Classic Hydronics question for Dan

furnacefigher15

I just finished reading the book this afternoon. I liked the book, it was a good read. I just wish you would have spent more time explaining plotting a system curve on an existing pump curve.



How is this done? What inputs / measurements are needed for the system curve?

bob_46

System curve

Page 13



http://completewatersystems.com/wp-content/uploads/2011/05/7534.pdf

MikeyB

Curves

You can also check out John Barba's Neighborhood on Tacos website, hes got a few good Webinars about pump sizing, curves/head/flow etc, etc, real good stuff

furnacefigher15

Thanks

Thanks Bob,

That clears up something that's been bothering me for years. I remember a gentlemen from Bornquist coming out to an RSES Meeting and doing quick rundown of pump selection. He brought up system curve, and I asked him about it, and he just said "It's easy just plot two points on a graph." I just left it at that. Apparently, I've been doing this all along, but I never put it to a graph.



I would generally figure out what gpm I need for my design delta T at the calculated head and select a pump that had a curve that fit my needs, or very close to it.

DanHolohan

Thanks.

I'm glad you enjoyed the book, and I'm sorry I didn't go into lots of detail there about system curves. The System Syzer booklet tells the story well. It starts with gauge readings across the pump to see where it's operating now. Pump head varies as the square of flow rate. In other words, if the gauges show you're pumping, say, 5 GPM at 5 feet of head (let's keep the numbers small for the example), and you need 10 GPM, the head will increase to 25 feet. That's because you can't compress water and you're trying to put 10 pounds in a five-pound bag.



The System Syzer (or a slide rule) has a scale to show you this squared relationship. You set it to the known condition you got from the gauge reading across the pump while it was on, and then, without moving the scale on the System Syzer, you look at the head developed at various flow rates along the scale. Plot these on the pump curve, connect them and there's you're system curve. On curves for large pumps, you'll see various impeller diameters. Where that particular diameter crosses the system curve is where the pump will operate once you change the impeller.



The nice thing about variable-speed pumps is that they do this all automatically. It's like having a pump with lots and lots of impellers, all ready to go to work.



Thanks.

Mark Eatherton

Nice find bob...

That is a REAL treasure for those that really want the hard facts/details. Takes me WAY back :-)



Thanks for sharing the find.



ME

furnacefigher15

Dan

Thanks, for your personal response. It means a lot to me, to know that even on a Sunday you care enough to take the time to respond to question.



Also, even though I am a 2nd generation heating guy, it was I guess 7 or 8 years ago now that I first read Pumping Away, and that was a real "ah ha" point in my career. It made me think a lot more about what I was doing everyday, and what I and even my Father had been doing wrong for all those years. When you stated that "if there ain't no air, it ain't an air problem."



That, reminded me of a story my Father told me about this one trouble job he inherited. One winter back in the 70's when it used to get brutally cold here in Chicago, there was this medical building that had an apartment wing that just would not heat for anything. The only thing he could figure was that is had to be an air problem, but he never got air, only water. But, he could not get the place to heat, but the baseboard would get hot after a while of bleeding. It was really cold had to be -10 for a high for a week, and there was no one available to help back then. He didn't know what else to do, but venting was getting heat, and at the same time keeping the pipes from freezing. Once the weather broke the problem went away, and it would heat okay. And every year without fail, on really cold days this would happen. He added air vents all over the place, and power purges and what have you. But, every year without fail, same thing. This went on for decades, until he found the mis-wired 3 way valve. B and W were reversed on the control side, and 90 percent of the time the flow was enough to heat the space.





Do you know if that slide chart is still available? I need to get my hands on one of those.



The method you describe sounds a lot like a Lau fan law calculator chart I have.



About the variable pumps, I've been using a similar approach for years now on commercial systems, to get them whipped into shape. It's a lot easier to just add a frequency drive to an over-sized pump, then it is to add a circuit setter (tripple duty valve) to add resistance or even change an impellar, and the benefit is significant reduction in consumed energy and in some cases, the frequency drive is cheaper. Even if the system was set up to maintain a constant flow as most of them were.

DanHolohan

Great story!

I've done things like that. Always consider them to be tuition. ;-)



You should be able to get a System Syzer from your local B&G rep. They may charge you a couple of bucks for it, but it's worth it. It's an old-school tool that does a lot.

Steamhead

Finally ordered ours, Dan

looking forward to reading it!

DanHolohan

Thanks!

Hey, I just found this interesting bit of history you'll enjoy. Guess who used to be big in the soda fountain business?



http://www2.tbo.com/lifestyles/life/2012/jan/08/banewso4-family-bar-is-part-of-1920s-soda-fountain-ar-344569/

Steamhead

Two booming businesses at that time

steam heating and soda fountains. Not surprising one company would be into both.