Mixing valve idea...

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Old 01-14-13, 10:10 PM
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Mixing valve idea...

Bear with me, this may be a crazy idea, but think about it and let me know your ideas.

What would happen if:

A standard mixing valve, Taco, Honeywell, whatever, were piped into a SYSTEM BYPASS line with the boiler supply going into the HOT port, and the MIX OUT going to the boiler return, and the COLD PORT IS CAPPED?


image courtesy pexsupply.com

Set the valve to say, ohhh, 130 or so.

Would the valve open and allow flow through when it was cooler and then shut down as the water flowing through reached setpoint?

I'm thinking of a cheaper way to implement a thermostatic system bypass.
 
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Old 01-14-13, 11:55 PM
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My understanding is that the valve will shut off if flow is lost to either inlet port.
 
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Old 01-15-13, 12:02 AM
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I think you need all ports active.

Check out the link Mike......3/4 of the way down........ Three port valves.

Control Valves : International site for Spirax Sarco
 
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Old 01-15-13, 06:29 AM
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Was going to post somthing else but I found the wrong info.....

I dont think it will work. Flow will stop I assume but not sure if all ports are not used... But that would be thinking in terms of pressure balance spools right?
 
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Old 01-15-13, 12:00 PM
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When I was reading through some Watts Mixing Valve literature a while back I came across this:

Thermostatic Mixing Valves - The Dangers of Hot Water and Scalding - Learn About - Watts

In the How They Work section of the article is a neat dynamic diagram that shows what happens in "cold water loss" situations.
 
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Old 01-15-13, 03:19 PM
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Thanks guys... I see that my idea is NFG...

I don't think these valves have 'pressure balancing spools' as a temp and pressure compensated shower valve might, for example, but I do see that they also aren't simple thermostats either.

In the event of a cold or hot water supply failure, the seat assembly moves to an extreme position shutting off the hot or cold inlet water port.
I wish they had expanded on this a bit... as I understand this sentence then, if EITHER inlet fails, it will shut the OTHER one off...

OK, another even crazier idea then:

WHAT IF:

One were to pipe the MIX OUT to the boiler return, but ALSO tee it back into the COLD INLET?

HOT INLET would still come straight from boiler supply.

Wonder what it would do then?
 
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Old 01-15-13, 05:59 PM
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It's a valid idea.
Place a bypass pump on the mix out, to the boiler return.
A tee from the boiler supply would then goto to the system supply (best to inject it into a system loop), and to the hot of the mix valve.
The return from the system loop would then feed into the cold on the mix valve.

The valve should then modulate to maintain a boiler minimun at what the mix valve was set at.

Now, the problem is the CV of mix valves do not allow too much flow.
This would limit you to under 100K btu boilers I would think.

In your first idea, the pump will pull from somewhere, and if you block the cold side of the valve it will pull from the hot side and quickly kill the valve.
I have seen this in poorly installed mix valves with DHW recirc lines. If the plumber does not return the water correctly, the mix valves last 6 months
 
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Old 01-15-13, 07:51 PM
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Old 01-15-13, 08:20 PM
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This was my next weird idea... would it work?

Using a standard mixing valve (if it works) would save about $100 or so.

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Old 01-15-13, 08:46 PM
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IMO those devices stink... I guess if you really have a bad condensation issue...

Those units start opening at 113f. I belive not fully open until 136f. So what happens when your on odr??? You have low system flow.

Dont sound too good to me....


Even for myself, why do I want to waste fuel heating to 140f? I rather send it right out to the system.

Why are you using the ODR anyway? Your over-radiated.... Set the boiler to 155f and forget about it... With that boiler your delta t should not be that large.... 10f?

Whats it do with the bypass off? No bypass?

I do not measure my delta t until the slug goes around a few times. Usually when the cir kicks off at 150f but there is still a call for heat.

The supply will be 150f and return 142F ( Highest return I have recorded at this aqustat setting.)
 
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Old 01-15-13, 09:10 PM
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My inclination is to just pipe a bypass with a globe valve on it and adjust manually.

I sorta agree about the ODR... so far this season ODR hasn't targeted a setpoint above the min that I have it set to which is 150. And that's fine... no problem with that as long as I can get the return temps up.

There is a pretty reasonable problem with condensation in the chimney which I will be doing something about in the spring by running a 5" insulated liner up the existing 6" chimney. And some other ideas to get the flue gases a bit higher than 200F.

I am sorta afraid to look inside the boiler at what I might find... but I will, maybe this weekend coming up... depends on the weather... inside work or outside work...
 
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Old 01-15-13, 11:07 PM
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Old 01-16-13, 05:19 PM
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Another bypass.
You can use a Taco 008VS circ to create a bypass in your boiler piping.
It would speed up the bypass pump as the boiler return temp fell below 130 or so.
This would steal flow from the house side, but would allow the boiler to get back to 130 again.

it's in the 00VS documentation on taco's web site if your curiuos.

Cheers
 
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Old 01-16-13, 05:24 PM
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Interesting mix valve .. thanks for the link.

I could have used that valves configuration a month ago.

I will remmeber that one.
 
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Old 01-16-13, 05:37 PM
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What about a 24-V, normally open, solenoid valve?
 
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Old 01-16-13, 05:41 PM
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Thanks TO, I have also been considering a pumped bypass and the VS 'setpoint' pumps were one thing I am looking at.

I like those valves too, but they seem a bit too 'single source' so might tend to shy away for that reason.

I'm pretty much settled on a simple pipe with a manual globe valve. It will give me a chance to use another of my NOS globe valves...

In the meantime, I'm going out this weekend to find me a flexible copper line and going to adapt it to the two boiler drains until spring time.
 
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Old 01-16-13, 06:00 PM
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would a 1/2" washing machine hose work ? Has female ends on both sides.
The braided might take higher temps..

If you had some 1/2" watts onix around you could make a high temp bypass hose. Need some I can send some down, I have lots of scraps around.
 
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Old 01-16-13, 07:09 PM
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I'm using a washing machine hose now, but I don't trust it. I know it's not got an O2 barrier in it, but I really don't think 6' of tubing is going to let enough air into the system to cause a problem... it's the heat I'm a little concerned about.

Let me think about your kind offer for a little while... sounds like a great plan!
 
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