Radiant loop flow

John M_5

I need help figuring out a flow problem. I recently installed a buderus GB 142 with 6 zones and DHW. So far everything is working well except the radiant zones.
I have 2 Manifolds, one 4 loop and one 2 loop. the flow on
the 4 loop manifold with all loops open maxes out at .4 gpm per loop and .8 gpm with only one loop open. loops are 262 ft, 275 ft, 175 ft, 163ft. on the 2 loop manifold I can't get more then .2 gpm per loop. loops are 276 ft and 280 ft. I am using a Grundfos 15-58 pump and tried all speeds. I also tried a grundfos 26-99 Pump and it wasn't much better. the pressure differentail with the 15-58 is about 7 psi. when I purge the loops I can get 1.5 gpm.

Pump is on the supply side
longest loop head loss is 280ft X .024 = 6.72 ft @ .8gpm

both manifolds are being supplied by one pump, with 2 zone vales and a pressure differential bypass set a 7.5 psi

I also bypassed the zone valve , no change in flow

Also looked for kinks, but found nothing. any Advice?

Thanks John M.

Nikolai

George Peteya_5

Just a few questions

John,

Any difference when the baseboard and fancoil zones are NOT running? What's the Cv of the 3-way valve? (BTW, that valve is the Prime Suspect. All the water that goes through the radiant loops has to go through that valve.) Any difference if you increase the differential bypass setting? Which circulator is in there now ... the 15-58 or the 26-99?

George

John M_5

Hi George
It doesn't matter if the other zones are on or off, the flow is the same . I put the 15-58 back. I took the 26-99 from my DHW just to test. the 3 way is a 1 inch taco 5000 series, I'm not sure of the Cv . also I have a ball valve befor the differential bypass, opened or close it's the same

John M_5

George the Just called taco, the Cv is 3.8 max gpm is 24

bert

couple thoughts

The Taco 5004 valve has a 3.73 cv rating. It also needs an approach temp of 15 to 20 degrees to operate properly.
Meaning the hot side has to be that much higher than the outlet temp or it could be doing just about any thing.
You don't say what the manifolds are, but if Uponor with their supply & return ball valves, check or even remove the strainer in the supply side.

John M_5

Manifolds have ball valves , air vents and purge valves with flow meters

John M_5

Manifolds have ball valves , air vents and purge valves with flow meters

Nikolai

Piping problem

John, your in-floor heating piping with three way mixing valve need changes. Please see attachement. Nick

John M_5

nick

the primary loop came with the boiler, will the zone valves flow better on the supply side? why the change int he mixing valve?
John

Unknown

I assume 1.5 GPM is the max value on the flow meter, when you hit it during purges? If not, that's fishy, you should be able to push it higher than that if you are purging with house pressure.

Were you a little overeager with the flow balancing valves on the manifold? Are they all full open?

Is it possible your 3 way valve is installed backward? Does flow decrease as you get closer to your desired water temp?

George Peteya_5

3-way valve

John,

I found the Cv on Taco's site just as you replied. A three-way valve will limit the flow through the floors because all the water has to go through it. You probably want 0.8 to 0.9 gpm PER LOOP to keep the velocity close to 2 feet per second. With 6 loops, and a total flow of 4.8 to 5.4 gpm, the pressure drop through a 3-way with a Cv of 3.8 will be 1.6 to 2.0 psi (3.7 to 4.6 feet of head).

All this stuff adds up. The manifold balancers add their own pressure drop too, as do strainers, as another poster mentioned.

This is why I wouldn't specify a 3-way valve for more than 3 loops of 1/2". I'd use a 2-way thermostatic valve instead, that you'd set up as an injection device that spritzes just enough boiler supply water, and is out of the main stream, rather than a 3-way valve that says, "OK, radiant return in here, hot water in here, you guys just have a head on collision, then make a left!"

John, if you need to visualize the 2-way valve setup, think of an injection loop. Take out the injection pump and put the valve there.

George

John M_5

Rob
when I purged the system all the flow meeter hit bottom, and 1.5 is the max on the meters. I checked the mixing valve and it is installed properly.

John M_5

George, If I only use the 2 loop manifold with the 4 loop manifolds shut off, and no differential bypass I can still only get .2 gpm on the 2 loop. I even bypassed the zone valve to see if it would help, but nothing. I know it's something stupid that I'm Missing. Thanks

Unknown

Ok, are they flow meters full open, or have you 'balanced' already? If you "balanced" already maybe you were way too aggressive tightening them down...

if they are all full open, you should be able to easily get one or two of these over 1 GPM with your pump as is, at least... unless you're on low speed.

You say "hit bottom", sounds like the flow meters are on the return. That's unusual. Is it possible you have the manifolds or the pump in backward? if 0.2 GPM is the minimum rating, you might not have any flow at all and are just minimum reading the value on the gauge.

You might have an obstruction in the mixing valve as well or pump intake as well, that would be pretty rare IMHO but it's possible.

Just guessin'... I can't see anything in the piping or layout I would call wrong if the OTHER zones in the system are off. If they are not off, I would question whether the pumps are "fighting" or not. But you said they were off, I believe.

John M_5

Rob, The flow meters are on the supply side. I tried all 3 speeds on two different pumps, and the balancing valves are full open. .02 is not the min on the meter, so I do see them move a little.

