Coleman Stirling Power Coolers

[jedwards]

We're not supposed to talk about commercial 'stuff' (sales) in this forum. You can email or PM me for additional information.

[WJM]

Originally Posted by Rayallyn

I am looking to add something to my 27 ft. Hunter Cherubini. At present it has and icebox. I can't find prices any where on these Sterling units

Mr. Edwards posted (attached) a pricelist earlier last year (page 3 of this discussion):

http://www.cruisersforum.com/forums/...9&d=1208368606

Note that, being from April 2008, it might not be 100% up to date, not just pricewise, but also model-wise, compared to the current Twinbird overview.
(and I am not 100% sure whether the GlobalCooling overview exactly matches that of TwinBird either....but all differences seem minor, and the pricelist gives a nice indication of the different models)

Perhaps Mr. Edwards has the 2009 pricelist available too?
(PS: not sure if it matches the business/web policy of GlobalCooling and/or Twinbird, but perhaps these documents could be online there too?)
(including the two posted recently, don't believe I had seen those before online either)

[WJM]

Originally Posted by jedwards

WJM

We are working to expand our direct presence in Europe and expect to have distributors there begin offering our portables before the end of 2010. The intital products will likely be the ULT25 and SC-DF25 with others following.

Good, this range of products & technology deserves a lot better representation & media exposure than the current one....)

There are so many options with a FPSC system that I am not even sure where to begin with my answers as it is difficult to explain all of the nuances of Stirling theory in this format. For each answer I provide, you seem to have three questions.

I noticed only afterwards/recently that the indentation/line-breaks in my original posting/editing goes lost when actually shown online, which doesn't really help when reading my long ponderings....

Will try to add another line break for each alinea, maybe that helps.

If you have more questions about the technical aspects of FPSC based cooling products and systems and how they work and can be integrated into custom insulated chambers, I would be happy to discuss them with you. PM me and I will give you my contact info.

Only the SC-C925 and its variants use the CO2 thermosiphon for secondary heat transport. The FPSC itself is also available seperately and can be integrated in several ways (see attachments). We also offer units that use forced convection which have no orientation limitations (SC-JS04 and SC-JS05)

As for a eutectic based systems, A FPSC system can take advantage of phase change materials just as much as compressor based system or any cooling system for that matter. Eutectic evaporator or plate based refrigerator systems use phase change materials as an energy storage method (think ice) in order to minmize energy consumption. Most FPSC systems don't worry so much about energy consumption (it's already about half of the compressor systems in our lowest efficiency system) and don't use phase change materials except in cases where the driving energy is being extracted from sunlight and it needs to stay cold overnight with out battery backup. Probably the biggest disadvantage to eutectic systems is that you are locked into a single temperature without using a phase change material with a eutectic temperature as low as you will ever need to set the unit combined with a secondary thermal regulation circuit/fan and many people seem to prefer the ability to change the temperature of their box from freezer to refrigerator and back. A very simple alternative would be to put eutectic material inside the box. If you want a temperature right about 0degC then use blue ice if you want it warmer there are several waxes that can be used. Just match the temperature set point you are using to the phase change material. If you really want to get fancy, fill the defrost catch tray on the SC-JS04/JS05 with your eutectic and set the temperature of the system acordingly to match and voila you have a FPSC refrigeration system with eutectic backup.

First, I should note that only recently I got a full grasp on 'eutectica', in both pure physics and the thermodynamics related to (compressor) fridges.

My understanding right now is that the concept is *more* than just a 'time-shift' or 'peak-energy' holding plate, cq competing with a battery.

It allows a compressor fridge to send all it's thermal energy in a relatively *high* temperature point, instead of going below that point every on/off cycle....and this 'deep-cycling' results in a lower thermodynamic efficiency (COP, thermal energy divided by electrical energy) than at this higher steady eutectic temperature.

But: that COP-benefit of eutectica is probably less relevant for the Stirling concept/cyclus, because it's COP doesn't 'crash' at higher delta-T (and/or higher ambient temperatures).

(but even the Stirling cycle will consume more energy with higher ambient temperatures of course; it's just that you can send an almost unlimited amount of energy into the Stirling engine, and still reach the targeted box temperature (all assuming the Stirling engine is large enough....but that is exactly why I like those superduper-deepfreezers....)

That said (and hopefully understood correctly, in both directions....), in that same context of compressors/Rankin-cyclus & eutectica, probably to a lesser extend also Stirling, I have a 4th argument/theory in favor of eutectica, more than just 'time-shift' (night-silence), 'peak-energy' and 'absolute' COP:

If you run that 'timing' in reverse, cooling at night (eutectic charging), idle /discharging during the day, you have an inherently better COP and/or efficiency for both Rankin and Stirling, because the ambient air is much cooler.


