RO/DI hooked up to cold AND hot supply

[spit.fire]

Originally Posted by shiftline

Doesn't hot water kill the RO membranes faster?

Yup

[hillegom]

If the pressures in house plumbing, hot and cold, are equal, why not put a john guest 1/4" ball valve in the hot water line and open it a smidgen. You would then use two one way check valves so that the hot and cold doesn't mix.

Just as an aside, hot water tanks have sacrificial zinc anodes in them.
they corrode before the steel does. Your RO membrane would have to take on the additional job of removing zinc. But I do not think that there would be very much of that in the water. The anodes last at least 5 years, the length of time most hot water tanks are warranted for.

[The Codfather]

Originally Posted by spit.fire

Yup

Agreed, hot water will damage the menbrane. As mentioned a mixing valve is the best way to blend the water, shoot for 20-21C for best performance.

[Myka]

Originally Posted by The Codfather

As mentioned a mixing valve is the best way to blend the water, shoot for 20-21C for best performance.

I never heard of one before this thread. Now there is an answer! I'm glad it's this simple. I even found a SharkBite one so I can install it myself. Thanks guys!

[mike31154]

There's a trade off to the better production ratio eh? IMO, save yourself the hassle. Not only are you using more energy for a bit or warm water, but the rejection rate with warmer water is worse, so you'll burn thru DI media faster. Personal experience with my unit in winter vs summer - summer RO TDS @ about 14-16 degrees C incoming water temp = 1. Winter RO TDS with incoming water @ about 8 degrees C = 0. I can live with a slightly lower production rate thank you very much. Incoming TDS for the most part is in the 160 to 170 range in my humble abode. That's Kalamalka Lake water. On the rare occasion they switch us to Duteau Creek source, TDS drops to 50!

[The Codfather]

Originally Posted by mike31154

There's a trade off to the better production ratio eh? IMO, save yourself the hassle. Not only are you using more energy for a bit or warm water, but the rejection rate with warmer water is worse, so you'll burn thru DI media faster.

The temp of the water here entering the house is right around 4C, so it does improve production quite a bit by increasing the temp. I have a zero waste, so i have no reject water, so i guess pending on your situation and your water quality to start with, it does make a difference.

[The Codfather]

M, do you have a booster pump? Or do you run on line pressure? I guess depending on what your requirments are, maybe youd be farther ahead by adding a booster pump instead of blending your water for better production.
If you go the cheap route on a blended control, it is not very accurate, also depending how you distribution piping is done, you may find that there is a large pressure difference between the hot and cold. There are a few factors to consider, id boost before i blend. I have access to the equipment through work, thats why i went cadillac on my system. Just my 2cents.