Evaporate cooling?

[Franziska]

Hi,


I just had a thought about cooling a boat cabin a few degrees without an AC overnight.
It's nothing more than a thought, I am no AC expert at all.

Evaporating cooling has been used for centuries down south to cool food. Usually its a clay jar with the food inside. Than a wet cloth is put on top and the contraption is put in the shade.

Now I wonder if you could not achieve a few degrees cooling of a cabin by attaching a small waterpump and a fan outside so that say every few minutes the deck is just kept moist over the cabin.
Then let a gentle breeze evaporate the water.
This is meant as an added effect to normal fans and ventilation inside.

Would that work to some degrees? Sounds a lot more energy efficient than a mini AC. Maybe someone with know how on heat calculations can run some numbers to check?
We are not talking about an AC sized effect but say 5 degrees centigrade from ambient, which could already improve comfort level considerably.

As I said, its just a thought in the wild.

[wingless]

Yes, evaporative cooling could provide the desired results. Periodic bursts of water sprayed onto the top deck will extract internal heat.

[valhalla360]

We've toyed with the idea but it didn't really have much effect, so we quit (southeast USA)

It's actually quite effective in desert environments. Swamp coolers are common in the desert SW. Problem is as the humidity gets higher, it doesn't work very well. The problem is all the water around a cruising boat means a lot of cruising areas have moderate to high humidity.

Also, if used regularly, a constantly wet deck will grow moss/mold and become slippery. If you are at anchor, presumably, you are pumping salt water onto the deck which most people don't find desirable.

[Franziska]

Interesting, good point on the humidity level.
We would only use it at night and at anchor and only in over our masters cabin on the bridgedeck. Water can run off easily there.
Guess one could rinse of the salt built up once per day.
We'll see, we might give it a shot in its simpelest way, checking the difference it makes by chucking a bucket over the area a few times...

Originally Posted by valhalla360

We've toyed with the idea but it didn't really have much effect, so we quit (southeast USA)

It's actually quite effective in desert environments. Swamp coolers are common in the desert SW. Problem is as the humidity gets higher, it doesn't work very well. The problem is all the water around a cruising boat means a lot of cruising areas have moderate to high humidity.

Also, if used regularly, a constantly wet deck will grow moss/mold and become slippery. If you are at anchor, presumably, you are pumping salt water onto the deck which most people don't find desirable.

[jmh2002]

Lots of info online about these types of coolers. They work well within a certain range, however that range is not necessarily what you always find on a boat, ie: humid tropical environments.

They add humidity, so at a certain point the air won't accept any more useful saturation.

There are the "fan and mist" types that are even used commercially at cafes, etc, and the small portable or desktop models sold as "personal coolers".

Both work on the same general principle of evaporating water.

Here is some info from the EvaPolar site that I collated a while ago for a family member: https://evapolar.com/

Hope it helps

How does evaLIGHT work – Evapolar Help Center
https://support.evapolar.com/hc/en-u...-evaLIGHT-work



Evaporative cooling: how to not feel disappointed – Evapolar Help Center
https://support.evapolar.com/hc/en-u...l-disappointed

[Sea Beezy]

You've put visions in my head of bracketing the roof with a windshield washer kit from a car. Pump, nozzles, tubing and reservoir are not that expensive wouldn't use much power. Then it could be spritzed manually or perhaps a Raspberry Pi could be used for automation. Could even incorporate a touchscreen with programming if you wanted to get fancy with frequency or a day/night cycle.

But that's complicated. Just assign a pesticide sprayer filled with water to a deckhand. Cost $10 and beer.

Next question: how much fresh water would this require?

[SVHarmonie]

Far more effective at keeping a boat cabin cool is a shade cover. Keeping the sun off the deck is the best return on investment you can have for cooling the boat.

[valhalla360]

Originally Posted by SVHarmonie

Far more effective at keeping a boat cabin cool is a shade cover. Keeping the sun off the deck is the best return on investment you can have for cooling the boat.

Agreed!!!!

There have been times when the air/con unit couldn't keep up in direct sunlight but a boom shade made measurable difference.

