Improvements & Upgrades to the FIGJAM bucket evap. cooler

[MaxBruno]

• Great build quality!
• The upper-evap/lower-reservoir bucket (container) layout is known and proven on the playa, providing both a
• Also watch for sealing the lower/reservoir bucket so you're not sucking hot dusty air through the lower reservoir, or through any air leaks between the upper bucket sitting on the lower, up into the middle of the upper bucket, where it has bypassed the evap-media and goes into your accommodations. Any leakage limits efficiency while allowing some dust to sneak through.
• And I can't tell from the photo if the drain fitting sits up high enough in the upper bucket to ensure a minimum water level to keep the bottom of the evap-media submerged to prevent hot air sneaking under. In some setups, the bottom surface can sag, or not entirely level, and there's insufficient water level in the upper/evap bucket.
• The drain hole looks like it should be a larger diameter, in case something manages to clog it. Particularly as the pump line runs up through it.
• A second fail-safe drain hole would be a good idea. Intake slightly higher (a half inch?) than the main one, and wide enough to take the entire drain-back. It would only drain water if the first drain somehow clogs or is restricted and the water level in the evap-bucket rises. As such, don't plumb the fail-safe drain with a drain pipe, but let any water that drains through it fall into the reservoir bucket, making noise, to alert you that the first drain has developed an issue.

[*]Shame you can't get more hole area going into the bucket. That's quite a restriction to pull air through.
[*]If you got more pre-filter area and more area for air flow into the upper bucket, you wouldn't need such a heavy and power consuming fan.
[*]Your design does have a thermal short-circuit.

• Hot air through the pre-filters flows against the metal fan shroud, inside of which is the chilled output air.
  As hot air going one way and chilled going the other, that counter-flow would be optimum for transferring heat from that hot air into the evap output, but it's even worse as the stack of pre-filters is supplying hot air along the full height of the shroud.
• This thermal short-circuit will limit the chilling capacity.
• It will be worse the hotter the playa air is, as the heat transfer through the shroud into the chilled air will be greater with a greater temperature difference.
• Any insulation you can apply to the shroud surface, ideally on both sides, will work towards minimizing that thermal short-circuit.

[*]A caution that the fan you chose is not for creating air flow, and particularly not for creating static pressure for sucking air through filters, but is for augmenting an already pressured air flow that has a long run. As such, the motor will be working harder than it is designed for, so its life will be reduced from its normal service. BUT, you're only running it for a week at a time on the playa - so how much will that matter...
[/list]

I've not seen anyone want to fill their playa accommodation full of hot dust-free air. But if anyone wants to do that, and is willing to pay for the air filters and replacing them, it looks like it will work. It would be useful during those times where the ambient air is not too hot.

Nor do the recommended Dura-cool evap media have an issue with fouling, as that is what filters the dust out of the air, with the water flow washing the dust off of the filter. It doesn't become foul. Your pre-filters "solve" a problem that doesn't exist. And if the "grain" of the evap media is respected, there is no need to 'cage' the evap media, at least at the CFMs used in the existing designs.

For cooling their accommodation on the playa, needing air filters, a power taking fan and 120 VAC power to run it, won't be regarded as an improvement by many people. The upper/lower buckets is a great enhancement (I like it), but most people don't want that complexity. If you want a fan upgrade, you can use the Endless Breeze fan, but good luck sucking through those automotive filters. You'd have much better luck with pleated furnace filters.

The bad news

That writeup will not be usable by the majority of people.

What would be very useful is to have the photos surrounded by white space, with all components labelled and with their size given. The layout is so simple that people would easily be able to build one if they had that info and a few pointers added to the white space around the photos.

