Buffer tank sizing help

Bob Sweet

With 185* S and 165* R temps: 6.1 minute on 24 minute off with 15000 heat loss. 7 minute on 16 minute off with 22250 heatloss. 9.7 on 9.8 off @ fuul load. I assumed modulating the Baxi to 75000 b tu output with 30 gal tank. Hope this helps. 65* ambient air around tank.

Tony_23

someone with HDS ?

Installed a Baxi 310i w/ 2 zones. Total load is 37KBTUH. Baxi will modulate down to a minimum of 35,500. Short-cycling constantly.
Don't want to do this twice, or over do it. How many gallons of storage should I install ?

TIA,

Tony

Tony_23

anybody ?

Bob Sweet

Tony

What kind of run times are you shooting for? Supply temps? And are the loads split evenly 50/50?

Tony_23

info

Loads are about 60/40. Baxi runs to 185 supply. Current burner run time is about 90 seconds, once it's up to operating limit temp.

I'd like to see it run for a bit longer

Tony_23

Thanks, Bob

What happens if the Baxi is modulated to 40,000 ? 50,000 ?

I think I can squeeze in a 20 gallon tank.

At first, before I realized how oversized I am at low fire, my return temp would fluctuate from 170 to 155 between firings. It wouldn't recover from 5F setback 30F above DTD for hours. I was using the internal circ for the system as well, with enough flow, but not enough load.

The customer, when I explained the problem, couldn't believe "that little thing is too big for my house"

Bob Sweet

Tony,

50000 output, 20 gal storage: full load 19 on 6.6 off, 15000 load 7 on 16 off, 22250 load 9 on 11 off. Dropping down to 40000 doesnt seem like a good match with 20 gal storage.

Bob Sweet

Tony

I input wrong values ,here are the revised numbers: full load 50000output 20 gal storage, 15 on 5.3 off, 15000 load 5.6 on 13 off, 22250 load 7 on 8 off

The Baxi's a pretty cool boiler, we just took the line on. Love the R-Max feature, makes it real versatile.

Tony_23

Thanks again, Bob

What a great place this is, huh ?!