RO/DI Running Cold

[Whys]

So it is somewhere in the low 40s outside my house at the moment. My water level needs topping off, and my RO/DI is outside doing what it does. But as I warm myself, it's got me wondering, other than freezing temperatures, are there performance issues with running an RO/DI in cold weather?

[Michael]

takes longer to make water if cold, will still do it though, just takes longer

[AZDesertRat]

Colder water slows RO production but improves the output TDS a little. Things you will want to do are measure the waste ratio in winter vs summer to see if it is still close to 4:1 waste ratio. If its not, and its probably wasting more with cold water, you may need either an adjustable flow restrictor to or a capillary tube type you trim for your exact condition so you can bring it back to 4:1. Increased waste reduces the pressure available to the membrane which further slows production.
You can also overcome cold water with a booster pump such as the Aquatec 8800. RO membranes perform well at 90 or 100 psi and increasing the pressure offsets the cold water. To get a good idea of hold pressure and temperature affect GPD take a look at the calculator at the top of this page. www.buckeyefieldsupply.com .
One thing you do not want to do is try and blend or temper hot and cold water to regulate the temperature, this is a very quick way to toast a membrane. Remember being in the shower when someone flushes the john or starts a load of clothes? You got scalded. Same thing happens to a RO membrane when you try to adjust hot and cold.

What do the 40's feel like anyway? We don't even get that cold in winter around here:D

If possible I would move the RO inside to keep it protected from the elements. You can hook it to a kitchen faucet or even the washing machine.

[Whys]

Wow. That's an encyclopedia of a response. Thank you.

"What do the 40's feel like anyway? We don't even get that cold in winter around here"

What do 40 wives feel like anyway? We don't even get polygamy around here. ;)

Sorry, just had to. :]

Thanks again.

[jgiannini]

Yeah, like DesertRat said, you can mix in some water from the hot side, but you are chancing it. It all depends on how your plumbing is setup. I was told by a gentleman at air, water, ice where I bought my RODI unit that you can mix in hot water, but anything above 90 degree water will shorten the membrane life. I've had good success with the hot water mix method, and I also use a booster pump....I get some good output. Hope that helps.

[AZDesertRat]

Mixing hot and cold is risky at best. Try mixing it once with a thermometer on the inlet side then flush the toilet. I'll bet you don't try to blend hot and cold anymore after that. You just cannot accurately temper or blend water out of a household faucet at the low flows you see with an RO/DI, a pressure change on either the hot or cold screws things up quickly.

[jgiannini]

Actually, I disagree. It all depends on your plumbing diameter, incoming street pressure, etc. That's why I said it all depends on how the plumbing in the house is setup. Now I'm not saying you also can just turn on both hot and cold full blast and not worry, but I'm only making the point that every house is different and the mixture of hot and cold will vary based on peoples houses. I have been mixing water like this for about a year now with no issues. This is just personal experience.

[AZDesertRat]

Stick a thermometer under the running water and have someone flush the toilet or run water elsewhere. You will be surprised. It sounds easy but its not so simple. A 75 GPD RO/DI at probably just under one quart per minute total flow is just about impossible to blend.

[Tava176]

Hot water will screw up your filter. Just sue cold water and buy a $20.00 submersable heater for the RO water. I live in Buffalo, NY... take it from a cold weather pro :)

the heater is the way to go.

[atvdave]

First off, I wouldn't have a RO/DI unit out side living in Spokane, WA. In the winter when the temps dip below the freezing mark the unit (when not in use) may freeze and crack the housing's, and your line's.

I live in Indiana and it gets darn cold here also. I have my unit in my garage. What I do is run about 50' of tubing from my incoming water line through my sump before it goes to my RD/DI unit. In the winter time it brings the temp up about 15 to 20 degree's.

[Tava176]

atvdave,

That is a really great idea! I may borrow that. :)