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Tekmar 256 ODR control help

#1
01-09-19, 10:09 AM
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Tekmar 256 ODR control help

Hi all looking for some input/thoughts before I give up on this outdoor reset control.

Honestly for some systems I think it's just a bunch of hype and zero value.

I have a properly sized boiler, but trying to tweak things a bit more, I have in wall convectors that are copper fin, not case iron. So these should run at 180 degrees water temp.

So I call Tekmar and they tell me if I set the differential at say 10 degrees it will do 5 degrees above the 180 and 5degrees below so essentially go to 185 or down to 175...why in the world would I want a controller to do that??

May be she didn't know what she was talking about and she should have said that I need to set the target degrees, and it will go 5 degree above and below that. Or if i said my differencial is 20 it would go 10 degrees above and 0 below.

So now I'm confused and basically looking to scrap the whole ODR thing

#2
01-09-19, 11:17 AM
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2014-

The quote below is from the manual, page 8. It looks like she was describing the Fixed Differential mode with differential = 10:

upper limit = [180 + differential /2] = [180 + 10/2] = 185

lower limit = [180 - differential /2] = [180 + 10/2] = 175

But it looks like Auto Differential mode is what you should use. You tell the tekmar you are using Terminal Unit = 4 (Fin-tube convectors) and it knows 180 is the Boiler Design water temperature, and supposedly it does the rest.

http://media.blueridgecompany.com/do...%20Install.pdf

Fixed Differential

The boiler differential is divided around the BOIL TARGET temperature. The contact will close when the supply water temperature is 1/2 of the differential setting below the BOIL TARGET temperature, and will open when the supply water temperature is 1/2 of the differential setting above the BOIL TARGET temperature.

If the Auto Differential is selected, the 256 automatically determines the best differential as the load changes. This setting is recommended as it reduces potential short cycling during light loads.

#3
01-09-19, 04:39 PM
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What I was to do is install the ODR and be able to open up its differential to 20 or 25 degrees, understanding he whole thing about not wanting to go below 140-145 because of condensation. My present OEM limit switch has a 15 degree fixed differential setting.
If I understand correct the ODR takes out and is in place of the OEM limit.

Do I understand this correct?

#4
01-09-19, 04:45 PM
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Start a new thread for another topic

Last edited by 2014gt; 01-09-19 at 04:47 PM. Reason: Start a new thread
#5
01-09-19, 04:49 PM
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Tekmar ODR Control Help

What I was to do is install the ODR and be able to open up its differential to 20 or 25 degrees, understanding he whole thing about not wanting to go below 140-145 because of condensation. My present OEM limit switch has a 15 degree fixed differential setting.
If I understand correct the ODR takes out and is in place of the OEM limit.

Do I understand this correct?

#6
01-10-19, 07:58 AM
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Join Date: Jan 2008
Location: Southeastern Pennsylvania
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If I understand correct the ODR takes out and is in place of the OEM limit.
I don’t have an ODR but it looks like the tekmar 256 is supposed to be used in conjunction with a safety LIMIT. It does not take the place of the safety LIMIT (page 8).

In your case, in setup when you define Terminal Unit=4 ((4=Fin-tube convectors), BOILER DESIGN is automatically set to 180, and BOILER MAX is always calculated as [ BOILER MAX = BOILER DESIGN + 10F], so in your case = [180 + 10 = 190].

When the tekmar calculates the BOILER TARGET temperature it will never set the BOILER TARGET temperature above BOILER MAX. So in your case, never above 190. So if you would set your safety LIMIT control above 190 you should be OK, and it would not interfere with the tekmar operation.

What I was to do is install the ODR and be able to open up its differential to 20 or 25 degrees,
I thought the point of the ODR is to let the target temp and differential be calculated by the ODR and vary dynamically so that the operation is more efficient? Sounds like you want to override the ODR for some reason. Do you suspect something is wrong?

#7
01-10-19, 11:16 AM
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Join Date: Apr 2014
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The Tekmar 256 takes human inputs and performs the aquastat/out-door-rest function. Unfortunately many users have a poor understanding of heating systems and controls resulting in undesired performance then negative comments.

Gauge 2014gt by the opening post:
“I give up on this outdoor reset control. Honestly for some systems I think it's just a bunch of hype and zero value.”

“I have in wall convectors that are copper fin, not case iron. So these should run at 180 degrees water temp. “
The whole concept of ODR is to adjust water temperature to what is needed at the day's outdoor temperature. 2014Gt does not need ODR for 180F water all season, he should just use ordinary aquastat. What he fails to understand is water temperature needed to match a days heat load varies over the season. Yes, the convectors spec 180F water for rated output but 2014gt needs it for only on the coldest days each season.

ODR's are widely used industrial, commercial and residential heating systems because they work, make buildings more comfortable and save money. Taco, a major heating equipment manufacture resells the Tekmar 256 as repackaged Taco PC700. Today most packaged boilers have ODR option. That is not "hype" or "junk".

The Tekmar “Auto Differential” feature is for those paranoid about short cycling. It causes extra long burner runs and overshoot of boiler water max set temperature. Also when burner flame stops, residual heat in boiler walls can continue to raise temperature to excessive levels.

I have a well instrumented 60 year old Weil-McLain boiler, Beckett AFG burner and Tekmar 256. With max temp set at 170F and 5F delta-T it overshoots to desired 180F max.

When Tekmar using Auto Differential was set at 180F max it over shot to 190F ++ due to longer burner run time resulting in lower efficiency.

Last edited by doughess; 01-10-19 at 01:02 PM.
#8
01-10-19, 11:44 AM
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I changed the title to better reflect the thread.

Just a quick short story. I was in a store that was an old converted house/general store. The entire front of the store was single pain glass. Building was over 100 years old. Little to no insulation in the walls. Very heavy heat loss. I couldn't do much about the situation. It had big radiators that were replaced with baseboard emitters. I had to run the boiler up near 200 degrees to get enough heat to keep the waiting room comfortable on cold days. At first I'd change the boiler temp based on outdoor temps manually and almost daily. A real pain in the a**. I built my own ODR to bring the boiler temps down to 165 on normal days. I ended up saving a lot of fuel oil.

The point of the story is.... setup correctly.... an ODR system is an asset and money saver.

#9
01-10-19, 06:44 PM
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Join Date: Jan 2014
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I hear you but can we agree that what dictates the ultimate on of of the system is the call and satisfaction of the thermostat setting. So, if say in a period of 8 hours let;s say the thermostat is set at 68 degrees.

With no ODR and limit of the boiler at water temp of 180 degrees, if you satisfy the thermostat in 30 minutes. OR

With ODR and water temp of 165 degrees, if you satisfy the thermostat in 60 minutes.

How can there be savings. My point is the duration of the running boiler is directly related to the BTU output for a certain period of time.

Am I missing something?

#10
01-10-19, 07:10 PM
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It costs more to keep the water at a higher temperature.
Instead of the thermostats cycling constantly they call for heat longer.

#11
01-10-19, 08:26 PM
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From a cold start I would agree, but also from a cold start wouldn't you say at 180 degrees I'll satisfy the thermostat faster than at 165 degree water?

Then once the boiler starts at least with my OEM limit having a 15 degree diff, you are just heating that delta. Doesn't matter if it's 165 - 180 or 160-175 or 155-170. The run time to heat that 15 degree delta is the same.

Not arguing just trying to get my head wrapped around a true benefit, or just Ebay the thing

#12
01-16-19, 03:28 PM
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Location: MA
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