Rules of Thumb?

Nick_11

I am planning a heating system based on the diagram an piping runs below.

Overall issues. Cold Climate. Mpls/Stp we can expect 3 to 7 days -15 to -25 every 2-3 winters. Extreme cold could be -30 to -35 for 1-2 days once every 10 to 15 years. We Average 0 to -10 about 10 days every yr. We can count on several days (usually in a row) every year where the lows are in the -teens and the highs are still below zero. (my own experience/guestimates)

Apartment issues: Old structure. Will never insulate like newer bldg.

Existing baseboard is 3/4" copper. I only need seperate zones for garage and indirect DWH.

I used following Rules of thumb I got from this site (heating Q&A) and from a Bell and Gossett zoning article (see BellGossett.pdf attached).

1. 67' per loop Max for 3/4" baseboard at 20 deg temp drop

2. 4' of head for every 100' of pipe.

3. 4 gpm max flow rate per loop.

So the total system contained 160' fintube, 570' total pipe. This calculation gave me about 23' of head. Both more than the rules of thumb above.

So I figured I had to break down my 160' of fintube (diagram on original post) to about 67' max which gave me 4 loops (53, 45, 32, 30). Head on each loop would be between 4 and 7 ft.(7', 7', 6', 4').

Then I took the 4gpm max flow and head req. for each loop and matched them to the grundfos operating curves and came up with the UPS15-58 FRC. If I fine-tune calculations for flow check valves, etc. The total ft of pipe in each loop will increase.

I ran the Heat load and circuit analysis thru Seigentaler acad. version CD and everything pump size (spd 1) looked ok for primary (used 16' 1 1/4" pipe w/FC on circulator) and secondary loops.

Though initial cost is higher by $405. each pump is about $95 and each flange set about $45 compared to larger pump of about $250; need pump for DWH in either case. I can keep a spare pump for $95, or swap one If I have a problem on SuperBowl Sunday when its -21 deg. My $405 difference could be eaten up pretty fast with service / repair on the larger pump.

Again, critical comments, less expensive workarounds or counter point appreciated. If the 67' rule of thumb isn't really necessary, There is no sense spending $400 if I really don't need to.

Thanks

Nick

don_9

Keep them at 67 feet you'll be happy you did.No insulation,
then you might want something with some mass to keep down
the chill.