Frigoboat 12 Volt DC Refrigeration

>Outback Marine is the Australian distributer for Veco  Frigoboat - manufacturer of marine and mobile refrigeration systems, equipment, parts and accessories for boats, caravans and mobile homes. We specialise in the design and supply of 12 volt DC Danfoss compressor systems based on Frigoboat components. Frigoboat equipment can be purchased direct or can be purchased from our Australia wide dealer network.

Our dependence on refrigeration is no less on the water then it is at home. On a 24 hour basis, refrigeration systems will consume more power then any other essential vessel service. An efficient refrigeration system means that less power needs to be generated which means that engine run time to charge batteries can be significantly reduced or maybe the system can be self contained to run from solar panels alone.

Using familiar Danfoss DC compressors, Veco have developed condensers sets that are efficient to run and are built to last. With the best gear and in house enclosure manufacturing capability, Outback Marine can supply a solution ranging from a DIY component kit to a fully integrated refrigeration system.

A recent development was an entirely new marine refrigeration system that would use otherwise wasted energy to heat the vessel’s hot water system. Unlike conventional water cooled marine refrigeration systems which pump condenser heat overboard, the otherwise wasted energy is recovered to heat the boat’s on-board hot water system. The system will heat water to around 40º C, which is considered sufficient for most showering requirements. A digital control panel is supplied to supervise refrigeration and hot water temperatures. This innovation by itself does not at first look like a big deal, but considering that with a solar panel array, the system eliminates the need for an on-board 240 volt generator or LPG. The benefits can be outstanding.

How to Build a Boat Refrigeration System

Lots of cold drinks; plenty of fresh food; sufficient ice for cocktails; ample frozen meat, fish and vegetable storage. Providing all of this does not mean that you have to run a generator for hours and hours each day. Our Frigomatic systems are designed from the ground up for marine applications. The right system will keep icecream hard in the freezer; will chill a slab of beer to drinking temperature in a matter of hours and will use a minimum amount of energy.

Outback Marine can engineer a system that allows you to enjoy all of these benefits on solar power alone or just a short period of generator set/engine run time each day. The cost and weight of such a system will be much less than common eutectic type systems.

A good refrigeration and freezer system becomes a priority for remote area living. This application brief covers the basics of an optimal refrigeration system design. The number and size of boxes can be varied to meet individual needs. Operational objectives are similar to household refrigeration except that unique aspects of a mobile installation accentuate certain requirements.

• refrigerator and freezer product need to be kept at required temperatures
• modular service capability by way of quick connect/disconnect fittings
• operation independent of an engine driven power source
• fast temperature pull-down for newly stored product
• versatility for varying storage requirements
• low maintenance and high reliability
• minimal weight and quiet operation
• high energy efficiency

Download: How to design a marine refrigeration system

Refrigerator Box Insulation

The amount of energy required to run a refrigeration system is related to the amount of energy lost through the box insulation and the coefficient of performance (COP) of the refrigeration plant. Additional factors include the energy that is required to bring stored product down to temperature and the energy lost through exchange of air that occurs with door openings. For the sake of practical design, these losses are small and are not considered in the following discussion on insulation.

• Temperature differential: the difference between the inside box temperature and outside ambient temperature.
• Insulation surface area: larger boxes (with more surface area) require more energy
• Insulation thickness: thicker insulation requires less energy
• Insulation factor: higher performance insulation requires less energy

Energy loss is expressed in BTU’s (British Thermal Units) per hour. The charts below show the heat loss in BTU’s per hour for refrigeration and freezer enclosures of differing surface areas and insulation thickness - assuming quality Urethane or Styrofoam insulation (.17 K Factor). First, calculate the outside surface area of the enclosure. For example, an enclosure measuring 700mm x 700mm x 700mm has an outside surface area of 2.5 square metres.

Reference the charts below to find the heat loss (BTU’s per Hour) for the insulation thickness used. It is evident by the charts that insulation thickness has a dramatic effect on heat loss and subsequent energy requirements. We recommend 100 mm of insulation for refrigeration and 150 mm for a freezer. In our example above with recommended insulation and a surface area of 2.5 Sq M., we would lose about 80 BTU/Hr for the refrigerator and about 70 BTU/hr for the freezer.

Freezer Heat Loads	Refrigerator Heat Loads

Compressor Coefficient of Performance

The COP influences the amount of BTU’s per hour that the refrigeration plant can transfer for a given amount of energy. It is a measure of system efficiency. Factors influencing the COP include:

• Evaporation temperature: lower plate temperatures decrease efficiency
• Head pressure: higher pressures require more power
• Compressor characteristics: higher compressor speeds decrease efficiency

Freezers require lower plate temperatures than refrigerators. In both cases however, selecting a larger evaporator plate will save energy as the plate temperature will be higher for any given box temperature. Spacing the evaporator away from the cabinet wall will effectively increase surface area as well. The head pressure (or work load of the compressor) depends on the system load and the efficiency of the condenser. As the head pressure is directly proportional to condensation temperature, good condenser design and installation practices will improve both efficiency and performance.

Most DC systems used in mobile applications use Danfoss BD35 or BD50 type compressors. The compressor speed needs to be high enough to meet the system load but not to high as to lose efficiency. The speed should be matched to system requirements.

System Tradeoffs

It is important to realise that compromising insulation thickness (maybe to gain extra internal volume), will come at the cost of more energy to run the system and will have an impact on actual refrigeration performance. Attention should be given to equipment capacity vs. box heat load: type and capacity of condensation system, evaporator plate sizing and technology, compressor size and box temperature. A system analysis should always include the cost of energy generation to support the system in addition to the cost of refrigeration equipment. More often than not, the perceived low cost system is actually more expensive when taking the overall system into account.

All of our refrigeration systems feature quick connect and disconnect couplings - in most cases you do not need to hire a refrigeration mechanic. The systems are powered from your 12 volt or 24 volt battery supply.

We can assist you in your own installation or if you prefer we can manage the whole job.