B&G Circulation Pump Upgrade

Jason5920

I help to manage a 1950s-era semi-commercial building with a hydronic heating system.  When the building was first constructed, it had radiator cabinets, most of which were later upgraded to Amana PTAC units for hydronic heat (with compressors for a/c). 



Over the years as the building was modified, some of the PTAC units were moved.  In some cases, when water lines needed to be re-routed, the risers were cut and capped off and the monoflo fittings were just left in the main.  Then in some cases when new risers were added (in some cases over long distances), they were plumbed like normal plumbing would be, without monoflo fittings off the main.  To make matters worse, there are locations in the system where the pipe configuration creates air traps that cannot be bled.



Several of the PTACs in one zone will not generate heat under normal circumstances (although others in the same zone work great, as to the units on other zones).  However, if the return lines on the problematic PTACs are shut and the air bleed valves on the units are opened and allowed to run, the units will receive warm water pretty quickly, but then they will cool down just as quickly when returned to a normal operating state.  In other words, if the resistance in the problem lines is lowered slightly, the units work correctly, but otherwise they don't.  For what it's worth, when the system is operating under normal conditions, the pump discharge water in the zone that I'm describing can be 20 or 30 degrees cooler than in the adjacent zone.



Based on what I described in the previous paragraph, a hydronic heating tech who worked on the system recently suggested upgrading the existing pump (presently a B&G Series 100) to a high velocity, low volume pump.  Off the top of his head, he suggested a Grundfos 26-99 or Taco 0011.  But I'd like to stick with B&G since our other pumps are all B&G.



Before somebody asks, it will be difficult to generate a truly accurate estimate of head in the zone in question, because while I have as-built blueprints from the original construction, I don't have any as-built info from subsequent modifications (some of which are hidden under floors and above drywall ceilings, etc. and can't be evaluated).



My question is, should I consider a B&G PR or a B&W HV? 

Performance curves can be viewed at

<a href="http://www.boilersupplies.com/images/Series100_curve.pdf%C2%A0">http://www.boilersupplies.com/images/Series100_curve.pdf </a> If there's no obvious answer to this, I can try to provide some educated guesstimates about how much head is currently in the system.



Many thanks for any insights or thoughts.

SWEI

what all has changed

since the last time the system was mostly working?  If no piping changes have taken place, the Series 100 is probably worth repairing or replacing.  Every part is still available -- if you have a lack of pressure the impeller is likely shot.



You can test this by measuring the head (differential pressure) across the circulator.  Older pump flanges frequently had small capped tappings for just this purpose.

Jason5920

Impeller inspection

Thank you for the feedback.



It's hard to know the last time the system worked correctly overall.  The system has operated in various states of disrepair over the years.  The PTACs are all 6 months old, and if one of the old PTACs wasn't heating, the failure was typically attributed to a stuck valve, circuit board that wasn't calling for hot water, etc. 



The Series 100 in question is relatively new.  I am not sure there are pressure testing fittings on the flanges but will double check.  I have had another Series 100 apart in the past and am aware that repairs are pretty straight-forward, and I may just remove and inspect the impeller to check its condition (I presume the only sign of problems would be deteriorated vanes, or signs that the impeller shaft was slipping on the couplings, correct?).



One other point -- if the pump is running and I close the upstream ball valve, there's a definite change in how the motor sounds, so I presume that the impeller is catching and moving at least SOME water, but it may or may not be enough.

SWEI

system head

Somehow you need to figure out if the Series 100 is actually the right pump for the job.  I don't see an easy answer without either measuring or calculating the system head.



Is there only one pump in the system, no primary-secondary?  What size and type of boiler is there?  How many square feet of heated space?  How many and what size radiators?

bob_46

Thoughts

Each capped monoflo tee is like a partially closed valve left in the main.

The heating coil in the PTAC's likely have more resistance than the

original radiators.

You say some of the new piping is plumbed like "normal" ....so the supply

to the PTAC tees off the monoflo loop with a regular tee and returns.......where?

Back to the monoflo loop with a regular tee ? That won't work.

icesailor

More thoughts:

"Orphan Monoflows" add resistance to the flow that can't be calculated. They should be connected with a bridge connection like it is the missing radiator. Any orphan pair that can be re-connected will improve the flow.