How to figure gpm

Bluenose_28

Steve, this system of staple up has eight zones controlled by zone valves. From zone valves to manifolds is 5/8" pex. Manifolds have 1/2" loops, don't know the lengths or how many loops per for each, I only eyeballed two manifolds when I was on site, one had three loops and one had four loops. Zone valves are on a 1.25" header fed by variable speed injection.
I guess this system didn't work last winter, customer fighting with original contractor. Customer has engineer friend that wants the gpm info.Heat loss in 97mbh

Bluenose_28

How do I do it

I've been asked to determine the gpm of a Grundfos 26-99 that is installed in a staple up system. I was thinking of installing a flow meter but I will have to wait weeks for delivery, seems they are not a commonly asked for item from my suppliers. I don't know the head of this system, how accurate would taking the pressure difference across the pump be in determining the head?And does anybody know of an economical manufacturer of a flow meter?I've had a wide range of pricing estimates i.e. $100 to $1400.The $100 one looks like it may do the trick, but is there anything I should look for?

Terry

curve

Get the pressure differential & refer to pump curve.
this will be v. close.

gl.
EIN

Andrew Hagen (ALH)

Flow

Like this?

Flow Meter


That's a big pump for most applications.

-Andrew

Steve Ebels_3

A 26-99? Hmmmmmmm

How many loops? what size tubing? All off one manifold? What size pipe feeding the whole deal?

Steve Ebels_3

Hmmmmmm again

At that kind of heat load and a 20* delta T, you should only need around 10 GPM for the whole place. If I understand you though, you are saying that the heated area is 7,500 ft not including the basement? That would be a heat loss of about 13 btu's per sq ft. Attainable? Yes. Common? No. I'd be double checking that first. Pay close attention to btu/sq ft loss by room and according to how the place is zoned. The staple up may flat out not be capable of doing the job if the btu/sq ft is above 15 or so.

If I had to place a bet, I'd guess that the contractor origionaly had a smaller circ on the system and then when it didn't heat kept going bigger. Maybe trying to heat the water with friction? I dunno. A 26-99 is a high head, high velocity, high GPM circ for a residential application. Even one that's 7,500 sq ft. Unless the loop lengths are out there at 500-600' the 99 is overkill. Running the water around faster doesn't make a lot of difference in the system performance under normal circumstances. That is if the rest of the system is designed correctly.

You need to do some detective work if'n you're going to get a handle on what's going on. Could be the guy just has the injection temp set wrong. Staple up with no plates is a fairly high temp application.

As far as your first question regarding GPM is concerned, you have to find out the lengths and number of loops in order to generate accurate numbers. Look close at the tubing, there should be markings indicating number of feet right on the tube. Most decent tubing suppliers will mark it in 3-5 ft increments. Find those numbers on the tube and check also to see if they are all fairly even length. Within 10% is good.