Pump Head vs. GPM


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Old 11-18-06, 02:56 PM
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Pump Head vs. GPM

Looking at the pump curve for the Taco 007 series made me realize I don't think I understand something... lemmee run this by y'all and see if I can get clear on this.

The curve gives 0 GPM at 11' of head.

I think that means that the 007 can't pump water to any height higher than 11' ???

So, it would be unsuitable for say a 3 story building, yes ?

[edit: I've been googling, and may have found this is not true. Since gravity is working on the return side of the pump, it seems you can pump to 22' (double) with this pump?]

[another later edit: I googled some more, and found this website that I need to study. Seems that in a closed hydronic system, STATIC head is non-existent. In other words, the height of lift is nil, because it is closed. If you are interested, here is a good tutorial on pump head in hydronic systems: http://www.fluidh.com/WebCalcPumpHead.htm ]

OK then, one more...

Let's say you have two heating loops, one upstairs, say 9' above the pump, the other downstairs, say 1' above the pump.

Will the upstairs loop have substantially less GPM flow than the downstairs loop ???

[answering my own question: NO, unless there is more friction loss in the upstairs loop]

Please help me understand my head!
 

Last edited by NJT; 11-18-06 at 03:53 PM.
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Old 11-18-06, 04:35 PM
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Your head is unlike the head that is used to measure circulator capacity. That work?

You're on the right track. Head in a closed hydronic system has nothing to do with elevation. It has everything to do with the resistance to flow (friction) in a piping circuit.

In looking at that web page, it's a pretty good description of what's going on. I like the description and distinctions between static, friction, pressure, and velocity head.

The ASHRAE graphs leave a bit to be desired, however. Too busy.

And I absolutely DON'T like "shortcut method for determining equivalent length." I think it all too often leads to the wrong pump size. These days it takes about 20 minutes, tops, to do an accurate head calc for a heating circuit using a spreadsheet.

Some very good "applied" reading on head and flow rates can be had at

http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf

and also

http://www.taco-hvac.com/uploads/FileLibrary/PumpCurves.pdf

Holler if more questions. I've studied this a lot.
 

Last edited by xiphias; 11-18-06 at 07:30 PM.
  #3  
Old 11-18-06, 06:42 PM
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Originally Posted by xiphias
Your head is unlike the head that is used to measure circulator capacity. That work?...

Holler if more questions. I've studied this a lot.
There ain't much capacity circulating in _my_ head! 'speshully after lookin' at all that cipherin' I've gotta do now that I've seen those Taco pages !

But, I think I have a pretty good grip now. I do have a few more wonderments I'd like to ask though.

Lets use the target of 10GPM (total for the two loops) for my system.

There are two loops, up and downstairs, no zone valves, but there are circuit setters on each for balancing, I will be adding zone valves (or possibly circulators) when I put in the new boiler next summer.

The supply from the boiler is 1" for about 15' where it splits into two 3/4" pipes. Let's say that we want an even split of 5GPM in each loop. These two loops come back to the boiler into a 1" manifold at the return side.

Soooo, since the 15' section is common to both loops, I need to figure the head on that section at 10GPM, right ? Then add that to either the up or down loop (at 5 GPM each), and find the worst case in order to size the circ... I think that's right, yes ?

This is assuming one circ with zone valves, if I zone with circs, then I would just size each circ for 5 gpm I think.

Real numbers are actually academic at this point, becuz I don't know how much of the existing piping I am gonna replace when I install the new boiler. I will probably use 1.25" manifolds, and reduce to 3/4 for the baseboard loops. I'm just wanting to understand everything before I start!

I'm glad you understand it Xiph!!!!!!!!!!!!!! cuz I'm not sure I can!

Thanks!
Jeff
 
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Old 11-18-06, 07:02 PM
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OK, I ran some of the ciphers...

I calculated the downstairs loop at 11.75 ' Hf ...

[edit: I used Taco's number for the "venturi tee", assuming that was the same thing as the monoflo tees. There are two of them on my downstairs loop feeding convectors in the bath and kitchen. 29' seems an awful lot for a lil ole tee, but I guess they are pretty restrictive!]

now, the system has been running for 22 years with the 007 on there. How can that be ? It seems to work fine !

I must have made a mistake.

[another edit: but, perhaps that explains why my delta T is around 30-35*, eh?, I bet if I went with the 0010 circ, my delta would go down, and the kitchen convector (end of the line) might run a little hotter (coldest room in house) ]

Must mention that the upstairs loop circuit setter has always only been open a trickle because as we all know, heat rises.

The upstairs of the house is new construction, and VERY well insulated, while the downstairs is insulated, but not as well. (we went "up" about ten years ago, and added a second floor).

So, it looks as though the 007 is just barely adequate for the job, according to my (maybe not so accurate) numbers.

