Anyone having issues with water being too hot for your A/C to run?

[smj]

Originally Posted by Chotu

We did discuss this. Definitely. There was a thread.



By far is right.



It's one of those things (like marine heads/refrigeration) where the marine stuff is needlessly complicated and prone to breakdowns and requires a lot of maintenance.



I almost used standard window units carefully built in to be concealed, but one of them would have blocked my view aft from the helm, creating a hazard, so I went with the through-roof units.

We have 2 5,000btu window units on our current catamaran which do the job well, though we haven’t found the need to use them yet.
We had a 16,000 btu reverse cycle marine unit and a 8,000 btu window unit in our old boat. At the peak of summer when the water was above 90 degrees the reverse cycle unit was pretty much useless and the window unit did a much better job of cooling.

[Chotu]

Originally Posted by smj

We have 2 5,000btu window units on our current catamaran which do the job well, though we haven’t found the need to use them yet.
We had a 16,000 btu reverse cycle marine unit and a 8,000 btu window unit in our old boat. At the peak of summer when the water was above 90 degrees the reverse cycle unit was pretty much useless and the window unit did a much better job of cooling.

how did you position them? I’m really curious. What I was going to do was put them on the aft wall or bulkhead where the salon doors are. In each far corner extremely outboard. Very far port and the other very far starboard. That way they would be hidden.

problem with mine is that you steer from the starboard side and the air conditioner was in the way for me to see aft properly

[GordMay]

Any AC has limits, no matter its age, how well it was installed, or its manufacturer, etc.
Generally speaking*, an air conditioning system [air to air] is designed to accommodate up to a 20°F difference [delta], between the outside air, and inside air while still keeping around a 55% humidity level, which is comfortable.

If you have your air conditioner set to a temperature that makes that differential more than 20 degrees, you’ll likely run your AC all day long, and still not reach those desired temperatures.

* The 20° Rule of Thumb applies to well insulated, modern buildings. A typical boat, with it’s poor insulation, single-pane glazing, and high infiltration, will [likely] have a much higher heat gain [than a house], so it’s A/C may only cool to a delta of ± 15°.

Most A/C techs will recommend an evaporator Delta T [difference between your supply air, and return air temperatures] of 16° to 22°F.
Experts generally recommend keeping a home’s relative humidity settings between 40% and 50%.

[rslifkin]

On a lot of boats (mine included), I think the single biggest limitation with air cooled A/C units is "where the heck do I put the outside unit?"

I think it really comes down to a lot of the marine A/C units being less than ideally designed (such as condensers too small for high water temps) and the installations in many boats are less than great. It's definitely possible for most boat to have better A/C than they do.

[smj]

Originally Posted by Chotu

how did you position them? I’m really curious. What I was going to do was put them on the aft wall or bulkhead where the salon doors are. In each far corner extremely outboard. Very far port and the other very far starboard. That way they would be hidden.



problem with mine is that you steer from the starboard side and the air conditioner was in the way for me to see aft properly

They mount in the two rear hatches that open into the cockpit. They cool the queen size bunks on the bridgedeck and we use box fans to circulate the cool air into the hulls.

[Chotu]

Originally Posted by smj

They mount in the two rear hatches that open into the cockpit. They cool the queen size bunks on the bridgedeck and we use box fans to circulate the cool air into the hulls.
Attachment 278939

That is NICE! Great setup

[Chotu]

Originally Posted by GordMay

Any AC has limits, no matter its age, how well it was installed, or its manufacturer, etc.
Generally speaking*, an air conditioning system [air to air] is designed to accommodate up to a 20°F difference [delta], between the outside air, and inside air while still keeping around a 55% humidity level, which is comfortable.

If you have your air conditioner set to a temperature that makes that differential more than 20 degrees, you’ll likely run your AC all day long, and still not reach those desired temperatures.

* The 20° Rule of Thumb applies to well insulated, modern buildings. A typical boat, with it’s poor insulation, single-pane glazing, and high infiltration, will [likely] have a much higher heat gain [than a house], so it’s A/C may only cool to a delta of ± 15°.

Most A/C techs will recommend an evaporator Delta T [difference between your supply air, and return air temperatures] of 16° to 22°F.
Experts generally recommend keeping a home’s relative humidity settings between 40% and 50%.

