Marine Air Conditioner Installation Questions

[SpaceRnglr]

I’m probably going to install a marine AC unit on my 44’ Dromor Athena. Most people seem to install them under the settee so obviously near the floor. I’ve got a locker above the settee that is an ideal size, above the waterline, allows easier air duct routing, and I think I could drain the condensate to a T fitting in the sink drain hose in the adjacent head (also above the waterline). I don’t see the downside, but the local dealer is telling me to put it under the settee I think just because that’s what he is used to... Any thoughts on my plan?

See attached picture and excuse the mess. It either goes in the open cabinet on the upper right or directly below that cabinet under the toolbox... Thanks!

[a64pilot]

I have one in a Locker above the Settee, and one under our bunk.
In my opinion ease of running the ducting and being able to gravity drain the condensate where you want to trumps all. But especially the ducting, cause that can be a real pain and it can eat up a huge amount of storage.
The one above the settee has about 1 foot of duct work.

[Coolerking]

You want to put it down low so you can get the air flow as far from the unit as possible.

[SVHarmonie]

From an air flow standpoint, the BEST place would be to have the intake for the AC unit sucking the hottest air from as HIGH as possible, and the cold air discharge as LOW as possible, Although most people don’t like the resulting “cold feet.”

A downside of installing an AC unit higher up in a locker is NOISE. Most boat lockers are pretty lightly constructed, and will resonate and amplify the sound of the AC unit. Getting the noice generating bits down under settees with foam cushions on top is a standard plan for a reason.

It’s also weight up high, and that’s never a good thing on any sailboat.

[slug]

Originally Posted by SpaceRnglr

I’m probably going to install a marine AC unit on my 44’ Dromor Athena. Most people seem to install them under the settee so obviously near the floor. I’ve got a locker above the settee that is an ideal size, above the waterline, allows easier air duct routing, and I think I could drain the condensate to a T fitting in the sink drain hose in the adjacent head (also above the waterline). I don’t see the downside, but the local dealer is telling me to put it under the settee I think just because that’s what he is used to... Any thoughts on my plan?

See attached picture and excuse the mess. It either goes in the open cabinet on the upper right or directly below that cabinet under the toolbox... Thanks! Attachment 218175

Hard to visualize size and possible locations

Remember ....The air con unit makes noise

Line your ac locker with sound insulation

Mount the unit on rubber feet

Drain holes on all corners ... boat are seldom level

Pipe the moisture to someplace that doesn’t contaminate the boat and bilge

Filter the incoming air ... standard household style filters are best ...


Insulated ducting is important .. high quality stuff is hard to find

When you plumb the seawater cooling circuit devise a way to flush , decalc the system without making a mess

[thinwater]

Originally Posted by SVHarmonie

From an air flow standpoint, the BEST place would be to have the intake for the AC unit sucking the hottest air from as HIGH as possible, and the cold air discharge as LOW as possible, Although most people don’t like the resulting “cold feet.”...

Actually, it is not done this way. The cold air goes in high, with a minimum velocity, so that you get good mixing as it falls.



(I did an install for an article, and was coached by Dometic engineers.)


My other concerns would be noise and vibration. A settee locker will be quieter than an elevated locker.


As for condensate, condensate pump systems are easy. That would not be the deciding factor. Duct routing is.


The other concern is the source of return air. You don't want to pull from the bilge, you want cabin air.


Thermostat location is also important. Not near a cold duct. Near the return is best.

[mvmojo]

I've got one mounted near the floor in the deck house and two units mounted near the ceiling in cabins down below. No difference in performance, they all work well. My choice of mounting locations was based on ease of installation including routing of the sea water cooling (I use one central pump for all three units), ducting, and where the condensate drain would drain best to an overboard fitting.

[OS2Dude]

We have a Webasto FCF16000. Our unit is under the nav station table, where the batteries used to be, so it is about midway high in our cabin. (1985 Catalina 30) The Raw Water thruhull has to be lowest, then the strainer, then the pump, then the A/C itself. (Each a little higher than the last.) You may have issues priming the inlet water with the unit very high. Can you duct the return air so it wont pull in air from the supply vents? Can you duct the return air with a large enough grill? You also have the raw water discharge to consider.

