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Old 14-09-2017, 19:28   #1
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Tellie, you there? H2O ???

Up until recently watermakers were not a topic for me so I knew squat.
I've been Googling so now know squat plus a bit.

The boat, watermaker and use, are irrelevant to this discussion.

I tried to make sense out of an old Passagemaker piece that I hope you can shed some light on or direct me to a simple man’s rendition.

In terms of a 700 GPD unit they said;
“All reverse osmosis membranes are tested and rated for 77degrees Fahrenheit water temperature; but their efficiency diminishes rapidly in colder water. The standard Filmtec SW30-2540 membrane used here produces 700 gallons per day at 77 degrees Fahrenheit, but it only makes 435 gallons per day at 55 degrees Fahrenheit, a typical summer water temperature in the Pacific Northwest.”

So, is this accurate and is a 20% drop in output efficiency for each 10 degree drop in temp a reasonable number to work with? If so, would those numbers (700 GPD) translate to 280 GPD (11.6 GPH) in Johnstone Strait, BC, in December with sea temps at 45 degrees?

That article also talks about it using about 20 gallons to flush the unit.
Correct?
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Old 15-09-2017, 05:57   #2
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Re: Tellie, you there? H2O ???

I'm not tellie and have nowhere near his knowledge, but we do have a spectra watermaker.

yes - watermakers produce less in colder water - tha's why spectra makes a 200T (tropical) which is designed ot use in warmer waters (produces about 20% more).

So your watermaker will produce less - although going down to 1/3 production sounds extreme.

20 gallon flush is also extreme - ours uses about 1/3 of its hourly production for a flush - in our case, it produces 30 liters per hour and uses 10 liters for a flush
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Old 15-09-2017, 06:02   #3
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Re: Tellie, you there? H2O ???

Quote:
Originally Posted by carstenb View Post
I'm not tellie and have nowhere near his knowledge, but we do have a spectra watermaker.



yes - watermakers produce less in colder water - tha's why spectra makes a 200T (tropical) which is designed ot use in warmer waters (produces about 20% more).



So your watermaker will produce less - although going down to 1/3 production sounds extreme.



20 gallon flush is also extreme - ours uses about 1/3 of its hourly production for a flush - in our case, it produces 30 liters per hour and uses 10 liters for a flush


Out of interest, how long does the flush cycle take per hour of production? Does the flush run sweet water through directly to wash (I'm assuming salt and gunk from) the salt-side of the membrane, or does it pulse?



I ask because you seldom see flush volumes being taken into account during discussions of production efficiency. Whereas many, I'm sure, will quote produced water rates, do all then account for water re-consumed during flushing and quote the net production rate? I'm assuming that flush volume percentages vary between models and manufacturers.



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Old 15-09-2017, 06:12   #4
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Re: Tellie, you there? H2O ???

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Originally Posted by Cavalier View Post
Out of interest, how long does the flush cycle take per hour of production? Does the flush run sweet water through directly to wash (I'm assuming salt and gunk from) the salt-side of the membrane, or does it pulse?



I ask because you seldom see flush volumes being taken into account during discussions of production efficiency. Whereas many, I'm sure, will quote produced water rates, do all then account for water re-consumed during flushing and quote the net production rate? I'm assuming that flush volume percentages vary between models and manufacturers.



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My view on flushing is that it need not happen on a unit in use every day. So the volume is a drop in the bucket of total production.
For instance, our watermaker, when in use, is run daily. We don't flush in this scenario. However if it's going to be offline for more than two days, it gets a flush (equivalent to 45 minutes output). Mind you we've got the midget watermaker with low output, so it takes more of the total output to create enough product water for a useful flush.
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Old 15-09-2017, 06:27   #5
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Re: Tellie, you there? H2O ???

According to this paper by Axion the output would drop to approximately 50% at 50 deg. F temp. (from 77 deg. F) everything else being equal. However if you are cruising in cold water most of the time you could use a membrane that has greater efficiency at lower temps.

Methods for Countering Production Loss in an RO System
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Old 15-09-2017, 06:29   #6
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Re: Tellie, you there? H2O ???

