Small boat A/C

[Bill at BOATS 4 SAIL]

I think if the water is so cold that you don't need AC, you could pump it thru a car heater core to give you AC.

[Scott]

Ba- dum pum!! CCCCHHHH!!!

Thank you folks, Bill will be here all night , try the veal, Dont forget to tip the bartender!!

[Greg]

I think if the water is so cold that you don't need AC, you could pump it thru a car heater core to give you AC.

Yup, then if the water is so warm that you need AC, you could pump it thru a car heater core to give you heat.

[k9piper]

Hi Folks,
I would like to start by saying that perhaps I was a tad bit short after reading Chiips' post. I do not think Chip get to frustrated at all nor over much. As a matter of fact I sort of like it when he and others get critical with me on topics or issue.
I do not have a vast number of years under my PFD in sailing , I'm rather new at this crazy thing. It is all a learning process for me and I am just trying to play catch up for all the time that has passed me by with this new found passion.I have learned so much here on theis board and I thank each and everyone who has taken the time to read my posta and to those who have commented bacck either pro or con ...thanks for the advice and or setting me on the correct path.
Maybe some of my own issues surface time and time again. It is sort of scary when your life changes so fast. Health issues surface that were never there before and the thought of retirement is somewhat freaky as well.Never had all this time to think, to write and to dream about new ventures. The thought of another cold spell, another snow storm and still more time off of the Mighty Hudson River is depressing but in a short time it will be making ready for the first sail of the season.

Thanks for your time folks enjoy your dreams!

K9piper

[waternwaves]

<--compliments chip on his restraint............

[Scott]

^
^
^
Friggin engineers always so smug with the facts and math and physics and thermo dynamics and....and.....and.....technical stuff.

Bruce Willis said

No thanks Ma'am, Im a cop, just the Fax please.

[Catigale]

Friggin engineers always so smug with the facts and math and physics and thermo dynamics and....and.....and.....technical stuff.

I hate those gals/guys,.they are always so.....right......

[Greg]

It amazes me how some topics on this board just seems to raise the hackles of some folks.
Feeling the barbs of the previous posts, I feel the need to clarify what I was trying to say.

I don't think and never said that 55-70 degree lake water would acclimate the cabin of the Macgregor like a 5000 BTU air conditioner.

What it could do, given the proper conditions, is dehumidify the air and maybe somewhat cool the interior. Pump water though a set of coils and condensation would form on the coils if the coil temperature is below the dew point. Blow air across the coils and the outlet air is somewhat dehumidified. Examples of bulb temp/relative humidity/Dew point: 90/90/86.5 90/85/84.7 90/70/78.4 88/70/78.4 85/60/68.9

A n old set of A-coils would work better than a car type heater coil. The condensate would run down the fins to a collection pan. The setup would need to be modified so that the water inlet would supply all the tubes and shorter loops instead of longer ones. As the water is pushed though the loop it is warmed up, therefore an excessively long loop would not be efficient.

The water flow would not have to be constant. The motor could be pulsed on and off to keep the fins below dew point. Then the starting current vs running current of the motor comes into play.

Air Cfm though the coils probably wouldn't have to be great given the small size of the Mac although needs to be enough to do the job. Also the fan wouldn't have to work as hard pushing air though A-coils as it would though a heater core.

Once the biggest heat exchanger was made to fit the installation, trial and error would come to play for water and air flow.

Setup of a lake water cooling system would be time consuming and the results would be inconsistent over the course of the spring/summer. I think it would have worked for us this summer when on Cayuga lake. That lake water is pretty cool and the air temp was 90+ and high humidity. Nights with 3 fans running, swimsuit only, and whole body wet with sweat while lying on the bunk made for some miserable evenings.

I forget the make of sailboat I read about some time ago, but it had a passive cooling system built into it's design. Fresh air was pulled into the cooler bilge area and stale air was exhausted though the mast. The air in the mast was warmed by the outside temperature and created a natural draft.

I think the best location for a cooler/dehumidifier, a real installed air conditioning or better yet- a heat pump system on the Mac is the wasted space in the sink area of the bathroom. Assuming no fowl odors or fumes in the Mac bilge, the inlet air could be pulled from the bilge, ported though the coils, then easily vented fore and aft in the cabin. The sink through hull can be used for condensate discharge.

After reading the other threads likeAir Conditioner Blues and Air Conditioner, I saw a lot of assumptions and assertions- not calculations. The efficiency of this setup would be hard to calculate because of all the variables. I did notice that most of the posters saying this wouldn't work were Northerners that mostly don't have the need for dehumidification. It may work for some- is it something I will try to set up on our boat? - most likely not but the way I see it the discussion may help someone that want's to try it.

Funny, I thought this was an arena for ideas and discussion.

