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Sunday, 20 Apr 2014

Marine Refrigeration

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Click Here for OzeFridge Technical Data

Ozefridge was conceived 15 ago in the hills of Adelaide and with the technology advancements and feedback from cruising yachtsman and clients this product has evolved into the most advanced  smart refrigeration system in the world today.
By using the Eutectic principle Ozefridge has been able to keep operating current draw to an absolute minimum while maintain a constant even temperature.


Some of the benefits of an Ozefridge are:

 

  • Fridge or Freezer
  • Multi voltage 12-24 or 110-240 volts AC or DC
  • Shaw Thaw Thermostats
  • Eco 2 power management
  • Optional water cooling (if required) For tropical conditions

And if any of this technology fails a simply override switch so you still have a fridge not matter where you are.
These system are available in 5 different size plates in either single or twin configuration, you can order them in portrait or landscape with piping lengths up to 4 meters. Ozefridge can still customise to your requirements.
Before leaving the manufacturing facilities in Australia, every system is run and checked overnight to make sure it operates within its preset parameters.
The entire system has been designed for the end user to install himself saving time and money for the customer. Shipping is direct from the factory to you saving time and money.
Please read the following pages for advantages and technical tips on why Eutectic is the best option for your fridge/freezer.

Just Cool It!

Keeping your cool on board can be difficult sometimes!
Refrigeration, unlocking the confusion:

Understanding the attributes of the various systems available is the first requirement towards selecting the most suitable equipment for each individual application and the peace of mind that follows.
The trend is overwhelmingly toward small 12-volt battery and 240-volt mains powered sealed compressor systems.  These are simple, reliable and very efficient as they function like a basic domestic refrigerator system and can continue running from shore or solar power when you are absent. 

A galley fridge / freezer system is simply providing domestic type refrigeration, albeit one that also operates from battery power, and kept simple does not have to be some monstrous Heath Robinson type conglomeration*!             (*A magnificently executed yet ineffective device that is both ingenious and totally impractical!).

Fortunately nowadays there are many excellent 12-24VDC / 110- 240VAC Marine Refrigeration Systems specifically engineered to provide very efficient galley refrigeration.  Being purpose built and simple, these products address the problems of restricted, erratic and different power supplies and can function in extremes of temperatures and at acute angles.  Most have condensing units powered by a Danfoss compressor with either a water-cooled condenser an air-cooled condenser or both. The condensing unit is then remotely coupled to one of three different types of evaporator.

Left: Danfoss BD35, BD50 and BD80 compressors are used in nearly all galley refrigeration systems.

With three methods of condenser cooling, three common sizes of Danfoss compressor and three different evaporator types, already there are many options and system combinations to explain.

The basics briefly:

Firstly, the key to unlocking the mystery of refrigeration is to understand that refrigeration systems lower temperatures by removing heat and not by adding cold! 
(It is impossible to add ‘cold’ but we can remove heat causing cabinet temperatures to be lowered).

Next, this diagram below and a brief description of the major components of a Marine Refrigeration System.

 

Located inside the refrigerator cabinet, the evaporator is the collector of heat. 
Located outside the refrigerator cabinet, the condenser disposes of this collected heat.
Also located outside the cabinet, the compressor pumps refrigerant gas through these components in a recycling manner.  (See diagram above for refrigerant gas flow as indicated by arrows.)
The refrigerant gas is pumped around the entire system collecting heat and disposing of it simultaneously whenever the compressor (heat pump) is running. This circulation of gases, collecting heat from one area and disposing of it in another, is similar to the water-cooling circulating through a car’s engine and radiator.
As can be seen in the diagram the refrigeration system’s major components are connected to each other in a loop each with gas entering and exiting.  These components rely on each other for efficient operation. For example if heat normally collected by the evaporator and forced into the condenser by the compressor was not being disposed of efficiently then the loop would be restricted. This condenser restriction would cause the condenser to retain heat, increases gas pressure and compressor load and finally the evaporator’s ability to collect heat. The result would be a system that consumes large amounts of battery power, runs excessively and doesn’t cool in hotter conditions, and all because it simply can’t efficiently get rid of it’s condenser heat.

Now to explore the more popular system options.

•    Air-cooled condensing unit with an aluminium evaporator plate. (Or with water-cooled option)

These are the ‘entry level’ systems most suited to smaller less demanding applications. They are basic, low cost and simple.
The aluminum plate evaporator has negligible temperature holdover therefore while it refrigerates quickly to shut off temperature, the system may cycle up to 40 or more times per day.
These systems can be operated at freezer or refrigerator temperatures provided that the cabinet size and insulation thickness are suitable. Water-cooled versions are available at greater cost but also with much more refrigeration capacity, especially in warmer conditions.

