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Tap or DI?

GroundUp
GroundUp Member Posts: 1,282
This is probably a dumb question to a lot of you, but I've never had it explained to me. It seems to be the common consensus that tap water is almost never acceptable for hydronic systems. Whether city or well, hard or soft, it seems to be eschewed in favor of DI, RO, distilled, etc depending upon who you talk to. I have almost always used DI water to dilute my glycol and add inhibitors accordingly (per the water testing companies we use), but I've been thinking a lot lately about the "hungry" tendencies of the DI/RO/distilled variety. Doesn't it all seek minerals from the system components, eventually causing more harm than good? If properly treated, what makes tap water any worse to fill your system with than something which has had all the minerals stripped from it? In my eyes, treated hard water should be the best option as it's not trying to eat any system components. If someone could please shed some light here would be greatly appreciated.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 17,049
    Not sure I can shed much light -- but I'll give it a shot.

    First, a fundamental principle: water is pretty darn close to the universal solvent. There are a few long chain plastics -- the unpronounceable polywhatnots (including polyethylene, but not including polyvnylchloride!) which it doesn't attack, at least a little bit. But pretty much everything else, yeah.

    That's step one. Step two is that, for all that, almost everything doesn't dissolve very much. There are exceptions -- sodium chloride is a notable one -- but that requires some qualification. Many metals, particularly, are quite soluble if they can ionize and if the anions present in the water don't form stable precipitates. Calcium, for instance. If there is enough carbonate around (relatively low pH) it will form calcium carbonate and we will get scale. Iron is another. If it ionizes to plus 2 (ferrous iron) it's surprisingly soluble. If it can ionize further to plus three, it can and often does precipitate as magnetite, which is almost insoluble (but wreaks havoc with ECM motors, among other things...). Iron is unusual, too, in that while the various iron oxides are relatively insoluble, most of them are also not particularly stable. Rust.

    There are some iron alloys which form a stable oxide coating, at least in the absence of chloride -- Corten steels, and the various stainless steels.

    OK back to the question. The reason that pure DI or distilled water is a problem is that all these things have a stable maximum concentration in water, beyond which solution decreases very rapidly, all else equal. Further, it has no or very little handy anions -- such as carbonate or sulphate -- which can combine with the hydrogen cation to stabilise the pH (called buffering) with dissolving anything else. What happens is that when you add DI or distilled water to a system, it will promptly set about dissolving whatever is available, provided only that there is some oxygen (most often) to ionize the materials in question, until the dissolved ions in the water are in equilibrium with the solid materials.

    So... there are really two approaches which can be used. Use very pure water (distilled or close to it) and control the pH with buffers, add something (often a phosphate) to form a protective coating on the metals, and control the oxygen with oxygen scavengers. This is the approach used in power boilers, and it works well -- but it does take adding the various chemicals in the correct amounts. The other approach is to run what you brung, as they say, and if necessary control the pH -- and either keep oxygen out of add an anti-oxidant chemical. This works well if what you brung is reasonable. Very hard water -- you'll have scale problems. Water high in total dissolved solids of whatever kind and you'll get foaming problems. Water high in sodium chloride leads to highly soluble compounds of both iron and copper. All undesirable.

    Most municipal water supplies are pretty good. The water company has a vested interest in not dissolving the pipes. There are exceptions (Flint, Michigan, anyone) which are problems in terms of corrosivity, and there are other exceptions (a lot of midwestern smaller communities) where hardness may be a problem, and a few which simply have excess chloride (usually in the northeast, from road salting). But usually...

    Similarly, most well water is reasonable. Usually the only problem is excess hardness -- and there is one example where using DI as a boiler fill is probably a good idea, provided you add anti-oxidants.

    I'm rambling. Does that help any?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    GroundUpIntplm.CanuckerPC7060
  • pecmsg
    pecmsg Member Posts: 2,321

    Not sure I can shed much light -- but I'll give it a shot.

    First, a fundamental principle: water is pretty darn close to the universal solvent. There are a few long chain plastics -- the unpronounceable polywhatnots (including polyethylene, but not including polyvnylchloride!) which it doesn't attack, at least a little bit. But pretty much everything else, yeah.

    That's step one. Step two is that, for all that, almost everything doesn't dissolve very much. There are exceptions -- sodium chloride is a notable one -- but that requires some qualification. Many metals, particularly, are quite soluble if they can ionize and if the anions present in the water don't form stable precipitates. Calcium, for instance. If there is enough carbonate around (relatively low pH) it will form calcium carbonate and we will get scale. Iron is another. If it ionizes to plus 2 (ferrous iron) it's surprisingly soluble. If it can ionize further to plus three, it can and often does precipitate as magnetite, which is almost insoluble (but wreaks havoc with ECM motors, among other things...). Iron is unusual, too, in that while the various iron oxides are relatively insoluble, most of them are also not particularly stable. Rust.

