Navien NCB-240 for this house? (photos)

[vanagon]

Hi delta-Ts are hard to maintain at very low boiler output temps. Most low-temp systems run 5-10F delta-Ts on the radiation when the temps are well into the condensing zone. It's all a matter of just how quickly the radiation can emit that heat into the house and the pumping rate- it takes a LOT of radiation to put much heat into a 70F house with 85F water, and you WON'T be seeing a 14F delta-T on the radiation.

I guess my basic question is whether this means that a Delta-T pump on the secondary loop is a bad idea, when using the outdoor reset sensor (since sometimes the boiler temps will be high, and sometimes low.) I want to avoid a scenario where the Delta-T pump slows down so much that the primary loop is recycling water. i guess at these temps I would be in the condensing range anyways, so that everything would be okay?

 

[Leon82]

You can still run that pump in fixed speed mode and keep the ecm energy benefits.

 

[Sponsor]

 

[vanagon]

Right. So I guess I'll try it out in Delta-T mode first, and if I'm getting significant water recycling in the primary loop, I'll switch to a constant speed.

 

[Leon82]

They are a bit larger than an 007 as far as external dimensions. Diameter and overall length.

The flange height is the same though.

 

[Leon82]

I think the conditions need to be right for a perfect scenario hence the reason for the Hydraulic separation.

It won't be perfect all the time.

 

[Dana]

Some smart pumps such as the Bumble Bee allows you to set a fixed GPM in 0.5 gpm increments as well as a delta-T mode. The Taco Viridian series (like the 1816) also allows you to run in a proportional pressure mode (useful for systems that get tweaked-in for room to room temperature balance with thermostatic radiator valves) or a fixed speed mode, which achieves the same thing as a fixed gpm. They are all far more flexible and power-efficient than old-school 3-speeds or single speed workhorses like the tried & true 007.