•    Air-cooled condensing unit with fan-forced finned evaporator.  (Or with water-cooled option)

The forced air evaporator system uses a fan to circulate air through cooling fins. These fin-coil evaporators are compact and provide rapid cooling but again have negligible temperature holdover and again will cycle very often. This system is only suitable for storage temperatures above freezing as it relies on continuous airflow over the fin-coil during off cycles for defrosting.

•    Air-cooled condensing unit with eutectic tank or plate evaporator.  (Or with water-cooled option)

These systems especially those with the water-cooled condensers, are the ‘Rolls Royce’ of marine refrigeration systems. The benefits of the eutectic tanks’ huge holdover capacity and the thermal storage of phase change make this method by far the most suitable for the majority of applications. A correctly set-up eutectic system only needs to cycle once or twice a day and can be installed as a freezer or as a refrigerator. Over a 24-hour period the eutectic system consumes far less battery power. While these systems have many worthwhile advantages unfortunately they do cost more initially.

The Eutectic Advantage:

We all know that a drink with ice in it will stay cold and drinkable at a constant temperature while the ice remains, but warm rapidly once the ice thaws. The ice was an example of a eutectic system absorbing relatively huge amounts of heat while it thawed. (Phase changed)
The term 'Eutectic System' refers to a refrigeration system that uses the phase change of a liquid medium to absorb and dissipate large amounts of thermal energy while remaining at a constant pre-arranged temperature. Phase Change occurs when we freeze a solution solid by removing its heat or as it thaws into a liquid again when it absorbs other heat.  The phase change medium or eutectic solution, is stored in the eutectic tank and acts like a re-new able ice block, freezing solid during run cycle and thawing during off periods and all the time maintaining a constant cabinet temperature like the ice did for the cool drink!  Any product such as an aluminum cold plate can absorb and dissipate thermal energy but when a relatively large volume of solution is used and it is allowed to freeze solid on the refrigeration run cycle, (then thaw during the off cycle), a relatively massive amount of stored thermal energy is in play.
In comparison with an aluminum evaporator plate system, the obvious advantage the eutectic system has is its far greater mass and therefore thermal holdover storage capacity. But this thermal storage advantage pales into insignificance compared to the other unique benefit that the eutectic system's phase change phenominon delivers.
This phenomenon called 'Latent heat', multiplies the eutectic's thermal storage capacity many times providing huge hold-over periods where the unit stays off for many hours even days in cooler times.
As an example, using a given quantity of water as a eutectic solution and knowing that its' phase change occurs at approximately 0°c, this water will absorb and dissipate 80 (Yes eighty!) times as much thermal energy while freezing and thawing as it would for any other rise or fall of a degree centigrade.

Therefore with a system refrigerating a solution through its' phase change temperature until frozen during each run cycle, then staying off while this thermal mass thaws completely before running again, many advantages become obvious including:
•    Tremendous 'hold-over' off periods due to the thermal mass of the stored eutectic solution and phase change. (Latent Heat)
•    Refrigeration run periods can be at a time that suits individual variations of power supply, or during cooler periods of the day when all refrigeration system are more efficient.
•    Much lower overall power consumption due to more efficient refrigerant evaporation in the saturated environment, and far less stop / start operations of the refrigeration unit.
•    The eutectic solution can be varied to have a phase change point at much lower temperatures than water to suit refrigerator or freezer cabinets.
•    As a eutectic system is virtually 'cooling in advance', use of shore power or other abundant power supplies allows a day or so of refrigeration in storage.
•    A day or two or three of sailing without the need of additional cooling is possible if battery power supply is down. (I.e.. solar but no sun!)
•    Storage of thermal energy at a third of the weight of equivalent stored battery energy.

Getting the best out a Eutectic System:

Many existing Eutectic systems do not function properly as true eutectic systems and usually for very simple reasons. I have found that either the eutectic solution mix is not appropriate for the temperature the cabinet is to be maintained at or more likely they are attempting to control the refrigeration system with a thermostat only reading cabinet air temperature or worse still using an ancient mechanical type temperature controller!
If the eutectic solution doesn't freeze on each run cycle then thaw completely during off periods, then the system is not operating correctly. It is as simple as that!
The systems manufactured in Australia by Ozefridge use their unique ‘Sure-Thaw’ control system which allows the user to digitally set the compressor cut-out below the eutectic freeze point and cut-in above the eutectic thaw temperature with a digital controller that also reads the actual eutectic temperature. This control method guarantees that every on / off cycle of the refrigeration system is benefiting from the phase change eutectic principle and power consumption is kept to a minimum.
The eutectic system with ECO2 power management, refrigerates when power is abundant, that is whenever the batteries are near full or 240 power is available thus reducing the run time required when power is limited. (from the batteries alone later) This often reduces the need for extra battery(s).

Click Here for OzeFridge Technical Data

Cool it, relax and enjoy.