Thanks for your feedback! To clarify, this worked flawlessly last year, so I consider the design validated. You raise good points, which I had taken into consideration:

• Yes, do pay attention to "static head" when pump shopping, given that it needs to lift water some 30" inches.
• There is gasket sealing drain to bottom bucket.
• Drain is made of PVC electrical box adapter, with threads raised into evap sump enough to form shallow pool in which media sits.
• Drain could be made larger, though I tested with pump running full-out and it was able to keep up as is.
• Thanks to filters, there was zero junk in water at end of full week; buckets and Duracool pads were spotlessly clean.
• The 20 7/8" holes have nearly the same area as 4" duct, which is itself not close to taxed at this airflow.
• Fan is overkill, admittedly. However, a close-vaned design of this type is needed to overcome static pressure, and this is also one of few that's both quiet and fits within footprint of bucket stack.
• Yes, steel fan housing does reduce efficiency slightly, but contact is brief and I was seeing 20F reduction regardless. Spraying/wrapping with foam might net another... degree? Less? Fantech fans use plastic housings, but forget why I favored Vortex. Pretty sure I had a good reason.
• The fan is used 24/7 in grow operations, often with long duct runs. It's bulletproof and barely breaking a sweat here. I run it at a fraction of top speed.
• I reduced or stopped water flow during evening when cooling not needed. Pressurized with clean air at all times, my tent was absolutely dust-free and my lungs as well. That's the greatest benefit!
• The caging of the media is required to hold it a uniform distance from the outside of the bucket, for greatest air flow over/though entire surface area.
• At just under 100W, this may not be ideal for those running on battery, or small solar. Although, even a small inverter will power it with ease, albeit with attendant efficiency loss.
• I didn't want to increase stack footprint or (transporting from/to NYC) compromise portability; furnace filters are inconsistent with this design goal, and I suspect they're more porous as well. Regardless, these three filters flowed amazingly well, even at week's end. I could likely get by with only two.

Is writeup not usable to many because they're put off by reading? Language barrier? I can type faster than I can illustrate.
But I'll consider your suggestion. A camp mate is preparing to replicate my design from my guide, so I'm expecting some constructive feedback as he goes.

[LowePro]

What do you use to power this? thanks

[MaxBruno]

What do you use to power this? thanks

Was that addressed to me? My fan and pump are 120V AC, about 100W together. A small generator or 12V inverter would do the job with ease (my camp has a generator).

[Sporkster]

Non-Engineer here: Does using a 7 or 10 gallon bucket (similar circumference as 5 gal) and scaling the height of the filters up (same thickness) and using a pump with a higher head height work, or are there other physics to consider. Asking for a friend.

[FIGJAM]

That will work fine.

[Popeye]

What do you use to power this? thanks

Was that addressed to me? My fan and pump are 120V AC, about 100W together. A small generator or 12V inverter would do the job with ease (my camp has a generator).

If you are using 120V with a submersible pump it would be a very good idea to use a ground fault plug.

[bonezo]

I'm interested in adapting some of the good stuff from this to enhance something closer to a regular-old figjam cooler -- in particular, the air filters!

If you were to simply layer some filter around the standard figjam intake holes, would this work? would it impede intake too much / require a larger fan? i imagine you'd need some kind of loose coarse filter and then maybe a relatively tighter cheesecloth?

[LowePro]

You don't need any additional air filters.
The damp blue pad itself acts as a dust filter and cooling surface. The FJ design is simple and efficient as is.

[FIGJAM]

That's why I'm still sticky after all these years!

[willyd]

Not claiming an improvement, but I am curious about an element of the design.

Is there an advantage to having a full rigid she'll around the entire height of the evap "cartridge", or can you have it freestanding up into the air with the fan sitting on top?

Like this:


It seems like this will allow freer airflow, but I'm sure there could be other factors I'm overlooking.

Also, has anyone explored the impact of pad thickness and at what point the airflow restriction outweighs the additional cooling?

[FIGJAM]

The pad is so breathable you could do many layers without restricting airflow.

Just have to figure out how to keep ALL those layers wet.

