Is there any way to cool a cabin using the river water?

In other words, energy efficient AC that isn’t compressor based. Like evaporative but without the wet air into cabin? Our river is never over 75° so I’m just curious if that could be used to cool a stateroom at night.

Is that 75 Centigrade or Fahrenheit. ?

You wouldn't be comfortable with 75 degree water circulating through a fan/coil unit.

To be comfortable at say 75 degrees you need about 60 degree air from the fan/coil unit and you need a compressor to pump the heat from the 60 degree fan/coil temperature to the 75 degree fresh water condensing unit temperature.

The only non compressor way I know to do this is with a Peltier effect solid state cooling system and they are very inefficient.

David

One key to air conditioning in humid climate (practically all marine environments) is the ability of the cooling coil to condense moisture from the air blowing over it. For this to occur, the temperature needs to drop below the dew point, this is pressure dependent but around 60 degrees, you won't get air below that with 60 degree water in the coil. You really want the coil temp 40 or less to cool the air adequately. This is one reason why hydronic cooling systems struggle to work well.

During the day the sun beats down and warms the structure of the whole vessel, but mostly the deck .

A pump to hose down the surface that is ez to soak , and cool helps a great deal .

If the boat has solid GRP below the waterline , either pulling up a couple of floor boards , or using a small computer fan to allow the boat to fill with water temperature air from the bilge is a big help.

Greetings,
Mr. IR. "Is that 75 Centigrade or Fahrenheit. ?" Unfortunately, the US is stuck in the 19th century and hasn't grasped SI units yet or they don't admit to it. Pounds, feet, miles/hrs etc. is their MO. Yet, ask most anyone what the size of the engine is in their car and it's X.X liters....
On the other hand, any body of water at 75C would almost be hot enough to boil a duck.

RT Firefly said:

Greetings,
Mr. IR. "Is that 75 Centigrade or Fahrenheit. ?" Unfortunately, the US is stuck in the 19th century and hasn't grasped SI units yet or they don't admit to it. Pounds, feet, miles/hrs etc. is their MO. Yet, ask most anyone what the size of the engine is in their car and it's X.X liters....
On the other hand, any body of water at 75C would almost be hot enough to boil a duck.

Click to expand...

Come now, the US is not alone, Liberia and Myanmar still use the English system.

Greetings,
Mr. rj.

Sea Word said:

In other words, energy efficient AC that isn’t compressor based. Like evaporative but without the wet air into cabin? Our river is never over 75° so I’m just curious if that could be used to cool a stateroom at night.

Click to expand...

In a word: no.

Evaporative cooling will only function if the air is dry enough to be able to evaporate lots of water. The cooling is a function of what's referred to as latent heat of vaporization. The water absorbs heat in order to change state from liquid to vapor. That's not happening on the water where the air temps are 80F + and RH is 90%. Physics just don't support evaporation.



If you want cooling, you'll need to involve some mechanical advantage. Current technology dictates some sort of refrigeration where mechanical action is converted to heat absorption.

rjwilliams11741 said:

Come now, the US is not alone, Liberia and Myanmar still use the English system.

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Real men use degrees Kelvin. Or joules, ergs and dynes. Or Newtons or kilo pascals. Interestingly, degrees F works far better for thermostat control than C, for me anyway. Smaller increments.

Sure hope the politicians don't insist that latitude and longitude go metric. What would we do without the knot or nm?

sunchaser said:

Sure hope the politicians don't insist that latitude and longitude go metric. What would we do without the knot or nm?

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Already there:

"The French originated the meter in the 1790s as one/ten-millionth of the distance from the equator to the north pole along a meridian through Paris. It is realistically represented by the distance between two marks on an iron bar kept in Paris."

A dehumidifier will make the cabin much more comfortable, and use a fraction of the energy of an A/C unit. It can be run on batteries.

Continuing the hijack though, I have a hard time seeing the point (or the difference) in the metric system. They have only one unit of length, the Imperial system has several to choose from. If you like using just one, then use just one. Milliiches, kiloinches, megainches. A mile is 63.3 kiloinches. I like cables myself. My boat is 0.057 cables long. 57 millicables. That's pretty short, so my marina bill ought to be very small. It displaces only 1400 stones, so my haul out bill should be less than if if displaced 89000 Newtons.

koliver said:

Already there:

"The French originated the meter in the 1790s as one/ten-millionth of the distance from the equator to the north pole along a meridian through Paris. It is realistically represented by the distance between two marks on an iron bar kept in Paris."

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Yes, apart from a few recalcitrant holdouts the world is mostly metric. Of course we are not really there yet, and still stuck with things like 360° circles. Would it not be better to have 400 instead? The French tried with grads (grade, gradian) but lost out to those confounded English.
https://en.wikipedia.org/wiki/Gradian

I had to lodge in application in Paris using grads once. Almost drove our draftsman nuts because of the particular location.

