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Posted by HeatPro on November 30, 2005 at 09:51:17:
In Reply to: Re: To HeatPro and Joe Brix posted by Joe Brix on November 30, 2005 at 08:53:33:
That's right Joe. He has the zero balance setup as drawn by John Siegenthaler, with a Taco 0012 pumping around in a circle from the boiler to the buffer tank. The 5 Taco 007 circulator zones feed two blower coils, an indirect and two other zones.
The problem here is the "one-size-fits-all" application of the zero-balance design to a large copper-fin boiler with little water content. Firing off 140,000 or 240,000 btuh depending on which firing stage is called leaves insufficient mass/time to allow the controls to shut the burner off before the little water content in the primary loop overheats. The boiler manufacturer has a tank to 'buffer' that problem, but it hadn't been part of the original installation, so the circulator died and the boiler made noise. A multi-zone system needs a place for the excess input that isn't being used. The newer fully modulating boilers like the Weil Ultra. Munchkin, or Fujitsu can handle such a system; but less finely controlled one or two-stage boilers need a buffer tank in the primary loop. Plumbers are just taking John Siegenthaler's recommendation and putting them in situtations that can make complaints because they aren't aware of the problem. Drawings of multi-zone systems would do better to warn against the problem of partial heat draws on multiple zones. You don't see the problem with large water mass cast-iron or steel as frequently.
The same problem will occur when using the HydroLink with an on-off copper-tube instantaneous water heater and multiple zones off the Hydrolink - that will also be a true zero-balance primary-secondary system with little water in the boiler and secondary. Expect to see this complaint as they are thrown together indiscriminately.
Putting the boiler alone as a primary loop off the intermediary secondary loop with the buffer tank could reconstruct the problem of insufficient water mass for the boiler and now mean tht he would be running two taco 0010 or 12's one for the boiler loop, one for the primary loop and 5 007's for the zones. Sure would make Taco and the supplier happy though. It would be kinder than having the water run through the copper-tube boiler; but that can handle it. Actually, the boiler is piped with a bypass now, which is making some problem through partial recirculation of heated water. (I still have the pictures of the installation from last year's email.)
The single-temperature control to 150F as Dave describes can do as well as reset, as the boiler loop would be over condensing temperature and none of the zones might need more than 150F water temperature. That is to be seen.
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