[MaxBruno]

You don't need any additional air filters.
The damp blue pad itself acts as a dust filter and cooling surface. The FJ design is simple and efficient as is.

The FJ design is indeed simple and brilliant. But the paper automotive filters trap far finer dust than furnace filters or the evap media alone, and the evap media won't capture nearly as much dust when not wet (i.e. at night when cooling not desired but a tent pressurized with clean air still is).

I just spent 10 minutes blasting my filters with compressed air for reuse this year. The clouds of dust were a potent visual reminder of what would otherwise have been lining my lungs.

[Kenshiro]

It’s interesting reading through all this and seeing a lot of posts that consider “improvements” to mostly focus on larger volume with little consideration of much else (energy expenditure etc). I think the better title for a thread such as this might have been “application-specific modifications to...”. The standard FJ bucket is really good within the context it’s specifically designed for.

It seems I’m interested in doing the opposite of what many others may be looking for. I’m just thinking for personal cooling in my double-wide sleeping bag only. If everything in my Shiftpod is unaffected by the heat and all I care about is daytime sleep and minimizing water consumption is a priority, then why cool the whole damn tent? So I’m actually considering making a smaller cooler that takes up even less room than the standard 5-gallon bucket.

[Token]

It’s interesting reading through all this and seeing a lot of posts that consider “improvements” to mostly focus on larger volume with little consideration of much else (energy expenditure etc). I think the better title for a thread such as this might have been “application-specific modifications to...”. The standard FJ bucket is really good within the context it’s specifically designed for.

It seems I’m interested in doing the opposite of what many others may be looking for. I’m just thinking for personal cooling in my double-wide sleeping bag only. If everything in my Shiftpod is unaffected by the heat and all I care about is daytime sleep and minimizing water consumption is a priority, then why cool the whole damn tent? So I’m actually considering making a smaller cooler that takes up even less room than the standard 5-gallon bucket.

That’s an interesting approach.

Based on a 2000 calorie consumption, us bipeds tend to release ~ 100W of heat, on average.

Might be more or less during sleep but that’s a good number to work with.

So the question would be how much phase change cooling is needed to sink out 100W from a well insulated environment.

100W is ~ 24 Calories per second.

H2O phase change is ~ 500 Calories per gram.

So a gram of water needs to evaporate every 4 seconds or so.

15g per minute.
900g per hour.

A gallon should give you a nice cold nap for ~ 4 hours.

Now, I’m guessing that removing heat at the same rate it’s produced by a body would be mighty cold.

Anyways, fun science stuff for sure. Wonder if there is a turnkey system for liquid cooled race suits or somesuch that can be used to test this.

I have those ice-water pumps they give you after bone and joint surgery ... lots of different pads and wraps for that. Could be some toys to play with ...

[Kenshiro]

I have those ice-water pumps they give you after bone and joint surgery ... lots of different pads and wraps for that. Could be some toys to play with ...

That would be a lot of potential fun. I actually decided to get one of those temp-actuated switches you can find online so presumably I’d just find whatever happy medium that lets me sleep comfortably. I’d like to hope I can get away with using a lot less than a gallon per day just for this purpose.

[Canoe]

... I’m just thinking for personal cooling in my double-wide sleeping bag only. If everything in my Shiftpod is unaffected by the heat and all I care about is daytime sleep and minimizing water consumption is a priority, then why cool the whole damn tent? So I’m actually considering making a smaller cooler that takes up even less room than the standard 5-gallon bucket.

(well, this is a lot longer than I thought it would be...)

