The laws of thermodynamics and ice chest coolers

[aerohead]

Originally Posted by Xist

I keep seeing DIY evaporative coolers using ice and\or frozen water bottles. This one claims to be "Very smart !" https://imgur.com/gallery/hwQbkDb

It definitely is not smart and I am not sure that it is very anything. Who puts spaces before punctuation?

Savages.

This is the only version that I have seen that blows cool air straight up, instead of in the general direction of carbon-based life forms.

There is a law irrevocably decreed in the intersewers that if someone makes something, people will insult them for not spending more money on something commercially available and vaguely similar. It is also human nature to latch onto bad ideas and defend them vehemently, so there are very mixed camps with these.

Yes, they do blow cool air, for limited time and duration, and each day you need more ice, which requires refrigeration, but they are trying to show how clever they are by not using refrigeration.

Directly.

People claim that you can pick up a window unit (if you have windows that you can use) for $100. The cheapest one that I saw at Walmart.com was $125.40 with tax, 5,000 BTUs, and allegedly adequate for 150 square feet. Of course, another question is how much electricity it uses, and people make various claims there, but I think there are too many factors to satisfy easily. How large is the room, how well insulated, are there any heat sources? How many BTUs do you need to reduce the temperature, and what is the humidity. How much does electricity cost?

"Just purchase a bag of ice every day." If you can run to a gas station and be back in five minutes that is one thing, but one five-minute thing every day for ninety days? If that bag costs $1.11 and you purchase ninety, you will spend $99.90, plus travel, etc., which is 80% the cost of that window AC unit, although that may cost another $20 a month in electricity.

How do they compare?

I read that it takes 144 BTUs to melt one pound of ice. A seven-pound bag would effectively have 1,008 BTUs, compared to that 5,000 BTU unit.

One guy said showed his big cooler with six three-quart water bottles that he froze every night.

How much does that cost?

People have made claims about the cost to make ice. Allegedly it is expensive. To make seven pounds you would need ten or twelve ice cube trays. That kid was putting eighteen quarts of water in his freezer each night. This says that it costs a little over half a cent to make a pound of ice, so perhaps 4¢ per night, but that is a commercial ice machine, and the refrigeration unit creates more heat.

People claim they make these for five, ten, or twenty dollars, but often include the cooler, fan, and perhaps other things that they had lying around, but others wouldn't necessarily have for free. This guy says he spent $100 and he includes everything:

He used a 20" box fan, ran plastic tubing through the ice, and connected that to copper tubing attached to the fan. The thing is, he is trying to cool down a two-car garage, which may not be insulated. The garage door definitely isn't insulated, but it has direct sunlight, it was 100° in Southern California (queue violin music) and the sun hitting his garage door hit 150°, making his garage, where he worked, 110 - 120°.

I think there are some more important questions.

Can he avoid working during the hottest part of the day? Can he spend $60 on foam board insulation? Are the walls insulated? It cost me just over $100 to insulate a wall and a half in my mother's garage. Is he committed to the cute windows? California Civic linked $13 window film, but covering them would be even better.

Can he put something in front of the garage door, with an air gap?

I see many ways that he could spend a hundred dollars and cool his garage more effectively. To properly cool his garage he would need wall and door insulation, window film (or cover), a 4" hole in a wall, and a $600 air conditioner. The Walmart one is rated 2.8/5. The Frigidaire one at Home Depot is rated 3.8/5.

The King of Random('s sidekick Nate) improved upon Household Hacker's design and tested variations:

This guy made a $350 one that uses rechargeable batteries for tailgating in Phoenix:

People politely insisted that he did not understand physics, but claimed that it would be a waste of energy to attempt to explain them to him.

Are the thermodynamic problems limited to freezers creating heat?

*Heat is a function of inefficiency in the system,a measure of entropy.
*Typically you perform a load analysis to determine how much heat will need to be extracted to maintain a design temperature and relative humidity,based upon the design delta-T across the entire envelope, the heat transfer coefficient of all the envelope surfaces (the reciprocal of the R-Factor for all the surfaces and dead-air films),the total surface area of the entire envelope,and internal loads (Btus) from solar gain,energy-using appliances,lighting,and occupants,plus recommended hourly fresh air ventilation exchange rates,either intentional or by random infiltration.
*A psychrometric chart provides the energy content (enthalpy) in Btus of any given combination of temp and relative humidity,per cubic foot of air.
*American Society of Heating Refrigeration and Air conditioning Engineers (ASHRAE) manuals will provide historical mean average winter and summer design outdoor air conditions and everything in between for most locals in the USA,to be used in the load calculations.
They also provide thermal loads for occupants.
I suspect that it's all software driven now.
-----------------------------------------------------------------------------------
*The SEER rating provides the consumer a window into the thermal efficiency of any particular unit.The higher the SEER the less entropy,as the Munroney sticker on a car helps consumers get a feel for mpgs.