Questions on ODR and Navien boiler on/off logic

TT_Vert

I'm trying to understand the logic of the boiler on/off temp vs. setpoint. From my understanding the (default but configurable) hysteresis is on 5 deg. under setpoint and off over 4 (Based on the manual burner on/off differential). My old boiler I believe was 20 degrees total and not adjustable. Reason I'm asking this is w/ my outdoor temp at 52 deg. my setpoint is ~ 102 deg using ODR high mass curve suggested by Navien. This has the boiler on at 97 deg. and off at 106 at this temperature. The issue is one zone does NOT ever get satisfied. I have a slab sensor which I have set to 80 deg. It seems to get to about 77 and the boiler constantly cycles. When I first installed using the default curve (Finned tube baseboard which is 120-180) it satisfied it fine and I believe never got above ~145 water temp. As a test I switched it back today and it quickly satisfied the call for heat and shut off. I thought this navien would attempt to modulate the boiler to stay in a water temp supply area that satisfies the ODR acceptable water temp (IE stay under 106 degrees when the boiler off output water temp is 106) rather than constantly heating the water slightly above the burner off temp causing it to cycle since it isn't satisfying the call for heat? I just set it to option 4 which is low mass radiant and It got up to 78 but it's not 45 deg out so we aren't seeing boiler temp much warmer than 116 (Factoring in the hysteresis). Is there any real harm in increasing my burner off temp from 4 to something higher so it isn't cycling so much and allows the boiler to actually satisfy that zone?

My old boiler was set to 140 deg I believe and I never did have issues (I have pex in concrete and insulated (Unsure of R value) pex under stone floor.

Including the default ODR curves below.


Thanks much guys,

Dave

TT_Vert

Any input/opinions?

Jamie Hall

The default curves are exactly that. Defaults. If you happen to have a house and system which matches the assumptions in one of the default curves, wonderful. Doesn't happen often. The solution is to tweak the ODR curve to match what you need.

TT_Vert

Jamie Hall said:

The default curves are exactly that. Defaults. If you happen to have a house and system which matches the assumptions in one of the default curves, wonderful. Doesn't happen often. The solution is to tweak the ODR curve to match what you need.

that i understand, given the curves are going to be linear no matter what I do and the fact i'm not satisfying the slab sensor in colder weather w/ the current boiler off setup i wanted to increase it but was hoping someone else had some input on the repercussions of doing this. Or perhaps someone who has done just this.

Thanks
Dave

Jamie Hall

The primary repercussion is that when you get it right it will be a lot more comfortable... and the whole system will work better. It's done all the time, and is part of the process of setting up the ODR to control your system. The on/off differential has noting to do with it. What needs to happen is that the slope and end points of the ODR curve need to be adjusted.

The procedure is buried in the manual and the menus. You might try low mass radiant instead of your present high mass radiant for starters, and work from there.

TT_Vert

Jamie Hall said:

The primary repercussion is that when you get it right it will be a lot more comfortable... and the whole system will work better. It's done all the time, and is part of the process of setting up the ODR to control your system. The on/off differential has noting to do with it. What needs to happen is that the slope and end points of the ODR curve need to be adjusted.

The procedure is buried in the manual and the menus. You might try low mass radiant instead of your present high mass radiant for starters, and work from there.

Thank you for that. I'm not very educated in these things and don't want to just go making changes without considering the downfalls.
Dave