• I trust you realize, but to be clear to others reading after you, an evapcooler needs to intake air from outside the shelter, process it and release it into the shelter, with a shelter-exhaust to let the air already in the shelter be pushed out. Running one cycling the air around inside the shelter will run until the humidity rises and, well, no evap.
• A well insulated shelter isn't a ten-day freezer-cooler. While it's rate of heat absorption is greatly reduced, it will absorb heat. Freezer-coolers have ice, dry ice or refrigeration of some sort. Your body heat AND that heat gain have to be addressed inside your shelter.
• Shade stops the direct sun's radiation, and barriers to the side block IR from sun-baked objects, like the ground. Shading the ground for two to three feet around a shelter also lets the playa under the shelter avoid getting heated and transferring heat inside.
• Things to get the heat gain down, so your shelter needs less cooling.
  .
  Also,
• In the heat of the day, a swampcooler on the playa should be giving you air with a 30+F drop (~33F) in temperature. If you're routing that air into your sleeping bag, as others sitting directly in the output of a properly designed/made evapcooler have found, you may find you suffer the same effect some people get with being in the output flow of an A/C or that it's plain too damn cold.
• That cool is what helps absorb the heat from the various sources, and the greater the temp difference the greater and faster that heat transfer/absorption. A swampcooler with a -25F or -20F drop output in playa heat is somehow defective, pretty much a fail; it will have to run longer, if not continuously, with more electrical use, and will only work for a much smaller shelter than someone expected it to.
• And there's a lot to be said for having that -30+F air mixing some with a larger air volume. A larger air volume is more stable. A temperature sensor in your sleeping bag controlling the swampcooler turning on/off may turn out like the guy who was scared of the dark. He installed a Clap-on/Clap-off in his home so he could turn the lights on before he stepped inside. Only he arrived home, clapped and entered, only to surprise a burglar, who clapped to turn the lights off. Neighbours described the scene with both of them running around the front-room, each alternating clapping to turn the lights on or off.
  Sleeping bag(s) are just too small. You could build a tent over them and dump the air into that, but you've already got a shiftpod. Unless you've got a lot of heat-gain that has hot air collecting above or a hot roof radiating heat down at you, you only need to have cool air in the shelter that's as high as you are for its cooling effect - see the next point.
• Mixing does not mean direct the air up to mix with the hotter air above. Just aim it out sideways, to mix with the lower air, so that now cooler displaces the hotter air above it.
• Having a tiny water reservoir may matter.
  * One interesting thing noticed about swampcoolers used on the playa, is that many upon start put out a smaller temperature drop, but after running a while - which also corresponds with the reservoir getting chilled from the excess water flow over the pads - results in reaching the 30+F drop. This strongly suggests that the pads are initially acting as a stage 1 evapcooler (that's not reaching the full evap chilling potential of the intake air), but once the water is chilled, we're seeing dual stage chilling effects - pre-chilling also occurring in the pad.
  * So a tiny reservoir will chill down sooner, but may get its chill depleted sooner, losing the dual effect/benefit. * A dual container, like the dual-bucket bucket-coolers, in addition to using the maximum amount of the pads (no high reservoir water covering the lower pad area, just a tiny depth to prevent airflow under the pad), can take more advantage of this by having the return from the upper bucket (with irrigated pad) go into a sub-container in the lower bucket/reservoir that the pump sits in. Holes in that sub-container ensures all of the reservoir volume is available to the pump, but the chillest water (that just returned from the pads) is around the pump to go to irrigate the pads, to maximize pre-chilling and to get that benefit soonest.
  * This also suggests that a swampcooler sitting outside a structure would benefit from having an insulated reservoir.
• One of the great things about a swampcooler, at least with adequately irrigated the duracool pads, is that the dust and even PM2.5 are filtered out. Let that air fill the space around your head, not picking up the dust you brought into your sleeping bag.
• And, last but not least. A swampcooler fills your shelter with cooled moist FRESH air. Do you really want to breath the swampcooler's air after it's been post-filtered by the sleeping bag's contents that's been touring all around the playa...

I can't think of any more curves to throw at you right now.

[FIGJAM]

Well, A big part of evap cooling is moving enough air to get a result.

Testing many fans has shown that that the 190cfm was pretty much the low end to get a satisfactory result.

