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12 Volt Refrigeration Systems

The Sea Frost BD Direct Evaporator System is an advanced design that will operate on 12- or 24- volt D.C. power. It is perfect for well insulated refrigerator boxes. The system consists of two components — the compressor, which is remotely located, and the stainless steel cold plate. The two components are connected by pre-charged copper lines attached at the plate. The rugged, half-inch thick polished stainless steel cold plate can be mounted on a shelf, wall or ceiling and offers the highest resistance to damage and corrosion. Optional ice-making trays are available for wall-mounted installations.

BD systems are factory pre-charged and require no special tools for installation. Popular Danfoss® hermetic compressors are used in both the BD and BDxp. These electronically-controlled, variable speed compressors feature state of the art efficiency.  BD compressors are totally enclosed with a brushless D.C. fan and efficient, oversized copper and aluminum finned condenser. Ducted air cooling creates the highest efficiency and allows for installation in confined locations. 

Sea Frost’s BD is well-suited for boats with adequate battery banks and charging equipment.  Thermostatic operation maintains the cold plate at even temperatures. The thin direct evaporator cold plate requires minimal box space. Dockside, the system operates through the boat’s battery charger.  

Options include custom plate sizes, custom line lengths, 2-plate freezer systems, freezer bin, remote thermostat, electronic control, air and water cooling and ice-making tray kits.  

The BD XP  The BDxp is has approximately 30% more capacity than the standard BD.   The BDxp should be used in larger refrigerator and freezer applications. The BDxp has an AEO (Adaptive Energy Optimizing) feature. This feature senses the amount of cooling needed and adjusts compressor speed accordingly.   The BDxp may be fitted with a speed control in order to manage power draw. Air cooling is standard; optional air and water cooling is available. Housing size/weight are identical to the BD.  See Charts on AMP Draw and Compressor Capacity.

The BDxpx

The BDxpx has the highest capacity of the BD series.   The BDxpx uses low temperature R-404a refrigerant.   For More Information and Pricing click on the link below.

BDxpx

Water Cooled Option

The water cooling option, added to the air cooled system, incorporates a copper-nickel tube-in-tube condenser. A remote pump, elected by a switch on the cabinet, operates with the compressor and fan. Water cooling should be used in engine room or other confined installations. This type of condenser  utilizes the scrubbing effect of water and is far more efficient than static water cooling.    See Condenser test.

Plate Sizing for Refrigerators  

BD systems use thin (half-inch), stainless steel cold plates. These direct evaporator plates provide excellent thermal conductivity for cooling efficiency. They’re mounted on stand-offs to allow air to flow on both sides.  Refrigerators require a single plate which should be mounted as high as possible in your insulated box. Approximately 20% of the wall area should be covered.  Click here to see available plate sizes. 

Stainless Steel Freezer Bin

For a small freezer within a refrigerator, the stainless steel freezer bin is ideal. Two walls of the Freezer Bin are double sided direct evaporator cold plates which freeze the bin on the inside, creating a small freezer, and refrigerate the cabinet.  The bin should be mounted high in the box, either vertically or horizontally, and operates best in a relatively small, well insulated cabinet. The standard built-in thermostat regulates the compressor to maintain constant temperatures. Other options include a remote thermostat, and a remote electronic thermostat /thermometer, bin lid and ice making tray kit. Custom widths are also available up to 12 inches.  Click here to see available Bin sizes.

Standard Bin dimensions:  Height: 11 inches; Width: 9 inches Weight: 22 lbs.; Freezer volume: .6 cubic feet

Freezers

Consider the freezer as an additional system with its own compressor and controls. This is the best way to achieve deep freeze temperatures.  

Plate Sizing

It is necessary to have more plate area in a freezer to get air temperatures close to plate temperatures.  Freezers require two plates in series, mounted on opposite walls of the same box to create a sandwiching effect. This helps eliminate problems with air flow in a full box. 60% of the wall area should be covered.  In series systems, a small copper line from the compressor runs to the first plate where an expansion valve is mounted.  An inter-connector jumper connects the first plate to the second plate; a return line connects the second plate to the compressor. 

Click on links below to see Freezer plate piping examples.

Plate layout - Figure A        Plate layout - Figure B        Plate Layout - Figure C

All our systems are built to your specifications.  Custom plate sizes and custom tube lengths are available.  Plates can be mounted either horizontal or vertical to fit the configuration of your box.  Click here to see available plate sizes.

To order a system, the following information is require: 

• Plate dimensions and orientation.  Both standard and custom plates available.

• Location of valve on plate. 

• The distance between the two plates for the length of the connecting jumper  line.

• Liquid line length. (Distance between valve on the first plate in the series and the compressor.)

• Suction line length. (Distance between the second plate in the series and the compressor.)

Installation and Use

The insulated cabinet is a big factor in the success or failure of a refrigeration system. Heat leaks into a chilled box. This heat is what must be removed on a continuous basis. Energy usage or compressor amp draw is all based on the amount of cooling needed (heat leaking in). This energy usage is based on box size, the insulation type and thickness, and the climate the boat is in. Heat travels into the cabinet from all directions so it is important to have a well insulated top and lid. Cold air will flow like water. All drains need to be plugged to prevent losing cold air. Lids require good air seals.

Inside a refrigerated box, temperatures will be lower at the bottom. Mounting a cold plate at the top cools the warmer air and the box more evenly. Sometimes fans help even out the temperature.  

Air is the medium that transfers the cooling from the cold plate to the food. Shelves should be vented to allow air to flow. A grating or baskets should be used to allow air to flow around the food. This is important in a freezer. Packing a boat refrigerator may require putting the lettuce at one end away from the cold plate and the beer and milk at the bottom or near the plate. 

Frost build up on cold plates will reduce the efficiency of the system. This frost is a product of humid conditions and wet products being refrigerated.

Compressor efficiency is about 3.5 to 4 BTU per watt in tropical climates. The BD compressors are variable speed; at low speeds there is low amp draw but a low cooling rate. Higher compressor speed results in more cooling but more amp draw as well. Amp draw is therefore directly related to the amount of cooling being produced and is not the way to compare system performance.  

See Charts on AMP Draw and Compressor Capacity.

Energy Conversion Estimates

A 2.3 cubic foot (16" x 16" x 16") box with 3" of 2 lb. density foam insulation used as a refrigerator in the tropics will use 25 amp/hours @ 12 volts per day.

An 8 cubic foot (24" x 24" x 24") box with 3" of 2 lb. density foam insulation used as a refrigerator in the tropics will use 57 amp/hours @ 12 volts per day.

A 15.6 cubic foot (30" x 30" x 30") box with 4" of 2 lb. density foam insulation used as a refrigerator in the tropics will use 68 amp/hours @ 12 volts per day.

Thermostats and Controls

Diagrams of an Air Cooled Installation
Click on pictures to view full size version.
 

Ducted air cooling creates the highest efficiency and allows installation in confined areas such as a sail locker, or under a cabinet or seat. The ducting eliminates re-circulation of the cooling air. The air temperature increase is minimal (2° to 3° F.). Air flow can be reversed.

SEA FROST, 372 Route 4, Barrington, NH 03825 USA
Tel: (603) 868-5720 ~ Fax: (603) 868-1040
1-800-435-6708 (USA, Canada & Caribbean)
e-mail: sales@seafrost.com