[craiglaforce]

Well, it is an interesting idea, but it will not work very well. What you are probably missing in your thoughts that is very apparent to an engineer, is that the heat exchanger, be it from a house unit or a car unit, is designed to function with freon evaporating on the unfinned insides at 40 deg F or so.
phase change heat transfer coefficients are usually around 10 to 20 times greater than sensible heat transfer coefficients. So for a given evaporator size and assuming lets say 75 degree water on a 95 degree day, you would at best get the cooling duty of the original air conditioner reduced by 20/55 and then again by about 1/15. multiplying these together you would expect about 1/40th of the cooling duty. However, on the finned side where you are doing the cooling, you would do doubt have a weaker fan operating than the original unit was designed for, so some additional reduction in cooling could be expected. Now we have also neglected fouling of the water side of the tubes. Lake water or salt water alike will foul after just a little bit of use and de-rate the unit a lot more. The tube passages are designed for a closed loop super clean freon stream, with zero fouling allowance. Biologicals, corrosion, and gunk will foul and plug those little tubes quickly.

Does this help a little?

Personally, I like hearing about new ideas, even if they all are not winners. But if you ask for advice, you have to be prepared for whatever replies come back. If everyone just agreed and said it would work great you might be disappointed if you went to a lot of trouble to build one and have it fail miserably.

[Frank C]

... been through this whole discussion at least twice before. l know it's not what you want to hear, but it's the truth. The only way you're going to get cooling out of the water around your boat is to jump into it.

Yeah, perhaps a little short, but clearly well-debated. I'm no engineer, but I'm willing to listen to them describe physics. Both Chip & Craig are making a very simple case ... all liquid-to-air exchangers require a temperature differential of 50*F to be energy-efficient. Otherwise you use amp hours to move water and air without receiving comcomitant benefits. The problem is, the water will gain minimal heat, and the air will be cooled less than necessary to make a significant difference. It might have some potential benefit on a 90*F day at Lake Tahoe, where the water is a constant 40 degrees.
(Unfortunately, Lake Tahoe retains that constant only at a depth of 100 feet, so pumping losses ...)

[Greg]

Appreciate the feedback, especially your information and calculations Craig.

Again, right now I'm not planning on building one of these because of the variables, such as water temp, I'm trying to make sense of the setup and what the performance would be. Maybe expanding the grey matter a little in the process.

Like you said Craig, most A/C systems have an evaporator temp around 40-45 degrees. This gives them a temperature outlet temperature 15-20 degrees below ambient air temperature, a very efficient dehumidifier and a fairly high fan speed.

Using your assumptions of 75 degree water, the water heat exchanger would have 1/40th cooling potential as an A/C system. Running the 5000btu A/C window unit in the foreward hatch of my X with the cockpit enclosure up and the hatch open on a hot night made the interior freezing cold after a short time. I'm not sure what the proper size BTU unit should be for the Mac, but assume or 2500 btu.

The evaporator coils on my A/C is 12"x7"x1". Since the water heat exchanger is only 1/40th as efficient as the A/C with the same size coils, increase the coil size by 20 or stack 20 12"x7"x1" coils for the water exchanger. The 12"x7"x20" stack could probably be installed below the sink in the head with an up draft from the bilge. That should give the approximate 2500 btu cooling capacity.

Correct me if I'm wrong, but if the air flow though the coils is slower instead of faster, more heat would be transferred. Of course if it was too slow, then efficiency would be lost the other way.

Two examples of this: 1. If the air flow over A/C coils is too slow, such as from a dirty filter or evaporator, the coils can freeze up. 2. Take the thermostat out of your car. The coolant runs too fast to pick up sufficient heat and the engine won't get up to proper operating temperature(although some internal parts can actually overheat even though the coolant temperature is lower- but that's another issue).

If the day temp is 95 and relative humidity is 90, dew point would be 91.4. If the day temp is 95 and relative humidity is 85, dew point would be 89.4. Both dew points are still above water temp so water heat exchanger should somewhat dehumidify the air, granted not as efficiently as the A/C though.

Agree completely on the gunk in the system. Not much good for efficiency.

I'm probably missing something else here, but feedback invited and appreciated.

Thanks,
Greg

[Chip Hindes]

Here is how to make best use of your A/C dollar. These are essentially water source heat pumps. Granted, very expensive compared to the WalMart window model in the front hatch. I understand from a guy who has one they work great.

I still think the best way to get air on the Mac when away from shore power, either with one of these or a cheap window unit, is to bite the bullet and also get one of those small inverter generators (Honda EU series). Of course, then you're up in the neighborhood of $2.5K total. The generator could be used for other stuff as well. These are more efficient than a standard AC so you could run them for longer on a good sized inverter/battery system.

Note as well for a hundred bucks or so additional some of these can be run in reverse for heating. Not so efficient as a combustion heater and not a lot of heat, but you avoid the expense and space consumed by another system and it's way safer than propane.

[Greg]

Agree the water source heat pump would the way to go, just not in the budget anytime on the horizon. My 5000btu window unit is 530w. I was in harbor freight last week and saw a small Kipor# KGE1000TI 1kw generator for $500. Anyone heard of these or had experience with one? It may need the hard start caps that Mad Mike uses, but should work.

[DLT]

Those Kipor generators do look promising.

Here is a shorter than I remember thread. The basic issue is that it is not a Honda, and therefore not supported like on. You'd be rolling the dice...

[Captain Kimo]

Your thread got me thinking about A/C in the boat, and I remembered a site that was advertised for a fan unit over a 28 quart Coleman cooler full of ice. The site is:

http://www.kooleraire.com/Boat%20Air%20Conditioning.htm

For $40 it sounds like something to try. I have not done so yet, but it look promising. Any comments?