Air conditioning 33 foot boat

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pcatterall

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I know there is lots of info on this subject so I will try to be specific with my questions.
Short term I have installed a domestic portable A/C 9000btu purchased from my local Carrefour 199 euros.
it works and cools the small saloon from 36 C to a pleasant 27 C, when the sunhas 'gone off' the boat we can open up through to the forecabin ( where we kip) and get this cool for the evening.
It has been a great success, so much so that it seems worth installing a more permanant system.
The existing unit takes up quite a bit of space ( I had to cut the companionway steps)and will need lashing down if we go to sea!!
Exhausting the hot air is a problem, currently it is into the engine space then out through a cunning hole in a ( temparary cover)
A forumite indicated that a big draw back is that the system has to draw in lots of ( very warm) air to replace what it is chucking out, this means that this type of unit will not be very efficient.
( I have experimented by drawing the air in through a damp hessian screen, this seems to reduce the incoming air temp from 35 ambient to 33 I wonder if it is worth doing a proper job of this?)

My main interest now is understanding what the options are for a 'proper job'
Lots of local boats use a split system with the main unit on deck I guess this coud be done on my boat but I would probably need to remove the deck unit to sail, I also wonder how big a separation there can be from the deck unit to the inside unit?

Another question is the size required, if my 9000BTU unit is just about ok what sort of size would I need for a split or water cooled system. ( I would, in fact, like a size up from what I have say, 1200BTU)

What I suppose is the 'proper system' would be a water cooled job with everthing inside in a locker. These do seem expensive and there seems to be a big difference between buying from thje USA ( but 110volts) or UK

Last question ............why do we still use BTU ( all the French ACs use this value) is this one up for the Brits??
 
Location : East Lancashire................. Gave me a giggle, although I did also see the reference to Carrefour- so maybe not :-)
 
Cant help you with the boat a/c but can say several years ago i fitted split a/c to our house, both 12k btu units, both very good, will pull temps down to 20 degc when well over 30 outside.
Only downer is the outside box is quite a chunky monkey, these are pre inverter types and i am led to believe the inverter types are smaller and much more efficient.
I used to have a portable a/c unit in an office years ago and quite simply the split units are way way better.
Reason i mention the above is at the next marina down from me is quite a large boat with a household a/c unit on the back of his flybridge.



Lynall
 
There is a type specifically intended for yachts, we borrowed one when ashore a few years ago. It sits above the central hatch, dribbles water down the deck. We were offered one two years ago and did consider it but it was very heavy, 44kg IIRC and took up lots of space. We would have needed to stow it in the aft cabin when sailing. They are obsolete now but come up on Ebay, made by Cruise Air. Photos and discussion in this forum thread http://www.cruisersforum.com/forums/f115/air-conditioning-for-boats-48642.html
 
For boat use, you ideally need a seawater-cooled unit. This gets rid of hot air exhaust hoses, and also means that you're not drawing in outside air all the time. By simply recirculating the air in the cabin, the cooling performance is enhanced. You can get a 10,000 or 12,000 BTU unit for less than £1000. They're fairly compact, say 50 x 30 x 35H, so could be built into a cockpit locker. Take a look at www.marineairspares.com for some ideas.
 
If you feel better on the boat with AC then why not.However I keep my boat in the Algarve and never saw the need for it.What I have is four opening ports and a forehatch.Thogether with an awning it never gets unpleasantly hot inside even when ashore the temperatures are around 37ºC .
 
For 199 Euros you have the makings of a very cheap boat air conditioner. It contains the main parts you need to make a boat A/C unit, but it is air cooled. If you open it up you will find that there is a compressor which circulates a working fluid though a system with a cold side and a hot side. The cold side has a fan to blow air over the cold element and out into the cabin, and the hot side has a fan to draw air in and blow hot air out via the hose. To turn it into a boat system you need to put the parts into a fixed installation and arrange sea water cooling for the hot side instead of air cooling. If you can figure out a way to do that it will work better because you stop drawing hot outside air in to replace the hotter air that the A/C unit is blowing out via the hose.
 
It probably won't last long if you put saltwater into contact with the materials used in a domestic machine.
 
Agreed, but one possibility is to make an indirect cooler with the hot side of the A/C unit in a bath of antifreeze mixture cooled by a coil of copper tube fed with seawater. If the A/C unit is capable of being re-gassed you could go one better by making a proper heat exchanger for the hot side.
 
pcatterall said:
Last question ............why do we still use BTU ( all the French ACs use this value) is this one up for the Brits??
Click to expand...

Bit of a lesson in thermodynamics coming on, so I apologise now ...

The more common measurement nowadays is simply the kW, but also the American Ton. 12,000 BTU = 1 AT = 3.517 kW. A small 'proper' split will be around 3.5 kW, or 12,000 BTUs. This will adequately cool a largish room, or the interior of a 36 - 40' boat.

An AC system is reducing humidity as well as local temperature. Reducing humidity allows your bodies perspiration to evaporate which makes you feel cooler as the heat is taken up by the water changing state from liquid to gas and absorbing latent heat in the process. Comfort is achieved by reducing an ambient of say 36c down to around 29c, especially if this achieves a reduction in humidity as well.

The hessian blanket in the cooling air flow is achieving exactly the same thing as human perspiration. The techy term for this is adiabatic or evaporative cooling. But as Relative Humidity increases evaporative cooling effect reduces.

All fridge systems are heat pumps, meaning they pump heat from one place and at one level to another place at a different, normally higher level. The energy a heat pump uses to do the pumping is less than the energy transferred, which means fridge systems are very efficient, you actually do get more useful energy moved than you put in, typically 3-4 times.

