Modify Car A/C for Use on Sailboat - Thoughts?

[Pblais]

You just are not going to get air cooled to work well. Water cooled is the way it works on an automobile. Instead of a radiator use a water pump. You just have no place for a big radiator. I can't say I agree with the whole idea but if you ever had a chance you at least need to not fight the laws of thermodynamics. You need to chill the coolant with water. The engine is already cooled that way so might as well go with what is known to work.

The reason why it won't really work is the boat sits in water warmer than the you want the boat. You can't cool the ocean. It takes continuous cooling that cycles maybe every ten minutes to keep the cabin cool. If the water is cold you don't even need A/C if you close up the cabin.

[Caribsailors]

Pblais has got it, thermodynamics. Good luck......keep the high pressure cutout. I do appreciate your frugalness, that's why we're sailors, we get the wind for free.

There is a big difference from the desert and the water front. Check a psychometric wet bulb temp difference and you'll see why you don't find evaporative coolers in the tropics.

You have to remove a lot of latent heat before you start to get any sensable cooling keep that in mind.

Take pictures

[Stillraining]

Go for it...

People have tried to convince me I dont need A/C in my boat a few times..it is an expencive system to be sure ...but I have a claustrophobic wife...I will be running a gen-set for an hour every single hot muggy night even here in Washington right before bed I guarantee you that if she gets "That Feeling"...whatever that feeling is..small price to pay for her to want to be on the water with me...and me wanting her there.
Also if you have ever had to work on anything boat and its stifling hot..Sweat running down every crevice of your body...well...tempers fly, shortcuts are taken and the job is just a down right pain...Preform that same job nearly sweat free and it turns into almost pleasant therapy. At least thats the way it is for me.

I look at A/C like I look at my Boat... I really dont "NEED" either one of them..


I agree with going water cooled though...for several reasons... but I dont agree with sea water being to warm anywhere for it to not work well..your cars system is getting cooled at times with hotter air passing its fins then any body of water you sail in can possibly get.

But I think you will find exhausting all the hot air produced by the compressor will be a challenge if done with fans inside the boat and what not...that a simple electric pump circulating raw water will do the trick more efficiently I would think. Yes a little more involved maybe but no worries of duct work or weather sealing vent penitrations and all that jazz.

Just my .02 worth..

[s/v Jedi]

It's like a previous poster wrote: plumb the heat exchanger (= condenser) for the A/C between engine sea strainer and engine raw water pump.

A handy thing to know is how many BTU that A/C unit is rated at. Also, you need to plan a way to deal with the condensation, ie. you need a drip pan and a drain.

On temperature: here in the tropics, it's not so much about temperature... it's the humidity. When we start a small 8000BTU A/C unit we notice the difference within 15 minutes. The temperature isn't down at all, but humidity went from 80% down to 60%. After an hour, temperature might be down 2 deg. and humidity at 50% and it's nice already.

cheers,
Nick.

[hellosailor]

Fish, car AC units are designed for a pretty specific job. The condensor just doesn't work right unless there's a 20-60mph airflow through it, unless you buy a big fat luxury model many cars just don't cool well at lower speeds. So, water cooling on a boat buys you a HUGE increase in efficiency, and you're going to need HUGE.

Think about the interior of a typical car, maybe 6 feet x 6 feet x 4 foot and half filled with seats. That's all that AC unit is capable of cooling, with the eventual target of reducing the air temp something like 30-40F compared to ambient on a non-extreme day. If your boat's cabin is six times that size...Okay, maybe you could get a 5 degree drop. If you get that condensor happy.

I hate to be a naysayer, but considering all the work in fitting and prepping a car AC system even on the car--I don't think you're going to be happy with the return on investment. I'd run the numbers (system btus, cabin size, condensor changes) very carefully before bolting up anything.

A couple of big fans, some witchhazel or alcohol wipes, even a washcloth with cold water...

Or, just steal the AC system from one honking huge luxury car, or minibus.<G>

But I'd sure love to hear how it works out, if you do it.

[Fishman_Tx]

Nick: Re: On temperature: here in the tropics, it's not so much about temperature... it's the humidity. When we start a small 8000BTU A/C unit we notice the difference within 15 minutes. The temperature isn't down at all, but humidity went from 80% down to 60%. After an hour, temperature might be down 2 deg. and humidity at 50% and it's nice already.

BINGO!



Ok, one last time. No Water! Air only! Gonna Happen!
I CAN"T shell out several hundred $$ on thruhulls, saltwater pumps etc etc ad-nauseum. Nor am I dropping a grand or three on a commercial system. I'm trying to make do with what I have. And what I have is a complete automotive setup that I don't have to pay for. All I was asking was for thoughts on AIR cooling the condensor in the engine compartment. As regards to cabin air volume, and cooling ability I already KNOW it will work as well as i need it to, that is not at issue so therefore plz don't argue with me about it.

What I was asking was for ideas on AIR cooling the condensor in the engine compartment. The cheapest water cooled condenser coil I've seen is several hundred dollars. And it's not designed to match this type of system(line sizes). BTW this rig is a matched set. The condensor size(and forced air volume) can be increased to accomodate the cabin volume.

You know what? Never mind. I've grown tired of being talked down to and this conversation is going nowhere. I may be new to sailing in general(sail NOT power), but I'm not an idiot. My mechanical and electronics knowledge and skills are QUITE varied and somewhat extensive in some venues. What I lack is the ability to apply them to the marine environment at sea. Fortunately, some things DON"T change regardless of environment and they work whether or not you think they will. Such as the ability to control the temperature of a specific volume of air in a humid evironment.

Yes it will work. No, not as efficiently as I would like. But it will work. I'll figure it out. Think I'll stick to the old "squirrel cage on the dorade" idea. At least it'll keep the engine compartment cooler with the addition of the condensor and help keep the smell down.

