Setting Temperature on a Navien NCB-240

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djdavenport

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This is one of those "understanding the soul of the machine" questions. I installed a NCB 240 last spring, so I never really had a full winter to put it though its paces. So, far it's been a very good experience and we're quite happy with it.

We have three zone, radiant in slab heat, single circ pump with zone valves.

In dialing in the ODR curve, (ours is option 5--high mass radiant) it programs in high and low water temps (high, I think is 120F and low is something like 75F). That part I think I get. And, I understand that bumping the low set point of the curve up or down will fine tune the system to (hopefully) the point where it runs nearly continuously (on cold days) and the thermostat acts really like a high-limit switch. If I've missed a cog in the logic wheel, please let me know.

So my question is this: On the front panel, it allows you to set the space heat temperature. Is that only for people w/o a ODR? For example, it will allow me adjust it all the way up to 180F (I set it at 120 to match the high point on the ODR curve). IOW, what happens if someone were to have dialed in a higher temperature on the "set SH temperature" but was using a curve that topped out much lower. Does one cancel out the other?

Sorry if my terminology is a little sloppy. I'm learning as I go.
 

Dana

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This thing is a combi-boiler. The Space Heating Temperature setting is independent of the domestic hot water setting, but if the ODR mode is enabled it shouldn't matter what you set it to, as long as the ODR mode is set to 5 for "high mass radiant". Go ahead and play around with it- change the Space Heating supply temperature (should be displayed as parameter A on the information display). Then take a look at the O/R indicator, in the middle , just below the alpha-numerical display- is it still on?

If your not sure, bump on down to parameter G, and see if it's still displaying "5", for high-mass radiant. If G is indicating "-:" it means that tweaking the Space Heating supply temperature over-rode the ODR curve, but I don't believe that it does. (I don't have one to play with to figure it out myself.)

See pages 7 and 10 of the manual .

In an ideal world the reset curve can be finely tweaked to where it never satisfies the thermostat, but it always keeps up with the heating load and never overshoots or undershoots. In the real world things like solar gain and wind-driven air infiltration mess with that a bit, but it's usually possible to get it pretty close, and that is indeed the comfort & efficiency Holy Grail you're looking for.
 

djdavenport

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Great set of protocols, Dana. Thanks. And here's apparently the deal. With ODR enabled, you can set the SWT on the front panel display to anything you like, and the ODR will over ride it. Right now I have it set on for 180F and it's merrily pushing out 87F water, which is smack dab where it should be on the curve. (The other indicators would back that up. ODR icon still lit, G-5 unchanged, etc.) A little bit confusing. They should maybe disable the SWT set option on the main display if you've already gotten the ODR set up.

Always appreciate your thorough (and occasionally patient) responses. Cheers.
 
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