    There are some iron alloys which form a stable oxide coating, at least in the absence of chloride -- Corten steels, and the various stainless steels.

    OK back to the question. The reason that pure DI or distilled water is a problem is that all these things have a stable maximum concentration in water, beyond which solution decreases very rapidly, all else equal. Further, it has no or very little handy anions -- such as carbonate or sulphate -- which can combine with the hydrogen cation to stabilise the pH (called buffering) with dissolving anything else. What happens is that when you add DI or distilled water to a system, it will promptly set about dissolving whatever is available, provided only that there is some oxygen (most often) to ionize the materials in question, until the dissolved ions in the water are in equilibrium with the solid materials.

    So... there are really two approaches which can be used. Use very pure water (distilled or close to it) and control the pH with buffers, add something (often a phosphate) to form a protective coating on the metals, and control the oxygen with oxygen scavengers. This is the approach used in power boilers, and it works well -- but it does take adding the various chemicals in the correct amounts. The other approach is to run what you brung, as they say, and if necessary control the pH -- and either keep oxygen out of add an anti-oxidant chemical. This works well if what you brung is reasonable. Very hard water -- you'll have scale problems. Water high in total dissolved solids of whatever kind and you'll get foaming problems. Water high in sodium chloride leads to highly soluble compounds of both iron and copper. All undesirable.

    Most municipal water supplies are pretty good. The water company has a vested interest in not dissolving the pipes. There are exceptions (Flint, Michigan, anyone) which are problems in terms of corrosivity, and there are other exceptions (a lot of midwestern smaller communities) where hardness may be a problem, and a few which simply have excess chloride (usually in the northeast, from road salting). But usually...

    Similarly, most well water is reasonable. Usually the only problem is excess hardness -- and there is one example where using DI as a boiler fill is probably a good idea, provided you add anti-oxidants.

    I'm rambling. Does that help any?

    Either that is a well worded explanation or
    Intplm.PC7060
  • Derheatmeister
    Derheatmeister Member Posts: 1,140
    Depends... PH,EC,Sal, TDS and Oxygen ingest levels are part of the Equation..
    We Install Deironized Water down to approx 20 EC in Conjunction with sacrificial Anodes from
    Magnetic Online.de
    Elysator also makes the Sorbox,
    I highly recommend reading VDI 2035 Blatt 1 and VDI 2035 Blatt 2 for more detailed information....
    Way to Much information to post here..
  • GroundUp
    GroundUp Member Posts: 1,282
    Thank you Jamie, that is similar to what I'd had cooking inside my head albeit less eloquently. Obviously this isn't a "one size fits all" question so I appreciate you taking the time to explain differing scenarios!

    There is a lot of hubbub on this subject from certain individuals and professionals alike, who make it out to be a "you must use (insert fluid here) and that's the right answer because I said so" answer which I do not agree with in the slightest. Many of the commercial buildings I work in hire out professional water quality techs to determine what the system needs to perform properly, and not once has the answer ever been anything besides DI or RO with these guys but they can never tell me why. I never really questioned it much, because they're obviously the professionals, but I'm coming to realize that it maybe isn't the correct route. I have mixed a few solutions at home and other residential sites trying to gather some data and in the areas I've tested, non-softened well water is easily the closest to ideal composition in terms of treatment requirements- which made me wonder more about why DI/RO is pushed so hard by some... I'd been using a deionizer with my non-softened shop water to dilute my glycol solutions prior to arriving on site which always turned out pretty well chemically, but recently mixed a few batches without the deionizer and it requires a very similar amount of treatment to match pH and nitrites but with higher hardness which I feel is possibly a better route (at least in my case) due to the lack of "hunger" from the DI.
  • Derheatmeister
    Derheatmeister Member Posts: 1,140
    edited June 10
    GroundUp
    Not saying this is "the way" but if you are interessted in Proper not so "Hungy" DI as per VDI 2035 :
    0.1mg/liter/day of oxygen ingest calls for under 100 EC which is DI ..
    0.02 mg/L/Day can have up to 1500 EC.. Which sometimes could be Tap water or a Mix of DI/Tap
    As you can see the lower the Oxygen ingest the higher the Electrical Conductivity (Micro Siemens) can be.
    Lower EC levels do not allow galvanic reactions between different Materials and or Minerals to settle out in the HX.
    Oxygen Ingest depends on many factors:
    1. No O2 barrier
    2. Steep "Night" setbacks which allow the system to Breath in Air.
    3. Leaks/Constant replacement of system fluid
    4. Inproper Piping Methodes.
    5. Unbalanced Systems/Expansion tank not adjusted correctly or "Open" expansion tanks.

