Flow Calculator

 
NoSmoke
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Post by NoSmoke » Sun. Dec. 27, 2015 8:09 am

Am I missing something here? (Please read this as a serious question and not another way as I know tone can be hard to convey via the written word versus direct conversation).

On my system I have a 3 speed Taco circulator that pushes warm warmer from my mixing pump (a variable speed taco tied into my Taco 705-2 controller) and then to manifolds that have flow controls. I thought to 'balance" the system you were supposed to adjust the flows so that the return temperature was 15 degrees less than what the in-flowing water temperature was; what I was told was a Delta-Tee ideal temperature. This is what I did, but now I am worried because my flows are only 1/4 of a cubic foot per minute. I do not have a Taco air scoop though but rather a Spirovent.

 
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blrman07
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Post by blrman07 » Sun. Dec. 27, 2015 8:17 am

There is no set number which applies to every situation. Many variables come into play which includes the size of the system, the boiler or heating unit, the type of radiation or heat transfer. Suffice to say we really can't give you a hard number without a lot more information about your system. All we could do is give you some rules of thumb which vary from 5 degrees to 30 or more degrees.

As Sting says....."It depends."

Can you give us a lot more info on the total system?

 
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lsayre
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Post by lsayre » Sun. Dec. 27, 2015 8:19 am

NoSmoke wrote:Am I missing something here? (Please read this as a serious question and not another way as I know tone can be hard to convey via the written word versus direct conversation).

On my system I have a 3 speed Taco circulator that pushes warm warmer from my mixing pump (a variable speed taco tied into my Taco 705-2 controller) and then to manifolds that have flow controls. I thought to 'balance" the system you were supposed to adjust the flows so that the return temperature was 15 degrees less than what the in-flowing water temperature was; what I was told was a Delta-Tee ideal temperature. This is what I did, but now I am worried because my flows are only 1/4 of a cubic foot per minute. I do not have a Taco air scoop though but rather a Spirovent.
The classic Delta-T is 20 degrees of drop from supply to return for hot water baseboards, but there is nothing wrong with having 15 degrees (or 10, or 30) of Delta-T.

20 degrees of drop merely makes it easy for the HVAC guys to figure out what is happening, since at 20 degrees of Delta-T the BTU's being delivered to the users each hour are 10,000 times the flow in gallons per minute.

Your flow is roughly 1.87 GPM. Taco say that they like to see a minimum of 2 GPM for their air scoops to work efficiently, but I would not put too much (if any) concern into this.
Last edited by lsayre on Sun. Dec. 27, 2015 8:26 am, edited 2 times in total.


 
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Rob R.
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Post by Rob R. » Sun. Dec. 27, 2015 8:21 am

Back to something Larry mentioned earlier in the thread. The fittings used in a typical run of pex tubing may or may not have a big impact on the flow rate, depending on how many are used.

WindyDave has a Taco 007 providing satisfactory performance with 600' of 1" pex. Two years ago another forum member was talking to me about how he couldn't seem to get any heat out of his EFM. The boiler was in a garage 50' from the house, with 1" pex lines underground. Boiler was hot, house was cold, and the Taco 0010 was running nonstop. Once we counted the number of tees, elbows, valves, etc in the system (there was a lot), we realized that the piping resistance of the pex loop was more than the circulator could overcome. He swapped the Taco 0010 for a Taco 0011 (more than double the pump head) and was amazed at the results. Quickly the boiler started to work hard and the house temperature began to rise.

The lesson is: Try to minimize the number of fittings in the system, and don't ignore the ones you have when trying to size other things.

More free advice: Two 007's can do a lot of work for short $ compared to buying a larger circulator, especially if you can get them used/free. I never even considered it until forum member Scottscoaled clued me in.
Two 007's.jpg
.JPG | 102.5KB | Two 007's.jpg

 
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Rob R.
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Post by Rob R. » Sun. Dec. 27, 2015 8:22 am

NoSmoke wrote:Am I missing something here? (Please read this as a serious question and not another way as I know tone can be hard to convey via the written word versus direct conversation).

