What happen?

unclejohn

This heating season I added a buffer tank to a seven zone system that is a mixture of cooper fin baseboard and raditors. I have a TT solo 110 and taco 3 wire zone valves. All is well and heating fine. When I first started the system this winter with BT I noticed that the alph 15-55 pump was moving much less water. With all zones calling befor the Buffer tank install I was moving 5 gal per min. After BT I was down to 3 GPM. Which I figured was less resistance. Now I'm up to 6 GPM with all zones and 3 with a single zone that has 2 eight foot BB and one small under the window rad 4 section. I pulled the pump this afternoon and found nothing in the impeller. Why the change in GPM?

Jamie Hall

Pumps

are very dumb critters.  Each pump model has a specific pump curve -- flow rate vs. head.  With very very very few exceptions, as the head being pumped against increases, the flow decreases.



Which sounds like it is exactly what is happening to you -- you have 6 gpm with all zones calling, but when you close off all but one of them you have increased the head loss the pump has to overcome considerably, so the flow drops as you have noted (I'm assuming that the zones are piped in parallel, which is the usual case!).



As to why it changed from last year to earlier this winter... haven't a clue, but something changed the head loss for sure.

Gordy

Yup

Like Jamie said, and don't count on the gpm read out being accurate either.



Like blowing through a straw with little effort will yield more air than trying to blow with all your might through a stir stick straw to get the same volume. Ain't gonna happen.

unclejohn

It's

A Grunfos Alph with is supposed to adjust its flow rate. Was just wondering why it seems to have changed so drastically in the middle of the season? When that zone called earlyer in Sept.it was pumping maybe 1 gpm.

Zman

Alpha

How is the alpha set.

If it is on the same fixed setting, I would expect similar readings.

The auto adapt will change over time. My understanding is that it resets when it is powered down.

I prefer the constant pressure settings.

As has been said, the GPM reading is approximate.

Carl

unclejohn

Set

On Auto. It's wired to an outlet that powers up on a call from any zone. So no call from the zones no power to pump. The TT pump circulates through buffer tank only.