating heat transfer through metal supports. The outside finish of the Sun Frost is superb. The RF-12 we tested was colored white in a flawless matte finish. The compressor (a Danfoss unit using a brushless DC motor), condenser, and all controls, are mounted on the top of the RF-12. This is done for better heat dissipation and easier cleaning of the condenser. The massive doors (both the refrigerator and the freezer have their own individual doors) are mounted on piano style hinges and close securely to the box with adjustable catches. The fit on the doors is very tight. The refrigerator compartment is equipped with three adjustable glass shelves, a light, and copious amounts of bottle storage in the door. All the inside surfaces are easy to clean, slick white fiberglass. The freezer compartment is unstructured and contains no racks or shelves. Installation & Test System On 23 April 1988 we installed the Sun Frost in John & Anita Pryor's system (see Home Power #2). This system consists of 4 Trojan L-16Ws (700 Ampere-hours at 12 VDC), 4 Kyocera 48 Watt PV modules, a 1.5 Trace inverter/charger, and a gas/12 VDC alternator backup. John and Anita were kind enough to let us set up the unit in their living room where the ambient temperature is kept at about 68¡F. most of the time. During the test period John & Anita used the Sun Frost in place of their regular refrigerator. They used it normally, opening the doors whenever necessary to remove or add food to the unit. We wired the Sun Frost to the batteries with about 16 feet of #10 gauge copper wire. We also installed an hour meter to keep track of the amount of time that the unit's motor was actually running. We measured the electrical parameters of the unit with a 3468A Hewlett Packard DMM and a Fluke 77 DMM. We placed thermometers in the compartments, along with all John and Anita's refrigerated food. Operation of the Sun Frost We turned the thermostat to the manufacturer's recommended setting of 38¡F. in the refrigerator section. The Sun Frost started immediately and took about 2.7 hours to pump the refrigerator compartment down to 38¡F. At this time the freezer compartment's temperature was measured at 7¡F. The first thing we noticed about the unit was how quiet it was. This is the quietest electric refrigerator that we've ever heard. About the only noticeable noise was an occasional soft gurgle as the Freon R-12 refrigerant circulated. The thermostat setting tracked exactly with our interior thermometer. The Sun Frost's thermostat is actually calibrated in degrees. Compare this with other units that offer a 1 to 10 type of calibration. Voltage levels in the system ranged from 11.8 to 15.2 VDC during the test period. Sun Frost rates the RF-12 for operation anywhere in the 11 to 15.5 VDC range. 24 VDC models are also available. Average current consumption of the RF-12 was 4.4 Amperes while running. Current consumption of this unit was 4.8 Amperes at 12.4 VDC after startup, with an initial startup surge of 14.6 Amperes. As the box cooled, the current consumption dropped and the motor's running current consumption averaged 4.4 Amperes during the test period. John and Anita continued using the unit until 10 May 1988. The duration of the test was 16.5 days or a total of 396 hours. The hour meter measured the operation of the Sun Frost's motor for 84.2 hours during the test period. This calculates to an average "ON" time of 21% or 5.1 hours daily. The 12 cubic foot Sun Frost refrigerator/freezer consumed an average of 22.45 Ampere-hours, or 277 Watt-hours, per day during this test. Sun Frost rates the RF-12's consumption at 28 Ampere-hours per day in a 70¡F. ambient temperature environment. What this really means is that, in most locations, two 48 Watt PV modules produce enough energy daily to run this Sun Frost refrigerator freezer combo. In fact, according to our test there will be energy left over from two PV modules (assuming a module produces at least 16 Ampere-hours per day). Cost The list price of the RF-12 Sun Frost is $1560, plus $50 for a crating charge, FOB Arcata CA. If the cost of powering the unit over a ten year period is considered then an additional $1,250 will be spent on energy at about $1.00 per kiloWatt-hour (a strictly ballpark average cost for home power systems). The total cost of buying and powering the RF-12 will be about $2,800 over a ten year period. This includes the refrigerator itself, the PVs to power it, and the batteries needed to support the refrigerator. An efficient type of household refrigerator will consume about 1,500 Watt-hours per day. This consumption is according to the US Department of Energy. If this refrigerator were to cost say $600, and we consider the cost of the equipment to power it (about $5,500 at $1.00 per kiloWatt- hour), then the total refrigeration cost is about $6,100 over a ten year period. Compare this to the $2,800 above and you'll see that eventhough the Sun Frost RF-12 is initially more expensive than conventional refrigerators, it is actually much cheaper to both buy and operate. The reason for this is energy consumption. The conventional refrigerator will require about 8 PV panels to supply its power, and additional batteries to support it during cloudy periods. As in most home power situations, it's not the cost of the appliance that really counts, but the cost of the energy it consumes. Conclusion The Sun Frost RF-12 is an extremely well made and ultra-efficient refrigerator freezer. It runs directly on 12 VDC (there are also 24 VDC models), thus bypassing the necessity and power loss of an inverter. Existing PV/battery systems can add the Sun Frost RF-12 and power it by adding only 2 PV modules. This refrigerator is truly a "Thing that Works!". It is designed for us Watt-watching, home power, folks. Larry Schlussler and the Crew at Sun Frost are making a truly amazing machine. If the cost of powering the refrigeration equipment is added to its purchase price, then the Sun Frost RF-12 is about half the cost of running conventional, high-efficiency refrigeration in home power systems. We like this refrigerator and are saving up so one can come to live in our kitchen. You can write Sun Frost for more information at POB 1101, Arcata, CA 95521 or telephone 707-822-9095. The RF-12 is only one model in their extensive line which offers larger, smaller, and freezer only units.