[a64pilot]

A swamp cooler is great in Desert environments, in West Tx, what they called refrigerated air was so dry that it would actually cause your wood furniture to crack, so you almost had to have a “Swamp Cooler”.
However in Florida for instance they would only make your hot house, a damp hot house.
Putting Water on a boat will cool the hull, and that helps tremendously, I have put an IR temp gun on the outside and seen temps over 130 or so, and inside I’ve seen 100. Teak decks are even worse, if your deck is so hot it burns your feet, good luck on keeping the boat cool.
So that’s where shade comes in, and it doesn’t have be real expensive, we have silver fabric used for green houses I think, it’s woven and let’s air and rain through, but blocks and reflects sun real well.

[Franziska]

I would use both! :-)

Originally Posted by SVHarmonie

Far more effective at keeping a boat cabin cool is a shade cover. Keeping the sun off the deck is the best return on investment you can have for cooling the boat.

[denverd0n]

Originally Posted by valhalla360

It's actually quite effective in desert environments. Swamp coolers are common in the desert SW. Problem is as the humidity gets higher, it doesn't work very well.

This ^^^^

My uncle has a swamp cooler on his house in Phoenix. Works great. Here in Florida, though? Not so good.

It is possible, even in humid areas, to get a little bit of cooling from evaporation, but it is only a VERY little bit. Not really worth the effort.

[a64pilot]

A swamp cooler is basically a fiber mat that water is dripped onto and a fan sucks air though it.
You can buy fans for outside use that do this, I have seen them at Sun-N-Fun in Central Fl, they basically blow a fine mist when it’s real humid because the air is saturated and evaporation can’t take place.

https://www.homedepot.com/p/PORTACOO...0GA1/305962288

But, running water over a boat hull isn’t really evaporative cooling, it’s cooling because the water absorbs the heat and carries it away.

Many years ago I worked at a shop where we built and drag raced motorcycles, in the middle of Summer we would put a soaker hose on the ridge pole of the metal roof and turn it on, the temperature drop inside of the building was amazing.

[valhalla360]

Originally Posted by a64pilot

A swamp cooler is basically a fiber mat that water is dripped onto and a fan sucks air though it.
You can buy fans for outside use that do this, I have seen them at Sun-N-Fun in Central Fl, they basically blow a fine mist when it’s real humid because the air is saturated and evaporation can’t take place.

https://www.homedepot.com/p/PORTACOO...0GA1/305962288

But, running water over a boat hull isn’t really evaporative cooling, it’s cooling because the water absorbs the heat and carries it away.

Many years ago I worked at a shop where we built and drag raced motorcycles, in the middle of Summer we would put a soaker hose on the ridge pole of the metal roof and turn it on, the temperature drop inside of the building was amazing.

If you are talking about a dark colored hull (maybe a teak deck) and you are spraying 70F water onto a 130F deck in 90F weather, yes, it will have a big effect as it is just the water absorbing heat and running off the deck.

If it's the typical white fiberglass deck, in the same conditions, the deck is likely pretty close to 90F...maybe few degrees higher. The water won't be able to pick up nearly as much heat as it rolls off. To be effective, you really need significant evaporation to have an effect.

[barnakiel]

YES.


I tried, and it works.


However, I found that building a 80% acrylic 'roof' over the boat can take away at least 5 degrees centigrade too. It needs to be at least 2 ft above the boat however. Higher is better. Think draft. Make draft.



What I have tested:
- bed linen,
- thoroughly wet,

- water (fresh in our case, we are at the dock),
- cover as much area as you can.


Result:


With all cabin top and about 50% of side decks covered, after three reloads, the temperature below was down by 1 degree centigrade.


The trial lasted about 1 hour.


To keep the linen wet it is enough to keep its topmost part in a bucket. Somehow water went up the edge then down along the threads. And quite swiftly too. I think some wicking / joined vessels / gravity at work here. Not sure if all canvas works like this, though.



Cheers,
b.

[bstreep]

As others have said, swamp coolers ONLY work where the humidity is low. We live in South Texas, about 120 miles from the coast, and they are only partially effective here.


They REQUIRE a temperature above the dew point. And they will only cool to the dew point. It's simple chemistry. Coastal environments rarely have nights that don't hit the dew point - so they won't work at night. Zero possibility of success if there's dew overnight.