Secondary loop issue

Vincent71

Hey all, looking for some opinions. 

I was asked to finish a secondary radiant loop on a project. There were two closely spaced tees with ball valves on the primary loop for me to tie into. The existing (but new, by someone else) primary loop pump is on the suction side of the secondary tees. There is also a zone of baseboard, with the pump for that zone near the boiler return,  then another zone of radiant, with the pump also at the return. Prior to the primary loop being installed, there was no means of boiler protection in my view. With all that said, I don’t like the current configuration, but was asked to merely pipe in the secondary loop. There are 8 loops that were recently installed by someone else, and have yet to run. They are 1/2”, ranging from 250-280 as per the customer. I selected a 1” x 1/2” 8 port manifold. All of the pumps on the project are Taco 007 pumps. When I ran it for the 1st time, I had 130 to my supply loops but something like 70 coming back after 2 days if running. I wasn’t able to really move any water in the secondary loop unless I closed off 6 of the 8 loops. When just 2 loops open, it ran far better. it could be any of the 2 loops, I verified each one had flow by running them one at a time. I had on my truck, a 011 Taco pump with much more GPM and head, so I tried that one as a test, which did not change the results.  My thoughts on next steps: Advise the customer that I want to repipe the entire boiler, installing the primary loop pump on the supply side of the boiler, immediately after the Spirovent, then also install the 2 existing pumps that are currently on the return side and install them on the supply side, ultimately correcting the existing radiant loop.

I am aware that there are existing piping flaws on the existing install piping side, but is that enough to cause secondary flow through only 2 loops when 6 are shut off? I’ve never experienced something like this, but I also have never piped a system in the way it is currently installed, specifically with everything except the 8 zone radiant loop that I did.  

See attached drawing of what the current layout is. 

Any feed back would be great!

EBEBRATT-Ed

The pumps should be 'pumping away" from the expansion tank.

To me you need 3 way valves on the radiant loops because the boiler needs to run at a higher temp for the baseboard load that the radiant needs

and a 3 way valve at the boiler for boiler protection.

As far as the radiant loops go are you getting flow but no heat? Maybe the slab has not warmed up yet it takes time. Or are you not getting flow?

You will have to calculate the radiant loops and figure the head to select the correct pump if your not getting flow

STEVEusaPA

Are you talking about the zone in red or the zone in green

Vincent71

It’d be the zone in Green. I’ve calculated the loops using TACOs TD10 calc tool. I’ve gone up with 1.6GPM per loop, with about 26’ of head.  I’ve had the 007 and 011 both react the same way.  Only able to get water flowing through the loop fast enough to do anything when just 2 loops are open. In other words, it the entire zone (all 8 loops) was running for a week straight, and I could see no more that 66 degree temps in the space.  Upon testing each loop, my return temps dive to 70 after about 5 minutes of opening a 3rd loop. With 2 loops open, I am able to see my return temps about 108-110.  

Vincent71

typo there. * I’ve come up with 

STEVEusaPA

So looking at this section, is the circulator in red only for this radiant zone? It appears to be based on the rest of the drawing.
Is there a mixing valve on the secondary circ to prevent the cold water, following the blue line, to just constantly recirc?

Vincent71

Steve, the pump in Red is the primary loop pump. The secondary circuit with 8 loops has a mixing valve right before the pump inlet. I circled it in red 

EBEBRATT-Ed

@Vincent71

looks to me like you need bigger pumps. Go to Supply House.com and look at the Taco pump curves. Your way short.

You have 8 loops @1.6 gpm so 8x1.6=12.8gpm

If your head calculation of 26 feet is correct you need to pick a pump that will do 13 gpm @26 feet of head.

Neither the 007 (which isn't even close) and the 0011 will pump the head and leave you short on GPM Shut off head on a 007 is 11' of head

If you put two manifolds there instead of 1 (4 loops/manifold) the you would have 6.5 gpm at 26' and a Taco 0011 on each manifold would probably do it

Vincent71

He Steve, appreciate the advice. However; I am only able to see any signs of heat when only 2 loops are open. At the 26’ of head, and 3.2 total gpm (2 loops) she works just fine.  When I add another loop, increasing my GPM to 4.8, I hardly move any water through all 3.  At 26’ of head, the Taco 011 can handle almost 7 GPM.  If I dropped the design Design to 1GPM per loop, the 011 would be just 1GPM shy. I’d expect some sort of expect heat out this loop, with a better delta T than what I currently have of 80, with just 3 loops open.  (30 delta with 2 loops). Curious to know your thoughts on whether or not you think I may have some restriction on the mixing valve feeding the 011 pump.  My thought is that I may have enough of flow through it to allow for 3.2GPM, but not anything more. 

EBEBRATT-Ed

@Vincent71

Head calculations are not perfect. You could have a few feet of extra of tubing or fittings. Your so close with the 0011 I think you just have tto much restriction to move the gpm you need. Your running the 0011 out at the end of it's curve.

Yeah every control valve has restriction. It has to to be able to control. Do you know the Cv rating of the valve you used? or the model#. That could well be the issue

Vincent71

The mixing valve is a 1” Taco 5000 series. Cv=2.3  

STEVEusaPA

Maybe there’s a kink, a restriction, air, or a problem with the mixing valve.
Did you try one loop at a time?
Otherwise it’s a pump sizing issue as @EBEBRATT-Ed mentioned.
I’m not clear on the need for a primary and secondary pump if they are both only serving that one manifold.
Also how many Btu’s does that 8 loop manifold need?

Zman

A mixer with a CV of 2.3 may be your issue supplying 8 loops.

Vincent71

I went back this morning. Clogged inlet strainer to the mixer. 

EBEBRATT-Ed

@Vincent71

a 2.3 Cv means with 2.3 gpm going through that valve you will have a 1psi or 2.3' of headloss through the valve

Can you imagine what the pressure drop will be at the 12 gpm you need? That valve is way too small

If you put 12.6 gpm through that valve your looking at a pressure drop of like 66' of head roughly 28 psi

Vincent71

All, I went out the site yesterday and found a clogged strainer to the inlet side of the mixing valve. I removed and cleaned it . The system began to perform nicely during my visit. The home is vacant at the moment, so we ran a stress test to see if we could bring the space up to 80 degrees through the night. Upon the GC entering the home this morning; we found the set point of 80, being met. See attached photo. Based off of the feedback I’ve gotten, we could make some improvements to the system, of which I will propose to the customer. Thanks for all of your comments and feedback. 

hot_rod

Why such high flow rates? Is this 1/2 pex? Typically .50- .65 gpm in 1/2' pex. Even 7 gpm through a 2.3 Cv valve is a big ask.

EBEBRATT-Ed

@hot_rod

I think the op has gone bye bye. I showed 66' with a 12.6 gpm through that valve above if i did it right. I don't see how that's going to work without a really big pump