RO Production rates go down in winter
- Thread starter acroholic
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So you don't have a pressure gauge on your RODI?
that's 30 gpd. The slowest ro unit I know of is 50gpd which I assume you have. You really need to get a pressure gauge and see how much psi your pushing. To be honest though, you should really invest in a much higher production rate rodi unit because your doing nothing but waste a ton of water with these little units.
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Let's back up a little.
A 75 gpd membrane can yield only 30 gpd if you feed it low pressure and cold water.
The ratio of waste water to purified water doesn't change in a properly configured RODI system regardless of the gpd rating on the membrane - should always be about a 4 to 1 ratio.
Russ
So your telling me that within those 4 hours he left his RODI running, he only throw out 20 gallons of water in the process? I don't know about you but a stream of waste water and 1-2 drops of product per second don't look like it's a 4 to 1 ratio to me. Try catching your waste water in a bucket and tell me how much you throw out before you reach a gallon of product water. I have one of the fastest RODI unit out of everyone I know (800+ gpd), my product water flows out faster then most waste water lines from our most well known vendors and I'm still putting out a 2 to 1 ratio. So again, it's hard for me to believe he's only throwing out 20-25 gallons in those 4 hours.
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My point was that it is not the gpd rating on the membrane that's the issue. It's likely low pressure causing problems. If you have low pressure, getting a new membrane with a higher gpd rating won't address the issue. So take ANY gpd membrane, feed it low pressure, and you'll see:
*slow production
*reduced rejection (becomes more acute at lower pressures)
*a waste to purified water ratio higher than 4:1
IMO, you really need a minimum of two tools to run these systems: 1) pressure gauge, and 2) tds meter that can read a)tap water, b)RO water, and c)DI water. W/out either of these two tools you can make water, but you're really flying blind if you need to do any troubleshooting of want to know how your system is operating.
Russ
That comment made more sense now but at the same time kind of backs what I was trying to say. I mentioned he needed to get a pressure gauge to see what kind of psi he's pushing but should have also mentioned that having the proper pressure is a key factor in proper production rate so sorry I left that part out. You are correct that no matter what RODI unit you have, not having the proper pressure will also result in low production and high rejection rates. Either way, I still think the least anyone should get in this hobby should be at least a 150 pgd unit. Anything less then that, you are wasting money by jus throwing water away and waiting hours to a whole day for a little bit of water. When I first started I made the mistake of buying a 50 gpd unit and it went out the window the first day and I went out and got my current unit. Now I don't expect everyone to spend $1500+ on an RODI unit, but at least 150+ gpd. You'll thank yourself when your in an emergency and need RODI water fast.
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low pressure yields LOW rejection rates
Having a lower gpd membrane doesn't waste any more water. It will make purified water <u>slower</u>, but in the end, in a properly configured system with appropriate temperature, pressure, etc, you'll have x gallons of purified water and 4x gallons of waste water regardless of the gpd rating on the membrane.
As you jump up from residential scale systems like most in this hobby use to more expensive commercial systems with a motor and high pressure pump, the ratio of waste water to purified water is often less than 4:1 due to the high flow rates and (often) softened feedwater.
Russ
Like I said, try catching your waste water with a bucket and let me know if your getting a 4 to 1 ratio on a 50 gpd RODI unit. Even IF you get exactly 50 gpd, that's 8.33 gallons every 4 hours, I promise you, you will not be throwing out just 33.33 gallons of waste water. I'll leave it at that.
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The key (from my post above) is the clause about a "properly configured system." If you're not at something close to a 4 to 1, regardless of the membrane gpd, then by definition, it's not properly configured. Flow restrictions, an inexpensive ($4), quickly changed part, present on every RO or RODI system controls the ratio. If you're not at a 4 to 1, change the flow restrictor!
Stock/"off the shelf" flow restrictors are sized based upon some assumptions including 77F feedwater and 60 psi. If you have colder water, of if you have lower pressure, you'll have a higher ratio (e.g., 6 to 1). Just change your restrictor to match your conditions.
Same thing applies to higher pressure. If you add a booster pump and suddenly you're getting 135 gpd from a 75 gpd membrane, you'll likely have a waste to purified water ratio lower than 4 to 1. Just realize that the lower the ratio is, the less water you have flushing the membrane, and you are risking prematurely fouling/scaling the membrane. If you have exceptional quality feedwater like some in the Atlanta area, you can probably get away with a lower ratio.
Hoang - I don't think we're disagreeing, I just think you made some generalities that aren't necessarily accurate.
Russ
Stock/"off the shelf" flow restrictors are sized based upon some assumptions including 77F feedwater and 60 psi. If you have colder water, of if you have lower pressure, you'll have a higher ratio (e.g., 6 to 1). Just change your restrictor to match your conditions.
Same thing applies to higher pressure. If you add a booster pump and suddenly you're getting 135 gpd from a 75 gpd membrane, you'll likely have a waste to purified water ratio lower than 4 to 1. Just realize that the lower the ratio is, the less water you have flushing the membrane, and you are risking prematurely fouling/scaling the membrane. If you have exceptional quality feedwater like some in the Atlanta area, you can probably get away with a lower ratio.
Hoang - I don't think we're disagreeing, I just think you made some generalities that aren't necessarily accurate.
Russ
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Hopefully it has a pressure gauge.
Regardless of membrane rated output, without proper pressure a 150 gpd setup will not produce much more water. The second membrane is recycling the waste from the first. If the first isn't getting enough pressure, the second one certainly won't have enough to produce much if any product. I think it's safe to assume to best utilize your well to RO supply, you are going to need a booster pump. You can wait to see the pressure but I betting it's very low...
If this is a Melev's unit, it prolly is not a dual 75 gpd membrane unit like the BRS water saver type (which I have). The only 150 GPD Melev unit on his website is a single membrane with a booster pump and pressure gauge, so OP should be set up after he gets it going. Looks nice.