I added a Venturi to pull the condensate out with the raw water.

Water Flow and Air Flow needs to be as straight and smooth as possible. Every little curve and dip impedes the flow. I replaced several sections of the flexible hose ducting with tin tubes to avoid dips and sags. Remember to move the insulation from the flexible hose to the rigid tube!

Also be aware that you can't just compress the ducting to press thru a tight spot. This is where all that math you learned in school comes in: area = r1 * r2 * 3.14. Simplified: (normal)D² <= (compressed)(D1 * D2). The area needs to be as close as possible to the round duct (Larger would be better) if you have to compress it any.

[Coolerking]

Hey guys/gals, we do this for a living, we've installed hundreds of marine air conditioning systems in every type of boat you can imagine.
Always try and pull air from the lowest point possible and discharge it as high as possible.
Do not direct the air to the return grill.
Place the alt air sensor, if supplied, in the return air flow at the grill.
Don't let it touch anything.
If the sensor is in the display, be sure the location is not in direct path of air or sunlight.
Keep the filter and the condensate pan clean, this is what ruins 75% of the units I replace
Boats are always a compromise, but these are the general rules...have a great day!

[mvmojo]

Originally Posted by OS2Dude

I added a Venturi to pull the condensate out with the raw water.

This is a great idea to prevent overflow from dirt clogging of the condensate drain line. Where did you get yours??

[rphdiego]

Cold air 'falls' so you want the discharge as high as possible.

[Djarraluda]

Supply air is introduced to the space as a jet, which promptly mixes with the room air and starts to change temp. When close to the ceiling, the Coanda Effect keeps the cold, high density air stuck(?) to the ceiling in contrast to falling quickly as what you might expect, so the design should consider discharge velocity and location (proximity to ceiling, plus not pointing straight at someone or something). Long, torturous duct runs reduce airflow and super-chill the supply air, always oversize duct and keep it straight where possible - I never use flex duct on bends as the airflow resistance is horrific.
Ideally, we size the jet, in relation to the temp difference between supply air and room air and locate the diffuser/grille etc such that the velocity decays before it hits the opposite wall. i.e. there is actually engineering involved in the layout, albeit that many installations are not properly considered, which is why some spaces have cold draughts, stuffy corners and similar.
As far as the sensor is concerned, whilst located in the return air is common, it also fails to actually monitor the room temp at the height occupants feel it. For best efficiency, use a wall mount sensor at occupied height in the room.
Roger

[SpaceRnglr]

Thanks everyone. the most compelling tip relates to noise and air flow in the upper location. It would sit directly behind your head if you sat on the settee--i can see how that would be annoying. I will try to install it below assuming I can find a reasonable hose run.

Regarding the ducting there was a comment to use rigid pipes--what type of pipes are used? I live in Singapore so very humid and hot, condensation is a big concern.

Thanks!

[Djarraluda]

Originally Posted by SpaceRnglr

Thanks everyone. the most compelling tip relates to noise and air flow in the upper location. It would sit directly behind your head if you sat on the settee--i can see how that would be annoying. I will try to install it below assuming I can find a reasonable hose run.

Regarding the ducting there was a comment to use rigid pipes--what type of pipes are used? I live in Singapore so very humid and hot, condensation is a big concern.

Thanks!

You can speak to an HVAC contractor for help as to what is available locally, or just go with rigid PVC(or ABC) pipework, drainage, rainwater etc are lots of different sizes. It also needs insulation, suggest a rigid phenolic foam which comes as preformed sections. Not the old soft fibreglass or mineral wool, as that absorbs the condensation. All joints could benefit from some spray foam in the joints if you make any custom fittings for the insulation.
Roger

[Coolerking]

https://www.marine-j.com/pdf/222000650.pdf