Navien NHB 110 OutDoor Reset

Doing_it_myself

Recently had a Navian NHB 100 installed. I wanted to used outdoor reset, but contractor would not (said I did not need it in Michigan). Although for in-floor heat, it could be questionable on the savings. None the less, I bought an outdoor temp sensor and did it myself. Unlike my Kinght/Lockinvar the Navian does not default settings.
The question I have is about the min/max settings for return water temp. Unfortunately this unit does not default. I have 3000' of 1/2 Pex in concrete. I think there are probably 15 or so circuits (but I will count them)
I am using the following settings
B5 (High Mass Radiant)
C15 (Temp where Supply Max will be used)
D60 (Them where Supply Min will be used)
N120 (Supply Absolute Max)
O84 (Supply Absolute Min), I would actually like this higher, but Navian forced a 36' spread
Now these next two settings are where I become lost
P95?? (Return absolute Max)
Q77?? (Rerun absolute Min) Navian forces a 18' spread
Can anyone help me with what acceptable return settings should be?
Navian Tech support refused to even try. They would not even talk about "theory" of what return temp should be.

GGross

I don't know about navian's controls or programming, can't help with the programming codes but many on here myself included would love to talk "theory" about this

The best thing to do would be to have a heat loss done with a radiant design, it is possible to do this post-install but would be a bit of a task. In lieu of that as you already have the install done, I will tell you that I design radiant systems basically all day in the tip of the mitt, generally the design will call for a supply temperature between 100-120 (pex in concrete slab) on design day depending on the heat loss of the space. The design delta T (the difference between supply and return temps) can affect overall comfort, ideally the floor sees a delta T of about 10 degrees. In floor radiant is the perfect candidate for outdoor reset operation, as ideally you will be circulating the correct temperature water through the system constantly.

Doing_it_myself

GG, I am no stranger to using outdoor reset. Makes total sense to me. Why cook the water at 120, if it is 60 degrees outside. So I am sold on using it. But the Knight Lochinvar that I have (on a different floor heat application) the return temperatures are taken care of by the controller, and I do not have to pick a temperature. I am very confident in my supply temp numbers and the C&D temps that actually create the heat curve. I just have no clue where the return temps should be.

Doing_it_myself

I was hoping there was some "ideal number" such as the return should be XX below the supply with 3,000 feet of 1/2" pipe.

Hot_water_fan

Why do you have to specify the return temps? Shouldn’t supply only suffice? If you can’t, a delta t of 10 for radiant floors is fine at design temp. 

Doing_it_myself

It appears with Navian when you turn the outdoor reset option on, and pick a load type (in this case B=5 which is high mass radiant) then the user must enter all of the values I listed above. If I do not enter a value for the return, then it is defaulted to 149 (which is the default for finn tubed baseboard with a supply of 180) which is not correct for a 120 supply temp. Navian engineers totally missed the boat in their progrmming of this control. What I was expecting is when you pick B=5 high mass radiant and 120 supply, that it would load defaults for all of the other settings. Not the case with this.
When you say delta T at design temp, are you saying a return of 10 less than the supply min/max settings?

PC7060

Yes, 10 less that supply. FYI: The Navian may shut off boiler if delta T class below that number. My HTP does this when DT falls below 5F but leaves the pump on. 

Doing_it_myself

Yes, I feel like it must be using the value to modulate the flame or something like that. But 10' less than supply with 3000 feet of pex pipe in concrete is not what i would have expected. I was thinking like double that. But, that is why I am here.

GGross

@Doing_it_myself

The 10 degree delta T would be for supply/return of the in-floor manifolds and is not a set in stone rule. Tighter delta T in the floor in essence just means you have a more even fluid temperature through the slab which should increase comfort. It is not necessary to run the boiler at a 10 delta T though.

Since you are already familiar with the type of system somewhat I would suggest you plan to make a few changes to see what suits your actual needs. Focus first on that heating curve, and max temps to protect the floor, see how it feels for a few days and then make any changes that are needed. Some heat exchangers may require a wider delta T for whatever reason, and 20 is pretty standard for hydronics in general

Adk1guy

In heating short hand delta T is the difference between the supply and return temperatures.