My very first used a 105cfm and the whole cooler used less than 1 amp to power, but wasn't affective more than a foot from the outflow.

The fan determines the water consumption, and the 190cfm WILL use 2 gallons every 5 hours. (depending on outside humidity)

[Token]

Well, A big part of evap cooling is moving enough air to get a result.

Testing many fans has shown that that the 190cfm was pretty much the low end to get a satisfactory result.

My very first used a 105cfm and the whole cooler used less than 1 amp to power, but wasn't affective more than a foot from the outflow.

The fan determines the water consumption, and the 190cfm WILL use 2 gallons every 5 hours. (depending on outside humidity)

Would be interesting to measure the tachometer output and figure where on the pressure vs. volume graph the big Delta fan lands on a well tuned setup.

[Canoe]

Would be interesting to measure the tachometer output and figure where on the pressure vs. volume graph the big Delta fan lands on a well tuned setup.

And then the same for the fan models that:

• have similar static pressure but higher CFM,
• have similar CFM but higher static pressure,
• have both higher static pressure and CFM.

It's a little hard to have something cheap that logs wet-bulb temps, but for all fans above, and the Endless Breeze speeds for its DIY swamp-cooler models, I'd love to see:

• air temps for pre-pad, post-pad and at the end of any ducting to the inside
• RH at those same spots
• water temps pre-pad and next to the pump intake
• fan RPM
• I don't know if there's a cheap pressure sensor so there could be one at each of: pre-pad, post-pad, post-fan.

Then graph them from startup on a hot dry day.
With correct irrigation and airflow dwell, Dial/Duracool pads are 95% efficient and should see around a 33.1 F drop at 95 F & 10 % RH, and around a 29.8 F drop with 95 F and 15 % RH (Aspen media is limited to 85% efficiency for some reason). With some pre-chill in play, one could get output drop temps greater than those. Even approaching what 100% efficient would give as more pre-chill occurs, as the 95 % efficient limited evap stage is doing less of the chilling.

Here's a neat formula for getting wet-bulb from dry-bulb and RH.
.

T wetbulb from T drybulb and RH.png

[Token]

Well I was gonna use the tachometer and spec graph to derive the pressure drop ... keeps things allot simpler ...


... but if you got the gear ...



I miss having a big lab full of acquisition gear and sensors ...

[Canoe]

Well I was gonna use the tachometer and spec graph to derive the pressure drop ... keeps things allot simpler ...
... but if you got the gear ...

I miss having a big lab full of acquisition gear and sensors ...

If the specs are accurate. And the tolerances good.

A Rasp Pi Zero should do the job. Most of the sensors are cheap or relatively cheap.
So many things to do.

[Kenshiro]

Thank you for the wealth of thought! I do have a half dozen burns under my belt and some background in thermodynamics, so I wasn’t flying blind, and most of what you went over I have been keeping in consideration as I go. You managed to mention a couple factors I definitely find useful and appreciate though.

Regarding the switch, much like a home thermostat it does have a window of operation where, for example, it can be set to turn on when the temp rises to say 80 degrees, then turn off when it reaches 75. So no worries about switch bounce.

As far as the playa dust etc is concerned, I wipe myself down every night (and/or shower), so things are pretty clean. So the bag (and myself) are quite clean every night. Even so, my head will remain outside the sleeping bag as I sleep. Or so I intend as of now at least.

I’m not thinking of going too ridiculously small with my reservoir, but for my little Nissan Juke that is already near capacity every drive out, that cylindrical 5 gallon bucket takes up a lot of real estate. Even a chop down to a 2-3 gallon bucket would be a tremendous boon.

[Canoe]

Thank you for the wealth of thought! I do have a half dozen burns under my belt and some background in thermodynamics, ...

It's always fun writing something that you hope won't get misinterpreted by someone coming along it later, but hasn't read enough and builds a disaster. The number of people who thought they were improving things, then wondering why then get low flow, dust, a reduced/small temp drop or no temp drop on the playa...

