DOUBLE TIER BB

an old wrench puller

I would connect it parallel. That would give you the most heat out put.

frankiewrench

DOUBLE TIER BB

It's been a long time since I've had a job like this and I forgot the proper method. Slant-Fin web site offers no help, so...........I have to install some double tier bb in a town house and I can't remember if it gets installed parallel or series within the enclosure. Any help appreciated.

Brad White_204

Another View

Hey Frankie, great to see your name again...

I have a different take so bear with me.

Parallel in general will give more heat output because each tier sees the hottest water to start. However, it works best with small tube FTR and on relatively short runs.

Because the flow is split, the velocity is cut in half and in larger tube sizes, this could be critical. Also, the heat output diminishes over the length, especially if the run is long. See below.

For most applications I design (and this includes condensing boilers and low temperature applications in general), I use series flow.

These are the principles and reasons I use:

1) Start with the hottest water on the top tier. This is a counter-flow measure such that the first tier sees the coolest air to wring out the heat from the leaving water and the warmest leaving air (that which was pre-heated by the lower element), sees the hottest water for a good send-off.

2) If piped in parallel and the run is long (say 30 feet or so), that first few feet will be quite hot and the last few feet quite cool, relatively speaking. Uneven heating potential. The starting point is hot and continually diminishes, as does the average water temperature.

3) By piping in series, every point along the path, no matter where you cut it, the average water temperature is consistent. If the supply is 180 and the return is 160 so the average water temperature is 170, this will hold at the connection end as much as at the U-Bend on the far end. Sketch it out and test this, you will see.

4) Another trick I use considers that dual-element radiation only gets you about 30 to 50 percent more output (per manufacturer's rating tables) because the second tier sees pre-warmed air; the delta-T is not as great so the second tier gives out less. So this is what I do:

If length permits, I stagger the elements so that there is fuller wall coverage and less overlap.

Say I have a 30 foot exposure but the heat loss requires 16 feet of dual element. I can run perfectly aligned pairs of 8 foot elements and get say, 900 BTUH per foot whereas single element might give me 600. By staggering the elements, I might have four to six feet of overlapped element at 150% and the rest would act as single element at 100% output. The net effect is greater wall coverage and heat output for the effort and allows use of lower water temperatures.

Does that make sense?

Paul Pollets

Why not...

use a wall panel radiator, sized correctly? It would look better, for sure!

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

frankiewrench

MORE INFO

Nice to hear from you too Brad. All the bb is 12' or less down to 2' as per drawings. About eight zones, front and rear [times] four story height. Twin ID-DHW tanks do that thing. The roughing has been set as a parallel arrangement, but as I see and read it, that shouldn't be a problem. N'est pas?

Rich Kontny_3

Stole my thoghts Paul

Why not larger diameter fintube or perhaps commercial size? I have installed many 1 1/4 " elements using 3/4 supply and return

Rich

Brad White_204

That length, in parallel

should not be a problem! My thoughts are for when you can exercise control over more of the design, just something for your back pocket sometime. You are good to go as I see it.