When I finish my Navien install, hopefully in the next 2 days, I will set the settings low with the smallest differentials or delta t I'll start with 10, and let my room temperatures tell me. If when 30F outside my room will only get to 60f I will inch it up. But if my room temp will get to 72 I will inch it down. Ditto when temps drop to our coldest. If you prefer your rooms warmer or cooler adjust accordingly.

I see no point in doing a heat loss calculation on a system that is already installed. A heat loss calculation is theory. An installed system is a practical working model.

The length of your radiant piping isn't a factor you can use for set up. It is the heat loss vs surface area of the floors in the rooms in which it is installed that matters. If you have a great room with a lot of glass and cathedral ceilings you might want to put in some generously sized panel radiators so you can keep your system temp as low as your room with the highest surface to heat loss ratio will accommodate. But for all I know you have one big warehouse room. Hopefully your 3000 feet is not the length of your longest run but the total tubing used.

BTW, I am not recommending for or against Navien. I bought one because it was accessible and the lowest price. A Viessman was 1/3 more. I cannot find instructions on how to clean the Navien heat exchanger. I hope I don't live to regret buying for price vs quality. I need to put in 3 more so I though I would try this Navien where I can live with it and watch it.

Hot_water_fan

Yes, I feel like it must be using the value to modulate the flame or something like that. But 10' less than supply with 3000 feet of pex pipe in concrete is not what i would have expected. I was thinking like double that. But, that is why I am here.

Remember, the pex is not a 3000' loop. It's usually 10, 300' loops. A delta T of 10 is fine. Try 20 if you want, you can always change back.

GGross

@Adk1guy

Navian did come out with a couple of models that are a standard fire tube heat exchanger, those are not too bad to clean, but still a bit more gizmos in the way than Lochinvar or Triangle tube. If you have a navian that uses the tankless water heater heat exchanger, then you might be out of luck on cleaning the fire side

I can attest to what you said about heating curves as well. I can talk until my face turns blue about outdoor reset, and still about 9/10 times I get called to a job the nice condensing boiler is running on fixed setpoint at 180 degrees. Such a waste

Doing_it_myself

I am blow away by my contractors statement "We don't use it (the outdoor reset) in Michigan, because the temperatures change to rapidly. It's like dude, that is exactly where it is needed the most. Manufactures go to all of these efforts to gain efficiencies, but yet few contractors/buyers take advantage of the. Getting the right heat curve does take time. Messed with a Tekmar at my church for two heating seasons before I got it dialed in right.
Yes, the 3000' is spread over at least 10 runs. Going to count them today.
This is one large shed/workshop. One room, One thermostat. Working there, not living there.
To ADK1guy, if by chance you discover anything specific in your Navian, please do share.
I do not like the 36' spread forced between Supply Min/Max, and the 18' spread between Return Min/Max.
Thanks to all of you this far!

Doing_it_myself

Did a bit more homework yesterday. Confirmed I have 10 runs of 300 feet. Got my Supply max set at 123. The supply min, I want higher but Navian forces a 36 spread. I have the return max set at 113. Yesterday it was maybe 35 degrees out, and the curve had it trying to make 109' supply water.
When I went there and turned up the stat a couple of degrees (for testing), the supply was down in the 80's and return in the 70's. I found it weird that it held the flame at 30% and never let it go to 100% even after running for an hour. I think I am going to have to go back to straight 120 with no outdoor reset. I just don't think the software is right using outdoor reset. Unfortunately Navian will not talk to me.

Doing_it_myself

I stand corrected on the above post. Navian uses the alphabet for their settings. For the flame % I was looking at letter "J" in the info page. Turns out letter J in the info page is DWH timeout value. But letter J in the diagnostic page is flame percentage. Nice job on the consistency Navian. My flame modulation is working just fine and up to 100%

Adk1guy

It sounds like 80 degrees was hot enough for the outdoor temperature and your indoor/outdoor reset was working. That's the whole point. Turning your thermostat higher doesn't raise your heating curve. Why have your boiler running higher than 30% if that is what is needed to offset the heat loss.