Help selecting a Circulator, Outdoor Reset Boiler Control, and 3-Way Thermic Valve

yeilon

Hi everyone,

We have a hydronic heating system with an old H B Smith CI gas boiler. Input of 150K BTU/Hr and output of 120K BTU/Hr (80% efficiency by design). Oversized for our house.

4 heating zones.

Argo ARM-6P switching relay with priority.

Indirect tank for DHW.

We would like to economize our heating system and would appreciate your input regarding the following:

1). Circulators: All zones and DHW circulators are Taco 007. We are considering replacing them with the high-efficiency Taco 007e. Thoughts?

2). We plan to add an outdoor reset boiler control. We consider Argo DPM2 or Tekmar 256. Which one do you recommend?

3). We plan to add a thermostatic valve on the return side to protect the CI boiler. We consider Taco 280 or Danfoss ESBE VTC. Which one do you recommend? Do you recommend the 130F or 140F thermostatic elements?

Thank you

hot_rod

What is the heat load, how oversized is the boiler?

What type of heat emitters? Fin tube, radiators?

Four zones with 4 circulators?

yeilon

First, I apologize, I was referring to Callefi 280.

The heat load is 70,000 btu/hr at 0F and 55,000 btu/hr at 15F. The boiler output is 120,000 btu/hr.

The emitters are a mix of fin tubes and CI radiators.

Yes. 1 zone - priority DHW with a circulator. In addition, 4 heating zones with a circulator for each.

hot_rod

are the fin tube and cast radiators in the same zone? The perform completely different. The fin heats quickly, within minutes, radiators need 15- 20 minutes or more to get up to speed.

Generally low mass fin tube systems do not need return protection. So it could depend on how many radiators you have, if the boiler is oversized the return protection may not be needed

Personally I would go with a single ECM delta P type circulator and low current draw zone valves. 70,000 is an easy load for one typical residential circ.

If you want max performance from the indirect a dedicated pump and 1” piping, or a 1” ZV with 7 or higher Cv.

yeilon

Thank you. This is very helpful.

In terms of the emitters, half are convector elements in one zone, and the other half CI radiators in the other 3 zones.

I also wonder if you could comment on the outdoor reset and thermostatic valve I listed above.

hot_rod

yes ODR can provide some better efficiency and provide longer run times when set up properly. Tekmar usually shows a choice of emitters in the set up program. Mixing low and high mass will be some compromise.

With a cast boiler you don’t have a wide temperature range to work with as the return temperature should be above 130, so maybe a supply of 150- 180.

Yes the 280 is a good choice to assure boiler protection. So one zone of just fine tube, 3 zones of just radiators

mattmia2

you might need a buffer tank if you're trying to zone and do odr with an already oversized boiler.

yeilon

Thank you, both.

Just one more clarification, the 280 comes in 130F or 140F. They are fully open at the cartridge temperature + 18F. I understand that for CI, the lower limit is 130F. In this case, should I buy the 130F cartridge + 18F = 148F when the valve is fully open? That would give me a wider range on the ODR.

Also, in my case, do I also need the highlighted secondary bypass loop?

hot_rod

Actually I would order the 115 sensor also. 115+18= 133° F29633 part number. The ODR may start ramping down the boiler before the 130+18 148° cartridge. Depends on how aggressive you get with the ODR settings.

No need for the additional bypass pipe with the 280.

I would add a ball valve at all 3 port so you can quickly service or change cartridge without draining down.

https://www.caleffi.com/sites/default/files/media/external-file/01223_NA.pdf

yeilon

Got it. Thank you so much, Bob.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1899126#Comment_1899126