Individual radiant mixing valve for each zone

JunkMonger

Couple of questions here.....

1) is it possible for each zone(1 or 2 runs) to have it's own individual electronic mixing valve? I'm too much of a hack to just buy a manifold and the individual thermal actuator so instead I have a manifold and a bunch of 0-10v 3-way Powermite 0-10v valves I was going to use them as simple zone valves with one side dead-ended making it essentially a 2-way. BUT then I got to the dangerous game of thinking and now I'm wondering what issues I would have using them as individual mixing valves specific to the temperature needed for each loop. The main loop would be mixed to the maximum temperature call of any active zone and all the other active zones would be mixed down to their temperature. The pump is a Grundfos Alpha in constant pressure mode. It is well within it's curve to pump the entire system.


2) Are there any commercially available manifolds that have flow-setters on the return side? That is vital in my estimation to prevent "overpumping" or just shunting to the zone-of-least-resistance. Or is my best bet individual flow-setters?

3) Would check valves be required from the 2 'supply' manifolds to prevent shunting?

Overkill for a ~2,000 ft2 house for SURE! I have too many variables, etc for any off-the-shelf control solutions so I'm having to run it off Bacnet controllers I'm programming. Here is the rest of the hydronic loop replete with solar hot-water collectors, towel warmers, and garage heater sections. If anyone has feedback about that I'd love to hear it too. Before anyone has words about the solar collectors....I'm in California and doing an addition that doesn't meet energy codes (Too many windows and too little insulation) but you can get around that by 'offsetting' energy use by incorporating more renewable "free" energy. Will it get used long-term after the final permit is signed off? Who knows...

STEVEusaPA

What a waste of time, money and resources. Practically everything in the drawings is wrong. But feel free to experiment on your own dime.

EzzyT

I agree with @STEVEusaPA. Try to keep it simple. 

Jamie Hall

Well, yes. Overkill for sure. However, piped correctly, it would certainly give you excellent control! However, using only one pump for all the entire secondary sides is going to be difficult. It will be much easier to control -- to put it mildly -- if each zone has its own secondary side pump. Then pull each zone off the primary manifold to the hot side of that zone's mixing valve, with the cold side of the valve coming off that zone's return, and the outlet of the valve going directly to the zone circulator.

JunkMonger

Thanks @Jamie Hall , I appreciate the input. That is my worry is how variable the pressures/flows will be as the different valves cycle.

I agree with @EzzyT about simpler/better and may give up on the individual idea and go back to a more 'standard' setup and use the valves as basic binary zone valves and a single dynamic diverter (#1) for temperature control.

@STEVEusaPA I'm here to learn, so rather than an unhelpful negative comment how about telling me the 2-3 biggest sins with either diagram so I can improve?

As for the #1 valve/actuator is it better to run it as cold-side diverter or hot-side mixing on either pump pressure side or suction side? I have a Viega Proradiant mixing station which I modeled this after but wasn't sure if that's the 'best' setup.

Jamie Hall

You really need back to basics here. First, let us consider a mixing valve -- or, for that matter, any system which works similarly. What you have at the mixing valve is two inlets -- one hot, one cold -- and one outlet, mixed. To get flow through the valve correctly, the pressure at both inlets must be greater than the pressure at the outlet. The two inlet pressures don't have to be equal, although it's helpful if they are at least close, but they must be higher than the outlet.

Now consider that mixing valve used to control the temperature being fed to -- let's say a radiant loop. The hot inlet is connected to a manifold or to a boiler. The cold inlet is connected to the return from the loop through a T. How do we get it so that the outlet has a lower pressure? Well, on the hot side that shouldn't be a problem. But on the cold side... hmm. In fact, in order to get any flow through the radiant loop and back to where the cold side can pick it up, you have to have a pump with suction attached to the outlet ((you could have a pump on the return from the loop, but before the T back to the mixing valve -- but that is not good practice, though it usually will work).

You don't have a choice. You have to have a pressure increase between the outlet and the return T, and the only way you can do that is with a pump.

Is it possible that you are confusing the piping and hydraulics in a system piped for primary and secondary loops with closely spaced Ts with the hydraulics of a system with a split return and a mixing valve taking part of the return to temper the hot feed water. The hydraulics are completely different, although a casual look at a piping diagram might be misleading.

JunkMonger

@Jamie Hall I'm sure I'm confusing much more than just that! That makes sense, I know it all works on the simple higher->lower pressure gradients to establish flow.

I keep looking at the Viega unit and wondering why it pumps return water into a diverter. I know the suction will 'pull' water through the loops but in my mind pump suction is generally less desirable than positive pump pressure. I'm reading your comment as confirming that.
System's like the Caleffi Mixing station are more what I think; pump suction on the outlet of a mixing valve to provide the lower pressure on the outlet and it will pull whatever the actuator sets. The the hot and cold/return water can basically have a pressure of zero but the suction of the pump will induce forward flow.


I'm 'planning' a primary/secondary with spaced-tees, here's a more basic revision.
I'm clearly no hydronic professional; I do plumbing on humans with blood in surgery but I'm still trying to find the arterial and venous sides of hydronics! I very much appreciate the help

Jamie Hall

Much better! Only I'm not sure what valve 2 is supposed to do?

EzzyT

Are you sure you need a mixing valve on this system if you’ll be operating the entire system zones within 10-15 degrees of each other? What are you using as a heating source? If your using a condensing boiler then just operate the system on one temp and no need for a mixing valve. Keep it simple no need to introduce an extra possible costly components to the system if it doesn’t need it. 

JunkMonger

Valve 2 is substituting an external valve for the traditional thermic zone valves which I'm not a fan of and I have access to a bunch of 3-way 0-10v valves for cheaper anyway, so just cap on side and call it a zone valve.

Fairly sure I will need a actuator mixing valve. It will be fired by a condensing boiler but the primary loop will also be supplying an indirect water tank for DHW and there will be the (required for code compliance) solar unit so I worry that the primary loop could have some fairly high temps throughout the lifecycle. Why not a thermostatic mixing valve? I'm in coastal california so the climate is mild, even though the design day is 35. "Set and forget" for the design day and I'm concerned about over-heating and getting excessive temperature swings even with a low-mass system.