And all that makes me wish for an eutectic option in the Twinbird boxes too....)

And for the true effiency bean-counters, it *should* matter to them too, squeezing out a few more percent of effiency from a fridge-constellation, in particular in the context of solar or wind energy.

Note that also only recently I read a research-report on eutectica versus battery power....seems eutectica is more efficient than batteries in the context of both volume and weight (although the subjective/emotional rating/weigh-factor of displaced food/beverage can challenge physics here....)


(note that the ideal holding plate, in particulary with evaporators/cooling elements perfectly surrounding the box/walls, also covers/surrounds each of the walls, for the same homogenous thermics (most important if you like being very close to 0C, but not freeze over your drinks (it doesn't flow well, and is annoyingly noisy at night, even if there is some fluid left among the ice-crystals....)

(this is also an aspect of boxes that is hardly mentioned by anyone, not by manufacturers, not by testers, not even by experts in their fridge-literature)

(actually, the only fridge I know that has both the evaporator and holding plate in the same ideal surrounding shape (other than a small 0-shape freezer compartment), is the Woick-modified Engel series (Woick is a German outdoor shop annex expedition outfitter)....each and any of the other brands keeps it at an U, L or even just I-shape (even some of the otherwise rather high-end Kissman boxes have I-shape elements))

Oh, before I forget, I should also mention why I came up with this 4th theory/benefit of eutectica, mostly in the earlier context of (COP-limited) compressor fridges:

My application is a deep-freezer inside one of the side cargo compartiments in an old Volvo 6x6 firefighter....since these side compartiments are covered by rolldoors, they can't be insulated....and being aluminium, with a roof also from aluminium, it gets rather hot in there in summer.

And while a regular compressor fridge, with eutectics, is happily chugging away in there, I don't trust the same location with a freezer, at least not without having the option of just sending in more power, like I can with a Stirling, instead of running into the limits of the Rankin cyclus.

As a general concept/argumentation:
After long contemplations, I considered & concluded that having 900L of water onboard (of a relatively small 6x6 vehicle), for showering in the desert, just wasn't decadent enough....I also must have icecreams on board....)

(in a more serious context I also want to have frozen pre-cooked food with me, for culinary highlights way out in the bush, especially in regions where the local kitchen is somewhat, eh, challenged)

(anyone ever travelled in Russia, far away from the main cities?....and you thought the English kitchen is a challenge?....or a restaurant service a la Fawlty Towers/John Cleese is unimaginable?....better reconsider, and prepare for something far worse than your imagination....)

(the good thing is that 20 years ago, it was even worse, much worse....)

(which challenges the imagination even more btw....8-))

Space Shuttle mission STS-60 in 1994. M223 Stirling Freezer used to provide low temperature storage for expeiments and crew rations. ONLY cooling technology approved for operation DURING launch, at least up to that time. Who knows what they have tried since.

That said, a LOT has changed over the last year or so, especially WRT pricing and availability.

I'm not sure why you are not getting a response from GCBV, but when you get my email from the above mentioned PM or from a couple of posts up, copy me to your request for info to GCBV and I will try to figure out what is going on. Since I'm not 100% sure of exactly what is allowed in this forum (Moderators: I'm just trying to help. I am not attempting to sell anything. I do not get anything like commision. In fact, it is a pain in my butt to sell to anyone but our distributors. However, if they want it and I can help, I'll give it a go but there is zero, maybe even negative, pressure), lets just say that GCBV gets their inventory from me and I ship inventory all over the world.

Good, I like transparant distribution channels & logistics....)

(even though (individual) shipping cost will probably make it inefficient to bypass any national party, assuming they order in bulk)

(if not, it might still help somewhat in the customs/VAT department....)

[jedwards]

WJM,

I have to say I really enjoy talking to 'power' consumers like yourself. ;-)

[WJM]

A few details were lost/overlooked in my ponderings:

The way I understand eutectica, in the context of this evaporation temperature (or just 'cooling' in case of Stirling), is that this higher temperature (with better COP) can only be achieved if the eutectic fluid is at least in very close contact with the evaporator, or (best) is completely surrounded by it.
(at larger distance, it would still freeze over time of course, but it would then *not* force the evaporator into this higher temperature point, and miss out on the thermodynamical efficiency)

And in that same context there seems to be another difference/variation in construction/configuration, *how/where* manufacturers mount their eutectic elements:

1) between insulation and evaporator

2) between evaporator and box-interior

Can't say I have seen #1 very often, nor am I sure whether the location is choosen with very good reason (other than constructive arguments), but just as with the overal shape of the evaporator, it should be something to check.