I wish there were an easy way to get a delta P across the pump!
 

Last edited by NJT; 11-18-06 at 07:34 PM.
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Old 11-18-06, 07:21 PM
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I'll guess mistake, but maybe not. I did for a while have a 007 pumping a zone that was about 13 ft of head. Still moved water, but not fast.

I just did a boiler replacement, re-control, etc. I am in general an advocate of zone valves, mostly to keep the "parasitic energy use" down. Why have two circs running if you only need one? But then I went to outdoor reset, which is nearly continuous circulation, and I have two zones with rather different head. So I went with two circs (plus a third for the indirect) after some conversations that suggested "circs like to run; zone valves don't like staying open forever."

The head loss in 15' of 1" or 1.25" piping is negligible (< 1 ft)and design programs like HDS often allow "negligible header piping" in diagramming heating loops. Head loss through the boiler itself is probably greater.

I would not sweat this stuff at this point. If you're not doing a boiler swap until next summer, for now I would concentrate on doing a good heat loss calculation to size the boiler, shop the brands and types (Burnham just introduced a couple modulating condensing boilers that look very nice), convince yourself that an outdoor reset control is worth the extra couple hundred bucks up front (it is), think about how you heat your DHW (if you don't have an indirect, maybe think about adding one). Etc.

Yes, 29 ft each for the monoflows.

If you want to play with a pump, try a Grundfos 15-58 superbrute. Has 3 speeds selectable with a switch on the housing. Speed 2 is a bit more than an 007. Speed 3 is pretty-high head. Would be interesting to test with your deltaT. You may well be right about why it's so high.

Note also that the 0010 has a LOWER max head than the 007. It's also a noisy beast in a residential application. Been there, done that. It's no longer!
 
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Old 11-18-06, 08:00 PM
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Originally Posted by xiphias
I just did a boiler replacement, re-control, etc. ...

..."circs like to run; zone valves don't like staying open forever."

...The head loss in 15' of 1" or 1.25" piping is negligible...

...I would not sweat this stuff at this point...

...(Burnham just introduced a couple modulating condensing boilers that look very nice), convince yourself that an outdoor reset control is worth the extra couple hundred bucks up front (it is), think about how you heat your DHW (if you don't have an indirect, maybe think about adding one). Etc.

...If you want to play with a pump, try a Grundfos 15-58 superbrute...
Did you go with p/s piping ?

Yes, motors do like to stay running once they start. I'm pretty familiar with well pumping systems, and current trends are to use a device called a "cycle stop valve" that throttles the flow to keep the motor running longer (and yields constant pressure too!)... I guess that's one of the ideas that make outdoor reset a good one.

The 15' of 1" has quite a few turns in it, I came up with 48' equivalent, not counting the air scoop. (what thinks the equivalent on an air scoop (not in taco's list) is?)

My DHW right now is electric! can you say $35 a month ? Yes, an indirect is in the plans.

One of the boilers I was looking at is the Burnham MPO. I don't think I saw the mod/con models on the website???? Maybe I just missed them. What you think of the MPO ? (sure looks easy to keep clean!)

[edit: I think you were talking about a gas fired unit... I'm running Earl Fired here]

I'm gonna google the grundfoss right now to see if it's pin for pin compatible (yes, that's an elect tech term!) with the Taco. If so, I might pick one up to try over this winter. I need to replace some flange gaskets anyway!

All this talk of Tacos is making me hungry!

C/YA!
Jeff
 

Last edited by NJT; 11-18-06 at 09:25 PM.
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Old 11-19-06, 06:07 AM
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p/s is built into my boiler (Burnham Revolution).

I've heard and read very good things about the MPO.

The Burnham CHG and Freedom CM are both gas-fired. There are no modulating oil boilers in the US. Not sure even in Europe. Bunch of condensing options in oil though.

Not sure why you'd need all that bending and turning near the boiler. My 1.25" supply comes up out of the boiler, makes a 90, then has a ~30" horizontal header after the air scoop where the three circs are. Same with the return. The 3/4" zone piping drops vertically to a horizontal 1.25" return header that's about 18-20" long. Makes a 90 down into the boiler. Very simple and totally negligible as far as flow is concerned. A piece of cake to pipe and service.
 
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Old 11-19-06, 09:24 AM
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Originally Posted by xiphias
...Not sure why you'd need all that bending and turning near the boiler...
The only excuse I can offer for that is the fact that it was installed in haste in December of 1984... by a guy who had the same work ethics that the guy that taylorj must have hired! But, in his defense, given the conditions he had to work with he did a pretty good job, it's run reasonably well for 22 years...

One of the (many) reasons that the MPO looks attractive to me is because of the "fit" to the existing space. Piping and flue connections will be MUCH more convenient!

Thanks for all the help Xiph!
 
 

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