How Cold is Cold? (A/C question)

[Converse48]

My salon A/C seems to have a tough time keeping the interior at anything more than 10-12 degrees below the outside temp. I would have expected more like 20 degrees below.

The forward unit has no trouble, but of course, there isn't all that glass up front like there is in the salon. Anyway, I measured the temperature of the air coming out of the vents and it is 51 degrees up front and 58 degrees in the salon. Seems to correlate with the cooling results, but why? The unit is under warranty and a call has been placed, but I don't think they took me very seriously since it was in the middle of a heat wave and lots of people were calling with issues. Yes, I cleaned the filter.

So, is 58 degrees acceptable, particularly considering that a same-sized unit up front is putting out 51 degrees?

 

[Four Suns]

My wife likes the inside temp like an ice box and our inside temps are set at 72 and the AC can keep it there without running all the time... even in the heat (100 degrees) we have had in the last few weeks. Maybe the unit in the salon is just too small?... What's the model number on the systems?

 

[xravenx]

I'm an HVAC guy...............expect 16 to 18 degree difference between your entering return air and your leaving supply air temperature. If you can lower your inside temperature about 20 degrees less then the outside temperature, you are doing good.............boats are not insulated very well.

John

 

[Four Suns]

If you can lower your inside temperature about 20 degrees less then the outside temperature, you are doing good

John

My wife would make me get a different boat....

 

[Morpheus]

This is interesting info. Although we don't have a large cruiser we plan to get one eventually and the Wife and I were wondering how well the A/C works on them. WE like it COLD we keep the house at 72-74 most of the time (except when we are not here)

If it's 100 out side in the direct sun (no shade) am I going to have problems getting a boat that can get the a/c down inside to below 74?

 

[Morpheus]

I'm an HVAC guy...............expect 16 to 18 degree difference between your entering return air and your leaving supply air temperature. If you can lower your inside temperature about 20 degrees less then the outside temperature, you are doing good.............boats are not insulated very well.

John

Why only 20? If you start at say 90 and it's able tp lower it to 16 to 18 then it's 82-84 but then that air is changed another 16 to 18 etc etc

If you never opened a window or door wouldn't get keep getting colder? I know at some point it can no longer cool as the heat from the outside won't allow it.

 

[Four Suns]

I know on my boat, I have no trouble keeping the staterooms, bridge, cabin, etc. at 70-72 degrees regardless of the outside temp and it does get 100 degrees here during the summer. However, the 480 has 5 AC systems (well... 4 systems but the bridge has 2 air handlers tied to a single compresser).

 

[xravenx]

I have no problems getting my cabin down to 72 degrees when it's 98 to 100 outside (like this past week in Maryland), they just runs longer. You can get your cabin more then 20 degrees cooler then the outside air, I'm just saying if you see at least 20 degrees less it's probally working pretty good, anything cooler is a bonus.

John

 

[Morpheus]

I have no problems getting my cabin down to 72 degrees when it's 98 to 100 outside (like this past week in Maryland), it just runs longer.

John

Thanks, that's good to know for future boat upgrade :grin:

 

[masmms]

a/c

slightly off topic , but my a/c fan is noisy (almost a rubbing type sound) except in the high position. anyone experience this? Is it normal? thanks

340 sundancer 2006

 

[Ryan]

A/C in salon

Hello everyone, I just purchased a 2006 52 Sedan Bridge - She is a beauty. We (my family) are very excited. I was in the salon today, and noticed a very similar situation to what you describe. Our room was very cold though... I was thinking it had to do with all the windows in the salon.

We are in Baltimore, Maryland, and it was 90+ today (at least it felt like it).

Let me know what you find, as I am very interested.

Thanks!
Ryan

 

[Dancin Dave]

I have no problem keeping the cabins cool. If I set it at 65 it reaches the 65 and then clicks on again when it drops 3 degrees. Even when it is 90.

Here are some tips. Keep the door shut. Dont decide to put the air on last minute. If you know its going to be hot, start it at a cool temp early, and leave it on. Install hatch covers, and keep the blinds and curtains drawn shut. 1 porthole will produce a lot of heat.

And keep the air filters clean.

 

[Asureyez]

Remember its about the Water Temperature!

The BTU exchange between air outside a boat and the inside air technically correct for a shore side system, as the exchange were being made on an air inside to air outside exchange. But in most boats the heat is removed from the inside of the boat and exchanged in to the sea water. The temperature of the water at the level of the intake will determine the efficiency of the exchange.

