Mixing Valve Question

smithsfan

So I'm doing a boiler install. I've got a mixing valve for the radiant infloor heat. I know usually you tie in the cold water side of the mixing valve into the return pipe of the radiant loop. Instead, is it a big deal if I tie it in to the return piping on the primary loop itself? It shouldn't matter correct?

Jamie Hall

The primary loop will probably be hotter than the return from the radiant piping, since it is also getting flow directly from the boiler. If -- and only if -- you tied in beyond the last return would it work reasonably well. Otherwise it is entirely possible that the primary loop would be at least as hot as your desired output!

smithsfan

Jamie Hall said:

The primary loop will probably be hotter than the return from the radiant piping, since it is also getting flow directly from the boiler. If -- and only if -- you tied in beyond the last return would it work reasonably well. Otherwise it is entirely possible that the primary loop would be at least as hot as your desired output!

Good points, I was thinking the same thing, having it last on the primary if I go that route. It does seem best practice is to tie it into the return on the radiant loop itself.

EdTheHeaterMan

Here is a diagram that comes to mind with your original query:
this one will work:


This one will not work:


Seeing it like this will help make sense of the fact that the return water to the boiler may be too hot to get the needed low temperature water to the cold side of the mix valve as @Jamie Hall stated

smithsfan

EdTheHeaterMan said:

Here is a diagram that comes to mind with your original query:
this one will work:


This one will not work:


Seeing it like this will help make sense of the fact that the return water to the boiler may be too hot to get the needed low temperature water to the cold side of the mix valve as @Jamie Hall stated

Thanks, I wonder if I should put the isolation drain for purging before or after where the mixing valve cold supply tees into the radiant return?

EdTheHeaterMan

smithsfan said:

Thanks, I wonder if I should put the isolation drain for purging before or after where the mixing valve cold supply tees into the radiant return?

Not sure of exactly your query is asking. Are you asking about purging air from the radiant loops in order to commission the radiant floor loops? I would think the purge valves and isolation valves were built into the manifolds. As a professional I always used the manufacturers manifold kits. they came with everything needed. If you are building your own manifold and purge system from scratch, you would get a picture of a "ready made" manifold and purge setup and copy that. Seems like a lot of work to reinvent the (Wheel) stuff others have already made easy for you.

Can you draw a diagram for clarity? As you can tell... I Like To See A Picture!

Edit: look at this video https://www.youtube.com/watch?v=5xrl_1k5YvY from supplyhouse.com

EdTheHeaterMan

Depending on your design this is how I might set up the purge valves and isolation valves.
The blue dash line is the water pressure from the fill valve of the entire system providing pressure to the loops. The individual loop isolation valves are all closed except for the loop that is being purged. the isolation valve after the purge valve is closed so all the purge air and water must come from the loop. As long as the water entering the "HOT" port of the mix valve is cool, that valve port will be open full to the "MIX" port for purging

hot_rod

you need need the cooler water returning from the radiant to mix down the hot from the primary. A mix valve can only regulate with a hot and a cold or cooler flow.  Needs to be about 20 degrees difference between mix out and ghost in to work. A Webstone purge ball valve simplifies purging

heatdoc1

Ed I know its off topic but what program are using for these piping diagrams?

EdTheHeaterMan

heatdoc1 said:

Ed I know its off topic but what program are using for these piping diagrams?

I am using Paint S on a MacBook. Windows has Paintbrush. It is time consuming but I can copy and past a screenshot to Paint S and use the drawing tools to place lines circles, other shapes and text where ever I want. one pixel at a time if i'm inclined.

This is how I take the existing drawing pr photo that you are already familiar with, and doctor it up with my idea and explanation. Easier to follow a small change to something you already understand.

Mr.Ed