I look forward to you reporting what you build and how it works out.

... Regarding the switch, much like a home thermostat it does have a window of operation where, for example, it can be set to turn on when the temp rises to say 80 degrees, then turn off when it reaches 75. So no worries about switch bounce...

While there's some thermal mass in the switch/sensor that will slow it's response some, I'm thinking that the air volume inside the sleeping bags is so small that the inrush of chilled air (and the air inside the bags quickly warming with its absence), will result in rapid on/off decisions, even with a wide hysteresis setting. It appears that width is adjustable in that switch?

I'd be considering having a variable speed control for the fan, to try and match the airflow to meet the required heat removal. I got a buck/boost converter from Hong Kong on ebay ($2.34, delivered, parts here would cost over $50), that would be an electrically efficient way of varying some VDC.

I still think you're going to end up with some very uncomfortable chilling in spots within the bag, even if you ran an uncrushable tube down the length of the bag with multiple outlet holes, sized smaller to larger so you get somewhat even airflow distributed down the length of the bag. A tube on each side?
Hmmm. I wonder if such a bag cooling product has ever been made. Google might show you what did the job well or issues a product may have had that you can build a solution to.

And with hot air rises and cool air falls, you might have better luck with chilling within a encircling "city wall" around your sleeping bags, with the chilled air flowing into it, displacing warmed air that flows over the wall into the rest of the pod. You'd have a much smaller volume than chilling the whole pod ) to chill for you to be comfortable, and you'd have some tempering of the chilled air, so you're more likely to be comfortable rather than intermittently warm, then cold.
In an RV, I had luck with building that wall out of Reflectix and foil tape, but that was what I had available that I could build with.
Then on the cold nights, that encircling wall got a Reflectix roof! Yes!

[Kenshiro]

Oh...another thing I forgot to mention, my sleeping bag is a double-wide. Which doesn’t wipe out the concerns you’re mentioning but there’s actually some room to buffer, etc, to mitigate the potential for hysteresis-like fluctuations, etc. It will definitely still be a bit of fiddling about, and whether or not I even have time to make a smaller cooler vs the 5-gallon bucket I already have is in question, as this idea only occurred to me a couple days ago, while I’m still hurrying a number of other little pet projects as it is.

[dragonpilot]

I've been using my Figjam cooler for about 5 years now...or whenever he started the thread. It has never worked well at all, but like a moth to a flame, I just can't stop using it...thinking "THIS will be the year it performs as advertised!"

[Canoe]

I've been using my Figjam cooler for about 5 years now...or whenever he started the thread. It has never worked well at all, but like a moth to a flame, I just can't stop using it...thinking "THIS will be the year it performs as advertised!"

So go over to the DIY cooler thread, list your parts and post your photos so we can diagnose what's going wrong. On a hot dry day, it should be putting out a 30+F drop. There's a number of ways you can shoot yourself in the foot. Let's find yours!

[Token]

On a hot dry day, it should be putting out a 30+F drop. There's a number of ways you can shoot yourself in the foot. Let's find yours!

And that there is a number that sets all kinds of wrong expectations...

Yeah, if you stick your Fluke thermocouples on the hot intake and cool exhaust and take readings ... bingo 30f delta! Victory!

Then someone shoved it into an RV window and the thermal mass is all outa whack so it ends up doing squat unless you duct it straight into your shorts.

Expectations do need to be set for the capability of the thing, and that math might be simple for us gearheads that know about the 2260 joules per gram of enthalpy in phase change ...

... but for the vast masses, it’s just a broke air conditioner and nothing like their house/apartment cooling.

A better value of comparison:

A typical 1-ton AC is ~ 4000Wh.

A bucket cooler running a liter of water per hour is ~ 500Wh.

There is a mismatch in scale here.

