MATCHING CIRC PUMPS

Jed_2

Rick, what characteristic of pump performance would the "vendors" want to match? i.e. head vs. flow? And, if you throw in a ^T function, re: System vs. Boiler; well...
>>>>>>>>>>>> Low Loss Header!!! With proper P/S piping, I'm a bit confused about "matching circulators". Typically, the expansion tank would be in the System piping, right? Pump away from that point. Some mod/cons have an exp tank on board, but not necessarily large enough. If you have a DHW load parallel to the boiler, then you will have to match the head/flow requirements of the mod/con.

If you're talking about matching circs on the "System" side; well that's a different ballgame with reference to the mod/con flow/head requirements. Time for much more detail about the System.

You need to get away from the "vendors", and get into the Manufacturer's IOM!

Jed

RICK JAMES

CIRCULATORS

Any one have any input on matching circulators on the modcons with primary secondary piping , most vendors say they should match is that the case and if so why???

EricAune

circs

Why wouldn't you size each circ pump according to the load, the load in the system will almost always be different than the loss thru the hx on the boiler. If you zone with pumps on a three zone system you might have four different size pumps.

Darrell_4

I edited this...see if I make more sense this time. I would be interested if someone, (Mark maybe!), can put some numbers against what I observe. Too often, in the field, I just grab the next bigger pump off the truck and make it work.

Some of the mod-cons, (Lochinvar for instance), supply a huge pump, (GFS 26-99), to overcome the head loss of he heat exchanger and maintain the required delta tee across the heat exchanger. The manufacture specifies that the boiler pump be installed pumping into the heat exchanger from the loop. The loop pump does not have to be very big in order to move the system fluid around a typically short and very low head loop, however, if a small pump, (GFS 15-58), is used as the loop pump it is possible, even probable, that the flow will reverse in the loop at the closely spaced tees for the boiler causing the boiler to short cycle. So the loop pump must be sized big enough to overcome the boiler pump flow at that point. I have replaced many smaller pumps on the loop that cavitated and burned up. It seems to be better if the loop pump pushes toward the closely spaced boiler tees. Moving the expansion tank to the proper place ahead of the loop pump also seems to help.

The individual zone pumps can be sized to meet the head and flow demands of the particular zone.

Strictly anecdotal information, probably one of the engineer types here can put some numbers to this.

Mark Eatherton

Huh??

With all due respect Darrel, you just confused the crap out of me :-) THe older I get, the easier that gets though...

"Pumping away" pertains to the expansion tank location, which is the point of no pressure change. ALL pumps should pump away from that point, even if they're on secondaries.

Which loop is the expansion tank connected to, and are all pumps pumping away from that point, even if it is just a secondary connection?

For reference, I ALWAYS consider the loop that the expansion tank is connected to as the primary, and all other loops are secondary to that point. Obviously, that varies by engineer and manufacturer. Sure would be great if we, the industry, could come to some kind of consensus on just THAT minor detail, NO?...

Thanks in advance for your excellent contributions.

ME

RICK JAMES

circ

IT Seems that there is no smoking gun on pump sizes ,the more people you talk to the sixteen differnt answers, you get the manfactures making recomendations on sizes for a reasons, flow rates ,delta t ect . It seems that in this case the comments were more about pumping away and placement of pressure tank ,which are very important but still not any intell on the matching of the large pumps

Darrell_4

It made so much sense last night at midnight! I edited my original post...see if it is better when I do it in the morning! If I could just draw this on a napkin or you at lunch...

bob_46

Who's on first?

Depends

jp_2

matching pumps

seems to me if you need to match the load pumps to the boiler pump then P/S isn;t necessary.

load pump should match the load not the boiler loop pump(primary loop).

Mark Eatherton

I'm still cornfused, so, let's start from scratch so no one else

gets any more confused.

The pump has to be able to move the required flow, overcoming the pressure drop of those items in THAT circuit at THAT time.

If it (the boiler) is on its own circuit with the expansion tank in THAT loop, then I would call it the primary loop, and that pump only has to overcome the pressure drop of THAT circuit, which includes the boiler, along with the pipes, valves and fittings EDL (equivalent developed length). In the case of Lochinvar, they use the three speed Grundfos to match the full line of residential boilers. One size fits all.

If the boiler is also doing DHW, then the circulator has to overcome the pressure drop of the boilers heat exchanger, the piping EDL, AND the pressure drop of the indirect DHW heater, which in some cases is fairly significant, and in some cases is nil (reverse indirect for example).

The space heating distribution circulators have to be able to maintain their maximum required flow with all circuits calling, and maintaining the required head to overcome the highest pressure drop seen within those parallel circuits. For clarification, that does not necessairly mean the longest circuit. It means, the HIGHEST pressure drop circuit, which isn't always the longest circuit.

As far as pump location is concerned, in order for the pumps to create all positive pressure, they MUST pump away from the expansion tank connection. Some boiler manufacturers have the pump pumping towards to heat source, some away, and that is not what is important. What is important to trouble free operation is that ALL pumps should pump AWAY from the P.O.N.P.C. (expansion tank connection).

In the interest of creating good system operation and promoting energy conservation, if the space heating load is a variable (space heat distribution), the pump should be an intelligent variable speed pump, i.e. Wilo or Grundfos pump.

Hopefully this answers any questions created by this post. If not, speak up or for ever hold your pee's :-)


ME