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

[GordMay]

Originally Posted by Bowdrie

I've read reports lately of the water in the Keys getting well slightly over 90F...

The current sea temperature, for the Florida Keys [July 16, 2023] is 30.7° C [87.27° F]
Yesterday: 30.88° C [87.59° F]
On July 14: 32.54° C [90.57° F]
1 week ago: 31.8° C [89.24° F]
Ambient air temperature: 30°C [86°F]

The average sea temperature for Florida Keys on July 16th, over the last 10 years, is 29.96° C [85.93° F], with a low temperature of 28.18° C [82.72° F], and a high of 30.93° C [87.67° F].

The warmest water temperature is in August, with an average around 30.5°C [86.9°F].
The coldest month is January with an average water temperature of 21.8°C [71.2°F] .

[MarinAirNoWorky]

Well, I'm not sure where that came from, but it's not accurate. Went out about a mile yesterday and it didnt drop below 91.5.


It has been above 87 for a month now.. it's actually cooler in my canal vs the sea temp. Going to head to a reef today and will take a picture of the temp, hoping for mid 80.

Although she's talking about the bay in this shot, I have actually been in the bay where it HURTS to put your foot in. At some point last year, and close to an island.

[GordMay]

Exact details aside [you're there; I'm not], we can agree that the air & water are hot.

Most A/Cs will be limited to a 20° temperature differential [Delta T].

As a rule of thumb, an air conditioner will be able to cool to about ±20°F [16-22°F], from the outside temperature, while still keeping around a 55% humidity level [anything between 40 - 70% RH is ‘comfortable’].
For example, on a 90°F Florida day, the AC can cool the interior of a house down to 70°F.
So, when it’s 95° out, your AC can cool your house to approximately 70-80°F.
Water-cooled marine air conditioners will have similar Delta T limitations.

The seawater requirements, for cooling water-cooled equipment is about 180 - 200 gallons/hour/ton [3 - 3.3 GPM/Ton] of air conditioning [12,000BTUs = one ton], at a maximum temperature of 100°F.

[Bowdrie]

Originally Posted by GordMay

The seawater requirements, for cooling water-cooled equipment is about 180 - 200 gallons/hour/ton [3 - 3.3 GPM/Ton] of air conditioning [12,000BTUs = one ton], at a maximum temperature of 100°F.

I suggested previously about measuring the temp of the water at both inlet and outlet of the condenser.
All the water flow in the world won't help if scale/encrustation is preventing heat transfer.
Now this is another easy check, and it's something I've seen several times on installations.
The typical AC unit uses a "Co-Axial" condenser, (a stack/coiled tube,) and they are designed to operate in a "counterflow" hook-up.
The refrigerant enters the top, exits the bottom, whilst the water enters the bottom connection and exits the top.
Sometimes the water connection is reversed during installation.
If so, the heat removal ability of the condenser is compromised.
To the OP, give that a check, ensure that the water connections are correct.

[CaptTom]

All this talk about air conditioning, and all this hot weather, has me thinking...

Does anyone make a 2-stage cooling system? I assume it would be more practical on a larger vessel. But with that 20-degree temperature differential as a practical limit, would there be better performance, and maybe even efficiency, if you cooled the incoming water by 15 degrees (or whatever) before sending it through the condenser?

[rslifkin]

Originally Posted by CaptTom

All this talk about air conditioning, and all this hot weather, has me thinking...

Does anyone make a 2-stage cooling system? I assume it would be more practical on a larger vessel. But with that 20-degree temperature differential as a practical limit, would there be better performance, and maybe even efficiency, if you cooled the incoming water by 15 degrees (or whatever) before sending it through the condenser?

It would likely make more sense to just design a system with a bigger condenser (more surface area) and more water flow so it could get the condensing gas temperature closer to the water temperature, allowing it to operate in hotter water. The downside is higher material cost, more weight, and a physically larger unit, which is likely why they aren't built this way.

[Bowdrie]

Originally Posted by rslifkin

It would likely make more sense to just design a system with a bigger condenser (more surface area) and more water flow so it could get the condensing gas temperature closer to the water temperature, allowing it to operate in hotter water.

I've used that approach in building some air-cooled refrigeration units.
Using, (for example,) a 1/2-ton condenser/fan, with a 1/4 or 1/3-ton compressor.
The use of hot-gas-bypass and head pressure regulators are common in large systems, however each time they cycle that is lost refrigerating capacity, (but it does prevent tripped breakers/blown fuses).
Automotive AC systems regularly operate at a larger Delta-T than the 20 degrees mentioned, they do so with brute force, (power requirements not a big issue,) circulating a large amount of refrigerant at high speed, getting into the range of a flooded evaporator and using a suction accumulator.
Using compressors in the ~3>5-ton range and controlling head pressure by engaging/dis-engaging the electric clutch.
Yes, you are correct, oversize water-cooled condensers can help in a marine unit.

[maury]

In New Orleans water temp is 91 and today my unit started quitting on me after five minutes.

[GordMay]

Originally Posted by maury

In New Orleans water temp is 91 and today my unit started quitting on me after five minutes.

Evidently, this week, the lake Pontchartrain water temperature, at the NOAA gauge, near the New Basin Canal Lighthouse, has been hovering around 95° ➛ 97°F.
That’s about 15°F higher, than the normal average, this time of year.

[GordMay]

With NOLA's air temperatures expected to reach 100°F, today, ANY air conditioner is going to struggle!

[Chotu]

My air cooled condenser units haven't missed a beat.

At anchor, they have been reliably putting out 36,000 BTUs (3 tons)day after day all day long lately in the heat dome that had moved east

not trying to be smug here, but more people should consider using them.

absolutely trouble free, maintenance free and cheaper.

if there ever were a problem and you had to replace it, it would only take about an hour to do so as well.

[smj]

Originally Posted by Chotu

My air cooled condenser units haven't missed a beat.

At anchor, they have been reliably putting out 36,000 BTUs (3 tons)day after day all day long lately in the heat dome that had moved east

not trying to be smug here, but more people should consider using them.

absolutely trouble free, maintenance free and cheaper.

if there ever were a problem and you had to replace it, it would only take about an hour to do so as well.

Are those the roof mounted RV units?

[Chotu]

Originally Posted by smj

Are those the roof mounted RV units?

In my case, yes. Best form factor for this boat. Very much out of the way.

But there are also through-wall/window and mini splits and things like that that could be adapted to work on monohulls as well with a little ingenuity.

[smj]

Originally Posted by Chotu

In my case, yes. Best form factor for this boat. Very much out of the way.



But there are also through-wall/window and mini splits and things like that that could be adapted to work on monohulls as well with a little ingenuity.

Glad they’re working for you. I believe we discussed this before while you were trying to decide what type AC would work on your boat. We used the RV unit on a catamaran years ago and was by far the best option for cooling that we’ve come across.

[Chotu]

Originally Posted by smj

Glad they’re working for you. I believe we discussed this before while you were trying to decide what type AC would work on your boat. We used the RV unit on a catamaran years ago and was by far the best option for cooling that we’ve come across.

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.