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gauvins · 31-05-2018, 02:25

Just about to commit myself to purchasing an Isotherm ASU 3701 to cool a small (60L / 2 CF) enclosure that will be used as a fridge.

The marketing literature for this unit is ambiguous. Says that it can be used for refrigerator/freezer, but, unlike what I read in refrigeration primers elsewhere, doesn't offer different eutectic solutions to match the intended usage. It looks like we should partition the enclosure, which would create a freezer on the holding plate side of the partition, and a refrigerator on the other.

Seems crude. I may have missed something. Yet there's one review on a well know merchant's site that suggests that the unit isn't the best at managing temperature.

I've contacted the manufacturer. But there are specialists here that may have answers.

Thanks in advance

Typhoon · 31-05-2018, 06:45

Hi Gauvins.

You are going to put a holding plate inside a 2 cubic foot box , you won't have any space for food .

Regards John
www.coldeh.com

gauvins · 31-05-2018, 07:00

not much indeed, but we need very little.

This being said - email to Indel. Was told that the buyer must specify which unit is needed. The default is refrigerator.

Was also told that in a small box, it could be to cold. (I.e. the refrigerator unit might freeze its content.)

Ended purchasing an evaporator + ISEC controller.

Richard Kollmann · 31-05-2018, 07:21

Quote:

Originally Posted by gauvins

Just about to commit myself to purchasing an Isotherm ASU 3701 to cool a small (60L / 2 CF) enclosure that will be used as a fridge.

The marketing literature for this unit is ambiguous. Says that it can be used for refrigerator/freezer, but, unlike what I read in refrigeration primers elsewhere, doesn't offer different eutectic solutions to match the intended usage. It looks like we should partition the enclosure, which would create a freezer on the holding plate side of the partition, and a refrigerator on the other.

Seems crude. I may have missed something. Yet there's one review on a well know merchant's site that suggests that the unit isn't the best at managing temperature.

I've contacted the manufacturer. But there are specialists here that may have answers.

Thanks in advance

I tested the Isotherm 3701 eutectic holding plate system in 2002. The new model uses a less expensive holding plate like several companies made from a food table stainless pan. The eutectic solution freeze point of 14 degrees would normally be considered as a refrigerator plate due to the temperature between frozen fluid and box temperature that will result in only a 24 degree F freezer. Other points in Isotherm literature are performance quoted is based on a 70 degree standard day and if used as a freezer the insulation must be increased by three times. When a 14 degree plate is used as a freezer plate it is no longer a holding plate because almost no additional energy is stored once solution is frozen. Below the eutectic froze solid temperature the system becomes a cycling evaporator system storing only one half a Btu per degree per pound of solution.

If you do a Google search of the Isohterm 3701 unit you will find West Marine has two interesting customer reviews on this unit.

gauvins · 31-05-2018, 07:59

Quote:

Originally Posted by Richard Kollmann

If you do a Google search of the Isohterm 3701 unit you will find West Marine has two interesting customer reviews on this unit.

Yes yes, I did read them. Interesting... Doubly interesting because I started with a holding plate system in mind largely on the basis of their advisory. (i.e. claim of much improved efficiency).

I then read the extensive conversation in this very forum. I am still not sure that I understand what's at play here (eutectic stores energy, but doesn't change the BTU equation; the compressor duty cycle of an eutectic system is radically different than that of an evaporator, which may explain differences in performance; eutectic systems take advantage of periods of plentiful energy (engine running, solar panels at noon, shore power), etc).

As I indicated elsewhere, we've settled on the tiny GE80 system, rated at 80L (2.8CF) + ISEC controller which, if I understand correctly, will make the compressor run at maximum speed when there is abundant power, and at minimum speed otherwise, or until the temperature rises above a critical point, where the normal pattern resumes -- kind of playing the thermostat as conditions change, with the promise of a 35% reduction in energy consumption. There was also the interesting idea of using bottles of water as a surrogate for eutectic plates -- drop several liters of water in the box when energy is abundant. They'll lose heat that'll be recaptured later on, such as at night, when there is no solar energy.

I plan to install a power meter to measure the total draw, and a temperature sensor to keep track of what's happening inside.

Funny that such a simple device can become the focus of so much attention. We bought our home fridge in 5 minutes and barely glanced at the Energy Star rating. I guess that the idea of being 100% solar has its drawbacks

john61ct · 31-05-2018, 08:32

Other way to look at it, is that unrealistically cheap grid energy causes heedless and very wasteful disregard for efficiency.

Hence our having got too used to an unsustainable infrastructure and lifestyle.

Richard Kollmann · 31-05-2018, 09:22

Quote:

Originally Posted by gauvins

Yes yes, I did read them. Interesting... Doubly interesting because I started with a holding plate system in mind largely on the basis of their advisory. (i.e. claim of much improved efficiency).

I then read the extensive conversation in this very forum. I am still not sure that I understand what's at play here (eutectic stores energy, but doesn't change the BTU equation; the compressor duty cycle of an eutectic system is radically different than that of an evaporator, which may explain differences in performance; eutectic systems take advantage of periods of plentiful energy (engine running, solar panels at noon, shore power), etc).

