Review of piping schematic

kensheets2

Hello
Would it be possible to get a review of my piping schematic.  Would like confirmation of the 3 way therm mixing valve location in piping to reduce flue gas condensation .  Each loop 30K BTU

Thanks
Ken

Zman

I think that the schematic will work.
The circs will all need check valves.
You would normally design for 3 GPM per loop. With all 3 loops running, that will put 9GPM through the mixing valve. The Honeywell valve has a CV of 3.8, it would be best if it was closer to a CV of 9. I get concerned when 3 circs are fighting to move water though the same restriction, there is usually a winner and a loser.
The best way to do this would be to install a high CV modulating mixing valve and have it controlled to give you outdoor reset and boiler condensation protection.
The Taco I-series does a good job of of this but they do not offer a large enough model. Tekmar makes several controllers designed for this type of control.

kensheets2

I was a bit concerned about less than perfect cv rate.  I'm actually only running 2 pumps, stubbing for a third though to upgrade for future use, thinking 3.9 cv mixing valve for a 6 Gpm application might cut it.  
Alternatively, would installing a primary/secondary purge tee and cracking it till I get 130 at the boiler return be an option?

Dave H_2

If you are looking for a thermic bypass valve for boiler return temp protection, you don't want to use a mixing valve for that. Wrong application.

You want a Thermic Bypass valve and here is the piping for that

Dave H.

hot_rod

You need to know total gpm to properly size control valves. High Cv valves for mixing at the boiler return ideally, most are fixed temperature, but any thermostatic mix valve could work.

Assume you may an 8 gpm load, here is what a common 3 cv valve looks like. So 8 gpm would be on the high side of what you might want to flow through a 3 cv valve

A 3.9 valve with 6 gpm looks much better. But if you plan on adding on??

The best option would be a boiler return protection valve. The 280 is a 10 or 14 Cv in 1 or 1-1/4"

Here is a piping schematic, although you may not need the mixing stations.

Zman

Dave H_2 said:

If you are looking for a thermic bypass valve for boiler return temp protection, you don't want to use a mixing valve for that. Wrong application.

You want a Thermic Bypass valve and here is the piping for that

Dave H.

I am under the impression that he is trying to get outdoor reset and boiler condensation protect in one device. I would use a modulating valve sized to your flow rate and a controller to accomplish that.

hot_rod

Zman said:

If you are looking for a thermic bypass valve for boiler return temp protection, you don't want to use a mixing valve for that. Wrong application. You want a Thermic Bypass valve and here is the piping for that Dave H.

I am under the impression that he is trying to get outdoor reset and boiler condensation protect in one device. I would use a modulating valve sized to your flow rate and a controller to accomplish that.

I missed the mention of ODR in the first post? If so a 4 way valve with actuator and controller. It will be a bit more $$ than just a return protection valve. Or just run the boiler on an inexpensive reset control, and protect return with a thermostatic?

Zman

Fair enough
There is absolutely more than one way to approach this...