Eutectic Refrigeration = greater efficiency.. here is why..
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 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 (Eutectic cooling pipes, inside the fridge cabinet), 2: Condenser (Disposes the heat outside), 3: Compressor pumps the refrigerant gas that transports the heat. These components are connected in a closed loop.
The evaporator collects heat from the eutectic tank and the compressor pumps / compresses it into the condenser where it is disposed of. 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 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 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.
(*All eutectic solutions with a colder phase change point than water also have a lower Latent Heat value. Expect lower temperature eutectic mixes to absorb and dissipate approximately 65 to 70 watts while phase changing)
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.
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.
Power Efficiency Tests: (Our testing)
A test to compare the daily power consumption of an aluminum plate system, with a eutectic plate system.
Both were coupled to similar *C450 refrigeration units. (*Earlier model) using a well insulated 160 lt. cabinet operating as a refrigerator.
Extreme conditions and normal usage were replicated.
The test required that the refrigerator cabinet remain between 1ºc and 4ºc. during ambient temperatures of 40c day and 30c night.
With the same sized C450 refrigeration condensing units refrigeration condensing units used on both evaporator types, the evaporator and plate were both installed in the same 160 litre cabinet.
This cabinet along with refrigeration systems, was then placed in a heated area 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. Each was set to maintain cabinet temperatures between +1c and +4c.
The accumulated run / off periods and power consumption figures were logged.
The aluminum plate system averaged 42 run cycles during each day. The average total run time was 12.1 hours per day. Average consumption was 4.97 amps / hour of run time. Total consumption of 60.1 amps/hours for the 24 hour period.
The Ozefridge eutectic system averaged 1.80 cycles per day. The average total run time was 6.26 hours per day. Average consumption was 5.37 amps / hour of run time. Total daily consumption of 33.6 amps/hours for the 24 hour period.
If ECO2 power management had also been used during this test, the benefit from the storage of abundant energy when available would see an even lower battery drain from the ozefridge eutectic system.
The combination of the ‘Sure- thaw’ controller, ECO2 power management, eutectic operation, unique air & water cooled condenser, and now a more powerful BE80 compressor, allows the Ozefridge Eutectic System to use far less battery power than other systems.
(Note: This test is typical of operating a eutectic refrigerator, power efficiency differences are less when applied to freezers)
Power Efficiency Tests: (Testing by others)
A very happy client sent us the following results he has obtained from his Ozefridge Package Four system. Our client used an icebox as the basis of his fridge project. As suggested Howard added insulation to the sides and underneath to improve the insulation properties and to allow the Ozefridge to work at it’s best and most efficient.
He completed his project then set about logging the power consumption as, like most others, consumption was most important.
Howards results even suprised us. Below is a copy of the unsolicited email he sent us followed by his power consumption graph with an insert of the 180 liter cabinet.
Quote: “Attached is my latest graph, 65 days out since installation. I have added a number of averages etc and also a graph of the upper and lower coolant tank temperatures that I have set on the compressor unit.
We are very happy and people are amazed when I tell them that we are running a 180 litre fridge on what is effectively 7 watts continuous!”
- Ozefridge A480 and AW480 systems are powered using the Ozefridge BE80 multi-voltage soft-start motor driver.
- This allows it to operate from any 12 or 24 VDC supply. (Nominate if 24VDC)
- And 12 VDC and 110 -240 VAC for both models with the optional 110-240 VAC converter that automatically use the highest voltage presented.
- No need for switching or mains power converters.
- Automatically resetting low voltage, over load and over temperature cut-out along with soft start, start delay and polarity protection with LED fault indicator, are part of the built in fail-safe protection.