Heat Exchanger Exchange

 
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StokerDon
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Post by StokerDon » Tue. Dec. 30, 2014 9:50 am

A lot of great disscusion points here. Some people seem to think changing the heat exchanger is not a good idea. For those people I would ask this question; If I had 150,000 to 200,000 BTU of standard radiation (baseboard , radiators, ect...) connected to a 110,000 BTU boiler would your answers be different?

I'm still new to this boiler heating thing, that is why I ask questions and do what I do. Being that I put my whole system together, myself, without realy knowing what I was doing, sometimes I start second guessing myself.

-Don


 
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Post by McGiever » Tue. Dec. 30, 2014 9:57 am

windyhill4.2 wrote:I seem to remember something about the limited output of 1" pipe, can't put my finger on it but seems like the 150k+btu exchanger is limited by the 70-80k BTU of the 1" pipe.Being no expert on the subject leaves me just stating non-factual opinion based on what I have read & learned over the yrs.
Yeah, but that's at a desired 20* Delta...breaking the rules will allow many more btu's...and this is where the trouble begins. (returning water below the 20* Delta)

 
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Post by Lightning » Tue. Dec. 30, 2014 10:23 am

StokerDon wrote:A lot of great disscusion points here. Some people seem to think changing the heat exchanger is not a good idea. For those people I would ask this question; If I had 150,000 to 200,000 BTU of standard radiation (baseboard , radiators, ect...) connected to a 110,000 BTU boiler would your answers be different?

I'm still new to this boiler heating thing, that is why I ask questions and do what I do. Being that I put my whole system together, myself, without realy knowing what I was doing, sometimes I start second guessing myself.

-Don
I think in that situation you would be forced to slow down the flow rate since reducing radiation wouldn't be an easy option. OK... how about this... install a valve (instead of swapping exchangers) to change water flow rate volume till you achieve the 20 degree delta that is recommended .. That would be my solution based on my limited knowledge of hydronic systems. My reason, I don't think the big exchanger is the problem. Like McG said, you can "alter" its size with water flow volume.

Oh wait... :lol: that ain't gonna work, if you slow it down it will come back colder.. BUT it will be less mass to shock the boiler...

HEY I got it!!! You can still use the bigger exchanger with less air flow! Yes that's it! Then the water will come back warmer.. :lol: But then using the smaller exchanger would have the same effect.. That's quite the debacle you got yourself going there. :? The smaller exchanger is going to limit airflow anyways. You could of solved the whole thing by covering portions of the COLD AIR return until you achieved the 20 degree difference you are looking for at the boiler. :)

My mind at work... :lol:

 
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Post by Rob R. » Tue. Dec. 30, 2014 10:30 am

If all you want to do is smooth out the ups and downs of the boiler temperature, choke the flow to the heat exchanger.

 
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StokerDon
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Post by StokerDon » Wed. Dec. 31, 2014 9:04 am

Lightning wrote:
StokerDon wrote:The thermostat triggers the aquastat. No, the water only flows through the heat exchanger when the boiler temp is above the aquastat low setpoint. The blower only turns on when the heat exchanger is hot enough.
Why not have the thermostat turn on the circulator that drives the exchanger zone? Or is that what its doing?

Yes I know... these are boiler 101 questions :lol:
Lee,

That is exactly what I am tring to get away from. When it was wired like that the blower/heatexchanger would drive the boiler temp down to 120 degrees regularly, sometimes less.

And I know Rev. Larry would say "step away from the boiler. It will recover", and maybe he is right. But, I won't be satisfied until I try.

-Don

 
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StokerDon
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Post by StokerDon » Wed. Dec. 31, 2014 9:13 am

Lightning wrote:
StokerDon wrote:A lot of great disscusion points here. Some people seem to think changing the heat exchanger is not a good idea. For those people I would ask this question; If I had 150,000 to 200,000 BTU of standard radiation (baseboard , radiators, ect...) connected to a 110,000 BTU boiler would your answers be different?

I'm still new to this boiler heating thing, that is why I ask questions and do what I do. Being that I put my whole system together, myself, without realy knowing what I was doing, sometimes I start second guessing myself.

-Don
I think in that situation you would be forced to slow down the flow rate since reducing radiation wouldn't be an easy option. OK... how about this... install a valve (instead of swapping exchangers) to change water flow rate volume till you achieve the 20 degree delta that is recommended .. That would be my solution based on my limited knowledge of hydronic systems. My reason, I don't think the big exchanger is the problem. Like McG said, you can "alter" its size with water flow volume.

Oh wait... :lol: that ain't gonna work, if you slow it down it will come back colder.. BUT it will be less mass to shock the boiler...

