Outdoor reset, boiler bypass, primary loop, 140 degrees?

vadimr

Hello, new member here and was hoping to ask a question.
Long story longer is as follows.
I bought a 17 year old house 3 years ago and I really disliked the baseboard heating on the first floor. I decided to convert the first floor to the radiant heating and keep the 2nd floor with the baseboard radiators. This was also required in order to achieve my kitchen expansion and etc. I have never done this before but I like a challenge. I designed and built the system by myself from some reference diagrams. I could not be happier with it, everything works exactly as I planned. I have no issues with the system at all.

I'm attaching a diagram that I had drawn up when I designed this back in 2016.
Pretty much the only thing I kept was the old cast iron Weil-Mclain boiler. It is going to be replaced with a mod-con boiler in the future but for now I am keeping it until I finish some other projects.

I have a Bell & Gossett 6 zone controller as my main zone controller and in order to run radiant and traditional baseboards from the same boiler I put in ESBE 3 way mixing valve with Tekmar 153 mixing controller for all the zones that are radiant and the baseboard comes off the supply prior to the mixing valve.

Now, I finally decided to add Taco SR501-OR-4 outdoor reset. Now the system works even better than before. However, I do not have an injection loop with a variable pump but rather have a primary loop out of which a supply and a return are fed. I set my OR to 140 degree minimum but I have a feeling that the boiler is not running long enough on these relatively warm days. Since the primary loop is 1-1/4" and the circulator I have there is 34GPM Grundfos circulator it can quickly move enough volume to get the OR to trip and shut down the boiler. The other pumps are 20GPM Grundfos that draw from the main loop.

Even prior to OR if the baseboard zones are not running and only the radiant zones are, the mixing valve would quickly prevent drawing any hotter water from the supply side and thus the boiler could turn off once it hits 180 degrees. However I felt that it always ran "long" enough to get the flue to proper temps.

I suppose to be 100% certain I can add an injection loop and Tekmar 361 or similar but I feel that would be an overkill. A thermostatic bypass is the easiest solution and probably can simply be added on the supply/return side line where it leaves the primary loop but I feel the boiler still would not run long enough because the volume would but not all that much.

So aside from injection loop with a variable pump, I either can leave it as is or switch over to a mod-con boiler?

Thank you!

hot_rod

Micro zoning and shoulder season conditions are hard to design out of a system like yours.

Yes to a mod con, and maybe even a small buffer. Determine how the smallest zone, matched the boiler output. With a mod con you get the added benefit of modulation and it does not require return protection.

Depends on how soon you will switch to a mod con?

Nice to see all the isolation and purge valves.

vadimr

I did more thinking and I noticed my current boiler is way oversized it is 175,000 BTU input and 145,000 D.O.E BTU. Doing the napkin calculations as described in this article:
https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new

I came up to 57,000 at 65 degrees and 63,000 at 60 degrees so even 1.7x it would be 97,000 and 107,000.

Considering my current boiler was only heating with baseboard radiators and I added like 10x more surface area with radian it still does not help with keeping it running consistently.

I am thinking mod-con in the 90,000-100,000 BTU max range with 1:10. Any recommendations for a particular boiler? Two family members of mine have NTI mod-cons but they are not very popular for some odd reason?

Thanks.

hot_rod

Something like 65 mod con choices on the market currently. Shop a brand with good reputation and support in your area. I've had great experience with Lochinvar. I've also used a bunch to HTP products in my own homes. Really any of the brand names have good product out now.

Stay away from tankless heaters would be my best advice.