Theory: having the eutectic plate between insulation and evaporator means that the evaporator can still perform it's direct cooling on the interior-side, so while charging the eutectic element, it would still cool the box content, and not have the element as an isolator until it completely freezes (with blue ice for example, it would stay at 0C all the time, while a normal evaporator, in direct contact/air-flow, would have a much lower temperature.

That said: this insulation-by-eutectica is also what some/most box manufacturers use as argument why such an (upgraded) box can not achieve the same overall low temperature as the same model without eutectica (with Woick/Engel there is 2 degrees difference, -16 vs -18C)


Further, in the context of consumer attitude, for wanting to have the choice of several types of eutectica, from fridge to freezer:

The ideal eutectic element should then be replaceble, changing it instantly for the application, but still meet the 'direct-contact' requirements as mentioned above.

And having the ideal evaporator/cooling element, O-shape, completely surrounding the box, that means that the eutectic element should also have this O-shape....which almost excludes consumers fabricating & filling up their own elements.
Ideal accessory/aftermarket policy would then be to offer such elements, shape-dedicated to each box, pre-filled or with instructions what to use as fluid.

PS: yes, my grasp of eutectica also includes the matter of true eutectica like water/brine/salt-solutions vs 'just' antifreeze fluids like glycol (not having a fixed point of freezing, but a somewhat larger temperature range, before all of it freezes)....)

[jedwards]

The same thermodynamic efficiency improvements realized with the eutectic approach can also be achieved by using an active expansion valve to control evaporator superheat, without the disadvantage of a fixed evaporator temperature. EEV's and TEV's are also much less expensive than eutectic systems but the added benefit of energy storage, combined with superheat control is the primary reason for the eutectic systems being developed.

The biggest reason that eutectics help Rankine cycle systems is that, as you seem to understand, Rankine cycle systems are very inefficient at high turn-down ratios and therefore typically operate at a single speed. This, combined with the nature of the thermostatic control regime and capacity requirements needed to insure relatively small temperature swings in the system, dictate that the compressor be (sometimes grossly) oversized. By utilizing the energy storage properties of a phase change material they are better able to match compressor capacity to the average load seen by smaller systems and still keep the temperature swings, that will always result from a non-unit dutycycle, under control. Even so, you are still limited to one evaporator temperature which is likely to be too low if you refrigerate most of the time (-18 or -19 degC) and too high if you want to freeze (0 to 4 degC). Any time you operate away from the eutectic point you are relying on the sensible heat instead of the latent heat of the substance and giving up the advantage of phase change for simple thermal mass. Also, any time you are not using water (0degC) as your phase change material you are giving up efficiency as well, because as far as energy storage and recovery goes, nothing yet, can beat water/ice in the energy balance game.

Stirling systems differ, in that they don't cycle, they modulate. This allows them to provide minimal energy consumption and precision temperature control at the same time. Since there is no superheat (even in our thermosiphons) the only use for a eutectic material in our system is as an energy storage mechanism and ,yes, you can run a system with eutectics at night when grid power is available and cheap and then 'coast' during the day using little to no power or run during the day on 'free' solar power and 'coast' through the night. Which way you design is really situationally and personally dependant. Even then you are still limited to a single condition (eutectic saddle) where the avantages of using a eutectic material is maximized

[WJM]

On the issue of having to chose a singular eutectic temperature point:

While not efficient in the context of box-content usage, one could avoid/solve the dillema by having both fridge & freezing eutectica inside the box; either each one on it's own evaporator/cooling-element, or side to side on the same single unit.
And as long as the eutectic element is between insulation and evaporator/cooling element, it can still cool the box content directly (although when charging not as efficient of course).

Btw, interesting point on water/ice having the best latent heat....never read anything in that context for brine or glycol....the easiest data-point to remember for water/ice is that it stores 80 times the amount of energy needed to change the same amount of water 1 degree celcius, or 160 times for the same amount of ice (ice being twice as easy to heat as water, never knew that before either).

Are there any similar rules of thumb for brine or glycol, for both typical temperature points, or does it require some more serious juggling with calories & joules?....)
(same decline of efficiency when going in the other direction, above 0C, with wax-solutions?)

[Extemporaneous]

So should I try to build my refrigeration around this technology or what??
Someone help.

Extemp.

[jedwards]

While not necessarily a simple undertaking, the rewards can be substantial.

[tvengineer]

Wow... I had not checked this thread in a really long time....
I'm glad somebody woke up the zombie thread.. and the discussion is really interesting..

Just as a note... I am the happy owner of TWO of the coleman units..(friends got the other 4).. and I keep my eye close on Ebay for the off chance to get another one or two..
They are the best thing since refrigeration was invented!

