More short-cycling

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  #1  
Old 01-21-12, 08:58 PM
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More short-cycling

My setup is a bit different, didnt want to hijack a recent topic on the same subject..

On my Olsen boiler (non mod/con cast iron), my L8148A is strapped at the TT terminal so it just runs within the 10f of the set point (which I keep at 150 typically). The 8148 doesnt run the circ's either, they are slaved to the end-switches.
I do get some short cycles.. sometimes in the 1 min range. This is probably when one of my 7 loops calls for heat then shuts down just as the boiler hits the (Limit-10f) point.

What I think I'd like to do, is have the boiler instead operate with a lower cut-in temperature. Instead of running 140-150f , maybe 110-150 ? I think I can go low with this cast iron boiler, since it has pumped bypass/primary. Only when there's a very aggressive load do I notice much of a difference in supply/return temps. With a forced high-limit of 150, the final return temps will be high enough to dry out the condensation, I think.

The 8148A manual shows an optional L6006 low limit controller.. but then when I google that, it has its own well rod and I dont have 2 aquastat mountings. Is there something else I can tie between the L1 and "3" terminal to use as a low limit controller ?

Otherwise, I guess I need a different aquastat. Any recommendations for a unit ? I only need high limit, low limit, and burner control.

(at $5/gallon here, you can see why Im looking to tweak things.. lol)
 
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Old 01-22-12, 05:14 AM
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Not sure if is going below 120 is a good idea.

You can use a L4006a high limit with a 30 degree differential, in series with the the burner output of the existing control.
Tie the L4006 to the supply pipe as near to the boiler as possible. set it for 120-150
The existing control will still be a high limit.
Might take a bit of tweeking of the temps to get the high limits of the two control to match up.

Possibly the by pass is contributing to the short cycling?
Maybe it can be closed a little bit, as long s the return tempps don't stay below 115-120.

I think the Bishop of wiring, the august NJTrooper, would say to get a taco controller and tie the end switch to the TT on the boiler.
Keeping it warm all the time is a waste, especially in the shoulder season.


Petrer
 
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Old 01-22-12, 02:23 PM
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What is the boiler delta-T on short cycling boilers?
 
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Old 01-22-12, 05:36 PM
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@Peter: Im pretty sure that if I was to tie the end switch array to the TT on the 8148A, it would shut the boiler down reguardless of temperature when there was no call for heat. In the shoulder season would this not make it run like a cold start boiler (with no way to ensure it will get up to toasty temps to prevent condensation) ?.

@rbeck: I'll try and see if I can get a measure on that tonight.
 
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Old 01-22-12, 09:42 PM
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Hello Dave,
I would think with a by-pass it would heat up rather quickly.

Perhaps some pictures of the system might be helpful, to better undertanding the set-up.

Peter
 
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Old 01-23-12, 08:20 PM
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Took some temp readings..
Boiler not running (so sitting ~145 (150 high limit -10 on this fixed diff unit remember)).
In and Out pipes at boiler showing 130 ish
Triggered a zone to come on (mid size of our various loops).
At around 150f output, the input was about 145.
At 180 output (??), the input was showing 167.
At that point, i pulled the zone off wondering wtf about the output temp when my limit is 150 and the front dial was still showing like 140. Is my thermal gun whacky ? (I was shooting the sched 80 black pipe.. noticed the fittings were about 10-15 deg cooler.. odd).
Within 10 secs, the boiler limit connected and it shut down (dont forget i have the TT strapped).

So it seem the delta spreads out the longer it runs ?

I have no worries about it condensing anyhow.. lol.
But with a cold-start as suggested, those out/in temps could be more like 130/110 etc when it shuts down on a short call after a warm day lets say. When TT opens, the boiler shuts down, no matter the temp.

Im gonna try to take some pics with my cell phone (main cam battery is dead again.. thx for the crappy battery ebay seller.. lol)
 
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Old 01-24-12, 05:14 AM
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Some photos..







 
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Old 01-24-12, 09:13 AM
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Hello Dave,
If i'm seeing correctly, it looks like a Primary Secondary system, not a bypass.
There must be another pump for the air hanlder?

I think it is a terrible waste to keep tha boiler blazing hot all the time.

The three way thermostatic mixing valve, could be replaced with Taco three way with outdoor reset and boiler protection.
https://www.pexuniverse.com/taco-i10...y-mixing-valve

A strap on aquastat on the return fromthe air handler, could be set to turn on the cirualtor only when the return temps go over 120.

Just a few ideas for ya to think over.

Peter
 
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