1 pump, 4 zones, 2 temps

balindir · September 18

Long story short will this plumbing work?

What I have now: Right my house is a single zone, baseboard radiators. I have the outdoor boiler, oil boiler and plate exchanger setup.

What I need: We are remodeling the house, and i'm removing all the old baseboard with the pipes running all up and down the walls, and installing staple up subfloor. 1/2" pex / Omega plates, 2 runs per joist space. Unfortunately there are 2 areas I can't or won't be converting to in floor heat. 1 is a concrete slab already, and other is a room that won't be remodeled. All that to say, as the title states, I would like to replumb this with zone valves using 1x VT2218 delta t pump.

The problem that i'm unable to get an answer for (and i have searched, and can't find exactly what we are looking for…): Can i put the pump on the return side of the zones, so that the pump is creating suction on mixed side of the TMV. I know that you aren't supposed to put the pump after the cold supply for the TMV, but given the attached drawing. Would it work in this way, with the pump "pumping" into the cold supply? If not, can my goal of 1 pump be accomplished as I wish or should i just do a 2nd circ pump? Keep in mind system totals are 5ft head @ 10gpm… well within the range of a single vt2218.

Thank you all in advance!

Jamie Hall · September 18

Nope. Pump has to pull out of mixed outlet of the mixing valve. Your arrangement has it pulling out of the returns from all four zones. It would work if it were pulling out of only the low temperature zone returns, with another one pulling out of the returns from the high temperature zones.

balindir · September 18

So if that is the case then there really isn't a way to do this with 1 pump, is that correct?

GroundUp · September 18

The heat exchanger should be on the return side of the oil boiler, not the supply. This will keep the oil boiler warmed up and resist firing as well as condensation. Regarding the circ, no it will not work like that for the reason Jamie mentioned above. You could switch the mixer to a manual or actuated version like a Tekmar 710 series and very possibly get it to operate correctly with some time spent in adjustment, but at that point you'd be far ahead from all perspectives (aside from possibly labor, depending how it's currently piped) just to add another circ for the mixed zones.

balindir · September 18

So this would be the optimal setup then? In this case I could probably just run 2x 007E3 pumps on green mode, and will initially cost me about the same as the 1x vt2218 anyways? But also at that point, I could just buy 4 pumps for the price of 2x pumps and 4x zones valves…

balindir · September 18

https://forum.heatinghelp.com/discussion/comment/1810889#Comment_1810889

Yes your are correct on the exchanger. It is on the return side now… negligence on the drawing on my part. Okay that's what i thought the answer was going to be… but i wanted to make sure. I will be doing all the work myself, but yes it will be labor extensive, pretty much completely starting over with plumbing. Thank you both for your quick replies. Much appreciated.

GroundUp · September 18

That would be a good option for piping IMO. However as you said, at that point, 4 circs may be more cost effective than 2 circs and 4 ZV. I prefer ZV myself but a system like this, I'd probably go with circs just for the cost and ease factor of being able to run a single 4 zone switching relay

balindir · September 18

Roger that, I have to agree, I think that is going to be best route. Thanks

balindir · November 17

Alright so here is the system. It's not complete and there are already some things I would like to change. But at any rate it's working so far. Only thing I'm not sure about is the flow im getting at my top left pex manifold is much lower than I expected... getting less than .2 gpm per circuit. Getting a delta t of 40° across the manifold, which is much bigger than i calculated... is the 0015e3 on high not enough to get more than than 0.2 on 5 circuits? That is only 1gpm total for that zone... I need to recalculate it all out... but I figure on 3gpm total for that loop. I bled the system very throughly... each circuit 1 at a time.

GroundUp · November 17

Open the flowmeters

balindir · November 17

They are open

hot_rod · November 17

that mixing valve may have checks with fine screens to protect them. If so remove both for hydronic use. What is the Cv number on that mixing valve. I've seen some brands as low as 2.9. So 8 loops at .75 gpm/ would be about the comfortable limit.

Screenshot 2024-11-16 at 8.23.03 PM.png

Screenshot 2024-11-16 at 8.19.28 PM.png

The pump on speed 3?

The white caps on the manifold backed all the way off. Or just remove them to be sure the valve is open 100%

The delta T will be high on first start. It could take hours to start lowering.

pedmec · November 17

You most likely need a mixing valve with a higher cv.

balindir · November 17

That mixing valve does in fact have screens installed. Ill try removing them, and see if that helps. Its advertised at 2.3cv so I'm assuming that's the major restriction then... not going to lie, looking back now, I probably didn't factor in the pressure drop properly for the mixing valve.

Pump is on high, and the white caps are in fact backed off. I can remove to verify.

As far as the delta T, I realize it will take a while to heat the floor and close the temp delta, but my problem is the flow is still very low for the calculated btu/flow for thay loop.

Any suggestion on a different taco mixing valve with a higher Cv that might fit into that same profile?

Thanks for help so far.

hot_rod · November 17

If it has screens it probably has plastic spring checks on H and C. Remove them, usually they snap in.

How many loops will you have total? Looks like 10 in the works?

Somewhere around .50 - .75 is suggested for 1/2” loops. The RadPad suggests .65 gpm.

10X6.5= 6.5 gpm total? With a 3 Cv valve that would be around 11' head. That is workable with that 0015 on speed 3.

Caleffi 5231 High Flow is a 7 Cv valve available in 1" sweat, press or MNPT.

You want the Cv as close to the actual flow as possible.

Screenshot 2024-11-17 at 7.52.44 AM.png

balindir · November 17

Yes will be 10 loops total (i unused loop on the bottom manifold), did calculations for .50gpm per loop, so 5gpm total Ill try removing the checks and screens.

I definitely messed up the pressure drop... think I calculated using psi instead of head for the mixing valve...

So my current mixing valve is almost 11' head at 5gpm, and the pex will add another 7.3' head + the coppers tee and 90° probably gets it close to 20' head... so makes much more sense now...

Ill see if removing the screens and checks will help it for now, and go from there.

Thank you all so much for the help!

balindir · November 17

Just pulled the checks valves and screens... getting .50+gpm on all loops on both manifolds!! Just made my day! Thank you @hot_rod !!!!!

hot_rod · November 17

Good save, an inexpensive fix.

You probably have an ASSE 1070 valve, or a dual listed 1017/ 1070 valve. 1070 valves, per the listing, are required to have checks installed for DHW use.

When you use pump curves calculate pressure drop in feet of head. Then you can read directly to the pump curve sheet. Most show metric units also.

With those circs, you can sometimes pump your way out of an undersized mixing valve.

Screenshot 2024-11-17 at 11.56.41 AM.png

1 pump, 4 zones, 2 temps

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