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Thermal battery for summer

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MadScientist267:
Determined to beat summer once and for all, I decided to take things learned from the fridge and the wax projects (still need to write the latter up lol) and put them together as a wieldy weapon for night when the real heat hits again.

I posted some sneak peeks on the scratch thread, but here's the rest, and a little "where it sits" muse.



About 80ea 500mL bottles, most of which currently contain soda, but will be replaced with condensate from the aircon as I drink/produce them, respectively. The box is an old 4 ft radar antenna shipping container. This works out to just over 10 gallons, and I currently have another 10 up in the "attic", 1 gallon each.

20 gallons was the settling point in terms of about what I figure is needed to do what I intend to do, but it's bulky and certainly doesn't help gas mileage, so it may very well get dialed back from there. All depends I guess on how efficient to the big picture I can make all this.  ;D

Foreground is lid showing mockup intake and fan placement.

For scale, the intake is standard dryer vent... Soda bottles are 500mL each, boosting fan is a 100mm computer box fan, counterrotating with an 80mm just above it (boosts maximum suction/pressure).

Here is the inside and outside of the lid detail... Fans are capable of a respectable flow, the resistance of the bottles and intake aren't an issue for them.

Intake outside of box...


Intake inside of box...


Discharge port and fans, outside of box...


Discharge port inside box...


Assembled detail...


And of course, the final product...


I've got a few ideas on what I'm gonna do to give efficiency a boost, namely bidirectional air flow... This has caveats that need to be dealt with... But in terms of dropping air temp (and due to construction limitations, to a lesser degree, raising in winter), before this part of the build was even complete, it had already showed signs of really helping shift the heat load in this thing at night.

I'm looking at doing a canopy type thing with the summer bed to reduce the load the box sees at night, similar to what's going on with the wax in winter (yet another side project that still needs to be officially documented methinks lol)

We'll see how things go haha but I'm determined to tame the hot months somehow once and for all without going over budget on any level... besides, adding PV is going to be interesting... there's nowhere to put it on the roof and not much viable real estate exists anywhere else, so the [upcoming] upgrade is gonna probably take the form of a "portable" rig ;D

Steve

DJ:

There is a real easy way to increase your cooling capacity and at the same time shed weight.

Freeze the water.
Frozen water has 144x the stored energy that water at 0C does. Don't matter how cold it's frozen, -5 is the same as -50, just has to have changed state, ie, be solid.  I'ts the phase change that is the key.  By freezing just one 500Ml Bottle you would have almost double the cooling capacity the other 80 non frozen bottles would have. Freeze a gallon of water and you are really ahead.

Maybe you could make up a freeze box out of peltiers or add some to one of those portable fridge freezers. Using the smaller bottles may be better than a gallon container as the smaller bottles will have more surface are allowing a faster freeze by better thermal conductivity.
 Energy Input I'm not sure as you would want to basically be able to do it in a day. If you were travelling should be no problem as you will have all the power you want basically from the alternator. Solar may be a bit different.

Critical thing is to FREEZE the water, even if a small amount because once it becomes Ice the energy value is 144X what cold water is.

MadScientist267:
I wish hehe

More than once I've kicked myself for not making the fridge more adaptable for the seasons. Unfortunately there, it's not a matter of availability of energy to be able to freeze the water, it's more about the whole thing canceling itself out. I ran tight on both space and time to find workarounds for some things toward the end of the major parts of the truck's build, and that's one of the things that paid the price.

Power budget to run the aircon is extremely tight and definitely no room for both it and the fridge, especially to work against each other... So once I determined that the fridge [considered by itself] was good and *could* do what it was designed to do, I now normally favor the environment. I rarely use it for actual perishables anyway, so no big deal.

End result, not even establishing the ice core for refrigeration, nevermind to use later for environment :-\

This is another one of those deals where I'm squeezing every last drop of what I can pull off the roof... Had I never brought aircon into the mix, I'd be between at and under budget power wise about 2/3-3/4 of the year for most of what I do. The air killed that lol.

hiker1:
Kool......    //www.youtube.com/watch?v=ITtlxjvLQis

MadScientist267:
Yeah but not solar powered, not applicable in the context of the truck, and presented in "voltage only format"... What's the intake temp?  ::)

I could bring in a bag of ice and blow air over it... for that matter I even already have the cooler... not quite the same shape but would work... I'm sure it would indeed make a notable difference, but that's not all that much better than running on genset to power the aircon...

For this to be considered "successful", the method has to get at least a fair percentage of its total energy requirements from the sun...

The volume of the space is largely the issue... I've already done this with great success (again, when viewed on its own) with the fridge project... Which does indeed use phase change to turbocharge capacity... I've managed to completely saturate the core with nothing but solar input, and it'll hold good regulation for anywhere from 5 to 7 days depending on ambient when it's disconnected from the supply...

But that's also only 5 cuft (total)... I simply don't have the means to make enough ice to "store the coolth" it takes to keep things in check in here... :-\

For winter, I exploit phase change as well with wax. Could use a doubling, but even the 1 gallon that's in play makes a huge difference when I can feed it.

I'm not even after the kind of longevity I can get out of the fridge... Just want it to hang overnight so I can sleep without murdering the batteries, similar to the wax... But that's 10% per hour in the dark, and humidity control takes a minimum of about a half hour, and if I want to do anything notable with the temp, a couple hours is usually required, at least. The wax "idles" at 9W input, wide open uses 36. The fridge uses 100 or so depending on conditions... Likewise, only a lot more of it, the aircon is between 450 and 550W (higher ambient, either or both, means higher... tack on the humidity here, makes ~august particularly difficult). I've got 800W label up top, which I net about 600 of after all is considered, even at high noon, summer solstice. This works out to only a few hours a day of aircon, with only a trickle left over for battery charging. It's a lot harder to get rid of heat than to make it... Cliche but absolutely true lol

For the record, yes peltier works for certain things, but this isn't one of them. 150W(e) worth running at a whopping 10 or 15W can keep the batteries in check. I wouldn't even be able to feel the difference, nevermind be able to freeze a useful quantity of ice, with the input I have on tap. They are similar to LED in the sense that the harder you drive them, the less efficient they get.

Hence the volume of liquid. I know it's not as efficient but brick walls are brick walls... There's no doubt this isn't an easy situation. :-\

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