Thus, you have say water temp of 86, External Air 92, the exchange will be off the 86 degree water and the theoretical efficiency will be something like 20-22 degrees less than the water temp, plus the heat loss through the hull. Good guess is the air exiting the system will be 86 degrees less 18 or 68 degrees. The temperature pull down will be based upon the vessel heat leaks and operator dynamics.

 

[Converse48]

Here are some tips. Keep the door shut.

I am so maniacal about this my family calls me "the door nazi"

Dont decide to put the air on last minute. If you know its going to be hot, start it at a cool temp early, and leave it on.

My parents, who live on their boat in the same town, turn my A/C on for me every weekend 24 hours before I get there.

Install hatch covers, and keep the blinds and curtains drawn shut. 1 porthole will produce a lot of heat.

I have a 90% sun shade on the front windows and the blinds are always drawn.

And keep the air filters clean.

Done.

Even with all of the above, the salon unit runs constantly, and can't keep up. Either it's undersized or underperforming (sounds familiar :grin: ).

Gary, I don't know the model numbers but both units are reported to be 16,000 BTU.

 

[Dave S]

If your dealer isn't taking you seriously, call Sea Ray's 800 number. :grin:

 

[Four Suns]

I would think that 32,000 BTU's would be enough to cool your cabin down nicely but that's assuming the vents are properly placed. Who knows though as I'm not an AC guy. Maybe the addition of all the dark glass compared to the earlier sized 400 DB is a problem with 32,000 BTU's. The early versions of the 480 DB (1999'ish) only had 30,000 BTU's of AC per the spec sheets and I've seen a few complaints on how it could not keep up. The later years, like mine, were increased to 38,000 BTU's of AC and there is a vent from one of the lower AC units up in the salon to help the salon unit out. I mention the 480 specs just to point out where the 32,000 number is relative to my boat.

Is it the actual temperature in the salon that can't get cool or does it just feel warm because of excessive humidity? I know that I had to rework my primary vent hose in my salon a few years back because it was too long on installation and had a low spot that filled the hose up with water/condensation and so the cabin was increadibly humid.

Maybe at the Aquapalooza on Saturday you can dinghy around to the other 44 DB's and crank their air down all the way to see what happens while the owners are on land partying. :wink:

 

[jg300da]

The size of the unit or the boat has no bearing on the design delta (entering evaporator dry bulb temp - leaving evap temp). 18-22 degrees is typical of most ac units. A 75 deg cabin will generally net about 55 degree discharge air. Whether or not that is sufficient is predicated on many factors; solar gain, insulation of cabin, number of bodies in cabin and other heat loads. Another factor is entering cooling water (raw water) temp. Design water temp is 85 deg with a 10 degree rise giving a leaving water temp of 95 deg. In southern climates where water temps may exceed 85 deg expect a derating of ac capacity resulting in longer compressor cycles and slightly warmer discharge air temps. Boat ac units are generaly well oversized due to the large loads placed on them and their poor insulation values. Gary's example above shows this to be true. The 32,000btu cabin unit he mentions is actually large enough to cool a 1200-1400 square ft home, many times larger than the cabin of his boat.

 

[Sea Gull]

Actually, with all due respect to xravenx the HVAC guy, these uits use sea water to cool. Their cooling capacity is related more to the temperature of the water than the ambient air. Of course keeping the blinds closed and doors shut will help too.

Our 58 has no prblem keeping the salon at 73 even in the hot sun on the Chesapeake Bay today. But AC is on my mind since I am sitting here waiting for the Cruisair guy to replace the seawater pump for my bridge AC unit. The darn thing stopped working last week and now I am wasting a day of vacation waiting on the tech.

 

[xravenx]

Sea Gull,

You are correct, they use seawater thru a heat exchanger to cool the refrigerant, that is why these water source a/c units work so well. If the unit is struggling with 75 degree supply water, there is something else going on with the unit. On a commercial water cooled application, 82 degree supply water is the norm.

 

[Robski97]

Is it me or do some people use way to many sentances to make a point. Ravens right on . I like my boat cold ... I set the cabin for 68... on hot days it never gets there.... and yes the cabin door is never closed ,,, thats a no brainer ... but with two young kids and a dog some battles u just dont pick. Butthe a/c unit on the 42 is only 12,000 btu's . Id have liked it bumped to a 16,000 btu unit . Same foot print. alittle more amperage ... its on the to do listfor next year...

And the cockpit a/c is joke ....


Rob