[FIGJAM]

Of course it doesn't work.

It's the longest running prank on the playa!!!

[Token]

Of course it doesn't work.

It's the longest running prank on the playa!!!

And lag screws too! That’s a crazy thing as well.

[Canoe]

On a hot dry day, it should be putting out a 30+F drop. There's a number of ways you can shoot yourself in the foot. Let's find yours!

And that there is a number that sets all kinds of wrong expectations...
Yeah, if you stick your Fluke thermocouples on the hot intake and cool exhaust and take readings ... bingo 30f delta! Victory!
Then someone shoved it into an RV window and the thermal mass is all outa whack so it ends up doing squat unless you duct it straight into your shorts.
Expectations do need to be set for the capability of the thing, and that math might be simple for us gearheads that know about the 2260 joules per gram of enthalpy in phase change ...
... but for the vast masses, it’s just a broke air conditioner and nothing like their house/apartment cooling.
A better value of comparison:
A typical 1-ton AC is ~ 4000Wh.
A bucket cooler running a liter of water per hour is ~ 500Wh.
There is a mismatch in scale here.

There's a mismatch if the capacity doesn't match the need. What's the need...

> someone shoved it into an RV window and the thermal mass is all outa whack so it ends up doing squat unless you duct it straight into your shorts.
And you know comments like that also set a false expectation. You know way better than most that one has to match capabilities to needs. (Damn. No no waving tisk.tisk finger emoticon...)

All three DIY swamp-coolers as designed and described by figjam can get the 30+F drop. But each has a different max shelter volume they can cool. The drop shows if your chiller is working properly (studies show that dial/duracool pads should be able to get 95% of perfect evap chilling, aspen only 85% for some reason). You want that max evap chilling so you can reliably use each size for the shelter volume they're recommended for. You want that max drop so the air you're flowing through the shelter can absorb and remove as much heat as possible.

Someone's got a picture window facing south, or a school bus with nothing on the windows, ain't gonna work - I think you'd have to tow a trailer with a portable multi-ton unit and something to power it. Someone's put reflectix on all glass (even north against radiated IR from sun-baked ground), and the plastic roof vent covers (man those let a lot of heat in), (or in one case, someone covered the whole side and roof!), then there's a lot less heat gain, so there's a lot less heat to remove. Does that need to have a multi-ton A/C run for two minutes using a bigillion watts, or is one content to run their evap chiller for twenty minutes while they 'bask'/chill in the flow while that happens - assuming that can stand sitting in air that cool. If it's 95 F outside, you could easily be sitting in 65 F airflow, or a little cooler (-33F). Way too chill if you've been out in 95 F, and way too chill to stay in that direct flow for long.

If you've done your homework and minimized the heat gain of the shelter, you can cool it with the least.

Which is one of the things that should be checked when someone says theirs doesn't work. Are they trying to chill an RV with nothing protecting heat gain from the glass, or roof vents, etc., with a bucket cooler?
And it's simple to run multiple cheap low-power using evap coolers for an RV. Redundancy too.

From personal experience with an RV with reflectix on glass and vents - on the inside (NOT optimum), it can be quite adequate on the playa, only needing to run a/c a few times in the week for a short period. Well within evap-chilling range. Had I had the reflectix on the outside, covering glass and their frames, and more layers over the roof vent assemblies, I bet I wouldn't have ever turned the a/c on.

You know it's not magic, it's about matching.

It's like comparing the floor standing portable A/C units. You have a single hose and a dual-hose: both use the same watts, have the same chilling capacity and have the same SEER rating, so same 'official' efficiency rating for the unit. Their only difference is single vs dual hose. But in actual practice, guess which one will cool your space sooner and cooler. Which one will need to run longer for greater running cost, and generating its own running heat while doing so and adding that to the load. Which one is unhealthy regarding soil gasses, air pollution and accumulated crap in utility spaces. You know, but most people wouldn't.