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  • Why Eutectic

    Eutectic Refrigeration, up to 45% less battery consumption. Here is why..

    Firstly this 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 showing the internals of a multi-voltage compressor, followed by a brief explanation.

    Above left:  Refrigerant gas is pumped around the system by the compressor, in a re-circulating manner somewhat similar to water circulating around a cars cooling system, collecting heat from one area and disposing of it in another.
    The three main components are: 1: Evaporator, 2: Condenser, 3: Compressor. These components are connected in a closed loop.

    Refrigerant gas expanding in the evaporator tubing collects heat from a liquid medium stored inside the eutectic tank. The compressor pumps / compresses this heat laden gas into the condenser where it is disposed of by compressing it to temperatures / pressures higher than the condensers surrounds. Therefore, each of these major components relies on the other. each doing their job effectively and proportionately.

    For example, if the condenser can not efficiently dispose of the heat load because it is undersized or has a restricted air / water flow etc., then the compressor is overloaded and stressed, the evaporator is unable to collect heat effectively and so on. The result of this chain reaction is a system that consumes excess power and provides poor, if any, refrigeration. Systems must be engineered with compatible components.

    Eutectic Refrigeration, 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 will warm rapidly once the ice thaws.

    The ice is an example of the eutectic principle, 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 plate 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!

    Other products such as a thin aluminum evaporator plate can also absorb and dissipate thermal energy but when a relatively large volume of solution is used as in the eutectic plate and it is allowed to freeze solid on the refrigeration run cycle, then thaw during the off cycle, a massive amount of stored thermal energy is in play.

    By comparison with a thin 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. (A thin slice of ice will disappear much quicker than a 60mm thick block would)

    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.

    A eutectic system will run for a long period while refrigerating the eutectic solution until frozen solid. It then stays off for relatively much longer periods while this thermal mass thaws completely before running again. All the time maintaining cabinet temperature.

    Eutectic systems have many advantages including the following..

    • Long ‘hold-over’ off periods due to the large thermal mass and more importantly because of the eutectic’s phase change.
    • Refrigeration can be at a time that suits the power supply, or during cooler periods when refrigeration systems are more efficient.
    • Much lower overall power consumption due to more efficient refrigerant evaporation in a saturated environment,
    • With ECO2 the eutectic mass is automatically refrozen whenever sources of power are abundant, reducing demand on batteries.
    • Virtually ‘cooling in advance’, use of abundant power supplies provides a day or so of refrigeration requirement in storage.
    • A day or two of sailing without the need of additional cooling is possible if battery power supply is down. (i.e. solar but no sun!)
    • Eutectic systems store energy at a third of the weight that would be required in batteries to provide the same refrigeration effect.

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    Comparing Eutectic and Cyclic Refrigeration systems  The test results…

    Given a refrigeration cabinet to refrigerate, the amount of heat to be removed (measured in watts) is exactly the same regardless of the refrigeration method used.  But, how the cabinet is refrigerated and the refrigeration method used, will determine how power efficient the conversion from electrical energy to thermal energy will be and the differences are extreme.

    The following charts are indicative of the two system types refrigerating the same cabinet. They indicate the power savings using the eutectic refrigeration method due to far less daily start-ups and operating in a COP range providing up to a 50+% better conversion of electrical energy. Read on, it’s a no-brainer!

     

    CHART A:        12 Volt DC Aluminium Cold Plate Cyclic Refrigeration:

    This lowest capital cost method is to use a cyclic refrigeration system employing a thin aluminium evaporator. (cold-plate)

    Advantages of this system:

    • Low capital cost.
    • Rapid initial cabinet cool down.
    • Light weight. (Although additional battery(s) may be needed))

    Disadvantages of this system:

    • Soft aluminium evaporator is easily punctured and prone to corrosion if/ when powder coating is damaged.
    • Virtually no hold-over thermal storage therefore power is needed all the time. Total reliance on battery supply.
    • Inefficient use of your battery’s electrical energy supply due to:
    1. Many cycles per 24 Hr/day (24 as in chart but often many more!) Each start of a cycle wastes power.
    2. Operating in an inefficient COP* range mostly less than 1.3. This relates to longer running per cycle. (Less heat removed for every watt of power consumed)

    *COP indicates the compressor efficiency. COP reduces as the evaporator temperature lowers. For example if a compressor consumes 100watts of electrical energy while removing only 130watts of heat its COP is 1.3. Operating at low evaporator temperatures and therefore low COP, is very inefficient and wasteful of battery power.

    The chart below is typical of a Cold Plate System refrigerating a 150 Litre insulated cabinet:

    The upper green line indicates that cabinet temperature was maintained between +2C and +4C, ideal fridge temperature.