Mine have been running 100 percent solar powered for nearly a year now..
with battery... but I have been toying with the idea of using some sort of phase change material and trying to run one on solar only with NO battery.

Even kicking around the idea of replacing the controller board with a custom circuit that would adjust the output of the Stirling unit to match the out put of the solar panel.. (like a Maximum Power Point tracker)...
but I don't want to mess with my Colemans.. they are so wonderful just as they are

I would like to buy one of the bare Stirling units from GC .. when I have some spare money.. just to have a go at using it with solar and phase change.. sort of like a "COLD BATTERY" for energy (or I suppose more accurately LACK of energy) storage..

OK. I woke the zombie thread up again... discuss amongst yourselves

[jedwards]

tvengineer,

The GOOD news is that the nature of the Free Piston Stirling Cooler (FPSC) is directly compatible with peak power tracking as the supply voltage is directly proportional to the drive voltage of the FPSC. This means that as voltage falls, so to does the maximum amplitude of the FPSC piston and therefore heat lift capacity falls to enable maximum use of available energy. The BAD news is that the Coleman has software related over and under voltage limits designed to protect a battery from discharging beyond an acceptable level and this cause an artificial shutdown and reboot of the system if the input voltage drops below about 8VDC even if the cooler itself will operate below 4VDC input. A small battery is the easiest way to insure that the voltage is locked at 12VDC but this can also be accomplished with a charge controller. We have run custom software packages on our BV25 model that have no problem operating on direct PV input with panels as small as 20W.

[S&S]

How would I set this up to have one FPSC run both a fridge and freezer?
I could see brine loops going to two differing eutetic panels with electric valves. Would that be the preferred set up?

jedwards- please PM me your contact info and we could talk about specific requirements.
Thanks
S&S

[ericb]

Originally Posted by tvengineer

Mine have been running 100 percent solar powered for nearly a year now..
with battery... but I have been toying with the idea of using some sort of phase change material and trying to run one on solar only with NO battery.

Tv-engineer, i've also got one set up with a solar panel/battery. I've noticed that 40W of panel and 15Ah battery is not enough to keep it running continuously. Could you provide some details of your set-up?

Regards, Eric.

[witzgall]

Eric;

I am going to take a guess that your battery is not large enough to handle to load overnight. If that battery is not in tip top shape, it will have less capacity to start with. If you have been regularly drawing it down close to zero, that will most likely be the case. It is a sealed motorcycle, or such battery? They are not designed for deep cycle application, which is what you are doing, on a small scale. I would want a much larger battery in there, to deal with nights, and cloudy days.

The panel may or may not be large enough, depending on orientation, where you are on the globe, etc.

If I were trying to build a system to power only a Coleman, I think I would have a 60w panel and a 55ah battery, like an Optima or other AGM.

Also , I assume you have the solar panel directly hooked up to the battery. Do you have a blocking diode between the two? If not, the panel will actually draw power away from the battery at night.

Chris


[QUOTE ericb;331508]Tv-engineer, i've also got one set up with a solar panel/battery. I've noticed that 40W of panel and 15Ah battery is not enough to keep it running continuously. Could you provide some details of your set-up?

Regards, Eric.[/QUOTE]

[ericb]

Originally Posted by witzgall

Eric;

I am going to take a guess that your battery is not large enough to handle to load overnight. If that battery is not in tip top shape, it will have less capacity to start with. If you have been regularly drawing it down close to zero, that will most likely be the case. It is a sealed motorcycle, or such battery? They are not designed for deep cycle application, which is what you are doing, on a small scale. I would want a much larger battery in there, to deal with nights, and cloudy days.

The panel may or may not be large enough, depending on orientation, where you are on the globe, etc.

If I were trying to build a system to power only a Coleman, I think I would have a 60w panel and a 55ah battery, like an Optima or other AGM.

Also , I assume you have the solar panel directly hooked up to the battery. Do you have a blocking diode between the two? If not, the panel will actually draw power away from the battery at night.

Chris

Well,I do have a cycle-battery
And yes, the panels have diodes. I have This SE-1500 from Sunsei and its predecessor SE-1200,mounted on the lid of a small luggage trailer. Actually,I started with the SE-1200 and later added the SE-1500. That's the great advantage of these panels.
The reason for this is that I use it in camping. With a tent, to be precise.
That means that I want to keep everything as small as possible and upgrade later on. When at home,the panels are used to keep the battery full all year. I don't really use the cooler then
I could add another SE-1500 and add an extra battery, i suppose.
I am really curious about the setup of TVengineer, though.

Eric