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Old 26-01-2018, 13:12   #1
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Is this a crazy idea?

Is this a crazy idea?

I was looking at water makers and they're FAR more expensive than I'd be willing to pay. The solar needed to run them away from shore power is quite extensive - about the same as running a small AC unit.

AC units always have distilled water condensate trickling out of them - especially in humid environments.

Would it make sense to have the same solar system, a small AC unit, have a cooler/drier cabin, and capture the condensate, run it through a sawyer filter, then add it to the clean water tank?
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Old 26-01-2018, 13:25   #2
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Re: Is this a crazy idea?

To run AC for any real length of time, you're probably going to want to use a generator. But if you're already running the generator, I don't see a reason why you couldn't use the condensate from the AC. I've always thought it was such a waste of fresh water to see all that condensate dripping out of a boat.
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Old 26-01-2018, 13:29   #3
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Re: Is this a crazy idea?

I’m not sure what watermakers you’re looking at, but what we’ve got now, and what is going to replace it are run by solar that wouldn’t stand a chance of running an AC unit.
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Old 26-01-2018, 13:32   #4
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Re: Is this a crazy idea?

The problem with AC condensate is that rather quickly it picks up things like Legionnaire's Disease as bacteria, mold, other nice things start to grow in it, especially in the coil fins. That's why it is not done. You can certainly set up a solar still, but that is a small output and requires a fairly level and steady platform as well.

There are reasons why people either buy water, or pay for the watermaker. Still no practical alternative on the market.
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Old 26-01-2018, 16:58   #5
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Re: Is this a crazy idea?

I'd cover the entire water surface with UV LEDs to keep the area sterile. Also, it would be accessible, so it could be regularly sanitized with bleach. An elegant, cheap and efficient solution.

Also, it is my intent to pass the output through a RO membrane anyway.
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Old 26-01-2018, 17:10   #6
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Re: Is this a crazy idea?

Quote:
Originally Posted by Peregrine1983 View Post
To run AC for any real length of time, you're probably going to want to use a generator. But if you're already running the generator, I don't see a reason why you couldn't use the condensate from the AC. I've always thought it was such a waste of fresh water to see all that condensate dripping out of a boat.
The cost of the RO filter system for saltwater plus the solar system, combined, is well into four figures. I think I can run a condensate cooler on 60 watts (and even then, it might be too cold and freeze - it just needs to get below the dew point).

I looked at peltier elements because I could use PWM to operate them only to the temperature needed. However, they're quite inefficient and draw over four times the current per BTU that phase change systems do.

I'm definitely open to suggestions.

My developing notion is to develop a control circuit, which can monitor temperature and humidity to calculate the dew point. Then it would cool the element to maybe 5 degrees below that point. In a humid environment with free air flow, a vertical metal plate 100x160mm in a 80% RH environment at 80F would extract around 0.2GPH for around 60 watts. It would likely cost under $25 to produce. It would be extremely easy to use and maintain.

I'll do some experimenting and report back.
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Old 26-01-2018, 17:23   #7
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Re: Is this a crazy idea?

Go outside and put a jar under your home ac and then decide if that amount is going to worth it
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Old 26-01-2018, 17:30   #8
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Re: Is this a crazy idea?

Each of the two window A/C units that I have pick up their evaporator coil condensate with the edge their outside fan and blow it over their condensing coil cooling the coil and thus increasing the unit's efficiency and cooling capacity. Little to no condensate drips from the units. If you are planning on using a window unit, you may not have any condensate to collect.
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Old 26-01-2018, 19:04   #9
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Re: Is this a crazy idea?

Maybe not "crazy" but more of a science experiment than practical
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Old 26-01-2018, 20:24   #10
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Re: Is this a crazy idea?

Mr. Pix, at the least you would have to run all the condensate through a particle filter to remove airborne dirt that accumulated in the condensate. And be sure toxic metals from solder in the coils and fins weren't mixing in.

Then you could indeed use UV-C to sterilize the water. But that's UV-C, which is very different from the UV-A and (harder to get) UV-B LED's that you can find. There are very few sources of UV-C LEDs and UV-C quartz fluorescent tubes are the normal source for disinfecting systems. It requires UV *C* specifically, and lots of it.
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Old 26-01-2018, 22:15   #11
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Re: Is this a crazy idea?

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Mr. Pix, at the least you would have to run all the condensate through a particle filter to remove airborne dirt that accumulated in the condensate. And be sure toxic metals from solder in the coils and fins weren't mixing in.

