water softener in a hydronic system 2

[bigwilly104]

So if you saw my earlyer thread I am having problems with a hydronic system getting clogged with solids. I got a lot of good advice and now I think I have a handle on what is causing my problem. The second company who tested the feed water said it was to hard and also had a little bit of iron in it but mostly silicates. So they sugested a water softener. Now as with life this raises another concern. I have never seen a system with a water softener on the feed or make up water. I am concerned about adding saline to the closed loop hydronic sytem and causing other problems. Has anyone seen a system with a water softener on it. anyone? Thanks

 

[MikeHalloran]

How much makeup water do you need? You can get distilled water in 5gal bottles at our supermarket. Probably the drinking water would be less corrosive.



Mike Halloran
Pembroke Pines, FL, USA

 

[quark]

Soften the makeup water. Generally, if the water is hard and if you have silica in the system, there are fair chances that magnesium silicate may form. This generally looks like white flaky substance. Removing magnesium by softening the makeup water is one option. But this doesn't take care of silica. Coagulation by non ferric compounds is a better option.

Try to use antiscalents after you do the softening. These antiscalents will delay the chances of magnesium silicate formation. I suggest you to contact Nalco.

If you get the following parameters tested for makeup as well as recirculating water, you can get better advice.

1. TDH
2. Hardness
3. pH
4. Alkalinity
5. Silica (reactive)
6. Iron

 

[bigwilly104]

Thank you both. As far as using distilled water for feed I had thought about that but it would take a lot of distilled water. When we flush the strainers wich we do about twice a year at this point it uses about 400 gallons. and the boiler and feed water systems are on a rooftop well accesable through a attic access.
Thank you Quark what i need is more recorcess like that to get testing that hopfully will show a real result. Like they say its not just what you know its who you know.
Thanks

 

[bimr]

Use of distilled water is a bad idea. The distilled water will be corrosive. However, you might be able to use normal tap water that has less hardness than the source that you are presently using.

The previous posters do not seem to recognize that at the temperature that you are operating your hydronic system, that you will get calcium carbonate precipitation. I was the one that recommended a water softener as well as getting a complete water analysis.

You do not have to be concerned at all about operating a water softener on a hydronic system. Note also that you should be doing a partial softening, by bypassing part of the flow past the water softener.

Completely softening the water to zero hardness will tend to produce a more corrosive water. You only need to soften the water to the point that you have a slightly positive langelier index.

 

[moltenmetal]

Though it is true that distilled or deionized water is corrosive to many metals in the presence of a continuous source of oxygen, many closed-loop systems constructed of carbon steel and copper-bearing materials work for a very, very long time successfully in CLOSED LOOP operation with distilled water as a first fill. Some corrosion occurs until the first charge's dissolved oxygen is consumed, then the system operates anaerobically and general corrosion basically shuts down. Thereafter, the corrosion rate is limited by the rate of re-introduction of oxygen through make-up or flushing such as what you're doing.

My suggestion: if there IS no source of continuous oxygen re-introduction, install some differential pressure gauges on the strainers and back-flush them only when you see unacceptable backpressure. You may be doing more harm than good by your "preventive maintenance". Keep the system truly closed loop and corrosion- and scaling-related problems will diminish. Don't confuse your closed loop hot water system with a steam system where steam is lost and hence make-up and blow-down are both required.

 

[bimr]

MM, Not disagreeing completely with you, but distilled water is a bad idea. There is no great need to use distilled water when good quality potable water will suffice.

You are probably aware that the typical corrosion control strategy is to use water with a slight scaling tendency such that you are trying to coat the exposed surfaces of the metallurgy with a very light coating of soft scale.

With distilled water, your strategy would be to allow limited corrosion to take place on the surface of the metallurgy.

There is a difference in corrosion control strategy.

With an installation where most of the application is non-plastic, you are going to get a lot of corrosion on the few square inches of metal that is exposed to the water.

The problem this fellow is having is not corrosion, but rather an excessive precipitation of calcium carbonate caused by heating water that has an elevated level of hardness and alkalinity.

 

[moltenmetal]

bimr: We're not disagreeing: given the choice, you are correct that a water containing a little bit of scale-forming material and a little pH buffering capacity would be a better choice than DI water. But if the first fill of the OP's closed-loop system contains so much scale-forming material that he has to shut down to flush strainers etc. after a few months, flushing with the same water and adding yet more scale-forming material, there's a problem there! He'd be better off with DI water as a first fill, since this will generate no scale. Don't you think?

Problems at an air/water interface stop as soon as the air space is depleted of oxygen, since the oxygen concentration cell that used to drive this corrosion is gone. With a solubility of only ~ 10 ppm, there's not much oxygen in a first fill of water to do significant damage to a large system principally constructed of carbon steel, so there isn't even a need to de-oxygenate the water before you use it. Again, this assumes the system is actually closed loop, with no in-leakage of oxygen or out-leakage of water requiring make-up which might carry water, food for microorganisms etc.

 

[bimr]

MM,

In recent hydronic systems, PEX radiant plastic tubing has been installed in a concrete mass. These systems are usually non-metallic except for the pump and boiler. bigwilly104 has not really said what he is doing, but he must be reaching the upper temperature limit.