Nick, Hellosailor, you seem to get it.

Carib, yeah your right the swamp cooler was bass ackwards of what I was trying to explain, oh well...excrement occurs.

Nick I'll let you know how it comes out. 2nd or 3rd week in September.

[LtBrett]

Fish,

To answer your original post, I would cut out a 4" vent hole, run a 4" bilge vent hose to a bilge blower blowing in. Feed the blower through your condenser using a cowling that forces all the air through the cooling fins. Mount the condenser low in your engine room and let it exhaust freely into the space. I would cut two more vent holes of the same size as your inlet at the highest point in the engine room to let the hot air out. I think this setup should maximize the cooling air flow while minimizing cost, power drain and noise. If you want more cooling capacity, use a larger fan and hose. You could use an electric automotive fan. Just understand you run the risk of high refrigerant pressure with this setup. Overload it, you'll likely cook your compressor.

Brett

[Dellin]

Hi Fish,

My first post here I saw your thread and took an interest.

I think this will work better than you expect cars are very poorly insulated and lose a lot of cooling by thermal transfer through the glass.

If this were my project I would get a metal pipe about 2 1/2 inch in diameter and about a foot long. Cap both ends and fit a 1/4 inch barb for a hose either end. Smear some heat sink compound on the outside of the pipe. Wrap the refrigerant line around the outside of the pipe in a spiral. You now have a heat exchanger that should do the trick nicely. If the engine uses raw water I would fit this as a 1/4 inch by-bass line otherwise something as small as a windscreen squirter pump would do the trick as you will not need a high flow rate.

Now as you are going down the air-cooled track I think your best bet would be to salvage a condenser off an old ac unit. I would guesstimate one off a 5hp unit should do the trick. As for a fan I doubt computer fans will be enough a thermo-fan for a small car would be closer the mark. I am not too keen on the the squirrel cage fan because it will be difficult to spread the air evenly over the cooling fins.

Best of luck with your project I'm sure it will work good.

[Talbot]

I have thought about this solution in the past - and what worried me was that the normal condenser fitted to a car is designed to make use of the wind flowing through the condenser due to the car's speed, and when stationary it doesn't work that well. I would suspect that you need to draw a lot of cool air from outside the engine compartment and blow it through a cowl with an electric fan, then exhaust away from the boat in order not to warm up the air in the compartment, and also to provide a better cooling effect.

[GordMay]

You haven’t told us what size your Auto’ A/C unit is, so it’s difficult to calculate the performance requirements.

I suspect that your engine compartment will over-heat, and you’re A/C condenser may freeze up (inadequate cooling air).

The maximum temperature of the engine room should never exceed 140 degrees F, within 3/4" of any electrical equipment (Alternator), and should never exceed 115 deg. F anywhere in the engine compartment.

You generally want about 400 - 500 CFM per Ton* cooling ambient (unheated) air across an A/C condenser.

Cooling by ventilation:
BTU/hr removed = CFM x 1.085 X delta T

* In North America, a standard ton of refrigeration is 12,000 BTU/h (3517 W).

[Fishspearit]

As Gordmay hints, I would think that the condenser and it's cooling fan would need to be outside of the boat. Too hot for efficient cooling in a small sailboat's engine room. Go put a thermometer in your engine room and run it for two hours. The ambient temp will be at least 20 degrees lower outside while the engine is running. The evaporator in the cabin, also outside of the engine room.

[Fishman_Tx]

Awright, now we're cookin'....

LtBrett: Great idea! I hadn't remembered about bilge blowers til during this thread. I got 2 nice 4" dorades that'll do for that, 1 in and 1 out. Using a commercial bilge blower would be preferable I think, since they're not too expensive. Put the forced air off the "intake" dorade thru hose and blower to the condensor. I could make a flat "cowling" with some mat and 'glass(maybe a luan core) and mount it all to the starboard bulkhead.
Maybe something like this: (see image below). Then a 2nd blower (exhausting) attached to the other dorade drawing air out of the compartment. That should keep hot air from being forced back into the main cabin thru the cracks and seams.

Dellin: I already have a complete system in hand. But I like your idea for the heat exchanger.

Gord:
Re: BTU rating: I'll have to check that. Re: overheating: that's why I want to use forced air in AND out. Remember this space is under the sole AND the combing on the starboard side and is a fairly large area with 2 cockpit hatches and flows into the aft/transom battery locker with 2 dorades above. Re: everything else: Dang, Gord, is there any subject your NOT well versed in??
See 2nd image for compartment area (yellow bordered).

Fishspearit: Yeah I know, I just spent a week in that compartment working on the engine! About passed out of heat stroke in there! This is why the need for a forced exhaust anyway, with or without the ac unit being put in as well. I could always install 2 more dorades.

found this on an automotive ac website:

"How powerful are automotive air conditioners? Most sedans have air conditioning systems that can approach 40,000 BTU (3.3 Tons) in capacity. A typical 3,000 square foot house can easily be cooled by a 36,000 BTU (3 Ton) system. Cars need massive cooling capacity in order to quickly bring down the interior temperatures on hot days (easily 130 degrees F) to comfortable levels (70-75 degrees F) in a few minutes. Houses, on the other hand, only need to handle temperature variations of about 15 degrees."

Like I said, it'll work!

[Intentional Drifter]

Suggestion: You might want to check the recommended rpm for the compressor to run efficiently. You might need to change the pulley size to increase/decrease the compressor rpm in relation to the engine rpm.

ID

[Fishman_Tx]

That's true. The original ran on a single serpentine belt system, but the main drive pulley on the crank looks near the same size. If it's off, it ain't by much. But something I definitly need to check.

[David M]

Keep in mind none it was ever intended for a salt water environment.