DDW said:

A dehumidifier will make the cabin much more comfortable, and use a fraction of the energy of an A/C unit. It can be run on batteries.

Click to expand...

I thought a dehumidifier was just an air conditioner with the evaporator in line with the condenser; in other words, it cools and dries the air, then puts the heat right back into it on the way out. I suppose a smaller compressor will use less energy, so there is that benefit. And it's true that hot, dry air feels much better than hot, humid air.

DDW said:

Continuing the hijack though, I have a hard time seeing the point (or the difference) in the metric system.

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I have to agree with you on this one. Note that the number systems used with computers are all based on powers of two; eight, 16, 32, 64, 128, etc.

Now consider the way US measurements work. A gallon is two half-gallons, four quarts, eight pints, 16 cups.

It's always far easier to double, quadruple, quarter or half a measurement in the US system. This base ten crap works great for adding or subtracting using your fingers, or manipulate decimal places on paper, but it's not intuitive. What's a half-meter? Quarter-meter? Eighth of a meter?

Running a dehumidifier will add a surprising amount of heat to the cabin and still require more power than most battery banks could maintain.

Greetings,
Mr. CT et al. "...but it's not intuitive. What's a half-meter?..." It's no less intuitive than the Imperial system. 1/2 meter is 50cm or 500mm.


The bottom line for those who had to learn the Imperial measurement system by rote is SI is new and different to them.

I went to school in the 50's and had to learn the 5,280'or 1760 yds in a mile, 160oz in a gallon, 40oz in a quart etc. When I started my professional career, everything was metric. Kg, degrees C, liters etc.

Sea Word said:

In other words, energy efficient AC that isn’t compressor based. Like evaporative but without the wet air into cabin? Our river is never over 75° so I’m just curious if that could be used to cool a stateroom at night.

Click to expand...

A system like this would basically be a geothermal heat pump. They work great for heating and air conditioning and are far more energy efficient than conventional HVAC. However, with a water temp of 75, I think you could only use it for heating. Groundwater used for cooling is typically much cooler than 75. Then again I have no idea what I am talking about so it might be worth asking an expert in heat pumps.

koliver said:

Already there:

"The French originated the meter in the 1790s as one/ten-millionth of the distance from the equator to the north pole along a meridian through Paris. It is realistically represented by the distance between two marks on an iron bar kept in Paris."

Click to expand...

Actually a meter is:

The Geneva Conference on Weights and Measures has defined the meter as the distance light travels, in a vacuum, in 1/299,792,458 seconds with time measured by a cesium-133 atomic clock which emits pulses of radiation at very rapid, regular intervals.

Rain Dog said:

A system like this would basically be a geothermal heat pump. They work great for heating and air conditioning and are far more energy efficient than conventional HVAC. However, with a water temp of 75, I think you could only use it for heating. Groundwater used for cooling is typically much cooler than 75. Then again I have no idea what I am talking about so it might be worth asking an expert in heat pumps.

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Ground source heat pumps (I have one) still use refrigerant cycles with a compressor, expansion valve, evaporator and condenser, they just transfer heat into or out of water rather than air. It is much more efficient and the reason marine air conditioners use sea water but there is definitely still a compressors in the system .

CaptTom said:

I thought a dehumidifier was just an air conditioner with the evaporator in line with the condenser; in other words, it cools and dries the air, then puts the heat right back into it on the way out. I suppose a smaller compressor will use less energy, so there is that benefit. And it's true that hot, dry air feels much better than hot, humid air.

Click to expand...

Gdavid said:

Running a dehumidifier will add a surprising amount of heat to the cabin and still require more power than most battery banks could maintain.

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A dehumidifier sufficient for a 40' yacht requires about 600W and yes that heat will be added to the boat. However once the moisture is out of the air, the upholstery, bedding, woodwork, etc., it will run on a short duty cycle. Mine is just now running about 15% of the time. So it's adding 90 watts, and consuming 7.5 Ah/h, maintaining 40% RH. A/C is better, and it both dehumidifies and cools, but takes way more energy than that. Idea is a small capacity A/C unit, works like a dehumidifier but dumps the heat outside.

ssobol said:

Actually a meter is:

The Geneva Conference on Weights and Measures has defined the meter as the distance light travels, in a vacuum, in 1/299,792,458 seconds with time measured by a cesium-133 atomic clock which emits pulses of radiation at very rapid, regular intervals.

Click to expand...

We can thank the French for all of this after the French revolution, 1789, they wanted to get away from the "Anciens" so pushed to get lots of modern things, their system of laws, etc, and with the scientific revolution happening, they were the ones to push for a standard measure of distance based on the physical world, instead of on Royal decree.

The yard has since 1959 officially been defined as exactly 0.9144 metre

The General Conference on Weights and Measures meets every 4 years at Sevres, just outside Paris, except for 2018 when it met at Versailles.

Actually it was Napoleon that introduced the metric system to France.
That aside, one of the systems in use on some hire boats incorporate a small radiator, a 12v pump takes water from the canal/river, a fan blows the cooled air from the radiator through a spur into the heating ducting to all cabins.

f you are going to draw water up for cooling purposes, then take it from as deep as you can. Surface water may be 75° but with a typical thermocline once you get down to,sa, 10' it will be much cooler.

Irish Rambler said:

Actually it was Napoleon that introduced the metric system to France.
That aside, one of the systems in use on some hire boats incorporate a small radiator, a 12v pump takes water from the canal/river, a fan blows the cooled air from the radiator through a spur into the heating ducting to all cabins.

Click to expand...

But does it work?

I guess that’s what I was afraid of. Oh well. Maybe I can try to pump bilge air up as bad an idea as that sounds lol.

"Maybe I can try to pump bilge air up as bad an idea as that sounds lol."

Not a bad idea since it actually works, as long as the boat is one level tall..

Its best if the bilge is clean and doesn't smell.

DDW said:

A dehumidifier sufficient for a 40' yacht requires about 600W and yes that heat will be added to the boat. However once the moisture is out of the air, the upholstery, bedding, woodwork, etc., it will run on a short duty cycle. Mine is just now running about 15% of the time. So it's adding 90 watts, and consuming 7.5 Ah/h, maintaining 40% RH. A/C is better, and it both dehumidifies and cools, but takes way more energy than that. Idea is a small capacity A/C unit, works like a dehumidifier but dumps the heat outside.

Click to expand...

To lower the humidity, you will need to keep the cabin closed up, no outside air flow to help cool the cabin, now you have devices and people in the boat generating heat and often a 1/2 ton of cast iron cooling off from 170-180 degrees, dissipating heat into the cabin. Even shaded windows are letting heat into the boat and you are doing absolutely nothing to remove heat from the environment. I don't see how this could be comfortable at all unless it is 70 degrees outside or lower to begin with. Dehumidifiers work great for protecting the boat from moisture and mold while you are away from the boat but it is always going to be hot when you enter the cabin.

I've slept often in a room of about 95-100 degrees F but which the dehumidifier brought the levels down. Certainly was not as comfortable as beautiful air conditioning, but it was bearable with a small fan blowing.

The water idea doesn't sound practical, so start with dehumidifying and see if that is adequate. The 600 watt hours quoted above is house battery-capable, as opposed to aircon drawing kilowatt hours.

FF said:

"Maybe I can try to pump bilge air up as bad an idea as that sounds lol."

Not a bad idea since it actually works, as long as the boat is one level tall..

Its best if the bilge is clean and doesn't smell.

Click to expand...

Well this is an aluminum hull also, and bullheaded from the rear where the smelly stuff is so it might be pretty clean. I wonder if I can stick heat sinking materials to the hull to increase its efficiency even more? That, coupled with the fact that 75° is sort of the record high, more likely the water will be 65-70° on most “hot” days, might get us the comfort we desire. Thanks.

Gdavid said:

To lower the humidity, you will need to keep the cabin closed up, no outside air flow to help cool the cabin, now you have devices and people in the boat generating heat and often a 1/2 ton of cast iron cooling off from 170-180 degrees, dissipating heat into the cabin. Even shaded windows are letting heat into the boat and you are doing absolutely nothing to remove heat from the environment. I don't see how this could be comfortable at all unless it is 70 degrees outside or lower to begin with. Dehumidifiers work great for protecting the boat from moisture and mold while you are away from the boat but it is always going to be hot when you enter the cabin.

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Comfort is a relative thing. In my opinion 85 deg and 35% humidity is more comfortable than 72 deg and 80% humidity. I spend part of my summers in the mountains where daytime highs are 90 - 95 and humidity 15 - 20. It isn't uncomfortable. If the outside is hot and the inside is hot, opening the windows won't cool it. You can run a fan to take advantage of our natural biological cooling (sweat evaporation) but that only works if the humidity is low. I do not suggest this out of theory - I've tried it on two boats and it works for me. In sweltering SE heat it isn't going to make you "comfortable" - just less miserable. I spent several days in Montreal one time and it was 100/100. Actually 104 deg and raining. The very small A/C unit in the saloon could not lower the temp, but did lower the humidity. That made it survivable, if not comfortable.