iron sediment in flat plate heat exchanger

mostlybirch

Hello,

I'm finishing putting together the closed loop radiant circuit for a garage slab heat system. Boiler feed DHW and will heat a glycol mix radiant system through a flat plate heat exchanger. Friend gave me a large 60 plate SS brazed heat exchanger of unknown origin to see if I could use it. Saw some dark sediment in the bottom and began flushing it. Black sediment flushed from both sides of the HX, tested with a magnet and it is iron. Flushed probably 40 gallons through each side, still getting small amounts of dark sediment (less and less).

Am I fighting a losing battle trying to use this instead of shelling $400 for a new unit? Haven't started with any cleaning agents like CLR or acid. One side of this will have DHW so want to be safe.

Thanks

mattmia2

Try soaking it in acid like citric acid or vinegar. If it is fouled the transfer will be degraded. Should find the manufacturer's transfer calculator and see if it is suitable for your application.

hot_rod

Take it to a radiator repair shop, they will cook it clean in their tanks.

Is it a brazed or bolted type?

mostlybirch

How will I know if it is fouled? I'll try vinegar tomorrow.

It's a brazwd type, B3-27-60 similar to this unit

https://www.dudadiesel.com/choose_item.php?id=HX2760

Mad Dog_2

I put all my HXs in with unions & service valves. Doesn't hurt to try & use it...it's FREE...mad Dog

hot_rod

A valve like this with a 1" G union nut would be perfect to service in place or remove for a acid bath. I think I have a fitting to make this work.

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hot_rod

I'd wonder what that used HX was flowing. Oil or some other non potable fluid? Hard water scale is often white or blueish.

I think officially it should have an NSF 61 listing to be used on potable water.

hot_rod

1" is a common size HX connection on residential sized plates.

This tankless valve opens the side port when the valve is in the off position. So you could use a tankless water heater cleaner kit to flush a HX with.

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mostlybirch

Thanks hot_rod. I have some webstone drain ball valves for just that case. Of course once I got a hold of them I found that they weren't lead-free compliant so I can only these particular drains on the glycol side. Will have to get others for the DHW side.

I can't find any NSF61 cert for this HX, is there potential for lead in a brazed HX?

mostlybirch

This HX could have been used for anything, looks like they are sometimes used in turbocharged motors.

I soaked the internals with white vinegar last night which pulled a lot of sediment, water came out black to green, pulling copper?

hot_rod

https://forum.heatinghelp.com/discussion/comment/1833711#Comment_1833711

I wouldn't worry about the stainless as much as the old leaded brass valves. Who knows whatb type of brazing zod they use to build them.

As long as you get it clean inside. I might try a few cleaners. CLR works, the tankless cleaners are citrus acid.

A kit like this is handy as you get some flow through all the plates instead of just a soak. There are a lot of small honeycomb passages in those plate HXers. I doubt soaking alone will clean it very well.

Any kind of plastic sump pump would work, put it into a 5 gallon bucket let it circulate for a day. It will warm as it circulates also.

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mostlybirch

I had purchases new drain valves, these here. Didn't notice they weren't lead-free until they landed

https://www.amazon.com/dp/B00CL0H4N8?ref=fed_asin_title&th=1

I'll try circulating CLR now

mostlybirch

Still getting black sediment flakes coming up. Maybe more CLR pumping will eventually get it all.

hot_rod

You know, a new properly sized HX isn’t all that expensive

Not knowing where that hx has spent its life

mostlybirch

Yeah I'm finding it difficult to get this HX truly clean. In interior Alaska the only stocked heat exchanger I can find is Energy Kinetics line, 14u or 18u, but they are both size 1/2" inlet/outlet and my system is 1" piping and circulators. I feel that would be a major constriction, dealer thinks it will flow fine. Leaning towards ordering a 20 plate with 1" online, much cheaper as well. Besides the price, is that 1 to 1/2" unreasonable? Thanks

mattmia2

B&G/xylem has a good calculator online for their heat exchangers as do most other manufacturers. That will let you pick one with the right flow, pressure drop, and transfer.

Are you drinking the hot water? There is some argument to be made that hot water is not considered potable water for the purposes of the code rules about low lead parts, in the same way it usually isn't considered to apply to a sillcock(at least by one of the major sillcock manufacturers).

mostlybirch

I've used the B&G online calculator to size a HX, getting around a model 400 10 or 20 plate. However I was looking at 1" piping to match my exiting plumbing and circulators and didn't model smaller thread size. The dealer for the Energy Kinetics HX said the little 1/2" HX they sell were rated at the right GPM and much higher BTU (230k vs 50-100k modeled for my system.)

I suppose I won't be drinking hot water and a non-lead free fitting might not be a concern for a couple fittings.

mattmia2

400 is a 3/4". there are others in the 400 (something like 410 or 412)series that are 1"(and somewhat more expensive).

With enough pressure you can get plenty of flow but you have to look at what pressure drop it will have in your system. You probably want a couple psi or less drop at the flow you need.

hot_rod

A btu rating doesn’t tell you much about a HX size. You need to know incoming temperature, acceptable temperature drop, desired outlet temperature and flow rate to size a HX.

Most programs default to a 3.9 psi pressure drop, so you do get into a high head pump requirement.