HEY I got it!!! You can still use the bigger exchanger with less air flow! Yes that's it! Then the water will come back warmer.. :lol: But then using the smaller exchanger would have the same effect.. That's quite the debacle you got yourself going there. :? The smaller exchanger is going to limit airflow anyways. You could of solved the whole thing by covering portions of the COLD AIR return until you achieved the 20 degree difference you are looking for at the boiler. :)

My mind at work... :lol:
You're starting to get it now Lee!

It's a bit of a Pandora's box! There are a lot of parts in motion here. Now that I have had a year to think about it, I realize just slapping this end of it together, I may have made a bad choice or two.

-Don

 
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Post by StokerDon » Wed. Dec. 31, 2014 9:26 am

Rob R. wrote:If all you want to do is smooth out the ups and downs of the boiler temperature, choke the flow to the heat exchanger.
Yes Rob, and you suggested that a year ago, I didn't understand what you ment then, I think I get it now.

I have shut offs and gauges on the inlet and outlet of the heat exchanger. I have been playing with them. The difference between inlet and outlet has been a constistant 13-14 degrees with the blower on LOW. This has been the case with both heat exchangers. I throtled the outlet valve and could easily get the difference up to 20 degrees.

Which valve would work better for this, the inlet valve or the outlet valve???
PEXexchangerComplet 007.JPG

Heatexchanger valves and guages

.JPG | 114KB | PEXexchangerComplet 007.JPG
That's and old photo but the gauges and valves are the same.

-Don
Last edited by StokerDon on Wed. Dec. 31, 2014 9:27 am, edited 1 time in total.


 
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Post by lsayre » Wed. Dec. 31, 2014 9:27 am

Don, have you been heating the home with the smaller heat exchanger for a few days yet in order to get any sort of feel for its suitability to the job, and/or its coal consumption vs. the larger exchanger?

 
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Post by StokerDon » Wed. Dec. 31, 2014 9:45 am

Larry,

I do not yet have an idea on coal consumption, but, it was cold here overnight (below 20*). It's cold now (22*). That is the coldest its been this season. The thermostat is set at 67*, the house temp is oscillating between 66* and 70*.

This smaller heat exchanger doesn't seem to have a problem heating the house. Lets also keep in mind that the house is only 1400 sq ft and the original oil burner is 60,000 BTU (I think).

-Don

 
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Post by StokerDon » Wed. Dec. 31, 2014 11:00 am

I have throtled the supply valve to the heat exchanger to the point where there is a 20* difference between exchanger inlet and outlet. Now I wish I had a pressure gauge between the pump and the valve. I don't want to pop the PEX!
ValveAdjustments 004.JPG

Throtled inlet valve

.JPG | 93.9KB | ValveAdjustments 004.JPG
ValveAdjustments 002.JPG

Throtled inlet valve temp difference

.JPG | 65KB | ValveAdjustments 002.JPG
NOTE!!!;
The gauges pictured have been proven to read about 28 degrees LESS than the Tridicator gauge on the boiler. So, 142 degrees supply is actualy 170 degrees boiler temp.

-Don

 
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Post by windyhill4.2 » Wed. Dec. 31, 2014 11:14 am

Well,i might get labeled as stupid or as an expert but my understanding is that a circulator does not pressurize the system. Your system pressure will be the same on both sides of the closed valve. Circulators move water.You only had a temp reduction of 13-14*,that is good,you should be happy with that,why do you want a bigger difference in *from in to out ? that only means you will shock the boiler even more.Complicated thinking only confuses the thinking & gets you going the wrong direction.

 
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Post by Lightning » Wed. Dec. 31, 2014 11:28 am

Windyhill, it shouldn't make a difference as far as the boiler can see. It will be lower volume at a bigger temp change or more volume at a smaller temp change. In both cases the same (or very close to it) amount of BTUs is taken from the water.

The better option in my opinion is to slow down airflow thru the exchanger.

 
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Post by windyhill4.2 » Wed. Dec. 31, 2014 11:40 am

Lightning, I guess some of those high faluting math courses do help,so it comes to 1/2 doz with partial throttle,6 with open throttle ? Well , I guess that means I wasn't wrong ,nor was I right :notsure: :) Lightning,you forgot the pressure issue . :what:

 
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Post by oilman » Wed. Dec. 31, 2014 11:52 am

You are not going to pop anything. If it makes you feel better, you can just put a 3/8" pex crossover bridge between supply and return before the valves. A poor man's pressure differential valve .
The only way to add pressure is to leave the feed valve on fast fill or something. Or, a runaway boiler going up past 250,etc.

 
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Post by Lightning » Wed. Dec. 31, 2014 11:58 am

I don't know how high water gets pumped in Don's house since gravity of it coming back coupled with suction of the pump is unknown.

If it's all at the same level it shouldn't matter which one he tweaks to reduce volume thru the exchanger, I'm venturing out onto thin ice with that though.. :lol:

Oilman's solution makes good sense to me.. :)


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