Thermal battery for summer

[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. 

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

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......   

[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.

[DBCollen]

solar thermal absorption cooling using calcium chloride and ammonia?
possible solution

[MadScientist267]

Actually I've wanted to play with that kind of thing to see how well it really might work on a few levels but that's a fun one, mostly the ammonia. I'd also need more rooftop real estate (possibly, likely) but could maybe work out something for future...? Dunno

[Pete]

If you drove the truck a bit and had a compressor on the motor you could use glycol to cool the bottles. Similar to what boaties use on their freezers. It depends on how often you drive really.
A tropical roof on the truck ( small gap above the roof with another roof above) would solve some of the problems with heat in summer, and may help a bit in winter with heat escaping. Depends again on whether you want to put a second roof on the truck.
Sounds like you have having fun with designs anyway.
Good luck
Pete

[MadScientist267]

Here's the latest update...
Performing very well so far but still doing some optimizing.



Got the paper towel "lagging" put up on the intake duct, and a couple of probes now monitoring the aircon temps.

Intend to put 3 more inside the box, one at the intake, one center, and one at the discharge, to get a better feel for the characteristics of the bottles internally.

Steve

[Pete]

Certainly appears that you are living up to your non de plume.
Good luck with staying cool.
Maybe in Summer you should camp near a lake and sleep on an airbed in the water.?

[DJ]

Maybe in Summer you should camp near a lake and sleep on an airbed in the water.?

If one were near water, it would be easy just to pump it through a condenser with a fan and have a nice cool breeze that way.

I used to manage a spare parts place in an old shop.  Was like an oven in there in summer. I got a heap of old towels, strung up some lines in the back store room and had some powerful old blower fans that came from somewhere Pushing air in through the back windows and in through the door to the shop. The difference it made was unbelievable.

Keeping the towels wet could be a chore though. On a hot low humidity day they could be near dry in 30 Min.
Another bloke came up with the idea of some Micro mist irrigation sprinklers which we put on a tap  and had spraying directly behind the fan. The towels caught any mist that didn't evaporate but that was a big improvement as well. We sure put some water through those misting nozzles over a summer!  :0)

People would walk into the place and comment how lucky we were to aircon in the place. Ya!   In the end we didn't need it.
Always expected to see things go damp and mouldy but they never did.

Wish it was as effective to heat the place in winter. Was like an icebox then.

[MadScientist267]

Yeah I use misting occasionally to help load the evap coil on the aircon once the air has dried out inside... And can attest it makes a difference. The trick is like you said, keeping things wet but not too wet and of course only the things that can tolerate the repeated spritzing (rags, non-porous surfaces, etc)... and then of course allowing the aircon to completely dry everything back out before it gets shut back down... otherwise the humidity spike will just turn around and get you again lol

[Pete]

Hi Steve, well it seems that you home made air con worked pretty well. In Australia we used to have things that were called "Coolgardie Safes".
Basically a metal perforated box, with a tray at the top and a tray at the bottom. The top tray was filled with water and had hessian cloth in it that hung over the sides of the box. Worked in the same way as your evaporative cooler.
I have also heard of folk putting wire mesh up around their verandahs, and putting charcoal in between two layers of mesh and dripping water through the charcoal to create evaporative coolers .
It gets pretty hot in the centre of OZ.
Good luck staying cool
Pete

[MadScientist267]

It's starting to get clearer the best way for me to use this thing...



I've tried "holding back" and keeping a smaller area cooler by allowing the air to stratify but it just doesn't really have the capacity to do that like I would really like... The humidity here counters it and once it's built up, while it may still be providing cooler air than what went in, it isn't enough to make things comfy.

Alternate approach is to let it immediately take the residual heat as the sun goes down... leaves it basically done for but the ceiling fan can keep regulation pretty well from there with its help.

The downside to all this is it's still seeking the mean... which is still only rising... and after the 21st, "is only gonna get worse"... I've got to angle getting humidity under control if I'm gonna beat this.

The box serves well enough in the temp department, but has between zero and nil capacity to do anything about moisture. I find myself intrigued by liquid desiccants for some reason, but I don't think that'll be practical at this particular point for this. Larger scale and I'd be looking into it... so only one other thing came back into mind as once again viable... Peltier.

Little more than a passive cold plate (pronounced massive heatsink) with a small stirring fan on the cold side to encourage condensation... Battery box cooling system has demonstrated that it doesn't take much input to get non trivial amounts of water out of the air... Not saying it would be universe bending performance, but may be enough to take a good bit of edge off at night. It's real prowess being that it can be controlled continuously variable, unlike the aircon compressor... So maybe. It wouldn't be worth two squirts for "cooling, cooling"... but humidity patrol? Quite possibly indeed.

LOL Still testing and experimenting... I get a bit closer to winning over summer each year I get to mess with it lol. Winter is beat. Summer ain't far behind if I got anything to say about it.

[MadScientist267]

Something to show a little better dynamic... I'll update this with a followup that shows the next chunk in time... but for now, I know it may not necessarily be obvious to anyone else (I need to hunt down comparable conditions before the box got involved)... but I definitely see and can feel the effects of it being there.

This shows how it handles a "shift" of internal heat (left side), and the dynamics of the aircon fighting day heat (right side) and the role the water plays in it. The "slack cooling" this morning, about center graph, was due to the water box fan not being on at the time, reducing it's efficiency.