The issue with what to do with the heat being moved to a higher and therefore hotter level presents a conundrum. There are two lots of heat to move - the heat energy from the cooled space plus the heat energy used to pump the heat, normally at the compressor.

Water cooling is far more efficient at heat transfer than air, plus if heating the air near the cooled space there is a good chance it will be drawn back in. This however is a major advantage for boatie's, as we are surrounded by water, and even if quite warm, say 30c or higher, this is still good for cooling the hot compressed fridge gas from the compressor.

So to size a water cooed condenser heat exchanger it requires to reject around 1.3 times the cooling duty, so 12,000 BTUs requires rejection of 16,000 BTUs, and must tolerate chemically aggressive warm seawater.

Hope the above helps when you look further into the commercially available solutions for your problem.
 
Lots of good info folks, many thanks.
We are using an awning system which shades the whole boat but still, below decks would be intolerable between, say, 1400 and 1900. The ac makes all the difference.
Using, and adapting a domestic system is appealing as the main componants are there. i will consider that idea but also investigate a 'proper' ( purpose designed ) unit especially if the price is around 1000 pounds rather than 2000 plus I have seen to date.
Thanks again
 
We fitted two marine units down below recently one 12000 BTU the other 10000 BTU company name Dometic. Excellent units and good back up. The installation was much more complicated than I first estimated. We needed two mains circ. pumps in the engine compartment plus all the pipework and in addition the condensate drains and air ducting from the units I did not want in the bilge. We ended up also having to upgrade the boat from 16 Amp to 32 Amp sockets and wiring. A quick job turned in to a month and a load of expense. Would I attempt it again sitting down below in Turkey during the heat of the day at 36 degrees C when below it is 25 degrees too right I would.
 
Here's our thinking, with a similar sized boat. We have been in the Med for almost ten years, April to October until recently, when health problems have forced change.

Once you go down the AC route you are a slave to 240 volts. You will be committed to marinas and ports wherever you go, or at the least you will need a sizeable generator. If your boat is like ours you will have little enough space for all this equipment - all the other stuff nearly fills ours and we try desperately to dump some when we can. The alternative is to anchor off as much as possible, using air flow and awnings. We have two wind scoops, an awning from the mast all the way aft, reflective curtains on all windows, water cooled refrigerator. Of course it is hot at times, it is 31C below now, although this is in a marina. But you get used to it and we never have big problems sleeping.

I think your domestic unit sounds like a good compromise, used when you are in port when the temperature will always be higher. Provided you can stow it I would stick with that. We don't have one but we do have a 240 volt fan that will run on the inverter if necessary, although it never has been. It's nice in port though.
 
One of the best things I bought for the boat in turkey is a box fan. Not easy to find there, but the fan is about 15 or 18 inches diameter, and slow turning relative to smaller fans, and is fronted by a rotating screen that directs the air up, down an sideways.
 
I have joined the total exodus of the northern Europeans from my Adriatic base and gone home for August - far too hot and crowded to stay with the start of the traditional Italian holiday period. What bliss to step from a 36°C hot garden into a cool house instead of going below from a similar ambient temperature into a +38°C cabin - a veritable oven of sweating discomfort, which becomes even more so as dusk falls and the mosquito screens have to be deployed, which restricts any potential air flow even more. And no air scoops are going to help with the typical windless nights we get; the only possible relief is from the fans that merely stir the same superheated air around the cabin.

A domestic unit would be the answer as the only requirement is when in the home marina, which is somewhat inland in a lagoon complex - anchored out I never have a problem as the sea proximity is cooling and breezes more frequent. But they are all just too big to fit in a 31' boat - even the OP's Carrefour unit ... already checked that one out.
 
( A domestic unit would be the answer as the only requirement is when in the home marina, which is somewhat inland in a lagoon complex - anchored out I never have a problem as the sea proximity is cooling and breezes more frequent. But they are all just too big to fit in a 31' boat - even the OP's Carrefour unit ... already checked that one out. )

It isnt just the size of the 'domestic unit' The other factors are
1) disposal of the hot exhaust air, vents etc.
2) the exhaust air above has to be replaced, the unit draws in external ( hot) air rather than recirculating cabin air.This hot air travels across the cabin space and negates some of the cooling process, I suppose it could be ducted directly to the unit but then a duct needed for air out and air in
3) the cold air is pumped out at low level rather than ceiling height.
4) the condensate has to be removed ( simple pipe to bilge in our case)


I am wondering if my unit could be 're-organised' in terms of the venting arrangements, Ideally it could sit outside the cabin with just the cold air being fed in ( high up would be great).
Anyway I am sitting in my cool cabin and planning phase 2 of the operation
 
pcatterall said:
It isnt just the size of the 'domestic unit' The other factors are
1) disposal of the hot exhaust air, vents etc.
2) the exhaust air above has to be replaced, the unit draws in external ( hot) air rather than recirculating cabin air.This hot air travels across the cabin space and negates some of the cooling process, I suppose it could be ducted directly to the unit but then a duct needed for air out and air in
3) the cold air is pumped out at low level rather than ceiling height.
4) the condensate has to be removed ( simple pipe to bilge in our case)
Anyway I am sitting in my cool cabin and planning phase 2 of the operation
Click to expand...
You see, despite all those hurdles you managed it and are enjoying the result. I would too if I could only overcome the initial placement problem. I only know that living on board in my present location and in high summer is no fun and, for me, totally unsupportable, much as I love living aboard and the local cruising.
 
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