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Old 04-20-2019, 04:07 PM   #1
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Is there any way to cool a cabin using the river water?

In other words, energy efficient AC that isnít compressor based. Like evaporative but without the wet air into cabin? Our river is never over 75į so Iím just curious if that could be used to cool a stateroom at night.
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Old 04-20-2019, 04:19 PM   #2
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Is that 75 Centigrade or Fahrenheit. ?
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Old 04-20-2019, 04:44 PM   #3
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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.

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Old 04-20-2019, 06:09 PM   #4
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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.
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Old 04-21-2019, 06:24 AM   #5
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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.
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Old 04-21-2019, 06:36 AM   #6
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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.


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Old 04-21-2019, 06:56 AM   #7
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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.


Come now, the US is not alone, Liberia and Myanmar still use the English system.
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Old 04-21-2019, 06:59 AM   #8
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Greetings,
Mr. rj.


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Old 04-21-2019, 08:30 AM   #9
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In other words, energy efficient AC that isnít compressor based. Like evaporative but without the wet air into cabin? Our river is never over 75į so Iím just curious if that could be used to cool a stateroom at night.

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.
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Old 04-21-2019, 08:37 AM   #10
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Come now, the US is not alone, Liberia and Myanmar still use the English system.
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?
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Old 04-21-2019, 09:31 AM   #11
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Sure hope the politicians don't insist that latitude and longitude go metric. What would we do without the knot or nm?
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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Old 04-21-2019, 10:22 AM   #12
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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.
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Old 04-21-2019, 05:34 PM   #13
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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."
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 360į 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.
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Old 04-21-2019, 06:18 PM   #14
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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.
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.

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Continuing the hijack though, I have a hard time seeing the point (or the difference) in the metric system.
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?
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Old 04-21-2019, 06:22 PM   #15
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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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Old 04-21-2019, 06:49 PM   #16
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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.
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Old 04-21-2019, 07:04 PM   #17
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In other words, energy efficient AC that isnít compressor based. Like evaporative but without the wet air into cabin? Our river is never over 75į so Iím just curious if that could be used to cool a stateroom at night.
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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Old 04-21-2019, 09:11 PM   #18
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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."
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.
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Old 04-21-2019, 09:34 PM   #19
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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.
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 .
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Old 04-21-2019, 09:54 PM   #20
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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.
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Running a dehumidifier will add a surprising amount of heat to the cabin and still require more power than most battery banks could maintain.
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.
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