Wanted to point this out:

The 20 degree delta is measured between the *intake* air of the air conditioner and the output air, not the outdoor air and the indoor air.

So, you can cool an enclosed space down up to the point that the delta T of the air conditioner is equal to the heat gain of the enclosure. That is the point cooling stops.

Unless of course, you lose your delta T of the air conditioner because it can't cope from seawater being too hot, evaporator or condenser dirty, low refrigerant, compressor overload, etc.

So you can cool an enclosed space significantly more than 20 degrees from the outside temperature. In fact, you could make ice in your boat and freeze ice cubes on the settee with an ordinary air conditioner if you had great insulation properties. Might get a little dry inside however.

It's all about the ability of the air conditioner to remove heat vs the ability of any enclosure to let it back in.

[GordMay]

Originally Posted by Chotu

Wanted to point this out:
The 20 degree delta is measured between the *intake* air of the air conditioner and the output air, not the outdoor air and the indoor air...

Yes, the 20°F [15° - 25°F ΔT] Delta T “Rule of Thumb” applies to the temperature differences, across the evaporator coil [or supply & return air],
AS WELL AS
the indoor outdoor temperature differences [ΔT].

Delta T [ΔT] is a change in temperature, typically displayed in the following equation:
T1 – T2 = ΔT

[MarinAirNoWorky]

okay, had a professional come out, ran some strong (but not muratic) acid through it and it's currently working. Thank the heavens!!

[MarinAirNoWorky]

WELL, guess what.. it's still a no go. Seems like the timing was JUST right to have the water temp drop below 90..ran great all night... water temp 91 this afternoon and it's a no go again. Sigh.

[Chotu]

Originally Posted by MarinAirNoWorky

WELL, guess what.. it's still a no go. Seems like the timing was JUST right to have the water temp drop below 90..ran great all night... water temp 91 this afternoon and it's a no go again. Sigh.

That is just awful. Sorry to hear it.

It’s just too hot for these types of problems to keep happening.

Can you do a stopgap measure and just get a cheap 5000 BTU air cooled AC set up through the companionway or hatch so the pressure is off and you get a little relief? That way you can think clearly and have less stress

[MarinAirNoWorky]

Originally Posted by Chotu

That is just awful. Sorry to hear it.

It’s just too hot for these types of problems to keep happening.

Can you do a stopgap measure and just get a cheap 5000 BTU air cooled AC set up through the companionway or hatch so the pressure is off and you get a little relief? That way you can think clearly and have less stress

It's all good - I've got a place to stay with lots of cool air, hopefully till the water cools back down. Just annoying spending 1500 on something a couple years ago and having it not working when it's needed most. Will work on a hose to pickup water from deeper water... shouldn't be too hard.

[MarinAirNoWorky]

Called the company. They told me that the GPH is too fast for the AC.. 1200 gph pump came with the boat but they only want 350 gph on it.

Is there really a chance that the water is flowing too fast and it cant exchange the heat because of that?

[AKA-None]

Originally Posted by MarinAirNoWorky

Called the company. They told me that the GPH is too fast for the AC.. 1200 gph pump came with the boat but they only want 350 gph on it.

Is there really a chance that the water is flowing too fast and it cant exchange the heat because of that?

Ever see a river freeze, fast moving water takes a long time to remove heat

So yes based on the above it’s to fast

[CaptTom]

Originally Posted by AKA-None

Ever see a river freeze, fast moving water takes a long time to remove heat

So yes based on the above it’s to fast

Interesting. That's the opposite of what I would have thought.

Flowing air certainly removes heat more quickly than still air. That's why we have "wind chill" tables. In first aid classes I've also heard the same thing about cold water immersion. Moving around makes it worse.

When I want to cool down a cooking pot or something outdoors which has been in the sun, I don't just spray water on it. I run a stream of flowing water over it. Ditto for treatment of a first degree burn.

My understanding of icing on rivers is that it's the mechanical motion keeping ice crystals from forming, not that heat is being removed more slowly.

If this intuitive understanding is wrong, I'd love to learn the physics behind faster flowing water being a less effective heat sink than slower.