Unknown

whups, I had that backwards in my head, sorry. did you verify pump direction?

John M_5

Yes, the pump is right. also called taco about the mixing valve. they said it shound not be a problem. I will go home tonight and check the strainer. thanks

George Peteya_5

OK, here's what it isn't

It's not the pump, the differential bypass, the 3-way (not at that flow!). Is there by any chance a strainer on the manifold inlet?

George

John M_5

No strainer on the manifold, but there is one on the return Line. I'm going to check it when I get home. It's the only thing left.

John M_5

ok I cleaned the strainer, still low flow. Here a a few pics of the system.

Unknown

John, have you tried closing your bypass valve entirely?

John M_5

Yes, opened or closed only a slight difference

Jeremy_14

Low flow

John, what size radiant pipe did you use? I'm assuming it's 1/2" and if so, then any loop longer then 220'-230' is a bad idea. I have run 280' 1/2" loops before and regretted it.

John M_5

1/2 viega pex longest loop 280, but even at that lengh it is still only 6.72 feet of head

Jeremy_14

Low Flow

What happens if only the 175' and 163' loops are open,pump is flowing, and the unessesary pressure bypass valve is closed (it only protects actuators from having to resist high pressure from circulator starting while they are closed, you haven't installed actuators). Compare that to when you only opened the 2 loop 275' and 280' manifold. I'm guessing there is a big difference in flow rate. I have been in the HVAC biz for 12 years, and I have been given expert formulas and estimates for how to install which do not hold up in real world applications. Does the radiant loop have an exessive ammount of 90 degree turns, crimped but "fixed", couplinged, which reduces flow in some brands like watts (I'm not familiar with viega). If you find that the loops might be too long, the cheap easy fix is to run a 5/8" or 3/4" common supply 1/2 way between your longest loops, unless this is an above subfloor concrete or gypcrete application.

One other though, earlier somebody was writing about opening all the balace valves, and by balance valves he meant you take off all those white open/close handles on the return header and turn counter clockwise (unscrew) all those valve stems. You probably already know this, I'm just making sure.

paul_79

hey john just a last ditch try. assuming the mix valve is ok and piped correctly. and you have no other obstruction. you might try to take the internal check valve out of the taco pump if it is still there. just for fun.

John M_5

Jeremy, with only the shortest loop open I get about .8 gpm . The radiant heat is joist mount so on the longest loops there are about 18 180deg bends.All the valves are wide open.

John M_5

Paul, the check valve is still in. But if I can purge the system at 1.5gpm flow then the water is getting thru the valve.

paul_79

john forget what i said on the check on the pump but i would try putting 24 volts to the zone valve because the manual setting hardly lifts the valve off of it's seat and since you can get flow by purging it maybe pushing past the zone valve better

Jeremy_14

Alright

What's wrong with .08 gallons per minute? Are there cold rooms/zones in your house? Was there a difference in flow rate between 2 short loops running and two longest loops? I'm just asking.

John M_5

.8 would be fine if all loops could flow at that rate. however with all loops open the flow is only .4

Mark Eatherton

Purge question...

When you purged the radiant circuits out, was the boiler running and supplying hot water? If yes, shut the boiler down, and cool the system as a whole off, then purge the system with COLD water, with the mixing valve turned as high (hot) as you can get it.

If the circuits are air bound, they will not flow correctly, and it just flat plain and simple will not flow correctly.

Here's the instructions for the valve.

http://www.houseneeds.com/shop/manuals/taco_5000manual.pdf

ME

MikeyB

cv

Hey guys, not sure if this was mentioned already but with the CV rating of the 1" mixing valve being 3.8, according to the Clifford Method 3.8 cV = 305' of 1" copper tubing, this could be adding to the problem.

John M_5

mickey Check you math 3.8Cv @ 4.8 gpm = 3.7 ft Head according to B&G Sizer Program

MikeyB

cv

Hey John, Im just reading what's on the chart, has nothing to do w/my math

John M_5

I wasn't trying to insult anyone. Sorry

Unknown

Oh man, you're getting the 1.5 purging through the pump? that makes it even worse. I assumed you were only purging through the manifolds.

Mark Eatherton

Cv defined....

I think there may be some confusion.

A Cv of 3.8 (flow) indicates the flow rate at which the device will experience a 1 pound pressure drop (2.307' of head). Doubling that flow rate will increase the pressure drop by 3.3 times. Halving the base Cv flow rate drops the pressure drop to approximately .3 of the original pressure drop.

http://www.engineeringtoolbox.com/flow-coefficients-d_277.html

ME

MikeyB

cv

No insult taken , by the way you do nice clean work.

Jeremy in DM

mix valve piping

i wonder if the piping of the mix valve is off. another poster showed the boiler piped secondary off the main. shouldn't the mix valve be piped the same? that way the pump for the mix temp zones is in a secondary loop by itself. it only has to overcome the pressure drop through the tubing, manifolds, and mix valve. by not truly piping the mix valve secondary off the main, the pump is overcoming more pressure drop, piping, strainer, etc. also, in your pics the boiler looked ok, but if the distance between the two boiler tees is too great, now it is flowing through the boiler as well, but it looked ok from the pics.

imho