Primary circ in a monoflow retrofit

rsellick

Greetings,

I've just spent the first winter in my hot-water heated home (1950's, northern NJ, 1400 ft/2) with a monoflow & CI radiator system on the first floor and a set of 3 fin tube baseboard (piped in series) in the basement. My primary motivation for changing things up with a manifold were to get the rooms heating more evenly (especially the series baseboards) and gain ceiling height in the basement by removing the monoflow circuit in favor of pex runs between the joists. However, this is unlikely to correct the gross short-cycling of my boiler (some days every 5 minutes) and the sky-high NG bills ($300 / month) it has resulted in.

Outdoor reset with near continuous circulation and boiler protection are now on my radar. After reading many of the publishings from Taco, Uponor, Caleffi, and Tekmar, I've honed in on a system with primary/secondary piping, a 4-way motorized mixing valve, ODR controller, TRVs on each radiator, and a per-emitter manifold.

The manufacture docs and Dan's EDR book helped to determine all my distribution system requirements, but I'm having trouble sizing the primary / boiler loop circulator. As this loop will not have a fixed delta-t due to the mixing valve, I'm unsure how to size it. My boiler (Peerless MI-05) lists no minimum flow requirements and I plan to use a pressure regulated distribution circulator (Grundfos Alpha2), however with the 4-way valve in it's fully closed position (boiler output -> boiler input) the circulator is completely removed from the primary loop. Obviously I would like to use the smallest possible device here to reduce operating expense, but I'm not able to determine how small is too small. Additionally, it seems the boiler is grossly oversized for the emitters installed in my home. It can provide 115k BTU/hr, while I have 45k of emitter capacity.

I've attached a simplified schematic of the proposed system, which provides the features I desire with the minimum amount of piping complexity. It's very similar to figure 6-12 on page 40 of Caleffi iDronics (and other docs). Any assistance the forum can provide to help me understand sizing the primary circulator in a system where the primary loop delta-t can be 0-20 degrees (depending on the mixing valve position) is appreciated!

Thanks,
-Ryan

EBEBRATT-Ed

@rsellick , I am sorry to break your bubble but your problem is the oversized boiler. That's what you should be fixing first.

You can install all the controls and expensive hardware you want and IMHO you are wasting a lot of money. You wont be any more comfortable and wont save any money. With the correct size boiler you system would probably work fine the way it is.

@rsellick said
Additionally, it seems the boiler is grossly oversized for the emitters installed in my home. It can provide 115k BTU/hr, while I have 45k of emitter capacity.

Paul48

And TRV's will compound the problem.

lchmb

I agree with Ed. Your spending a lot of money on a boiler that is 2 times to big. Why not invest in a properly sized boiler that has all the bells and whistles attached and do it right...

rsellick

Thanks for the comments guys.

Being that I have all cast-iron sewer piping and no simple means of attaching another drain to the main stack, I had planned to upgrade (downgrade) the boiler with another conventional CI and not a condensing model at some point. The peerless and WM models do not have any of the bells and whistles I desire.

We recently had to remove some sections of the basement for a french drain install. With the ceiling removed, it's opportune to at least make the pex-al-pex and manifold distribution changes. I understand installing the mixing setup will not yield the desired results right now, but is it detrimental to building it while the walls and ceiling are open? I may be able to replace the boiler before next heating season, but I can't guarantee that. Unlike the distribution system changes, I won't need to alter any portion of the finishings to swap the boiler.

Thanks again,
-Ryan

JUGHNE

Is the drain needed for the condensate from a ModCon if you installed?? With a neutralizer you could run it into a floor drain.
Or, using a neutralizer and cond pump, somewhere in the basement must be a sewer cleanout that could be extended...or washing machine drain standpipe.....and some have even drilled and tapped the cast....might not be code but it works well.

hot_rod

pump it in to the french drain, it will get neutralized also

rsellick

Appreciate the feedback Gents, but I'm still not able to determine how to size the primary circulator in such a system. Of course this assumes the boiler is a 1/2 the size, 55k BTU conventional model. I just need to construct the mixing system now and leave the ODR and mixing valve fully open until the boiler replacement is feasible, but am unsure how to proceed.

Can anyone advise?

Thanks, -Ryan

rsellick

Additionally, question for Hot Rod: my supplier says the 171 series manifolds have been discontinued, contrary to the Caleffi website. Is this in fact true?

Gordy

If you install a fire tube mod/con the mixing valve goes away, and possibly the p/s piping with that another circulator disappears. Your ODR then has way more potential due to allowing unlimited low return temps to the boiler. Sub 130 rwt has huge efficiency gains to the boiler.

hot_rod

rsellick said:

Additionally, question for Hot Rod: my supplier says the 171 series manifolds have been discontinued, contrary to the Caleffi website. Is this in fact true?

The 171, motorized mixing group is gone from the 2017 catalog. the 172 thermostatic is still in there.