Small AC

[pbouchar]

Hello Jef

Marineair has a 3500 btu AC working on a 12V DC battery bank, it is far from perfect but it might be a good compromise compare to a genset.

http://www.marineair.com/pdfs/L-2425C.pdf

Pierre

[Sandero]

Good catch Pierre. Do you know how much these puppies cost?
jef
sv shiva

[GordMay]

At about $2,400, the Marine Air 3,500 BTU/Hr "Cuddy dc" unit draws about 30A* @ 12VDC, and would be suitable to cool a V-Berth or very small cabin.

Their “Cool Mate” line provides better value (5,000 BTU/H @ about $1700, or 10,000 BTU/H @ about $2,400).

* This will deplete a pair of T-105 batteries in about 3 Hours run time.

[Tropic Cat]

Jef, sounds like yer gonna need a long extension cord to keep the admiral happy

What I was thinking about is the older style engine driven compressors designed for onboard refrigeration. With a different evaporator core, could they be adapted for air conditioning?

[Sandero]

I think the cost is prohibitive of the Marine Air systems.

I am curious at how effective a small 110v ac like 4.6 amps or so is for short runs cooling off a very small non stand up aft cabin with regard to battery life.

I use a 5000BTUH in my home office and run it intermittatly on the hottest days with a ceiling fan... and this room is much more voluminous than the entire boat.. and it is prefectly adaquate at cooling the room to a comfortable level.

Does anyone have any knowledge about automovitve AC... how many BTUs and so forth?

jef
sv shiva

[hellosailor]

Jef-
The big difference between your boat and your office, is that your office probably has a lot more "thermal mass" and doesn't boil in the sun the way your boat would. Then again, at night the cooler water under your boat is an advantage to be had. In theory you can cycle some of that water through a regular hydronic system (hot water baseboard radiators, as most of us call them) and use that to chill the air. Problem being you need a raw-water heat exchanger and two pumps, and an intake to drop below the thermocline (possibly 10' down).
I don't know anyone doing it on a boat--but "chilled water" air conditioning systems are normal in commercial buildings and other uses. The same system can be switched over to a hot water source and used to heat an entire boat (or building).

Automotive AC is something to avoid. It is designed to be run from cheap power and steals typically more than 5hp from the engine, IIRC. It is also designed, even with that power, to cool a small passenger cabin only. Sit in the back of a real station wagon or full-sized SUV and you'll notice.<G> You'd need something more akin to whatever they use on busses. And no doubt, a similar engine to run it.

If this was "just for sleeping comfort" I'd suggest fooling around with NASA's cooling vest technology. They run yards of plain vinyl tubing (like aquarium tubing) with chilled water, pumped by a small low power pump, to a central reservoir of ice/water/slush. It cools whatever is in contact with it (your body, which puts out about 650BTU/hour when awake resting) instead of the whole world around you, so "just a little" power is enough to cool what counts.

Running something similar, on a mattress-topper or sheet, might do the trick while using reasonable amounts of power. If you try that--use oxygen mask hose, not aquarium hose. The oxygen hose has inner ridges that prevent it from collapsing when there is weight on it.

[Sandero]

hello,

I hear you on the AutoAC... but my sleeping quarters which is what I want to cool is a very small volume... and it has a door to separate it. I am not looking to cool the whole boat.

Shiva is quite well insulated and our cabie is especially well insulated as it is surrouned by cabinets and there is only a few sq ft which is simply the hull for heat gain... which is not an issue in the evening.

The boat is actually pretty cool even in the summer and the slightest breeze through an open hatch is all it takes. Humidity is the problem and only AC can remove moisture from the air.

My concern is not getting it cool enough, but it would be too cool and use too much power.

I've even though about blowing the chilled air from the bilge, but after the engine has run this is not possible. The reverse works in the winter of course, using the hot of in the engine "room" to warm the cabin.

jef
sv shiva

[Pblais]

If you look at all the units and divide the watts by 12 volts you'll get some number that represents the amps. The DC Airco 4400 will use 25 amps (300 watts divided by 12 volts). More or less amps based on watts required. It's a pure power problem. Volts X Amps = Watts. Nothing is 100% efficient so you'll lose a few BTU's along the way.

The fridge probably takes about 5 amps cycling 80% in hot weather (just a ball park). So you are talking about a unit 5 times more hungry than your fridge.