Here is raypak's recommendation:

Water Quality

Though often taken for granted, the quality of water mixed with glycol concentrate can have an enormous impact on system performance. Marginal quality water can lead to the development of scale, sediment deposits, or the creation of a sludge in the heat exchanger which will reduce heat transfer efficiency. Poor quality water can damage the system by depleting the corrosion inhibitor and promoting a number of corrosions including general and acidic attack corrosion.

Since it is vital to use high quality water for glycol dilution in order to maintain system efficiency and prolong fluid life, you must ensure your water is of sufficiently high quality. Good quality water contains:

Less than 50 ppm of calcium
Less than 50 ppm of magnesium
Less than 100 ppm (5 grains) of total hardness
Less than 25 ppm of chloride
Less than 25 ppm of sulfate
Check with your county or city water department to determine the chemical properties of the local water. If your mixing water will be drawn from a well, which typically has extremely hard water, or the local water authority cannot provide an accurate profile, we recommend either testing the water yourself or hiring a commercial water treatment specialist to analyze the water.
A simple test used by Dow Chemical Company to ensure that water contains less than 100 ppm of hardness, is to fill a small sample bottle with 50% glycol and 50% water. Let the solution stand for 8-12 hours, shaking it occasionally. If any whitish sediment forms, the water is too hard and should not be used to dilute the glycol.

In those cases where tap water does not meet the standards for quality, Dow recommends using demineralized water that has been distilled, deionized, or passed through a reverse osmosis process to remove harmful minerals and salts. A suitable corrosion inhibitor must be used with demineralized water since the pH of the treated water may be measurably less than seven.

http://www.raypak.com/afreeze.htm

 

[cub3bead]

If you use the DI water for makeup to this system you will then have to dope it with about 3,000 ppm of sodium nitrite (NaNO2) to protect the mild steel from corrosion.

Nitrite inhibited systems have to be monitored for O2 ingress which oxidizes the NO2 and for bugs which like to feed on the NO2. Nalco and Betz both sell the nitrite based inbitors and non-nitirte based inhibitor packages for closed systems.

 

[bigwilly104]

looks like a more compleate picture is in order. first of this is a reheat system in a commercial bld. that means coils in the air flow throughout the bld that heat air supplied by a large vav air conditioner. There are about 35 coils per bld. These are three story buildings with all the equipment in a rooftop well. This well is only accessable through a attic access. So getting any kind of water to the rooftop were the make up water is would really be dificult. Also is would require a small pump and bladder tank to diliver the water after I had it on the roof. The system is all copper and runs ar 180 deg F. I also have quite a bit of experiance with DI water working at the JDS Uniphase plant and I really dont want any of the problems that come with it. We had more trouble with the DI eating pipe than I want to think about. I have been treating the system with nitrate and this is not solving much. I will be hearing from a rep from Nalco. Having a sytem that removes my problem from my existing feed water is ideal because once its up there I am done. Thank you all for the posts.

 

[moltenmetal]

Yes indeed, DI water will corrode copper- if it's very acidic and/or there's a continuous source of oxygen! But hot, deoxygenated distilled water does not corrode copper at an appreciable rate in practice. Otherwise, the hundreds of miles of 0.035" wall copper steam tracing tubing out there in industry would be eaten through every couple of years- and it is not.

If your system is truly closed loop and all metallic as you describe, and there are no leaks, you do not need make-up water, and hence there is no source of continuing corrosion and scale-forming materials. If you have an expansion tank with a breather etc., or leaks on the suction lines of your pumps etc., all bets are off. Otherwise, flush, clean and drain the system, then rent or buy a small RO unit or buy a bunch of disposable DI cartridges and put them on the potable supply line you're using for your first fill to eliminate the (presumed) excessive amounts of scale-formers in your potable water. Rig the unit up on a board and move it from building to building. If you're worried about the DI corrosion issue, dose some sodium bicarbonate solution to the loop to give the DI water some buffering capacity against strong acidity. As long as there's no continued source of oxygen to the water, the copper tubing should outlast you.

 

[bimr]

Steam tracing is exposed to steam from a boiler and would have different corrosion mechanisms than that from exposure to DI water. The steam tracing corrosion would depend somewhat on the boiler's chemical treatment program.

One can't talk about copper like it is a generic material. There are all sorts of copper alloys out on the market. There is no universal corrosion chart for all of the different copper alloys.

 

[moltenmetal]

Steam tracing carries a whole lot of condensate, which is hot, deoxygenated distilled water. There are lots of places in a functioning tracer system where there is no "steam" present at all except during start-up. The condensate does not, in practice, dissolve the copper in these tracer lines at an appreciable rate, whether there's a vapour corrosion inhibitor system on the boiler or not. So sorry, I'm not buying it!

And we're talking principally about copper pipe and tubing here, not "copper alloys" in general. If we start talking about brasses and bronzes, where there could potentially be issues with de-zincification etc., and agreed that's a wider debate. But consider this: what is used to connect most of that copper steam tracing tubing to its headers, at joints in the tubing etc.? Yellow brass tubing fittings! And these aren't corroding away every few years either!

I don't mean to say that one should draw the blanket conclusion that copper is resistant to deionized/distilled water under all circumstances- that clearly is not true. But it is similarly untrue that copper is an unsuitable material for use with pure water under any circumstances.