Actual water yield per hour from 100GPH RO/DI?

[torero500]

Looking into which size to buy, 100 GPD or 150 GPD. I was wondering how long it actually takes to make five gallons of RO/DI water from a standard washer hookup without any booster pump. Water pressure is decent.

I know that the math says a 100GPD unit should make 4 gallons in a hour, but have heard it's far below that.

[chimmike]

I think the terminology your using is wrong, it's 100gpd

24hrs per day, 100gpd/24=4.17gph. some are overrated, some underrated.

[Eel Freak]

If the unit truly is making 100GPD (it's Gallons Per Day, not GPH...) then you're looking at about four gallons an hour. Pressure and temperature are the two big factors here. It's most likely a DOW/Filmtec membrane so it is rated at 100GPD with 50psi pressure and water that is 77 degrees. To correct for pressure take your pressure and divide it by the rated pressure. Save the number. Here's a chart from SpectraPure for temperature correction.

Calculation of Temperature Correction Factor (TCF): The output (GPD)
also decreases with decrease in temperature. This is because water viscosity
increases with decrease in water temperature.
Temperature Correction Factor Table (TCF)
°F /°C TCF °F \°C TCF °F \°C TCF
41.0 /5 0.521 59.0 /15 0.730 77.0 /25 1.000
42.8 /6 0.540 60.8 /16 0.754 78.8 /26 1.031
44.6 /7 0.560 62.6 /17 0.779 80.6 /27 1.063
46.4 /8 0.578 64.4 /18 0.804 82.4 /28 1.094
48.2 /9 0.598 66.2 /19 0.830 84.2 /29 1.127
50.0 /10 0.620 68.0 /20 0.857 86.0 /30 1.161
51.8 /11 0.640 69.8 /21 0.884 87.8 /31 1.196
53.6 /12 0.661 71.6 /22 0.912 89.6 /32 1.232
55.4 /13 0.684 73.4 /23 0.941 91.4 /33 1.267
57.2/14 0.707 75.2 /24 0.970 93.2 /34 1.304

using that, take your rated GPD, multiply it by the number from the pressure calculation and then multiply it by the number from your water temp based on the chart above. This will give you your true production rate as long as you're restricting the water on the waste appropriately.

[sslak]

I have an air/water/ice 75GPD unit and I get about 3.5 to 4 gallons per hour out of mine.

[chuckreef]

All of the above are too complicated.
When purcahsing figure you will get about half the rated value.
So a 100 gpd will make about 50 in 24 hours or 2 gallons an hour.

[RokleM]

Originally Posted by chuckreef

All of the above are too complicated.
When purcahsing figure you will get about half the rated value.
So a 100 gpd will make about 50 in 24 hours or 2 gallons an hour.

Not really true. My 75GPD is doing about 99GPD right now due to pressure and temp. The "XX GPD" numbers are from the manufacture based on a specific temp and specific PSI. You will be plus or minus anywhere from a very small amount to HUGE amount dependent on your setup.

Make it easy (doesn't have 150gpd, but you can calculate the rest):
http://buckeyefieldsupply.com/calc.asp

[NewBostonConst]

Mine has always put out about right what it is rated for, new or old cartages.

[Levito]

Eel Freek is right, it will absolutely depend on the pressure coming in, the temperature, and the restriction on your waste line. Assuming your pressure is relatively normal, the temp is in range, and your waste line is restricted properly, you should get pretty close to what the unit says it will output. I have a 50 gpd RO/DI. Ideally it would put out 2.1 gallons/hour. In reality I find it to be pretty close to that mark, maybe a little under. It takes me about 2:45 to fill a 5 gallon bucket.

[Eel Freak]

Originally Posted by RokleM

You will be plus or minus anywhere from a very small amount to HUGE amount dependent on your setup.

Make it easy (doesn't have 150gpd, but you can calculate the rest):
http://buckeyefieldsupply.com/calc.asp

Good link, and my 75GPD DOW/FilmTec membranes get 135GPD with my booster and temp figured in. (90psi @ 77 degrees)

[sedor]

I don't know whats wrong with my pressure but it takes about 2.5 - 3 hours to fill a 5G bucket and I use a 100 GPD unit. I usually fill my buckets from the hose spicket outside. I can't tell you how many times I forgot and overflowed buckets onto the floor when I used to run my system inside.

