Indirect water heater and boiler mixing valve

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Old 01-03-14, 08:21 AM
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Indirect water heater and boiler mixing valve

I currently have 2 zones of old cast iron radiators. I added a mixing valve to the return on the system because the boiler was just barely making it up to 140 degress.

I'm now looking into adding a third priority zone for an indirect water heater. Will this work with the mixing valve in place? I'm guessing it will only cause a delay while the boiler heats.
 
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Old 01-03-14, 09:55 AM
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What mixing valve did you add and how did you hook it up?

Can you show us a diagram of what your piping looks like?

In general, you want the indirect 'close' to the boiler. There really isn't any concern with cool returns from the indirect, the water in the tank is already hot and shouldn't come back to the boiler cool enough to be a problem.
 
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Old 01-03-14, 10:01 AM
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This valve:
AM102R-US-1 - Honeywell-Sparco AM102R-US-1 - 1" Union Sweat Mixing Valve, 70-180 F (Heating Only)

This confirguration:
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Everything is within 2ft. of the boiler (besides the runs obviously). The new indirect would also be within 2ft.
 
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Old 01-03-14, 11:10 AM
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I've looked at that application in the past but never sat down to try and understand what is going on with the flows and temperatures. That brochure calls that a 'constant return temperature' application.

What are you seeing when the system is in operation?

I'm having a hard time understanding how this is what you really wanted on your system...

It appears to me that starting from a cold boiler, the return from the rads eventually comes up to the setting on the mixing valve with all (or the majority of) the flow going from M to H and back through the boiler.

Let's say the valve is set at 140... so when the return from the system gets to 140 it begins to divert some of the return from the system away from the boiler (boiler bypass) and recirculate the flow through the system.

Since the return from the system is fixed at the temp setting of the valve, that also means that the return to the boiler will be fixed at that same setting.

So the supply to the rads is also going to be fixed at the valve setting temp, say 140 PLUS the delta T across the system... and the flow through the boiler will decrease ... which will increase the rise across the boiler (because of the decreased flow) ...

To me, the action of this seems backwards from what you really wanted...

You are bypassing the boiler AFTER the system comes up to temperature.

Wouldn't you want to bypass the SYSTEM UNTIL the boiler comes up to temperature? In other words, all (or MOST) of the flow through the boiler on startup, then as the boiler got hot, gradually introduce hot water into the system until everything is hot?

In other words, something like this?



In this case, that 'thermic valve' has a setpoint... let's say you've chosen the 113F model for an oil boiler... Heat call happenz, boiler starts, (almost) full flow through boiler until such time as the temp reaches 113 and thermic valve begins to close bypass port and start feeding water to system. As system heats up and return starts to come up to temp, thermic valve opens more and more to system until fully open.

Answer to your question next!
 
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Old 01-03-14, 11:12 AM
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You want the indirect return to boiler piped between the mixing valve and the boiler, and preferably on it's own pumped loop.
 
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Old 01-03-14, 11:37 AM
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Agreed. That is the ideal install, but do you think there would be a large hit to performance if I install it as a third zone?

I think the mixing valve basically acts as a variable bypass; opening up and closing depending on temperature.
 
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Old 01-03-14, 12:56 PM
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Agreed. That is the ideal install, but do you think there would be a large hit to performance if I install it as a third zone?
It will take a hit... because if you pipe it to the mixing valve side, the supply temperature going to it is going to be limited and it will impact your recovery time.

Realize that running the 'constant return temperature' also means that the SUPPLY temperature is going to be limited to the RETURN TEMP PLUS THE DELTA T across the zone, be it radiators or the indirect.

I think the mixing valve basically acts as a variable bypass; opening up and closing depending on temperature.
Yes... but from what I can see the 'action' is backwards as explained in previous post.

You don't start bypassing the boiler until AFTER the system return comes up to 140, so the boiler is still going to take a long time to heat up.

You want to bypass the SYSTEM, UNTIL the boiler heats up in order to allow the boiler to come up to temperature faster.
 
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Old 01-04-14, 02:35 AM
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Old 01-04-14, 08:00 AM
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Yes... which is the same thing as the 'thermic valve'.

This does not change the answer of how to pipe the indirect. Still goes on the BOILER side of any mixing valves.
 
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Old 01-04-14, 09:29 AM
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Great info. Thanks for all the info.
 
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Old 01-04-14, 11:42 AM
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Note about Diagram -- Diverting Application (Constant Return Temperature) Fig. 4. Single Loop for Multiple Loops.

Fig 4. flow diagram is wrong, do not use.
 
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Old 01-04-14, 01:27 PM
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Fig 4. flow diagram is wrong, do not use.
Please explain how it's wrong. I don't think it is. The valve CAN be used 'backwards' in that fashion if the application is correct for it.

Do you mean that it's wrong for his application? I've already explained that.

What exactly do you mean to say?
 
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Old 01-04-14, 03:08 PM
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Water that goes into a T' has to leave the T'.

Start with the boiler and system cold:

When the water at M' is below the setpoint: H' opens and C' closes and all the cold water flows to the boiler return riser. (No protection to the boiler there.)

3) When the water at M' is above the setpoint: H' closes and C' opens sharply reducing the flow to the boiler. (No flow in boiler.)

As you can see no mixing happens at all in this configuration, only throttling of the flow. So the only mixing point is where boiler out joins the system riser at (2) on the diagram.

More??
 
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Old 01-04-14, 04:11 PM
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Right... I understand all that... and have pretty much said that in previous posts.

But why are you saying that the diagram is wrong?

When the water at M' is above the setpoint: H' closes and C' opens sharply reducing the flow to the boiler. (No flow in boiler.)
When the water at M reaches setpoint, the valve will modulate and divert SOME water to the SYSTEM, and SOME water to the BOILER. It's not a 'one or the other' valve.

The valve will control the temperature from the return at setpoint. In doing so, as some of the flow is diverted from the boiler and sent back to the system to recirculate, the temperature rise of the boiler will INCREASE and HOTTER water will be available from the boiler supply. This hotter water will blend with the water coming out of the C port and ultimately the system MAY reach thermal equilibrium.

I don't think the equilibrium will ever happen though because the boiler will keep getting hotter until the heat call ends... or the boiler hits high limit (which MIGHT happen)

The bottom line here is that you still have not told us what you think is WRONG WITH THE DIAGRAM.

I asked: "Do you mean that it's wrong for his application?"

And you didn't answer...

So, what exactly are you saying?

As you can see no mixing happens at all in this configuration,
Yes... I see that... but it isn't DESIGNED to be a MIXER in this configuration... the TITLE of the diagram CLEARLY says that it's being used as a DIVERTER.
 
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Old 01-05-14, 03:59 AM
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To: NJ Trooper,

First, my apology for stepping on your thread. I should avoid that word [......]

I asked: "Do you mean that it's [that word] for his application?"

A: Yes. And I was talking to npeltier, as you know what the circuit does.

A: Yes it's a diverter not a mixer.

Q: Why would you set a high limit for the return temperature, real world example anyone?

Thank you for your time.
 
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Old 01-05-14, 08:29 AM
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Not a problem... I strive to keep everything clear and understandable, and is why I questioned your post. Since we're not 'preaching to the choir' it's easy for someone to come away with wrong ideas... we need to remember the audience.

Q: Why would you set a high limit for the return temperature, real world example anyone?
I honestly have no idea. I'm sure that someone, somewhere, can think of an application where that would make sense, but I can't.

I suppose that if someone were doing in-floor radiant with a water heater as a heat source, it might make some sense in some cases.
 
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