Then you could indeed use UV-C to sterilize the water. But that's UV-C, which is very different from the UV-A and (harder to get) UV-B LED's that you can find. There are very few sources of UV-C LEDs and UV-C quartz fluorescent tubes are the normal source for disinfecting systems. It requires UV *C* specifically, and lots of it.
All ACs manufactured since 2005 use lead free bismuth-containing solder. I am in the electronics business, so getting any LEDs of any time by the reel is not a problem. If leaching of metals was a problem, over time the condenser would fail from that reason alone - it is not even a minor reason for failures, so leaching isn't a problem. That said, AC units with a SEER less than about 13 will be too burdensome to run. There are mini split units that are SEER 20 and use just 800 starting and 600 running watts for 8000-9000 BTUs. These units have encapsulated condensers.

The amount of UV-C needs to be high if the exposure is brief. However, if the exposure is continuous, it only takes careful control of the exposure geometry, for example passing the water very slowly over a very narrow tub that is filled with UV LEDs to create a 'firewall'... 40mJ/cm3 is the standard. A single LED into a 1x1mm tube, where the flow rate is 1mm3/sec would achieve that. 60ml/min or 3.6L/hr. For that intensity, volume and flow rate, a 25mA LED would achieve 40mJ/cm3.

It really helps that condensate is clear, not cloudy, and would have a very low biological content even if the condenser were loaded with slime molds, bacteria and etc. However, a cleanable, flat condensation surface could be provided - even a simple plain double-sided PCB would be a very economical and cheap 'heat' pipe. It would also be non-toxic and cleanable.

Just a case of finding which technologies fit best.

I understand a 12v 5a peltier element can easily condense 500ml in a humid environment.
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Old 26-01-2018, 22:22   #12
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Re: Is this a crazy idea?

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Each of the two window A/C units that I have pick up their evaporator coil condensate with the edge their outside fan and blow it over their condensing coil cooling the coil and thus increasing the unit's efficiency and cooling capacity. Little to no condensate drips from the units. If you are planning on using a window unit, you may not have any condensate to collect.
I wouldn't consider a window unit. They top out at around SEER 12. Also, they're too large and noisy. I do have a Haier portable unit I picked up and converted to run off 600W solar and a few LiPo cells as a start booster - its SEER 17, smaller, quieter, and when you reconfigure all the air handling it's quite efficient.

However, it's still too large for this application.

I'm just stuck on phase change cooling being an order of magnitude more efficient than peltier elements. It would take an 80W panel just to run a 60W element for most of the day. A 150W panel would allow for 24 hour operation, with a battery as intermediary.

One off the wall idea is that 1 liter of alcohol, evaporating, should produce cooling to condense 1.3 or 1.4 liters of water, in an emergency. However, that's not routine daily use like I envision.

If this mini-system could also do double duty as a heat pump, that would be a double bonus.

Am I over thinking this?
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Old 27-01-2018, 00:33   #13
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Re: Is this a crazy idea?

You’re miles ahead of me technically so I can’t comment on that aspect but I’ve still noticed two flaws:

1. You’re going to want to at least double the solar panels than you think you need because of all the loss; they get dirty, it’s cloudy, you forget to re-orient them every hour or your boat rolls and sails too much, (plus the normal electronics and cable run loss of easily 2% and the inefficiencies of battery charging of easily 20%). This all adds up to a total loss of up to 20 to 50% over the 5 hours or so a day that the sun is high enough for good efficiency.

I choose to put my panels in a fixed position and got double the capacity of what I would nominally need after losses to cover my 24h electricity needs with a 5h recharge time. This works well with surpluss production most days and never any need for a generator boost at anchor. Under sail I might still need a boost every few days when you add in the navigation lights and electronics and the potential for the sails to block out the sun.

2. Your end game of only 0.2 gallons/h seems thoroughly not worth it unless it’s a hobby project. You’d only produce 1/10 of what two people need a day if you ran it for 5h.

I had been thinking about this too but the production pales compared to reverse osmosis. I do have a large boat though which allows me to throw on all the solar panels I need. That space requirement is the limiting factor for solar powered RO with generous production volume. (Plus if you’re going through the trouble of installing solar you want it to power your whole boat, not just RO.)
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Old 27-01-2018, 01:10   #14
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Re: Is this a crazy idea?

Also 60 W for 0.2 Gl/h isn’t power efficient compared to for example 600 W for 25 Gl/h for RO. But of course you have to be able to generate the 600 W which is the bottleneck on small boats.

And you’re totally dependent on air hygrometry while the sea is always wet...
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Old 27-01-2018, 02:53   #15
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Re: Is this a crazy idea?

Quote:
Originally Posted by hellosailor View Post
The problem with AC condensate is that rather quickly it picks up things like Legionnaire's Disease as bacteria, mold, other nice things start to grow in it, especially in the coil fins...
Indeed.
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