    So, yes as you said: "One size fits all"approch does not work..
    Good thing that you are using DI on your Mixtures and hopefully you are at least at 20% for MIC prevention..
    For enviromental reasons and when justified we personaly try to keep the Chemicals out of our systems :*
  • JeffM
    JeffM Member Posts: 174
    If you're patient, IAPMO is working on a standard which will outline minimum requirements for hydronic fluids and provide guidance on this topic. I've participated, as did Bob Rohr and some others here. Should be published by the end of this year.
    GroundUp
  • hot_rod
    hot_rod Member Posts: 15,022
    Turns out hungry "purified" water doesn't stay in that state very long. Remember mother nature hates imbalances, temperature, pressure, water chemistry , etc :)

    We on several occasions have filled systems with 100% DI water with ph in the 5's. Within a week the ph buffers itself into the 7's. The hungry water will pull some from the various metals in the system to buffer. Rarely does it pull enough material from any one component or fitting to cause failures. We have studied systems for many years in Europe that have our DI systems on the fill water to know this.

    IF this is a concern, a small amount of hydronic conditioner could be added to that DI water at the time you fill. Those 12 oz aerosol cans treat 35 or so gallons.

    Those hydronic conditioners, scavenge O2, buffer ph, have organophosphates (sp) to plate out new metals to protect them from aggressive water or glycol mixed down the road, I think they have value especially if you worry about purified water.

    RO, DI, and distilled are 3 means of getting pure water. The cost per gallon is the biggest decision when deciding which to use. The distilled water in the grocery stores is often plain RO or DI water.
    Distilling is an expensive, energy intensive way to purify large quantities of water. Although most desalination plants do millions of gallons of public with RO.

    I would add to Richards comment about O2 ingress, temperature is a huge factor. The high temperature 180° non barrier rubber systems, staple up for example, often failed in the first years, 100° radiant not nearly as much.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Derheatmeister
    Derheatmeister Member Posts: 1,140
    edited November 26
    hot_rod said:

    Turns out hungry "purified" water doesn't stay in that state very long. Remember mother nature hates imbalances, temperature, pressure, water chemistry , etc :)

    hot rod said: We on several occasions have filled systems with 100% DI water with ph in the 5's. Within a week the ph buffers itself into the 7's. The hungry water will pull some from the various metals in the system to buffer. Rarely does it pull enough material from any one component or fitting to cause failures. We have studied systems for many years in Europe that have our DI systems on the fill water to know this.

    IF this is a concern, a small amount of hydronic conditioner could be added to that DI water at the time you fill. Those 12 oz aerosol cans treat 35 or so gallons.

    Those hydronic conditioners, scavenge O2, buffer ph, have organophosphates (sp) to plate out new metals to protect them from aggressive water or glycol mixed down the road, I think they have value especially if you worry about purified water.

    RO, DI, and distilled are 3 means of getting pure water. The cost per gallon is the biggest decision when deciding which to use. The distilled water in the grocery stores is often plain RO or DI water.
    Distilling is an expensive, energy intensive way to purify large quantities of water. Although most desalination plants do millions of gallons of public with RO.

    I would add to Richards comment about O2 ingress, temperature is a huge factor. The high temperature 180° non barrier rubber systems, staple up for example, often failed in the first years, 100° radiant not nearly as much.



    Oh yes.... the dreaded Low PH with DI water..

    After collecting thousands of samples over the years we certainly see a dip in the PH after a couple days of installing DI ..
    I remember Max visiting our shop and asking if i was a smad scientist and what was up with all these Colorful system fluid samples.
    Sometimes depending on various factors the PH of a system filled with DI will not go back up to accepted levels..
    In the past we tried to balance the PH by using Chemicals but this is very time consuming,Frustrating and sometimes it felt like you are playing with a yoyo.
    We would dose the system as per manufactuers instructions with PH up,PH down or sometimes just use a can that promised that it will just take care of it.

    I have found that some of the European "Premium Resins" have a "Secret ingredient " which helps balance the PH from the get go !
    The benefit of these "Premium Resins" is that it does not Raise the electrical conductivity of the system fluid which helps reduce the Galvanic reaction between the Materials..
    In conjunction with the premium resin we like to install a sacrificial anode which will assist with the self alkalisation process such as the Elysator or the HWR from Magnetic GMBH
    https://www.innovativehydronics.net/..
    IMO it is easier than playing Chemist..