Eutectic Systems:

 Refrigeration and the Benefits of Eutectic Systems.. (A brief explanation)

The diagram below is of a simple eutectic refrigeration system showing the basic components and how they rely on each other and below right  is a cut-away of the Danfoss BD 50 compressor,  followed by a brief explanation.

        

 

Refrigerant gas is pumped around the system in a re-cycling manner somewhat similar to water circulating around a cars  cooling system, collecting heat from one area and disposing of it in another.

The evaporator collects heat from the eutectic tank and the compressor pumps it into the condenser where it is disposed of. Therefore, each of these major components relies on the other doing their job effectively for proper operation. For example, if the condenser can not efficiently dispose of the heat load because it is undersized or has a restricted air flow etc., then the compressor is stressed, the evaporator unable to do its job properly and so on. The result is a system that consumes excess power and provides a poor, if any, result.

Ozefridge quote:  "Temperature is only lowered by removing heat"

The major sections of a System are the eutectic tank located inside the cabinet and the remote C350 (C380) unit..

The ozefridge Eutectic System has all of its components assembled into two distinct sections. (Keeping it simple and tidy!)
Eutectic tank:   The stainless steel Eutectic tank is located inside the cabinet and has an insulated hose that carries refrigeration pipes, filter  and the temperature sensor wire to the C350's location. The eutectic tank acts like a large renewable block of low temperature ice, refrigerated automatically by the C350 condensing unit.
Refrigeration condensing unit:  The C350 condensing unit houses the Danfoss BD50 compressor, water and air cooled condensers, fan, 12-24 &110- 240 volt electrical components, controller, LED readout, failsafe protection and refrigeration couplings.
 

Eutectic Systems: An explanation...

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 from a solid to a liquid. (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 while it absorbs heat.  The phase change medium or eutectic solution is stored in the stainless steel eutectic tank and acts like a re-new able ice block, freezing solid during the refrigeration 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 cold plate, the first and most obvious advantage the eutectic system has is its far greater mass and therefore thermal hold-over storage capacity. 

But this thermal storage advantage pales into insignificance compared to the other unique benefit that the eutectic system's phase change phenomenon 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 quantity of water as a eutectic solution and knowing that water's 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. 

(*All eutectic solutions with a lower phase change point than water also have a lower Latent Heat value. Expect low temperature eutectic mixes to absorb and dissipate approximately 65 to 70 watts while phase changing)

With a system refrigerating a solution through its' phase change temperature until frozen solid during each run cycle, then staying off for very long periods while this thermal mass thaws completely before running again, many advantages become obvious including the following..

*    Tremendous 'hold-over' off periods due to the thermal mass of the stored eutectic solution and more importantly because of the eutectic's phase change.

*    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 a saturated environment, and far less stop / start operations.

*    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!)

*    The eutectic system stores energy at a third of weight that would be required in batteries to provide the same refrigeration effect.

Ozefridge Sure-Thaw Controller and its importance.

The vast majority of Eutectic systems do not and simply can not function properly as true eutectic systems. We have found that either the eutectic solution mix is not appropriate for the cabinet temperature therefore phase change is not occurring, and / or the system is controlled by a thermostat reading cabinet air temperature or worse still, also using an ancient mechanical type temperature controller! 

If the eutectic solution doesn't freeze on each run cycle and then thaw completely during off periods, then the system can not operate correctly. It is as simple as that!

The Ozefridge Sure-Thaw control system 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 controller that reads the actual eutectic temperature. This unique control method guarantees that each on / off cycle of the refrigeration system provides proper phase change and benefits of the eutectic principle.

Comparison of Aluminum plate system with an Ozefridge eutectic system.

The following test was conducted using a well insulated 160 liter cabinet operating as a refrigerator with normal usage but with extreme conditions* replicated and required that the refrigerator cabinet remain between 1ºc and 4ºc.        

System A was a C350 condensing unit connected to an aluminum evaporator plate.

System B was a C350 condensing unit connected to an Ozefridge T45-30 eutectic tank (evaporator).

With the  same sized C350 refrigeration condensing units used on both evaporator types, the evaporators were both installed in the same 160 litre cabinet.

This cabinet along with refrigeration systems, was then  placed in a heated room at controlled temperatures.

Each system was operated individually for seven days with the room heated to *40ºc for 14 hours and 30ºc for the remainder of each 24 hour period.

The accumulated run / off periods and power consumption figures were logged.

The aluminum plate system averaged 46 run cycles during each day. The average total run time was 14.4 hours per day.

The Ozefridge eutectic system averaged 1.82 cycles per day. The average total run time was 6.7 hours per day,

Outcome:     

The 'Sure- thaw' controlled Ozefridge Eutectic System used far less battery power than the aluminum plate system.

 IMPORTANT:  As Ozefridge Industries Pty. Ltd. supplies refrigeration systems to be installed by others in the owner's existing cabinet that has insulation properties we can not be assured of, we do not guarantee cabinet temperature or system efficiency in this or any other quotation or statement.