Maintenance of flat plate heat exchangers

[headrc]

I am going to start a new thread here on this .... as indicated in another of my threads ....I was and still may use heat exchanger(s) with my OWB in conjunction with radiant panel heating. I have received advice from a pro that he would design the system without them and go unpressurized throughout and use bronze pumps etc. One of the reasons he gave is that heat exhangers require yearly cleaning etc. I was not aware of this ....can someone give me some insight into the maintenance of heat exchangers. I plan on treating my water to keep the proper ph in it. Thx, RH

 

[itsme again]

I thought the same thing. I was told that they can scale on the inside. I have a lot of lime in my water and have had shower heads replaced sometimes yearly due to reduced flow. I took my heat exchanger off this past year to see if there was any problems and it was clean as new.

Once you put water in your system, it doesn't mix with the house water. As long as your levels aren't crazy or you use something to get the proper levels, you shouldn'y haveanyo problems. Adding a small amount of water to keep the water level correct shouldn't be enough to bother the heat exchanger.

All being said, the old saying hold true, an ounce of prevention.......

 

[Eric Johnson]

I've been told that on open systems, like most OWBs, it's a good idea to flush the open side of any flat plate heat exchangers out with water on an annual basis. Apparently there are very close tolerances in flat plates, and any crap in the water can plug them up. You can plumb a flush arrangement right into the connection, so that you can just hook up a hose and blow water through it whenever you feel like it. I don't have a diagram, but it's nothing you couldn't do relatively easily with a couple of hose bibs or boiler drains and isolation valves.

 

[micifus]

Vinger does a great job of breaking up lime deposites.

 

[Redox]

I used to work for a chiller mfr that used BPHXs for both sides of the refrigeration system. Great little devices, but the internal clearances are TINY compared to any other type of HX. The HX manufacturer would not warrant clogs unless good water treatment and an appropriate (fine) strainer was in the system. We had very little problem with closed systems, but open systems had lots of issues. Even a little biological growth would create high head pressures.

The best way to clean them out was by backflushing them with a flow greater than the normal system flow and then circulate descaler through it until it stopped fizzing. Any strong acid will work, but there are commercial descalers that are very effective. A small chemical pump in a 5 gal bucket of water can be used to set up the recirculation and then the descaler added SLOWLY to the bucket usually did the trick.

Hope this helps...

Chris

 

[headrc]

So even if I am maintaining good Ph and have fine strainers for the heat exchanger .....will I still be faced with having to clean them out on a yearly basis? RH

 

[jebatty]

With proper pH and fine strainers there should be no corrosion in the system and any loose particles would be trapped before they reach the hx. I use a hot water filter on my system to do the same thing as a strainer.

But the issue is scale, that is, minerals in your water, resulting from use of hard water. With a closed system should be minimal to no issue, and the mineral deposits, if any, will be miniscule. If you are continually adding hard water to your system, then descaling may be called for. As mentioned in the post above, descaling, if needed, is quite simple to do. A muriatic acid solution (hydrochloric acid) will work; vinegar (a weak acid) may work also.

If you have hard water and a water softener, then the water you add to your system should result in minimal, if any, mineral buildup.

I regard an occasional, if any, cleaning of the plate hx as a normal maintenance procedure to perform as needed. BTW, a coil hx is not immune to the same issue, and any scale forming on the inside of the coil hx tubes will act to reduce heat transfer, perhaps significantly, over time.

 

[BrownianHeatingTech]

So even if I am maintaining good Ph and have fine strainers for the heat exchanger .....will I still be faced with having to clean them out on a yearly basis? RH

The manufacturers recommend yearly cleaning. That covers them from warranty claims, if someone has bad water and does not keep up on maintenance.

I've seen flat plates that have been in place for well over ten years with zero maintenance, that still work great. It all depends upon water quality.

Treat your boiler's water properly, and you'll be fine (for the closed side, I like 8-way - the color pH indicator is nice). A yearly backflush with plain water is good preventative maintenance, like getting your car's oil changed. If you notice issues down the road, an acid flush may be required and, as folks have noted, even vinegar can be used.

I have a pumping system for doing acid washes... it sits in the corner gathering dust. A yearly backflush will cover you in most cases.

Joe

 

[micifus]

Distilled water is great, it leaves behind almost no build up we use it in all our humidfiers. Of course we buy it on gallon at a time I am not sure if anyone sells it in bulk might be worther looking into if you have really hard water.

 

[Johnny Ringo]

just to be safe I put a cartridge type filter on mine, two actually, both sides of the heat exchanger. OWB side and residential side. I found the filter and cartridge from cb. page 10 of their heating accessories online cat. I think it will work fine but it's only rated to 160 degrees. I suspect since they have been using them for years with no problems the unit was probably rated with sanitation temps in mind. So I put them in with a bypass if I have any trouble I'll just pull a few levers and go around it.

 

[headrc]

Thx guys ...lots of good info here and it really helps because I believe I am going to stick with the heat exchanger idea on my system. RH

 

[ISeeDeadBTUs]

I've had rum with lime, cola with lime, vodka, gin and tequila with lime, but NEVER vinegar with lime.

Thanks for giving me something else to add to the list of things to get done before snow flies. I have never flushed the 20-plate HX in my system. I add water frequently, due mostly to a sloppy, hurried installation contractor.


Sorry, no time for PM's . . . my opinion on GW is succinctly summarized https://www.hearth.com/econtent/index.php/forums/viewthread/20406/P15/

 

[jebatty]

don't mix vinegar with lime - stay with your other choices. ;-)

 

[in hot water]

Install the HX with those clever Webstone valves on both sides. This allows you to connect a couple wash machine hoses and wash, backwash or run a cleaner through it.

Note the delta t when installed and as time goes by to help determine when a cleaning is needed.

Here is an example of that valve. Also a plate HX I cut apart to see inside. This had been on a solar DHW system for 16 years.

hr

 

[Redox]

That HX looks pretty good for 16 years of use. Was it cleaned regularly? How long did it take you to cut it apart? ;-P

Chris