Sailmonkey, do you not wash out your prefilters after every use?
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Old 15-09-2017, 06:37   #7
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Re: Tellie, you there? H2O ???

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Originally Posted by DeepFrz View Post
Sailmonkey, do you not wash out your prefilters after every use?
Nope, The single pre-filter goes (water clarity dependent) about a week without being pulled and rinsed with seawater. Like i said though, when we're using the watermaker it is in use daily so we don't get the stink water (only occasionally).
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Old 15-09-2017, 06:41   #8
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Re: Tellie, you there? H2O ???

Quote:
Originally Posted by Cavalier View Post
Out of interest, how long does the flush cycle take per hour of production? Does the flush run sweet water through directly to wash (I'm assuming salt and gunk from) the salt-side of the membrane, or does it pulse?



I ask because you seldom see flush volumes being taken into account during discussions of production efficiency. Whereas many, I'm sure, will quote produced water rates, do all then account for water re-consumed during flushing and quote the net production rate? I'm assuming that flush volume percentages vary between models and manufacturers.



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WE normally use our watermaker every 3-4 days (we have two 170 liter tanks) or whenever one of our tanks is empty. While we don't need to flush if we use this often, we do because 10 liters doesn't mean that much.

When we aren't using the water (hudson river/ICW) we simply flush it every 5-6 days. WE just pickled it for the first time last week because Capri will be hauled and be on the hard for about a month.

We've never worried about the amount of water used to flush - it simply isn't an issue.

a flush in our system takes 4 minutes - there is some pulsing of the water but not much.
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Old 15-09-2017, 08:00   #9
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Re: Tellie, you there? H2O ???

Quote:
Originally Posted by carstenb;
in our case, it produces 30 liters per hour and uses 10 liters for a flush
Thanks for that, casstenb.
All good information but I’m still wondering if there is a scale, curve, flow chart or something to determine production loss in relation to temp. There doesn’t seem to be any standards; one watermaker rates output at 77 degrees while another is 68.

Does year round boating in temps of 45-55 degree water have a huge impact and is there a way to calculate the loss. “Go bigger” doesn’t answer that.

Points to ponder from your post;

Is your 30l/hr a year round average, or just summer production?

30l/h = 6.6 imp or 8 US gallons which even at a conservative 15gpd means a lot of generator and RO time, just to keep up.

Copenhagen minimum temps are reported to be 10 degrees (F) higher than ours.

A conservative use of 15gpd is camping, not comfort, which is to me the goal of a watermaker.

EDIT...
Quote:
Originally Posted by carstenb;
When we aren't using the water (hudson river/ICW)...
I just saw this and realized you are not in the real Copenhagen so, our temp differences might be even greater.
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Old 15-09-2017, 08:29   #10
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Re: Tellie, you there? H2O ???

Thanks for the posts ...... interesting comments and learnings
I sent Tellie an email about two weeks ago (not via CF) ... we were communicating before he went to Europe on holiday and have not heard from him since
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Old 15-09-2017, 08:44   #11
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Re: Tellie, you there? H2O ???

Englewood,

We have an older Spectra [Santa Cruz model] that doesn't vary much on output in the waters we frequent between 56° and 61°N.

In summer the raw water temps reach mid 50s F, and go down to mid to low 40s F in winter. However, when we go into a fjord with a tidewater glacier, the water quickly gets into the 30s F [and we typically turn the watermaker off if in turbid, glacial water to save the prefilters...]

My casual observations of the flowmeter on the unit over time as correlates to raw water temperature are: [Note: We always run 2 infeed pumps...]

55°F - 12-13 GPH
45°F - 10-11 GPH
35°F - 9-10 GPH

Power consumption averages about 1.1 AH @ 12VDC / gallon in this temperature spread.

Edit: Regarding flushing, our unit is supposed to be flushed with fresh every 5 days if not used more frequently than that. A typical flush cycle is 5 mins and uses about 1.5 gallons/minute. A minimum flush cycle is 3 mins.

The bottom line for us is the unit suits our needs very well in all the conditions we experience. The 8+ year old membrane still produces sub 150ppm product. Therefore we don't give raw water temp a second thought [unless we fall in! Then we find it difficult to think at all...]

In case this is useful.

