Basic Zoning Question

[JonBodd]

I've had trouble finding a direct answer to this question.

First the theoretical. Imagine a 100 ft loop of 1/2" pex with a Taco 007. Now lets say tees are added before and after the circulator to split the 100 ft loop into 2 50 ft loops, with no increase in total pipe length or fittings. The flow (gpm) through the circulator through the 2 50 ft loops should be twice the flow through the 100 ft loop, correct?

Now for the practical. How well does this actually translate in the real world? If I split my house from 1 zone into 4 zones, but have to double the total length of piping to do it, could I still expect the flow through the system to double when all zone valves are open?

Thanks.

 

[Dana]

Not correct.

Try using some online tools to figure this out and make your life easier.

A 100' of half-inch PEX is about 10' of head at 2 gpm. But a Taco 007 can't deliver 2 gpm at 10.1' of head, it'll settle in at a somewhat lower flow. (See curve #5 for the 007). At 1 gpm 100' o PEX has only about 3' of head, which is well BELOW the pump curve You can see from the pump curve that it will settle in a bit closer to 2 gpm than 1 gpm. Poking around a bit with the online head calculation too, at ~1.9 gpm the head of a 100 footer is about 9.5', which is roughly where it fits the curve.

If you split it into a pair of 50 footers, the pumping head is cut in half per section at any given flow, so each branch is going to be getting quite a bit more than 1.9 gpm, but nowhere near twice 1.9 gpm on each branch. At 2.8 gpm the head of a 50 footer is about 9.5' , close to the curve, so each branch would be getting about 2.8 gpm, if it were only pumping a single 50 footer, but there's a pair of them- the pump would be delivering roughly 2 x 2.8= 5.6 gpm.

That is about about 3x the 1.9 gpm number for the single 100 footer, not 2x. This is a bit of a simplification, it'll actually be a bit less than 3x, way more than 2x, but it's a reasonable ball park number of what to expect with a dumb single-speed circulator like the 007.

You can take some of the mystery out of the hydronic design and save a lot of pumping power if you scrap the Taco 007 and install a programmable pump like a Viridian or Bumblebee, which can target points under the curve, not just the curve itself, but you have to be sure that the combined head and flow falls at or below the upper limits of the pump curves. If you set it up with a fixed delta-T or fixed back pressure it'll pretty much pump whatever it needs to, which will vary by the state of the zone valves, but ONLY as much as it needs to pump, with a motor that's both more efficient at any head & gpm, and varies the amount of power drawn with how much pumping is actually needed.

A Viridian VT 2218 can operate anywhere between curve 1 and curve 4 on this chart, depending on how you set it up:

The BumbleBee can operate anywhere between curve 1 and curve 4 on this chart, depending on how you set it up:

But either one will use only a fraction of the power of an 007. The pumps are 2x the cost of a dumb old school circulator like the 007, but can reduce the number of circulators on a system, and lend some flexibility to the design.