ODR and lowest functional temp of fin tube baseboards

northlakes

Finally testing out the ODR curve on my modcon boiler (IBC VX 199) Prior to this I was cycling about 1-2x per hour using thermostats, at default settings from installer, deltaT was constant around 20.

Design supply temp: 170
Design outdoor temp: 14
Summer shutdown temp: 85
Max supply temp: 190
Min supply temp: 145
Supply differential temp: 20

I'm still experimenting with settings and still shaky on how they influence the curve (this unit has an "advanced" reset I'm not currently using which has settings for "design indoor" and "indoor setpoint".) After a couple of days with thermostats in all zones wide open in 30-40F weather, I've changed params as follows:

Design supply temp: 150
Design outdoor temp: 0
Summer shutdown temp: 70
Max supply temp: 190
Min supply temp: 110
Supply differential temp: 20



The heatloss estimate I did on this building a while ago was around 105k with 315' of baseboard. Target space air temp is 68-70. With design supply temp at 170 and design outdoor temp at 14 it was overheating the space a lot, so I dialed it back and boiler now seems to be holding ~50btu (of 199.) Not all the way turned down, but I think this one only goes down to 30. Assume I'll need more time to see how it goes, but at the moment I'm curious about the lower temp limit where baseboards can perform properly.

Current snapshot:


- There's an oversized secondary loop circ (addressed in another thread) which I assume is contributing to the low deltaT, at 10*. Appears to me that the lower the supply temp drops, the delta decreases. (The planned replacement for this circ is a more accurately-sized ECM.)

- Honestly shocked baseboards could do much to heat a space at supply of 130* and below, but I keep lowering the curve bit by bit, and temp in the space isn't coming down much, just holding steady. (Maybe I'm just burning crazy amounts of fuel without much benefit?) Is there a lower limit where baseboards are no longer really doing their convection to transfer heat? This could also contribute to low delta?

STEVEusaPA

I mean technically if the water in the baseboard is 1° warmer than the surrounding air temperature it will transfer heat. I'd keep lowering it until that zone runs nonstop, then bump it up a few degrees. If people aren't comfortable, then bump it up a little more.
Also flow rate is a consideration.

hot_rod

The room thermostat should turn the system off before the space over-heats? Regardless of how the settings are adjusted on the ODR. Fin tube responds quickly both up and down.

It takes a number of tries to fine tune ODR. You need to get to a design day condition to know for sure if you have the high end temperature set high enough.

Some boilers have "boost" function that allows the boiler to increase temperature if it runs for a period without a temperature increase. Read the manual to see if you have that function and if it can be enabled with ODR. It is a simple way to make sure you never fall behind the heat load.

Snoop around for a You Tube video that shows how to program your specific boiler control . Often it is easier to understand compared to the manual. manufacturers usually have some training videos available.

northlakes

hot_rod said:

The room thermostat should turn the system off before the space over-heats? Regardless of how the settings are adjusted on the ODR. Fin tube responds quickly both up and down. It takes a number of tries to fine tune ODR. You need to get to a design day condition to know for sure if you have the high end temperature set high enough. Some boilers have "boost" function that allows the boiler to increase temperature if it runs for a period without a temperature increase. Read the manual to see if you have that function and if it can be enabled with ODR. It is a simple way to make sure you never fall behind the heat load. Snoop around for a You Tube video that shows how to program your specific boiler control . Often it is easier to understand compared to the manual. manufacturers usually have some training videos available.

Thank you. I meant overheated as I’m tweaking ODR by setting thermostats at 80, target space temp is 68-70, once it stabilizes I would set the stats lower. What does seem to happen when I use the thermostat to keep it from overheating is like a short cycling of ZVs (not boiler) as it quickly heats that zone back up to temp and shuts them again. Yes, would surely need a design day to get it right and I’ll look for a boost mode…

My brand (IBC) is a bit less common and haven’t found much online that helps me understand the “real world use” of controls, I was actually thinking of asking if there was anyone here with IBC experience that would remotely consult, as I have it all wired up for that.