Cheers! Bill
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Old 15-09-2017, 08:53   #12
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Re: Tellie, you there? H2O ???

Quote:
Originally Posted by Cavalier;
...seldom see flush volumes being taken into account during discussions of production efficiency.
Great point, Cavalier. Trying to be educated on ROs reminds me of the old days trying to compare "stereos." Every maker use their own rules for output and power specs.

I like that Cruiser RO states GPH not GPD.
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Old 15-09-2017, 09:02   #13
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Re: Tellie, you there? H2O ???

Quote:
Originally Posted by wrwakefield;
In case this is useful.
Bill, yes, very helpful. Always nice to know what the immediate neighbours do.
Quote:
Originally Posted by wrwakefield;
We have an older Spectra [Santa Cruz]
Hoping not to turn this into an anchor debate, if replacing it or moving on, would you go Spectra again?
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Old 15-09-2017, 10:14   #14
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Re: Tellie, you there? H2O ???

Quote:
Originally Posted by englewood View Post
Thanks for that, casstenb.
All good information but I’m still wondering if there is a scale, curve, flow chart or something to determine production loss in relation to temp. There doesn’t seem to be any standards; one watermaker rates output at 77 degrees while another is 68.

Does year round boating in temps of 45-55 degree water have a huge impact and is there a way to calculate the loss. “Go bigger” doesn’t answer that.

Points to ponder from your post;

Is your 30l/hr a year round average, or just summer production?

30l/h = 6.6 imp or 8 US gallons which even at a conservative 15gpd means a lot of generator and RO time, just to keep up.

Copenhagen minimum temps are reported to be 10 degrees (F) higher than ours.

A conservative use of 15gpd is camping, not comfort, which is to me the goal of a watermaker.

EDIT...
I just saw this and realized you are not in the real Copenhagen so, our temp differences might be even greater.
Our unit produced the same in the Baltic and northern scotland (summertime). Water use is a personal thing - we use about 30-35 liters per day (10 gals or so) and this includes bathing etc. We do not ration water, we use as much as we please, we can always run the watermaker.

Our solar gives us 40 liters of hot water per day.

We do normally bathe in sea water and then rinse off throughly with fresh water. When we sail passage - we shower in fresh water
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Old 15-09-2017, 10:18   #15
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Re: Tellie, you there? H2O ???

Yeah sorry for not being as available as normal. I did go to Europe. First vacation in five years cut me some slack<grin>. Of course no sooner than I came back Irma was threatening us down here so I have been a bit preoccupied. I see more premature membrane fails and bio-fouling because the fresh water flush was never properly set up. My input about fresh water flushing is this and is generally for all brands. Unless you run your watermaker every day you need to flush your system after each use. You're not saving enough energy, money, or time, to make not doing it sensible. 20 gallons is way over the top to flush a system unless it is a huge 20,000+gpd. But every watermaker is going to be different even identical watermakers on different boats should have their flush cycle carefully matched to the boats capabilities. The amount of fresh water and time should be determined on an individual basis. Most of this depends upon your boats house pressure pump. These come in all difference capacities as far as pressure and flow go. A boat with a 5gpm flow is going to flush the watermaker faster than a 1.5 gpm pump will. I always check the brine discharge ppms to determine both flush duration and gallons needed to perform a proper flush. At the very end of your flush cycle you should be reading below 1000ppms at the brine discharge. Once you figure this out, this is the amount of time to set your flush for. Then the simple math of time X gpm rated house pump and this will give you a close enough idea on how much fresh water is being used to flush your system. Again, every boat will be somewhat different depending on how the boat is set up and how the watermaker is installed. If the plumbing for the watermaker is elaborate and spread out or the install is short and compact the flush will take either a bit longer or shorter, and the volume will be different. The same with production in warmer and colder waters. Even watermakers of the same brand and size will give different results on different boats. There are a lot of variables. The membrane being one. Even the same size membrane from the same manufacturer will different in production one to another, it's just the nature of the membrane beast. Power curves on identical boats are usually all over the charts, again the nature of the beast because of the ships owners chosen other power systems. So in short, looking for number claims from manufacturers while a good basis to start from are never going to give you the real story in real world application.


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