Air con - cooling limited by warm sea water?

[PEJ]

It was my first experience of August in the Med this year. Warm isn't it?!

I found that the air con in the cabins could not quite get the temperature down as low as I wanted and despite setting it to 16 on the display it always hovered around 18 /19.

I wonder if this is because the sea water temperature is higher than I am used to? I heard it said that the cooling effect of the air con can be limited if the sea water is too warm - is that right?

 

[Portofino]

No
It’s the other way round the heating effect is dependent on the external sea temp in winter .

In the summer the sea just cools the comp motor and the compressed gases much like your main engines and geny .
The seawater pump should be man enough to shift enough vol through .
If the comp overheats it shut s down .

Those compressed gasses are now liquid which are then evaporated off back to gas giving the cooling effect .
Your cooling effect the function of the liquid / gas interface with the latent heat of evaporation .
Your compressor should be able to condense the refrigerant gas as required regardless of a variation in sea temp .

If it’s any good ?

 

[jrudge]

Seat temp will only have a marginal difference i suspect as whilst relevant to getting rid of heat the sea temp does not vary much in the scheme of things ( in the med).

If you managed to get the temp down to 18/19 I would say you are doing very well. That is COLD...

The system will have a cooling capacity for each cabin. You then have heating from below ( 24 degrees ish of sea water) and sun from above. So there will be a limit to the cooling capacity and how low it can go.

Most systems I have had tend to have a floor around 18 degrees in any event ( cars included).

The most common cause of issues ( which I dont think you have) is the strainer blocked by sea weed or dirty filters slowing airflow. If the strainer is part blocked then the first warning is usually that the air con is not quite as goos as it was a few days ago. Leave it long enough and you will get a High Pressure Fault.

Deleted User may want to buy your boat!

 

[MapisM]

despite setting it to 16

Wow, you must have a huge stock of wine onboard, if trying to cool the whole boat is easier than putting the bottles in the fridge...

 

[vas]

the forum never ceases to amaze me!
no offence guys, but serious are you able to sleep at 16C with an ambient of 30C and then wake up in the morning and not have any problems?
Even worse, can you have an afternoon nap with ambients in the mid 30s in a 16C cabin and not suffer when you come up outside?

I'm really impressed!

us southerners have developed methods to live with the heat, and using aircon at 16 or 21C is definitely NOT one of them!
It's actually quite easy to catch bad colds and even pneumonia like that.
Mind this summer was one of the mildest I've experienced in the last decade.

cheers

V.

 

[Portofino]

This summer at the warmest July August it’s been 38 in the saloon .
Combo of outside bit lower say 32/34 ,solar heating ( even though it’s a “cave “ white roofed and small windows ,and engine bulkhead heat soak .
Takes about an hour to chill it down to the preset of currently 23 .

This seems fine at night too in the sleeping cabins to be cool enough to warrant a sheet and thin blanket to kip under .
We keep our running as soon as we’ll hook up on shore power .
However having said that when I lived predominantly in the U.K. we used to set it at 18/20 .
Also there’s been a few very humid days ,still no breeze at anchor and I have turned the geny on for the cruise back to the home port .The main engines drowned out the geny anyhow so you don,t know it’s running .
This means the boat by the time we park and hook up etc has had a head start Aircon wise chilling .
It was 32 last week in La Napoule btw according to the car .

But as said in MikesF thread we run a 42 K btu comp cooling water to 7 for 28;k btu airhandlers - it’s well on top of the job .
The bug bear for me is the ER heat soak .
In mild times at the end of the season the cockpit floor ( outside sitting areas ) is like under floor heating from the heat soak .

The moral of the story is for a few weeks of the summer in the Med you need a mega specced aircon esp if humid .
I guess that’s why you se brokers blagging on about “ tropical “ spec in Med boat sales particulars .

 

[PEJ]

Wow, you must have a huge stock of wine onboard, if trying to cool the whole boat is easier than putting the bottles in the fridge...

Well the display says 16 and hovers around 18/19 but I think the temperature sensor is wrong. It feels about the same as the saloon in the cabins and that is set to 21. I have a thermometer in the saloon and usually reads about the same as the air con panel at 21C or 22C.

I find the cabin just a little bit too warm for full comfort when sleeping

 

[superheat6k]

Yes as the cooling water temperature increases the capacity of the system reduces, and by quite an amount if for instance your seawater increases from say 25 to 35oC.

The capacity rating of a particular system is stated at one specific condition, so say 42 k btus/ hr at say 25oC so condensing at ~40oC could reduce to less than 35 k btus at 35oC, when the condensing increases to ~ 50oC. The higher the condensing temperature the higher the discharge pressure and with that the higher the compressor motor load. So higher Amps too. High humidity will also increase the relative cooling load so may make the system less able to reduce temperature to levels achieved in dryer conditions.

A dirty or fouled condenser will reduce capacity still further, whilst the power required will increase. This is because a fouled condenser experiences the same effect as though the cooling medium temperature had increased.

I am surprised you are trying to achieve 16oC. In the UK sites generally try for 20-22 in temperate conditions, but in warmer weather a 5oC drop outside to in will immediately be felt as being cool, so if it's 33 out, then 28 inside is not so uncomfortable, bearing in mind that at such conditions the AC will also be stripping out excess humidity too. Comfort is as much about keeping humidity under control as it is temperature.

 

[MapisM]

if it's 33 out, then 28 inside is not so uncomfortable, bearing in mind that at such conditions the AC will also be stripping out excess humidity too. Comfort is as much about keeping humidity under control as it is temperature.

Amen to that. Moving in and out to/from a space cooled around the low 20s with an outside temp in the mid 30s, as is normal for instance in the hotter parts of the US, is a recipe for sickness.
Then again, they also eat big macs... :ambivalence: