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Old 15-06-2019, 22:15   #1
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Watermaker Energy Calc's

Has anyone calculated / shared numbers for watermaker energy / liter (gallon)?
I'm working out power calculations for a large solar array and need to budget for water consumption.
I saw a few numbers on AH, but KW/Hr would make more sense if running from batteries and using inverter for AC motor.

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Old 16-06-2019, 00:14   #2
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Re: Watermaker Energy Calc's

Which watermaker? Their efficiency is radically different. Worst being high volume AC units to best being Spectra 12v DC units.
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Old 16-06-2019, 00:24   #3
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Re: Watermaker Energy Calc's

Ah per gallon is a common way to calculate for **energy** efficiency, and yes if you search using your watermaker that's been psted for many, varies very widely.

But gallons per hour is the other kind of efficiency, so gallons needed per week with X people aboard, coupled with

how many hours per week you want to listen to the wm cranking, or how many hours per week average you run your engine or genset anyway, all can get factored in.
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Old 16-06-2019, 01:54   #4
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Re: Watermaker Energy Calc's

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Ah per gallon is a common way to calculate for **energy** efficiency, and yes if you search using your watermaker that's been psted for many, varies very widely.

But gallons per hour is the other kind of efficiency, so gallons needed per week with X people aboard, coupled with

how many hours per week you want to listen to the wm cranking, or how many hours per week average you run your engine or genset anyway, all can get factored in.
Looks to be about 16wh/L for CruiseRO and 4wh/L for Spectra
Not important if running a genset
Very important if solar.
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Old 16-06-2019, 02:19   #5
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Re: Watermaker Energy Calc's

Greetings and welcome aboard the CF, Paul.
I assume you're aware that the Cruise RO is a 120V AC unit, and the Spectra 12V DC.
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Old 16-06-2019, 02:42   #6
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Re: Watermaker Energy Calc's

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Greetings and welcome aboard the CF, Paul.
I assume you're aware that the Cruise RO is a 120V AC unit, and the Spectra 12V DC.
I would estimate equal efficiency.
DC Perm has greater current lossed
AC Induction has greater efficiency losses
Both would be about 60-70%, depending on a bunch of sizing factors.
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Old 16-06-2019, 03:22   #7
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Re: Watermaker Energy Calc's

Welcome Paul.

All the manufacturers list the specifications so just lookup the data for the model you are interested in. As others have posted there s a major difference in power consumption between the energy recovery watermakers, such as Spectra, and the others so this feature is important to decide early in the planning process.

Generally AHrs is the better unit to use for most power calculations on a boat. Close to an AHr can be recovered from the battery for each AHr produced by the charging system. This is not true for WHrs. If you are considering an AC (120 or 240v) watermaker you may find it easier to use WHrs. If the watermaker is powered directly from a generator then battery inefficiency is not a factor, but working with the same power unit for all your boat calculations is usually sensible. AHrs is usually easier than WHrs and generally more accurate although a conversion is needed between higher volt AC and lower volt DC syatems.

Spectra produce realistic data and in the real world you will general achieve their published numbers. I have heard some other watermaker manufacturers are not quite as realistic. It might be sensible to assume slightly worse real life production and slightly higher power consumption than the brochure indicates. Also all watermakers will consume some power when rinsing and before the product water is acceptable. This does not add up to much but you are likely to need to generate more power per litre than a simple calculation from the published number suggest. So allow a fudge factor.
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Old 16-06-2019, 10:37   #8
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Re: Watermaker Energy Calc's

Also keep in mind that the lower the water temperature and the higher the salinity, the lower the product output for a given energy input.
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Old 16-06-2019, 11:10   #9
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Re: Watermaker Energy Calc's

I'll respectfully disagree with Noelex on Spectra's published accuracy. For the most part they are close but they are very voltage dependent. Their units are called "12V" but are rated (and factory tested) at 13.8V. If you have solar and make water while the sun is shining you may be running at this value, but we find the production drop at lower voltage to be about 1.5x the drop from 13.8 (and thus energy/unit increases). This is my experience with units that use the Shurflo diaphragm pump, I haven't used any of the vane pump units. The output of the Shurflo pump is the driving factor and is very voltage dependent.

Our old Powersurvivor 40, while small, slow, and an energy hog by comparison was much closer to published values across our entire "12V" operating range.
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Old 16-06-2019, 12:45   #10
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Re: Watermaker Energy Calc's

Approx. power consumption, in AHrs. Multiply by 12.4V to get watt hours:

0.9 amps/gallon Large scale desalination plant
1.1 amps/gallon Spectra
2.5 amps/gallon Large DC watermaker
3.0 amps/gallon Small DC watermaker
4.0 amps/gallon Very small DC watermaker (i.e. PowerSurvivor 35)
6.0 amps/gallon Efficient AC watermaker (assuming 100% inverter efficiency)

Source: some estimates, some published materials, some real numbers, some guesses.
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Old 16-06-2019, 15:22   #11
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Re: Watermaker Energy Calc's

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Originally Posted by Dsanduril View Post
I'll respectfully disagree with Noelex on Spectra's published accuracy. For the most part they are close but they are very voltage dependent. Their units are called "12V" but are rated (and factory tested) at 13.8V. If you have solar and make water while the sun is shining you may be running at this value, but we find the production drop at lower voltage to be about 1.5x the drop from 13.8 (and thus energy/unit increases). This is my experience with units that use the Shurflo diaphragm pump, I haven't used any of the vane pump units. The output of the Shurflo pump is the driving factor and is very voltage dependent.

Our old Powersurvivor 40, while small, slow, and an energy hog by comparison was much closer to published values across our entire "12V" operating range.


Itís why I dislike amps and AH as measurements.
The amount of power in an amp and an AH varies depending on voltage. An amp at 14.3V is significantly more power than an amp at 12.3V.

Actually I agree with Spectraís testing at 13.8V, you have to test at something and itís generally agreed upon that most systems that have 12V batteries operate at 14V plus or minus .2V
Assuming they publish testing voltage, they are being open and straightforward.
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Old 16-06-2019, 15:52   #12
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Re: Watermaker Energy Calc's

OK, I'll vent my frustration with Spectra a little more fully.

I've never seen any advertising or any literature where Spectra acknowledges this key voltage dependence. Only when you buy a unit and get the factory acceptance test paperwork do you see that nugget. And nowhere in the manual does it talk about the drop in production related to voltage, and especially not an acknowledgement that it is more than the slope of the voltage difference. Spectra's advertising focuses on a value of 13.8Wh/gallon with no reference to required voltage and the increase in energy/unit at a lower voltage.

Then they test with 13.8V at the pump terminals. This is a nearly impossible scenario in the real world, especially on units that claim to be suitable for use straight from the batteries. Even their larger units are small enough that you don't want to have to run a generator/engine for the entire water making period.

Lastly, they do acknowledge, but only in the manual, that actual production will be reduced by the approximate half hour of production that is used to rinse the unit at the end of use. If you run 4 or 5 hours that equates to at least a 10% increase in energy/useable unit. This is a harder one for advertising because I might want to run for two hours and you for 10, but I think it should be acknowledged somewhere other than deep in the manual.

Sorry for the rant, but overall I personally find their advertising practices deceptive, and deliberately so.
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Old 16-06-2019, 16:26   #13
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Re: Watermaker Energy Calc's

CJD Watermakers list their 60 LPH / 15.85 US Gallon/hr unit as 16A @ 13.0VDC
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Old 16-06-2019, 16:35   #14
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Re: Watermaker Energy Calc's

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Originally Posted by Dsanduril View Post
OK, I'll vent my frustration with Spectra a little more fully.

I've never seen any advertising or any literature where Spectra acknowledges this key voltage dependence. Only when you buy a unit and get the factory acceptance test paperwork do you see that nugget. And nowhere in the manual does it talk about the drop in production related to voltage, and especially not an acknowledgement that it is more than the slope of the voltage difference. Spectra's advertising focuses on a value of 13.8Wh/gallon with no reference to required voltage and the increase in energy/unit at a lower voltage.

Then they test with 13.8V at the pump terminals. This is a nearly impossible scenario in the real world, especially on units that claim to be suitable for use straight from the batteries. Even their larger units are small enough that you don't want to have to run a generator/engine for the entire water making period.

Lastly, they do acknowledge, but only in the manual, that actual production will be reduced by the approximate half hour of production that is used to rinse the unit at the end of use. If you run 4 or 5 hours that equates to at least a 10% increase in energy/useable unit. This is a harder one for advertising because I might want to run for two hours and you for 10, but I think it should be acknowledged somewhere other than deep in the manual.

Sorry for the rant, but overall I personally find their advertising practices deceptive, and deliberately so.
Every watermaker has the same flush issue. You flush out a portion of what you made after every run. That is why longer runs are more efficient.
Using a lower voltage on the Spectra still leaves you with the most efficient watermaker available for small marine use. My old dc Village Marine was also voltage sensitive.
As long as the manual is freely down loadable before purchase, it's a stretch to call them deceptive.
It sounds like you are not happy with your Spectra unit.
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Old 16-06-2019, 16:41   #15
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Re: Watermaker Energy Calc's

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CJD Watermakers list their 60 LPH / 15.85 US Gallon/hr unit as 16A @ 13.0VDC
Do you know anyone who uses one? Sounds interesting and very efficient. Odd marketing when they say both "Non proprietary components" and "Patented Low RPM energy recovery pump".
I don't see a price on their site.
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