As I indicated elsewhere, we've settled on the tiny GE80 system, rated at 80L (2.8CF) + ISEC controller which, if I understand correctly, will make the compressor run at maximum speed when there is abundant power, and at minimum speed otherwise, or until the temperature rises above a critical point, where the normal pattern resumes -- kind of playing the thermostat as conditions change, with the promise of a 35% reduction in energy consumption. There was also the interesting idea of using bottles of water as a surrogate for eutectic plates -- drop several liters of water in the box when energy is abundant. They'll lose heat that'll be recaptured later on, such as at night, when there is no solar energy.

I plan to install a power meter to measure the total draw, and a temperature sensor to keep track of what's happening inside.

Funny that such a simple device can become the focus of so much attention. We bought our home fridge in 5 minutes and barely glanced at the Energy Star rating. I guess that the idea of being 100% solar has its drawbacks

If you wish to believe the creative sales pitch of boat refrigeration salesman and novices in the law of thermodynamics, then you must believe the evaporator components of a boat’s icebox conversion refrigeration can create energy. Holding plate evaporator energy can neither be created nor be destroyed. If you wish to believe the energy produced by the refrigeration condensing unit then receives additional energy from a eutectic plate then buy a eutectic holding or eutectic cycling holding plate. The important thing to be concerned about is if you put 100 watts into a system is that it converts to a form of box heat removal equal to 100 watts.

I still believe the only way to justify a eutectic plate is to store surplus energy from alternative energy.

Typhoon · 31-05-2018, 09:32

Quote:

Originally Posted by Richard Kollmann

If you wish to believe the creative sales pitch of boat refrigeration salesman and novices in the law of thermodynamics, then you must believe the evaporator components of a boat’s icebox conversion refrigeration can create energy. Holding plate evaporator energy can neither be created nor be destroyed. If you wish to believe the energy produced by the refrigeration condensing unit then receives additional energy from a eutectic plate then buy a eutectic holding or eutectic cycling holding plate. The important thing to be concerned about is if you put 100 watts into a system is that it converts to a form of box heat removal equal to 100 watts.

I still believe the only way to justify a eutectic plate is to store surplus energy from alternative energy.

I agree with Mr Kollmann and his years of experience in this market . More then half our business is from clients removing there large holding plates and replacing them with our copper thin plates . We are new to this business and can only speak from our experiences and what we have done .

Regards John
www.coldeh.com

**a64pilot** · 31-05-2018, 09:32

Quote:

Originally Posted by Richard Kollmann

I still believe the only way to justify a eutectic plate is to store surplus energy from alternative energy.

John, I’m no fridge guy, I don’t have a dog in the fight. However I agree with you, any efficiency increase may wiped out by box size loss, be more efficient maybe to lose that box size with extra insulation and run a thin evaporator? Too many variables, to many what if’s.
However what you describe as storing surplus energy from alternative sources, I think that describes the vast majority of cruising boats.
My fridge compressor has been off since 10 this morning. (I know this is not the timing one would want to harvest Solar, but I don’t want to stay up all night). I’m trying to determine how long it’s logical to use the phase change of the plates to maintain box temp, and what box temp the plates will maintain, if it’s not well below freezing, then the experiment is a wash, cause no matter how much energy it would save, I can’t thaw my freezer every night

However it looks as if what Pete was describing may be possible, that is my plates may carry me through the night, or most of it anyway, and then of course my compressor runs hard all day to refreeze them and store that free “excess”energy.

Time will tell, if it works it looks like a simple timer is all I will need, to shift the off cycle to nighttime of course and keep it there. I can’t be counted on to remember to cycle the C/B

gauvins · 31-05-2018, 09:50

Quote:

Originally Posted by Richard Kollmann

I still believe the only way to justify a eutectic plate is to store surplus energy from alternative energy.

Makes sense. As a matter of fact, your very statement has made me reconsider my initial beliefs.

This being said, there is the argument that fewer compressor cycles may explain why a holding plate is more efficient. And there is apparently data to support this notion.

OTOH, I've read here and there that holding plates vs evaporator made no noticeable difference in energy consumption.

As of now, my thinking is that the logic of holding plates is anchored in two core ideas. (1) One is thermal mass. It can be duplicated at little cost by putting water, salt water, or some solution, depending on your intent, in an evaporator-based ice box. (2) The other is the compressor's efficiency. Evaporator systems cycle frequently, irrespective of how much "excess" energy there is. Holding plate systems may be better able to use excess energy, but that crucially depends on the logic of the system. I've bet that ISEC is a good way to negotiate energy supply and thermal needs. Their claim of 35% gains in efficiency is close to what I'd have expected from a holding plate system.

Last, the deal-breaker in our case was the inability to get such system to work, temperature-wise. In a small box, even a small holding plate is "too cold" to act as a refrigerator.

Anyways, was great to learn about this.

---

maybe one more thing. Most discussions are about large enclosures (7+ CF) where the challenge is to get enough refrigeration capacity. I don't remember reading that one can install "too much" cooling power. I remember reading that one has to match the evaporator size to... and I assumed that it meant the compressor. I still don't know if an evaporator system capable of handling a 7CF enclosure can be used in a 2CF enclosure (with a compressor running less frequently at lower speed). Or, to put it differently, which system will be more efficient : a big system running below capacity, vs a small system running at capacity.