View Full Version : adding zone, please review my design draft
02-01-2012, 10:16 PM
Our existing CI baseboard one zone water heating system is not enough now. We are starting finish the basement and planning to replace the family room’s electric heating with water heating. The boiler is 2yrs old Burnham alp105 gas boiler and supposes it is big enough for the coming new baseboards.
We plan to do the following:
1. Split two bedrooms out from the existing zone, add the family room, which is using electric heating now, into it;
2. Add one zone for those two bedrooms and another downstairs bedroom;
3. Add another zone for all basement rooms, except the bedroom and utility room;
By using Heatloss Explorer 2, I figured out the family room needs about 30ft Slant Fin 30 baseboard. I will do the heat loss calculation for basement later.
I have two diagrams, attached or bigger version from the link below, to show you what we have now and what the new design is. Please review it and let me know your professional comments.
I also need your help to select new circulators and switch relay (zone control panel).
Bigger version diagram link (http://www.flickr.com/photos/bostonjames1980/sets/72157629115886707/detail/):
With a mod-con like the Alpine it's worth buying better low-temp heat emitters than fin-tube (even if it means scavenged CI baseboard off Craigslist.)
There needs to be either enough radiation or thermal mass on even the smallest zone to ensure that the ALP105 won't short-cycle at low temp, or you won't be able to run it deeping into condensing temperatures without shortening it's lifespan. Cast-iron has significant benefits over fin-tub the thermal mass front, and more comfortable & predictable low-temp output to boot.
Min-mod on the ALP105 is 21KBTU/hr. Ideally you'd like to be able to run temps as low as 100F or lower water to reap higher condensing efficiency during lower heat loads, which won't be possible with fin-tube (due to unreliable low temp output), but with CI baseboard you can. At 21K-in/20K-out that means you'd need about 125' of baseboard to run fully balanced (heat out=heat in) with 110F water. With the thermal mass of cast iron baseboard you could get away with 1/4 that (your 30', as-designed) and still get decent burn lengths out of it but fin tube you'd better have at least 50-60', and 80' is even better. Since there's no thermal mass to speak of buffering the output you need the fin tube to be delivering a good chunk of the 20K input to avoid short-cycling.
A single zone of 30' of FineLine 30 will short cycle like crazy, since it has less than a gallon of water in it,maybe 10-12 lbs of water in the whole loop, and at 110F (the lowest temp they'll give any spec for) it's only (160BTU/ft x 30'=) 3300 BTU/hr, which is barely 1/6 the minimum output of the boiler. Going with 30' of CI, (or even 40') would be preferable with that boiler. With
The output of cast iron is comparable to fin-tube. see: http://www.usboiler.net/products/baseboard/baseray/assets/io-manual.pdf (http://www.usboiler.net/products/baseboard/baseray/assets/io-manual.pdf)
If you take the fudge-factor coefficients given for 110F water in the BaseRay sheet and apply it to the 10 footer, you'll see that it's ~164BTU/foot @ 110F, pretty much like the calculated rating they use for 110F water in the FineLine sheet, but in the BaseRay case it's a very real number, whereas with fin tube the error bars get very big at 110F and lower, which is why they don't even TRY to spec it any lower (and it's a stretch as-is.)
It's usually possible to find used cast iron baseboard for $20/foot or less on Craiglist (http://boston.craigslist.org/search/mat?query=cast+iron+baseboard&srchType=A&minAsk=&maxAsk=). The stuff is nearly indestructable, and it cleans up & repaints nicely.
If you need or want a more modern look, Runtal UF-2 & UF-3 is a decent mid-mass convecting radiant-baseboard choice, but you'll have to pay a bit for it.
BTW: I'm guesstimating that the ALP105 is on the order of 2x oversized for the true design condition heat load. What did the Hydronic Explorer 2 come up with for the whole-house load? (That tool regularly overshoots by 30-35% above measured reality.) The ALP80 modulates down to 16K-in/15K-out at low temp, making it slightly easier to deal with on systems with smaller zones.
02-20-2012, 09:48 PM
Thank you Dana. I bought 130ft WeilMcLain CI baseboards at $550 (sale price) + $200 (crashed my utility trailer and towed back fee) + $140 (two tailer tires changed on my way home). Those baseboards are new!
My whole house load, including basement, is 54073BTU/HR according to the HeatLoss Explorer 2. Basement has much less heat loss comparing with the first floor. My house is a Ranch house.
The Heatloss Explorer 2 reliably oversizes 25%+, so don't be surprised if your true heat load (measured) comes in at ~40K or a bit less.
Good deal on the CI baseboard (even with the crash premimum it's under $7/foot?)