Left you last time with Dave Edmunds’ “Queen Of Hearts.” Don’t know why, but part of me prefers this version…
Okay, okay, I know why…
Huge hit for Juice Newton back in 1981.
Gotta love a girl named “Juice.”
Last time we shared what would happen with a Wilo Stratos-Eco Delta-P variable speed pump installed in a specific zone valve application, with “out-of-the-box” default programming. We learned the circulator would only vary its speed under certain conditions. The circulator would still run at full speed with 3 or 4 zones calling.
But what would happen with “proper” programming? Here’s a look…
The red programming dial would have to be set as close to 5′ of head as you can manage. In this case, the circulator will, in fact, vary its speed virtually all the time. And at first glance, the operating requirements line up fairly well with that funny looking inverted-V shaped pump curve.
Closer examination, however, shows Points A & B falling slightly above that curve. Under design conditions is it possible the circulator may actually “under-pump” the zones? It would seem so, but only when you have reached your outdoor design conditions (<2.5% of the heating season) and only if the heat load is dead-on accurate, with no added “fudge.”
Point C appears to be right on the pump curve, while Point D is below the pump curve, but not by all that much.
Well, that’s at design conditions.
However, this Delta-P pump is going to run on that line all winter long, despite the ever-changing BTUH load. It runs that speed in January. It runs that speed in October.
When you’re at or near design conditions, you’ll have close to the right flow, more or less. The rest of the heating season the circulator still operates on that line.
So what happens under milder conditions, at 50% heating load?
You see the new requirement points. However, the pump is still running on its fixed pump curve. So even though the requirement with all zones calling is 5 GPM, the Stratos-Eco will still give you around 10 GPM, and the resulting system Delta-T will be around 10*.
And keep in mind roughly 50% of the heating season is spent at 1/3 load or less. So even when programmed “properly,” this circulator delivers the “right” flow rarely, and by coincidence.
Does this mean the system “doesn’t work?” Nope, not at all. But we can do better.
How would the BumbleBee fly in this same application? Remember it comes out of the box programmed for a 20* Delta-T…
Those 4 lines are the BumbleBee’s capabilities in the Fixed Speed mode. The shaded area between lines 1 and 4 is the Variable Speed Delta-T operating range.
Because GPM = BTUH ÷ (DT × 500), the BumbleBee will vary its speed accordingly to hit Points A (almost full speed), B and C, as well as the requirements of any combination of zones.
The line representing Speed 1 is the BumbleBee’s minimum speed. When only Zone 1 is calling, the BumbleBee will “over pump,” and the actual operating point will be very close of the Stratos-Eco’s operating point.
But now look at what happens at 50% load…
Are we “over-pumping” in this example? Pretty much, but we’re now operating at the BumbleBee’s lowest possible speed for the bulk of the heating season – with a power draw of roughly 9 watts. You can extrapolate the system curve lines to see where they intersect the Speed 1 line. Not perfect, but considerably better than what we had with the Delta-P circulator. Note with all 4 zones calling we are delivering almost exactly 5 GPM, which is what is required.
How about that?
Now, it won’t be varying its speed at this point, but at a power draw of 9 watts and with flow rates a darn site closer than its “variable speed” brethren, we’re in very good shape.
Will the system Delta-T at this point always be the 20* you designed for?
Nope. It’ll be a tad lower. But as we stated in a previous blog, Delta-T is not the target. BTUH delivery is the target. Delta-T is simply an aiming device to help you get there as efficiently, effectively and economically as possible.
So what’s the significance of all of this? Is it the difference between one system “working” and the other “not working?”
No, far from it.
It’s the difference between an okay system and an exceptional system operating at its peak for comfort and overall efficiency. It’s about knowing how things work, what they do, and matching the right product for the right application.
There’s one big elephant in the room, however. When it comes to Delta-P programming, how the heck do you determine the system head loss, especially in a retrofit?
Great question – one we’ll address next time.
Okay, okay, enough of that. How about a tall glass of Juice from the MTV years?
Try getting THAT out of your head for the next few days.
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