You can't just cool the volume of air in the cabin and go to sleep as the surrounding mass in the cabin will reheat the air back to what it was pronto. You'll need 25 amps for most of the night in hot weather because the mass surrounding you is hot and holds far more heat than the air inside. You'll do best in colder waters as the mass under you will be the same temperature as the water. If you are in 80 degree water you have a problem that will need it on most of the night unless it cools so you can open hatches. Running for say an hour then shutting it off will perhaps be pointless in 10 minutes after you shut it off.

[Sandero]

Paul,

First, our frig is engine drive and so when we run it we produce amps not use them because of the high output alternator.
Second, even on the hotest nights, by 3 or 4 am it is pretty cool to the point that we need a sheet over or a light cover and the fan is off by then.

The boat is not terribly hot.. in fact it is cool enough to be covered in dew in the am... sucking the moisture from the air. I really suspect that what happens in the aft cabin stays in the aft cabin... that is not too much cooling will be required to make it comfy.

I can only base this on the heat which is a forced air system and must be turned off because it get too hot. It has a very low cycle which allows the T stat to kick in for more heat if the temp really drops... but it doesn't. That is my experience and I am hoping cooling might be like heating... but I could be... and usually am... completely wrong.

jef
sv shiva

[Pblais]

Jef ,

To me it sounds like you really don't need A/C. Anchoring out we have none and the times we have been caught out on the hook that were bad it was bad all night long. Today would have been a killer it's 10PM and still 85 F with wicked humidity. It was 93 F at 7:30 PM. If you need it you can't make it off a battery bank. (Amps X Volts) = Watts. Nothing can beat the the rules of electricity. Dropping the humidity is the same thing. You need to condense moisture and that is A/C by a different name but the same Watts.

A/C on the hook without a genset is the dream that never really happens. Sometimes the quiet is worth the extra heat. Hella 12 volt fans can work a lot better than you might think. Big hatches with a wind scoop is all very great too.

[Sandero]

Paul,

The Hella is right over our heads and works great, but this whole thing is to make the wifey more comfy... like her AC'ed bedroom.

It's the wifey stupid!

jef
sv shiva

[Pblais]

but this whole thing is to make the wifey more comfy... like her AC'ed bedroom.

Not everything worth doing is worth doing well! Sometimes the best shot falls short and would it be better to have stayed home. You get to that point at some level some time. So do you stay home because it might get too hot or do you take a few hot nights because you get the really really great ones too?

I forget the really bad ones quickly only because the memory of the good ones last so much longer. It's also how I tend to see things. If it were all that "under control" I think there would be less enjoyment of the better times. So once in a while you find an A/C outlet and are tied to shore. There is such a thing as compromise. OK, so you miss once in a while. You'll be in deep trouble sooner or later any way. Being married lends itself to those situations.

[Sandero]

I go to the bateau rain, heat, snow whatever. I lived aboard, wifey stays home at times and so:

Whether the weather be good or
Whether the weather be bad
I'll weather the weather
whatever the weather
whether I like it or not.

jef
sv shiva

[hellosailor]

Jef-
Well, here's a small one:
Sharp EnergyStar Window Air Conditioner (6000 BTU) - White

from Sharp, 10+EER for $200 and 6000btu. There are some claiming EER's over 12, but also more btus or more expensive. Still, even at a relatively efficient "10+" this puppy would draw about 45A while compressing. If you figured a 50% duty cycle in your small cabin, 23A per hour...If you could squeak it down to an average of 15...times an eight hour night, that's some 120AH per night. Probably $5-600 worth of battery could accomodate that as a 50% discharge, assuming you had an inverter that could run the starting surges.

That's overall about an $800 solution, let's say $1000 since no one gives back change from boat bucks.<G>

So assuming you recharged that battery bank every day--is your wife's comfort worth a thousand dollars to you? The vastly increased battery capacity is of course a side benefit, you can use it for electric heat in the winter months.<G>

[Pblais]

There are some claiming EER's over 12, but also more btus or more expensive. Still, even at a relatively efficient "10+" this puppy would draw about 45A while compressing.

This is the same numbers no matter how you do it. There is small error in your math. The unit uses 4.5 amps AC. You would need a large inverter to make all that power. 45 DC amps is a bit optimistic if not impossible. Startup current is always an issue as well. I'm not sure I buy the 50% duty cycle either. A 12 volt solution above would use less power and not require an inverter that makes heat. Both solutions suffer the problem of too many amp hours. Were you to find a 100% efficient unit it's still a lot of power.