    The blue line indicates how the evaporator cold plate quickly lowers in temperature when the compressor runs but then quickly rises again during off cycles. No hold-over.

    The green and yellow blocks below indicate Run (Battery use) and Off periods, with totals to the RHS.

     

     CHART B:        12 Volt DC Hold-Over Eutectic Refrigeration:

    This has a similar Refrigeration condensing unit to the Cyclic system described above but the evaporator and it’s operation mode is vastly different. Eutectic refrigeration uses a refrigerated stainless steel holding tank to store thermal energy. (Eutectic Plate)

    Advantages of this system:

    • Longer life expectation due to more rugged stainless steel evaporator, less run time and far less start ups.
    • With stored thermal hold-over to support the units cooling ability, there is less cabinet temperature rise when adding warm products.
    • Less rapid movement in cabinet temperature between cycles.
    • Although heavier than cyclic systems, project weight overall is less due to not requiring as much battery storage.
    • Far less use of electrical energy (Battery) due to:
    1. Only one or two run cycles per day so less start up losses.
    2. Operating in a very efficient COP* range mostly approx 2.0. This being a 50% more efficient COP factor than a cyclic system means shorter run time per cycle and far more efficient conversion of energy.
    3. Full fail safe automatic resetting. Manual over-ride switch to bypass all control system if needed.

    Disadvantages of this system:

    • Higher capital cost.

    *COP indicates the compressor efficiency which reduces as the evaporator temperature lowers. For example if a compressor consumes 100watts of electrical energy while removing 200 watts of heat its COP is 2.0. Operating at higher evaporator temperatures and therefore higher COP, is very efficient and conserves battery power.

    The chart below is typical of a Hold-Over Eutectic System refrigerating the same 150 Litre insulated cabinet:

    The upper green line indicates that cabinet temperature was maintained between +2C and +4C, ideal fridge temperature.

    The blue line indicates how the evaporator cold plate slowly lowers in temperature when the compressor runs as the Eutectic mass is frozen, then slowly rises again as the Eutectic thermal mass thaws during off cycles.

    True hold-over refrigeration.

    The green and yellow blocks below indicate Run (Battery use) and Off periods with totals to the RHS.

     

    CHART C:        12 Volt DC Hold-Over Eutectic Refrigeration with ECO2 .

    This has a similar Refrigeration condensing unit and Eutectic evaporator as described above but with the addition of an in-built ECO2 power management system. ECO2 monitors the voltage(s) presented and if the DC exceeds 13.7 volts (or if the optional 110 / 240 VAC power supply kicks in) it knows that batteries are topped up and further power from solar etc is now otherwise wasted, so it tricks the digital controller into run mode. We call this ‘using abundant power’, power that is otherwise wasted.  ECO2 is standard now on all Ozefridge Eutectic systems as is the automatic failsafe bypass system.

    Advantages of this system:

    • Longer life expectation due to more rugged stainless steel evaporator, less run time and far less start ups.
    • With stored thermal hold-over to support the units cooling ability, there is less cabinet temperature rise when adding warm products. Less movement in cabinet temperature.
    • Although heavier than cyclic systems, project weight overall is less due to not requiring as much battery storage.
    • Far less use of electrical energy (Battery) due to:
    1. Only one or two run cycles per day so less start up losses.
    2. Operating in a very efficient COP* range mostly approx 2.0. This being a 50% more efficient COP factor than a cyclic system relates to shorter run time per cycle and far more efficient conversion of energy.
    3. Full fail safe automatic resetting. Manual over-ride switch to bypass all control system if needed.
    4. ECO2 automatically causes running when power is abundant reducing the demand on battery(s) ECO2 also increases compressor speed to make best use of abundant power.
    5. ECO2 often eliminates the need for additional battery power to service the fridge unit.

    Disadvantages of this system:

    • Higher capital cost.

    The chart below is typical of a Hold-Over Eutectic System with ECO2 refrigerating the same 150 Litre insulated cabinet:

    The upper green line indicates that cabinet temperature was maintained between +2C and +4C, ideal fridge temperature.

    The blue line indicates how the evaporator cold plate slowly lowers in temperature when the compressor runs as the Eutectic mass is frozen, then slowly rises again as the Eutectic thermal mass thaws during off cycles.

    The green and yellow blocks below indicate Run (Battery use) and Off periods with totals to the RHS.

    The brown area indicates running without battery drainage whenever ECO2 sights 13.7VDC or optional AC. (Automatic)

    Please note: The data indicated in the charts above was obtained from actual operating models then averaged and presented so as to provide a fair and understandable comparison. Systems and logging equipment used to obtain these outcomes can be seen at Ozefridge.  Visitors welcome.

     

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    Ozefridge Sure-Thaw Controller: Its Importance.

    The vast majority of so-called 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 required 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.


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