Is Your Heat Exchanger Installed Correctly?
- coalkirk
- Member
- Posts: 5185
- Joined: Wed. May. 17, 2006 8:12 pm
- Location: Forest Hill MD
- Stoker Coal Boiler: 1981 EFM DF520 retired
- Hand Fed Coal Stove: Jotul 507 on standby
- Coal Size/Type: Lehigh anthracite/rice coal
Some of you may have already seen my comments on this last fall when I had a new oil fired boiler installed. But I thought a would start a topic on it as I believe it to be important. I use the hot water from my boiler in a water to air heat exchanger in my forced air duct work. I plumbed it myself. After all these years of use, the heating contractor who was installing my new oil boiler took one look at it and said its plumbed backwards! It's a double pass coil and I had the hot water going into the top of the coil. My heat exchanger is in the return so the hot water was in the half of the coil that "sees" the return air first. I have thermometers on the input and output sides of the coil and in general the forced air would knock the water temperature down by about 5 degrees.
The heating contractor re-plumbed it and said I would probably see a modest increase in performance. Fast forward to now with the hot water entering the bottom half of the coil that "sees" the return air last. NOW it drops the water temp by 20-25 degrees. I think that's pretty amazing! Obviously the whole system works so much better. Moral of the story is I'm an idiot and double check your heat exchangers to see which way they are plumbed.
I was concerned this would knock the crap out of my Harman boiler and it would never recover. Ironically it will drop the temp to about 165 in the coal boiler and it will recover to 185 better than it did before. I guess its because the heat cycle demand is shorter. Full disclosure, it still struggles in extreme cold and wind. But for our normal winter weather it now works better than ever.
The heating contractor re-plumbed it and said I would probably see a modest increase in performance. Fast forward to now with the hot water entering the bottom half of the coil that "sees" the return air last. NOW it drops the water temp by 20-25 degrees. I think that's pretty amazing! Obviously the whole system works so much better. Moral of the story is I'm an idiot and double check your heat exchangers to see which way they are plumbed.
I was concerned this would knock the crap out of my Harman boiler and it would never recover. Ironically it will drop the temp to about 165 in the coal boiler and it will recover to 185 better than it did before. I guess its because the heat cycle demand is shorter. Full disclosure, it still struggles in extreme cold and wind. But for our normal winter weather it now works better than ever.
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- Joined: Wed. Jan. 29, 2014 1:42 pm
- Location: N/W Pa. Meadville, Pa.
- Hand Fed Coal Stove: Sears circulator air tight stove.
- Other Heating: Crown 115,000 BTU oil fired boiler(house) Weil Mclain 150,000BTU oil fired boiler(Shop)
Steam is in the top and out the bottom as the system uses gravity to return the condensate to the boiler, and Hot water is in the bottom .
I have seen them plumbed wrong all the time. I heat my shop with a FCU (fan coil unit) and when I moved the boiler out of my shop space and into a separate room, I goofed. I reversed the pex coming from the manifold. Hot water was sent into the FCU from the top. I knew something was wrong from the first time I ran it, I did the smart thing and checked to see if I had the piping correct which I did not and than switched them around and the system works fine now.
Dan.
I have seen them plumbed wrong all the time. I heat my shop with a FCU (fan coil unit) and when I moved the boiler out of my shop space and into a separate room, I goofed. I reversed the pex coming from the manifold. Hot water was sent into the FCU from the top. I knew something was wrong from the first time I ran it, I did the smart thing and checked to see if I had the piping correct which I did not and than switched them around and the system works fine now.
Dan.
- McGiever
- Member
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- Joined: Sun. May. 02, 2010 11:26 pm
- Location: Junction of PA-OH-WV
- Stoker Coal Boiler: AXEMAN-ANDERSON 130 "1959"
- Hand Fed Coal Boiler: BUCKET A DAY water heater
- Hand Fed Coal Stove: Warm Morning 414A
- Coal Size/Type: PEA,NUT,STOVE /ANTHRACITE
- Other Heating: Ground Source Heat Pump and some Solar
Perhaps an illustration would help define this concept???
Here's what I found, has great illustrations and also a good read:
https://www.emergentcoils.com/blog/posts/7-water-coil-piping
Here's what I found, has great illustrations and also a good read:
https://www.emergentcoils.com/blog/posts/7-water-coil-piping
Drainability
Counterflow
Air Entrapment
Rules of Thumb:
To make it easy, here are some more general tips (or the TL;DR version).
Horizontal Airflow Water Coils
Supply low, Return High
Water flow direction should be opposite of air
Vertical Airflow Water Coils
Water flow direction should be opposite of air
- coalkirk
- Member
- Posts: 5185
- Joined: Wed. May. 17, 2006 8:12 pm
- Location: Forest Hill MD
- Stoker Coal Boiler: 1981 EFM DF520 retired
- Hand Fed Coal Stove: Jotul 507 on standby
- Coal Size/Type: Lehigh anthracite/rice coal
So here is my fan coil. This duct is a return and the air flow is down. I previously had the supply going into the top of this coil first. Now goes into the bottom first. So the air gets heated at the upper part then passes through the lower part of the coil with 185 degree water. The difference is understandable but I'm surprised how much difference it makes, 5* vs 20-25*.
- hotblast1357
- Member
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- Joined: Mon. Mar. 10, 2014 10:06 pm
- Location: Peasleeville NY
- Stoker Coal Boiler: 1984 Eshland S260 coal gun
- Coal Size/Type: Lehigh anthracite pea
- Other Heating: air source heat pump, oil furnace
so what about a single plate heat exchanger, like in a modine? does it matter which is which?
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- Location: Fair Haven, VT
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- Coal Size/Type: Pea, Buckwheat, Nut
- Other Heating: LP Hot air. WA TX for coal use.
Huh, never knew there was a difference either. Guess it's time for a look at my own setups. Thank you Sir.
- Sting
- Member
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- Location: Lower Fox Valley = Wisconsin
- Other Heating: OBSO Lennox Pulse "Air Scorcher" burning NG
There is a tide in the affairs of men.
Which, taken at the flood, leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
On such a full sea are we now afloat,
And we must take the current when it serves,
Or lose our ventures.
Which, taken at the flood, leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
On such a full sea are we now afloat,
And we must take the current when it serves,
Or lose our ventures.
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- Member
- Posts: 2344
- Joined: Wed. Feb. 04, 2009 7:13 am
- Location: Fair Haven, VT
- Stoker Coal Boiler: Hybrid Axeman Anderson 130
- Baseburners & Antiques: Sparkle #12
- Coal Size/Type: Pea, Buckwheat, Nut
- Other Heating: LP Hot air. WA TX for coal use.
They already passed the marijuana law out there Sting?
- hotblast1357
- Member
- Posts: 5661
- Joined: Mon. Mar. 10, 2014 10:06 pm
- Location: Peasleeville NY
- Stoker Coal Boiler: 1984 Eshland S260 coal gun
- Coal Size/Type: Lehigh anthracite pea
- Other Heating: air source heat pump, oil furnace
so far anyone interested, with a single plate heat exchanger, hot goes in the bottom, cold comes out the top, I had my modine plumbed the other way, hot in top, cold out bottom, just like my multiple coil exchanger in the furnace duct-work (which works correctly), and I could only get about 10-12 degree differential with it, when I installed my second modine in the garage, I swapped the lines, now I get a 20 degree differential with both modines.hotblast1357 wrote:so what about a single plate heat exchanger, like in a modine? does it matter which is which?