What good is the "DHW Boiler Offset"?

Gordy

Boon said:

@Harvey Ramer I will review a couple videos I took previously because I'm not in a position to do a live test. I'm pretty sure the supply & return temps only bump up a degree at a time in lock-step and very gradually.



For those of you in front of a toasty fireplace this evening:



Hat>> it's a control issue

Gordy>>> Correct so what's that saying loch wants......



Gordy, Loch may want a 190 set point and if they do then it would be nice if they weren't so passive-aggressive about it. If they want 190 then (1) they shouldn't give me a default set point of 180; (2) they shouldn't even give me an option to select a different set point.

Getting inside a designers head. This is one of the biggest challenges in most engineering problems that were designed by others, and you are left to figure iout why would they do that.

If everything is set up "properly" as @Harvey Ramer is alluding to. Then the next step would be why the designer wants the control logic as such. You have to remember there is a wide range of indirects, and maybe the portion of the control logic that is not working on yours. Would work flawlessly on other indirects.

Surprisingly most times once the designer states his case it's crystal clear, and how did I miss that moment. Other times it can be a deer in the head lights of what were they thinking.

keyote

Yes but my exact same system works flawlessly at 185 setpoint but my offset is 10 degrees. I would try changing the offset to 10 degrees and the setpoint at 180 or 185 which work for me.
That said I thought I might change to 190 why not hotter and faster?
When I get a call
The boiler immediately begins to ramp up modulation until it hits 100%, the temps probably about 150 by then, the DT remains fairly steady during this
It holds 100% mod as the SWT rises, both the s/r, the flue gas temp, and the DT between the tank and the swt all seem to maintain a DT relationship thats remarkably steady throughout
It also seems to hit 180 degrees by the time the tank is at about 137-140 so it rarely has to mod more than 1-3 degrees and only that for the last minute,during which time it either holds 180 or flashes between 180 nd 181 with the modulation say flashing between 98 and 97%- its flawless.
besides the 10 degree offset the only differences are boons pipe runs and flue runs are very long while mine are super short, i am using hiest speed on wilo but the med speed worked just as well

rick in Alaska

Has any one ever tried doing something really simple like calling Lochinvar tech support and asking them about it? Seems to me like you can get the best answers (usually) by going to the source.
Rick

Boon

@rick in Alaska yes I was on the phone with them and exchanged emails. Sent them links to a video of the offending last moments. Didn't go anywhere but I should probably revisit this with them even though it works at 190. Being a DIY installer is tough. Almost no one, including some tech support folks, takes me seriously. Of course they think the DIY'er has done something wrong. I don't blame them, but it sure makes it tough.

@Harvey Ramer I'm pumping between 10 and 11gpm. It is priority not zone and it is programmed as priority. I just watched a previous video I took and all the way up to shutdown (set point + offset) there is no spike in return water temperature.

I'm pretty much discounting the supply sensor as [part of] the problem since DHW calls behave normally [don't short cycle, don't exceed set point] at set point of 190.