On my system I have a 3 speed Taco circulator that pushes warm warmer from my mixing pump (a variable speed taco tied into my Taco 705-2 controller) and then to manifolds that have flow controls. I thought to 'balance" the system you were supposed to adjust the flows so that the return temperature was 15 degrees less than what the in-flowing water temperature was; what I was told was a Delta-Tee ideal temperature. This is what I did, but now I am worried because my flows are only 1/4 of a cubic foot per minute. I do not have a Taco air scoop though but rather a Spirovent.
That sounds ideal for a radiant system. Are you warm? :)

 
NoSmoke
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Post by NoSmoke » Sun. Dec. 27, 2015 8:28 am

Yes, but I am a numbers guy like you.

I do apologize, I only read 1/3 of this thread before my first reply and then realized you were helping a specific person with a specific issue. I should not have chimed in.

If I was to do a do-over in life I might have stuck it out as a mariner, but my second choice would have been being a boiler tech. I enjoy this stuff, and am fascinated by the numbers many of you come up with. I stand in awe and deep respect...


 
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lsayre
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Post by lsayre » Sun. Dec. 27, 2015 8:32 am

If I'm perceiving the entire Delta-T thing correctly, the biggest concern with a huge Delta-T (temperature drop from supply to return) is that for the case of a huge drop the "users" on the far side of the loop are seeing less heat than the users on the front end (which is always the case to begin with, but which is multiplied for the case where there is a huge Delta-T).

Short version: Narrower Delta-T's mean more even heat distribution if I'm seeing this correctly.

This is an open thread. Glad you chimed in.

 
NoSmoke
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Other Heating: Munchkin LP Boiler/Englander Pellet Stove/Perkins 4.108 Cogeneration diesel

Post by NoSmoke » Sun. Dec. 27, 2015 8:50 am

Recently I added a 3rd zone to a formerly two zone system.

I noticed that as I balanced the system, my Taco 705-2 controller showed 70% output, but then dropped down to less than 10% as I limited my flow from 1 gallon per minute to 1/4 gallon per minute. That also allowed my Delta T to get back into sync with what it should be. I was not aware that it should be 20 degree drop and not a 15 degree drop. I might leave it though because 1/4 gallon per minute is already pretty low, and if it should be 2 GPM and I am at 1.87 maybe it is best to let it ride.

One difference here however is that I live in a ranch with on-grade slab so I have a lot of thermal mass.

 
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lsayre
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Post by lsayre » Sun. Dec. 27, 2015 8:53 am

NoSmoke wrote:Recently I added a 3rd zone to a formerly two zone system.

I noticed that as I balanced the system, my Taco 705-2 controller showed 70% output, but then dropped down to less than 10% as I limited my flow from 1 gallon per minute to 1/4 gallon per minute. That also allowed my Delta T to get back into sync with what it should be. I was not aware that it should be 20 degree drop and not a 15 degree drop. I might leave it though because 1/4 gallon per minute is already pretty low, and if it should be 2 GPM and I am at 1.87 maybe it is best to let it ride.

One difference here however is that I live in a ranch with on-grade slab so I have a lot of thermal mass.
I thought you said 1/4 cubic foot per minute, which is 1.87 GPM.

For radiant the 15 degree Delta-T may well be better than a 20 degree drop. There is no magic in 20 degrees. It only makes the math easier for the HVAC guys to fathom.

 
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blrman07
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Post by blrman07 » Sun. Dec. 27, 2015 8:56 am

My rule of thumb has always been

Big Delta T,,,,,
Part One.....Loop or end use is too large for the supply or the supply just aint getting down the pipe.
Part Two.....if the supply temp stays constant and doesn't drop with a big delta T, the boiler is "probably" right sized.
Part Three ....If a user is complaining their always cold, split them off onto their own loop whenever possible.

If nobody is complaining part one......Like Will Smith said in Men In Black......If you don'ts start nothin there won't be nothin....

If nobody is complaing part two. The Beatles song.....Let it Be

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