What controls variable speed pumps?

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GG, I'm installing a loading unit to manage storage temp and the big pump to get hot water from near the top of the storage tanks in the boiler barn. Just like the schematics found on the Tarm site. The only thing I've never read was for a forced air system do folks turn the demand pump on and off with the blower. It wasn't intuitive to me if that made sense or the common practice. It apparently is one of those things so painfully obvious it's never discussed.

To all the other kind posters helping me on this topic. Alaska and others mentioned the Grundfos Mega for my high flow and head application. Well you mentioned it was a little pricy..... I fingered maybe $600 or so...... NOT $1900!! Holy moly. Next week I'll start researching
 
Well afternoon HM. You'd think by now 5 years in I'd have a better handle on my real heating load. Embarrassed to say nope. Not sure how to get a handle on it. So yeah I see your point, since way back when my goal was to provide more or equal to the capacity of the barely adequate propane furnace I never really got a handle on the no kidding load. Probably my best indication is % time idling which during normal temps is about 50%. So I see your point I sized for the worst case not real need. But if I can't get to the ~11 gpm on those very cold days I may not be able to keep up.

Your suggestion controlling on temp drop and variable speed sounds perfect! That serves as the feedback from the house! Is Taco the only pump manufacturer that does temp drop sensing? See, I never heard of such a thing ('course no surprise, that's why I'm here learning). I guess it has a temp sensor in the supply to house line. So with this approach the pump would run continuously but at a much lower rate when the return temp drop was near the supply correct? And, I'll gladly send you $20 if it works. I also agree that probably 90% of the time 11 gpm is way too much flow with my fixed flow pump. Does the Alpha offer temp drop control?

BTW found a plumber that does boilers for commercial buildings down here... Finally. Thanks, keeps getting better.

I think I'll look into some type of monitoring system so I better understand what's going on with energy consumption.
 
Grundfoss Alphas are delta-P (pressure diff.), Taco Bumblebees are delta-T (temp diff.). They both are ECM pumps and vary flow, one by maintaining a pressure differential, the other by temperature differential.

I think I would maybe settle on one or the other, but make accomodations in your piping that you could easily add in a second pump if that was not enough flow. Thinking say for instance if a Bumblebee couldn't keep up on real cold days, a second pump would kick in for more flow. That second pump could maybe even be a cheap 15-58 three speed. Not sure how you would control it, maybe a separate controller like a Johnson A-419 with its temp sensor on your return line and powered when there was a call for heat - then say whenever the sensed temp on the return was below setpoint during a call for heat, the 15-58 would kick in.

I really like my Johnson too (have one on my DHW circuit) - not quite as much as the Alpha, but it's a neat and very capable gadget that sets up very easy.
 
Your suggestion controlling on temp drop and variable speed sounds perfect! That serves as the feedback from the house! Is Taco the only pump manufacturer that does temp drop sensing? See, I never heard of such a thing ('course no surprise, that's why I'm here learning). I guess it has a temp sensor in the supply to house line. So with this approach the pump would run continuously but at a much lower rate when the return temp drop was near the supply correct? And, I'll gladly send you $20 if it works. I also agree that probably 90% of the time 11 gpm is way too much flow with my fixed flow pump. Does the Alpha offer temp drop control?

Sounds perfect until you read the fine print. The Taco HEC-2 ('Bumble Bee') runs only as slowly as its 'minimum speed' curve allows. For your circuit this means it will deliver at least 3 gpm whenever it is powered up, which is enough flow to mix a thousand gallons of storage completely every 5.5 hours or so.

Nobody else offers a deltaT or setpointT ECM circulator since there is really so little need for one. One actual need would be a reverse-acting setpoint temperature control, but Taco has failed to deliver on this feature.

If you plan on leaving the pump in the boiler room without running temperature sensor wires to the WAHX then the deltaT pump will run at its lowest speed at least 2.4 minutes before it sees that the fan is running, and then it will run at high speed for at least 1 minute after the fan turns off.

These delays would go a long way towards defeating the whole purpose of using a variable speed deltatT pump to respond to demand.

If you plan instead on going with quiet ECM pump in the house then just go with an adjustable B&G and turn it on and off same as the fan.
 
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