Improving RODI filter water conversion

[zeroinverse]

In the cold winter months RODI water filters do not work that well due to the cold water being denser and significantly lowering your filtering ability and increasing time to filter water.

Normally, you may get a 1:4 ratio of filtered water vs waste water. With the denser cold water, your ratio may go to 1:6 to 1:8 or more. That means (a) you are wasting more water down the drain. For a 20 gal water change that means maybe 120-160 gal of waste water instead of 80 gal.

Also, it takes longer time to make the same water. A 75 GPD (filtered water device may decrease to a 40GPD filter, etc.

The culprit is water temperature/density.
RODI filters are meant to be run optimally at 70-80 deg F. Cold water, especially during winter is like 45-50 deg. That's 20-30 deg difference.

My solution, use an anti-sweat valve.

 

[zeroinverse]

Anti-sweat valves are used in areas MUCH colder than California where very cold water enters warm houses (in particular toilets). This causes the cold water to cool the toilet reservoir so much that water condenses on outside of the toilet reservoir and causes a lot of "sweating" onto your bathroom floor.

Anyways, anti-sweat valves work by combining cold water with an adjustable hot water. You could do this with a T-fitting, but you would probably end up with higher cold water back pressure pushing cold water into your hot water pipes. Not a good idea if your RODI will be running for 4-10 hours to make water and you try to take a shower. You'll get luke-warm water.

Anti-sweat valves have one-way valves built into each inlet. This means no cold water can enter hot water inlet line and no hot can enter the cold inlet line.

Anti-sweat valves allow you to adjust HOW much hot water you want to mix/combine. So you basically adjust it to around 70-80 deg F outlet temperature.

NOTE: remember, when it is summer, your cold water line will get warmer, so either you need to adjust it again as weather warms up, or you need to lower the mixed outlet water temperature now a few degrees (during winter) so water can rise a bit and not exceed 90-100 deg F.

Too hot water temperature (above 100-120 deg F) will ruin your RO membrane.

 

[Grant W]

Go Ron. I've noticed the drop off during colder times also. My RO unit is in the garage so def affected.

 

[zeroinverse]

So how do you make it and how much does it cost...

Parts:
Anti-sweat valve ($15 on Amazon)
I bought a used one on Amazon - $8 (free shipping)
This uses 1/2 FIP for inlet & outlets.

Dual outlet shutoff valve ($18 each, need two, one for hot, one for cold water)
(I used dual outlet with teo knobs so I can independently shutoff the water lines to RODI).
My house copper pipes are 5/8, so I got a 5/8" compression inlet with two 3/8" compression outlets.

3/8" compression to 1/2" FIP braided faucet connector (12" long in
my case). ($6 each, need two, one of hot, one for cold).

1/2" FIP to 1/2" FIP braided pipe ($8, new one)
Connects outlet of anti-sweat valve to my RODI filter (in this case, it goes to a ball valve & then RODI Johnny Quest 1/4 plastic piping.



Total cost:
$15+$18+$18+$6+$6+$8
$71 total cost.

Technically, you should already have some of the parts already if you hooked up your cold water faucet line to RODI.

For me, it cost me about $50 for the modification.

And no I can make water faster (in case I forget to make it ahead of time). And less water goes down the drain (volumetrically).

Yes, some people will argue I am dumping lukewarm water down the drain and therefore also wasting natural gas that is used to heat my water heater. But for me, I just want to cut my RODI water production time in half (during winter months).

 

[zeroinverse]

Go Ron. I've noticed the drop off during colder times also. My RO unit is in the garage so def affected.

Yup! That's what I noticed. I turned it on overnight and maybe only got 10 gals in my 35 gal Rubbermaid trashcan when I woke up. That's like 6 hours for a 75 GPD that should be doing like about 20 gal for the 6 hours.
So I researched it and found that I could use a electric water heater in vat of water to warm up a long tubing before running it into RODI filter. That just seemed more expensive (electricity vs natural gas), plus the heat transfer is not that great so I may only raise water temperature by 10 degrees if that. That's 45 deg up to 55 deg and I'm trying to get it up to 70-80 deg.

In order to do that your water vat & electric water heater would need to be like 100 deg F so that the cold water can meet halfway to get to 70-80 deg F.
That's probably like a 200-300W heater running for 6 hours.

Since we already use so much electricity for fish tank (ie we are in a higher electricity price tier)... I wanted a "cheaper" solution.

 

[Grant W]

I think we are going to have to rename you our mad scientist LoL. Fun to see another reef maniac having fun with it.

 

[Reef Bass]

+1 go Ron! It's nice to know there are options.