[Eel Freak]

Originally Posted by sedor

I don't know whats wrong with my pressure but it takes about 2.5 - 3 hours to fill a 5G bucket and I use a 100 GPD unit. I usually fill my buckets from the hose spicket outside. I can't tell you how many times I forgot and overflowed buckets onto the floor when I used to run my system inside.

What's the pressure and temp of your source water and are you restricting the waste line?

[torero500]

How do you restrict the waste line? And why does that increase output?

[Eel Freak]

It can be done in various ways. When you buy a unit it should
come with one either a valve or a smaller diameter pipe (called capillary-style) that slides into the normal waste line to restrict it. It increases production because it puts pressure on the membrane allowing some water to pass through. The more you restrict it the more you produce, however if you restrict it too much, it can cause membrane scaling which will deem the membrane useless.

[Thumbster]

RO membranes get their ratings under ideal conditions. Some are rated for 50 PSI some a little higher. If you have a higher PSI you will make water faster, to a point.

Check the rejection rate of the membrane. Some have 98% rejection, meaning they reject 98% of the TDS (bad stuff) in the water (under ideal conditions). Some higher GPD membranes make more water by skimpimg on the rejection rate. I've seen 150 GPD membranes with only a 90% rejection rate.

All that being said, i have a well with pressures between 45 and 70 PSI. I have a Dow/Filmtec 75 GPD membrane with 98% rejection on my RO unit and i am making 2 gallons an hour with 15 TDS. My water before going into the RO is about 350 TDS.

Forgot to add...don't get wrapped around the axle worrying about restricting the waste line. If you buy an RO unit it should come with the appropriate flow restrictor that just hooks onto the waste line. You might ask though if you request a different GPD membrane than originally came with the unit.

[RichardJ]

Originally Posted by sedor

I don't know whats wrong with my pressure but it takes about 2.5 - 3 hours to fill a 5G bucket and I use a 100 GPD unit. I usually fill my buckets from the hose spicket outside. I can't tell you how many times I forgot and overflowed buckets onto the floor when I used to run my system inside.

Same for me ... minus the overflow - so far and fingers crossed on that!

[Agu]

Input water temperature has a huge influence. In Minnesota in January I was lucky to get a gallon/ hour from my 100 GPD RO/DI (Water temp in the 50's F). In Florida an output of 5/gph is normal in the summer when tap water is close to 80 degrees F. Same RO/DI, different climates.

Some of my friends in Mn used a mixing valve to raise the input water temp. They're sold for use with toilets to keep the tank from sweating due to cold water.

[Bri272]

Originally Posted by Thumbster

RO membranes get their ratings under ideal conditions. Some are rated for 50 PSI some a little higher. If you have a higher PSI you will make water faster, to a point.

Check the rejection rate of the membrane. Some have 98% rejection, meaning they reject 98% of the TDS (bad stuff) in the water (under ideal conditions). Some higher GPD membranes make more water by skimpimg on the rejection rate. I've seen 150 GPD membranes with only a 90% rejection rate.

All that being said, i have a well with pressures between 45 and 70 PSI. I have a Dow/Filmtec 75 GPD membrane with 98% rejection on my RO unit and i am making 2 gallons an hour with 15 TDS. My water before going into the RO is about 350 TDS.

Forgot to add...don't get wrapped around the axle worrying about restricting the waste line. If you buy an RO unit it should come with the appropriate flow restrictor that just hooks onto the waste line. You might ask though if you request a different GPD membrane than originally came with the unit.

[Buckeye Hydro]

You can find our calculator here: http://www.buckeyehydro.com/calculator/

Russ

[ReefsandGeeks]

I have good water pressure, and typically get around 60-70 GPD out of a 100 GPD unit with new filters. You will also potentially lose some flowrate when the filters clog. Backflushing the RO membrane occasionally can help with this, but you still need to change the pre-filters on time.

I'd say if your tank is in the 75+ gallon range, it'sd be worth it to get the 150 GPD unit. It's nice to have the ability to filter quicker in the event of an emergency.

[Fraq]

I have a 150GPD and it takes me about 25-30 minutes to make 5 gallons, this will all depend on your water pressure though, so it'll vary.

[Buckeye Hydro]

Originally Posted by devastator007

Backflushing the RO membrane occasionally can help with this...

Just so no one gets confused, you never, ever want to BACKflush your membrane. Never reverse the flow direction through a membrane.

Russ