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post #1 of 12 Old 05-26-2019 Thread Starter
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Air Conditioning

If we are using shore power, why don't we use a potable air conditioner and vent the hot exhaust out a vent? Why do we need a seawater cooling system for AC? Is it space? Interested in your opinion!
Thanks, BB
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post #2 of 12 Old 05-26-2019
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Re: Air Conditioning

I guess it depends if you want to manhandle the thing off the boat or store it somewhere every time you go sailing.
What you propose is fine for dock queens, but portable A/C units are kinda hard to install permanently on a small boat, and if you have a bigger one, why not have a built-in marine unit that one can use off the dock with a genset?
As for those A/C units on wheels with a hose out a port, a friend of mine lost his boat when he left it running to go to the store for a few minutes. Came home to a flaming inferno in the marina.
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post #3 of 12 Old 05-26-2019
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Re: Air Conditioning

Not a classy look but if you need some AC on the cheap.


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post #4 of 12 Old 05-26-2019
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Re: Air Conditioning

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Originally Posted by capta View Post
I guess it depends if you want to manhandle the thing off the boat or store it somewhere every time you go sailing.

What you propose is fine for dock queens, but portable A/C units are kinda hard to install permanently on a small boat, and if you have a bigger one, why not have a built-in marine unit that one can use off the dock with a genset?

As for those A/C units on wheels with a hose out a port, a friend of mine lost his boat when he left it running to go to the store for a few minutes. Came home to a flaming inferno in the marina.
If you only want A/C at the dock, and you have the place to put a portable unit on board, then why not? You can get up to 1 ton of cooling out of a 110v 15a circuit.

I don't think you need to worry about a portable A/C turning your boat into a "flaming inferno". There are millions of portable units in use in homes all over the world, and they certainly do not have a reputation as being a fire hazard. If one was associated with a fire on a boat it is more than likely a faulty electrical system on board to blame, not the unit itself. Portable air conditioners are as safe as any other household appliance.

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post #5 of 12 Old 05-30-2019
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Re: Air Conditioning

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Originally Posted by RI.Brooks View Post
If we are using shore power, why don't we use a potable air conditioner and vent the hot exhaust out a vent? Why do we need a seawater cooling system for AC? Is it space? Interested in your opinion!
Thanks, BB
Air conditioners (and refrigerators) work by pulling heat energy out the air in your house/cabin, and dumping it somewhere else. For a window or portable AC like you see in homes, they dump the heat into the air. That's why the part of the AC which sticks out the window blows hot air.

A boat presents an interesting tradeoff because water has over 3000x the heat capacity of air for a given volume. That is, if the AC normally requires 400 CFM of outside air (about how much is pushed by the big fan in the outdoor unit of a residential central cooling AC), it can accomplish the same amount of cooling with less than 1 gallon per minute of seawater. On top of that, seawater tends to be cooler than the air (during the day when you're most likely to be running the AC), which improves the efficiency of the AC unit and can reduce the amount of water required even more.

So it boils down to a choice between a simple install with a big fan blowing a lot of air, or a complex install with an inlet and pump which only needs a little water. For any substantial cooling (larger boat, higher heat load like with an engine), water cooled is always preferable. But for a smaller boat the simplicity of a window or portable AC unit may be more desirable.

There is a type of portable AC which dumps the heat (or tries to) into the water it pulls out of the air as it dehumidifies. You can tell them apart because they don't have a hose to send hot exhaust air or water out the window. I don't have much experience with them, aside from knowing you need to empty the water tray occasionally or it'll overflow.

Also note that air conditioners are just heat pumps. If you get a reversible one, it can work as a heater in the winter. In that case it'll be pulling heat energy out of the seawater, and transferring it into the cabin air. The water will also tend to be warmer than the air (in winter), making it operate more efficiently in this capacity as well than a heat pump venting to the air. Heat pumps tend to become inefficient when the heat sink drops below about 40-50 F, and most of them come with an electric heating element which kicks in when the temperature gets too low.
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Re: Air Conditioning

Quote:
Originally Posted by Solandri View Post
...There is a type of portable AC which dumps the heat (or tries to) into the water it pulls out of the air as it dehumidifies. You can tell them apart because they don't have a hose to send hot exhaust air or water out the window. I don't have much experience with them, aside from knowing you need to empty the water tray occasionally or it'll overflow...
Actually, what you are probably seeing is a unit that has hot air exhaust, but no intake hose (only one hose). These are VERY inefficient, because they are constantly drawing warm, humid air into the space.

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post #7 of 12 Old 05-31-2019
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Re: Air Conditioning

Quote:
Originally Posted by Solandri View Post

There is a type of portable AC which dumps the heat (or tries to) into the water it pulls out of the air as it dehumidifies. You can tell them apart because they don't have a hose to send hot exhaust air or water out the window. I don't have much experience with them, aside from knowing you need to empty the water tray occasionally or it'll overflow.
This is not correct. Portable a/c units have either 1 or 2 air ducts. With a single duct unit, some air is drawn from the conditioned space, through the condenser, and then outside. This is not ideal because you are wasting cool air, and creating a negative pressure in the space which will draw warm moist air back into the space. The 2 duct units are better because they draw outside air into the unit, through the condenser, and back out, so the heat rejection air is completely separate from the conditioned air. Most a/c units DO re-evaporate the condensate they produce, but they do so using the compressor's hot refrigerant gas discharge line. This actually helps efficiency a bit because some of the condensing is done before the condenser, but the primary purpose is so that you don't have to drain the condensate.

All portable a/c units have at least one duct. If there are no ducts then it is a dehumidifier not an air conditioner.

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post #8 of 12 Old 05-31-2019
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Re: Air Conditioning

Quote:
Originally Posted by RI.Brooks View Post
If we are using shore power, why don't we use a potable air conditioner and vent the hot exhaust out a vent? Why do we need a seawater cooling system for AC? Is it space? Interested in your opinion!
Thanks, BB
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post #9 of 12 Old 05-31-2019
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Re: Air Conditioning

Years ago we saw an interesting A/C setup using a window unit. The sailor had a prefab dog house on the dock at his slip in the spot where others had a dock box. The dog house had a window A/C unit installed in its side. Coming out the door of the dog house were two insulated hoses. One hose went to one port on the boat; the other hose went to another port. The first hose brought cooled air from the A/C unit to the boat; the second carried warm air from the boat back to the A/C unit. When the sailor left the dock, he stuck the hoses into the dog house door and left it all behind. When he came back he hooked up the hoses and had a cool boat.

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