Calulating Your Systems Differental Setting

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Stoker Coal Boiler: AXEMAN-ANDERSON 130 "1959"
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Post Mon. Oct. 24, 2011 11:18 am

Maybe this is flawed for the response time of our coal fired boilers, but take a look...

Found this interesting, there is a formula to finding the correct differential setting for a system;

Code: Select all

                  Btu/hr input                          100,000 Btu/hr
Differential =  System US GPM x 500        Example:    20 US GPM x 500   = 10°F 
Anyone have any comments,as to, if this is going to be too far off with 'solid fuels?

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Location: Napoli, NY

Post Tue. Oct. 25, 2011 3:05 pm

This is an mass flow energy equation, not a calculation for the setting on a differential control.

Differential is temperature differential of entering and leaving fluid in a heat exchange system, IE flow through a boiler or supply and return to radiation.

500 is a rounded number for plain water - 8.33 lb/gal x 60 min/hour /(specific heat =1 btu/lb/deg f. for plain water) = 499.8

For other fluids, use specific heat of fluid and correct with specific gravity.

Best written as:

BTUH = gpm * 500 * (delta t)

This is a universal equation for any plain water system regardless of heat source.

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Post Tue. Oct. 25, 2011 7:11 pm

Pretty good free videos explaining basic hydronics.

For some reason the course pages only opens up in IE, and not in firefox, uncle bill must own stock in taco Inc.

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Post Thu. Nov. 03, 2011 5:50 pm

I have a Harman sf 360 wood/coal burner, I am using johnson controls first to control my water temp. is is A350 series electronic temp control from that is the power module(y350R) then pluged into that is system 350 stage module.

I am running my Harman at 180F which is the A350 module
then I am using the last box which is the sytem 350 stage module I am using this for my dump zone incase the boiler would over heat.
I cant keep a wood fire to last through the night the past few nights it has been a low of arounf 27F I have been loading it at 10 pm and when I check it at 6am it is completly out.
i am wondering what I should have my differntials at on both the electronic temp control and on the system 350 stage module it has a offset potentiometer and a differential potentiometer.
and I have been playing with it to try to set but not sure where I should them? any help would be great
fyi I am using this unit to preheat my oil furnace so it does not run

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