Converting a zone to direct injection mixing

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Old 12-19-10, 06:13 PM
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Converting a zone to direct injection mixing

Greetings. I would like to convert one of the two zones of my existing hot water system to direct injection mixing in order to have an independent and lower water temperature for that zone.

I've done just enough reading to be dangerous, so I figured I'd post my proposed plan here and see what kind of advice I get. I will also add the disclaimer that I neither designed nor installed the existing sytem (save for the Tekmar controls) and am in no way responsible for the multitude of sins that were no doubt committed.

The existing sytem uses circulator zoning and has two zones and outdoor reset managed by a Tekmar 420 and associated thermostats. The zone for the first floor operates almost exclusively in continuous circulation and dominates the boiler target temperature. The zone for the second floor operates only occasionally and demands significantly lower water temperatures (maybe something like 25%+ lower).

The pictures below show my existing system (top) and my proposed changes (bottom).



My proposed changes are:

* Form a new isolated loop for the second floor zone, with a new circulator, as shown in green.

* Form a boiler loop using the existing circulator, connected to the second floor loop via injection risers and tees, and a balancing value, as shown in red.

* Replace the Tekmar 420 with a 422, which can manage both a boiler water temp and an independent mix temp via variable speed injection.

Does this proposed design look anywhere reasonable? If not, what would you change?

Given that I don't know any of the design parameters for the existing system, how should I go about sizing and adjusting the injection setup?

Thanks for any help and advice.
 
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Old 12-19-10, 09:37 PM
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That seems like an awful expensive way to add a 'mixing valve' ... I'm pretty sure there are way cheaper and easier ways to do that ...
 
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Old 12-20-10, 06:54 AM
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Thanks for your reply, Trooper. Would I be correct in assuming you're thinking of a "static" (i.e. not electronically controlled) mixing valve to lower the temp in the second zone?

Clearly I'm no expert, but I'm unsure whether that type of solution would work with the existing controls. The thermostats play a role in choosing the boiler target temp and adjust their cycling to the actual water temp supplied by the boiler.

Lowering the temp in one zone "outside" the view of the controls might have unexpected effects.
 
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Old 12-20-10, 03:40 PM
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Something like this would be simpler, less expensive, and just as effective. A whole injection setup for one zone seems like overkill.

http://www.taco-hvac.com/uploads/FileLibrary/100-19.pdf

There are other manufacturers out there, this one just leaped to mind as an example.
 
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Old 12-20-10, 05:06 PM
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I wish I remember where/when I saw it... might have been one of Siegenthaler's 'glitch and fix' columns... but there was a setup that would run a lower temp zone off a higher temp one, and would be 'responsive' to the boiler water temp... IIRC it used a MANUAL balancing valve, which once set properly would simply track the temp in the boiler loop, but at a lower temperature.

May I ask why the second zone requires a lower temperature? Different emitters I presume? perhaps radiant?
 
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Old 12-20-10, 06:20 PM
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NJ Trooper's first comment about mixing valves got me thinking a bit and, after doing at bit more reading, I've come up with a much simpler plan for getting mixing control on the second zone. Changes from the existing system are shown in green and blue:



While the plumbing for this is vastly simpler than my first iteration, the overall component cost is higher: the floating action mixing valve isn't cheap.
 
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Old 12-20-10, 06:26 PM
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xiphias--

I may have dug this grave for myself, but I'm already bought into a full Tekmar tN4 system (controls, thermostats, etc.)... Which is why I'm headed further that way

My latest design, though, does use a similar valve--Tekmar 711 + 471--but still requires replacing my existing 420 outdoor reset with a 422...
 
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Old 12-20-10, 06:42 PM
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Looks like it may work.
............
 
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Old 12-20-10, 06:42 PM
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NJ Trooper--

I was wondering when someone would ask "why" I am trying to do this In a nut shell: bad system design.

The 2nd floor is plumbed with 1" and 3/4" copper to old-style free-standing cast iron radiators--tons of heat from very low water temps. The 1st floor is fitted with in-wall radiators (Sunrad??)--still cast iron, I think, but much newer. Here's the kicker: these are plumbed with 1/2" PEX in series.

The 1st floor requires significantly higher water temps to be effective. It also had serious flow problems with the original Taco 007 circulator. When I figured out what was going on, I ran some head/flow calculations myself: the 1st floor is something like 50-80ft of head! So I replaced that poor 007 with a massive Grundfos. No more flow problem.

All of this is clearly hackery, but the entire system is new, the house newly-rennovated. (Neither by me!) And I'm unwilling to tear into the entire house to fix this properly; nor am I willing to throw out the new boiler.

So I'm trying to hack on this as best I can in the basement and try to make lemonade out of this system...

Back to mixing. The problem with the system as it stands now is that it is unstable when the 2nd floor zone cycles. It only comes on once an hour or so (or less) and dumps a ton of cold water into the system pretty quick, kocking the supply temps down 40-50 deg. Since the temp is still pretty high, the zone shuts off again within a few minutes.

Meanwhile, the boiler cycled on when the supply temp dropped, but as soon as the 2nd floor shuts off again the temp recovers very fast. So the boiler is short-cycling whenever the 2nd zone comes and goes.

There's also some serious pipe banging when the very hot water is pumped into the cold 2nd floor zone....
 
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Old 12-20-10, 06:45 PM
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Try adding some room temperature feedback to each zone.
 
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Old 12-20-10, 06:52 PM
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xiphias--

The system already has room temp. feedback.

The controls consist of the Tekmar 420 (outdoor reset) and 336 (zone relays) at the boiler and two thermostats, the 545 and 541. These are all networked together and combine outdoor reset with indoor feedback to manage the target temp.

Adding these controls did wonders for the badly-plumbed system. The 1st floor runs continuously, essentially modulating the target temp to keep the setpoint. The room temp pretty much never wavers from 68deg.

The 2nd floor thermostat struggles, though, since the water temp is so much higher than it needs.
 
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Old 12-20-10, 09:16 PM
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While the Tekmar is a great system, replacing an existing 420 with a new 422 is going to cost some money.
You may want to look at a taco I valve. Basically a motorized 3 way valve complete with ODR built in. Need a second outdoor sensor, but loose indoor feedback.
Nice integrated fast easy upgrade.
In you case indoor feedback may be important.
Just offering some alternatives.

OPPS just read further down.
Already ben suggested, my bad.
Feel free to delete
 
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Old 12-21-10, 05:28 AM
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You should double check where/how that valve should be piped. In between a flowcheck and the circulator may or may not be an OK place. Maybe ask tekmar or your local tekmar distributor.

Flowchecks are typically used on the outlet side of circulators, not suction side. Sticking a valve in there could impact how the circ/check functions. But at least you appear to be pumping away from the expansion tank. That's good.
 
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Old 12-22-10, 02:39 PM
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xiphias--

Thanks for the hint on the valve placement.

I may have my terminology mixed up, but the thing I've labeled as a "flow check" is a Watts Regulator No. 2000. I think that's a flow check...

In thinking about it more, it would seem that the mixing valve would probably go better before the flow check, so that the flow rate/volume through the flow check would not be affected by the operation of the mixing valve.
 
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