Slab tempering valve help/advice needed

[welderboyjk]

I've presently got a shop, 28*48, with 4 loops of 1/2 pex feeding the floor. It is currently running off of a baxi. There is a "header" loop of 1" copper and the floor feeds off of close spaced tees. Floor pump is currently wired to run continually. I plan on hooking a plate style exchanger fed by a boiler and run the floor pump off of a line voltage thermostat and shut off the baxi.
I wanted to run from the pump to the HX to the floor. Can I use one of the three way mixing valves like this;
https://www.hearth.com/talk/threads/65991/
look at post # 20
Can I run my pump into the top with my return from the slab into the right? Keep in mind there are close spaced tees just above this.
I would rather not temper the water coming from the boiler just in case I, in the future, want to put in a forced air liquid to air exchanger for those "need heat right now" situations, as I usually keep the shop in the low to mid 50's.
I have thought about a valve trio but I would rather have something I could "set and forget".

 

[RobC]

I'm not sure I follow you idea about having a heat exchanger. You can run your radiant just like other zones with it's own thermostat.
You questioned a mixing valve. They are not all the same.
Pex supply has all the items you would need to install a start to finish set up. From basic to all the bells and whistles.
Here is a reference page that has all the parts needed. http://www.pexsupply.com/resources/radiantHeat at the bottom of this page there is a glossary with links.
For a thermostat I would suggest one that has a sensor in-floor at a minimum, and an adjustable mixing valve.

 

[welderboyjk]

The shop system is filled with antifreeze and the baxi will not run without something like at least one bar of pressure, so that system needs to stay "sealed".
The boiler, the loop feeding the shop, and the loop feeding the house will be part of an "open" system.
What I was wondering is if I put a mixing valve in plave of the purple circle if it will work or not. I can always add a valve at the yellow "x" if I need to get some back pressure to push some of the cold return to the mising valve.

Legend for attached pic
top black loop, "header off of current boiler
brown circle, pump
red, hot water
blue, cold water
pink, warm water
purple circle, mixing valve?
yellow x, valve
yellow box, plate xchanger
bottom black "things", headers going to floor

 

[RobC]

Yes that is where you would want a mixing valve. On the supply to the mixing valve you possibly need a check valve and you need to add a circulator in the radiant loop you are creating with the new mixing valve. Here are some design layouts, open, closed and with HX's.
(broken link removed to http://www.radiantcompany.com/manual/Manual_web-2009.pdf)
Running an open system can be problematic while your rebuilding with mixing valve etc. you may want to consider pressurizing this side too.
Sorry I can't help more. Hopefully a boiler guy will jump in...

 

[Piker]

There is another option to the three way thermostatic when using a brazed plate... use a two way thermostatic valve with remote bulb/capillary that closes on temperature rise. Put the valve inline on the supply side of the brazed plate from the boiler... and the bulb in a well on the line coming off of the brazed plate to the radiant zone. This reduces flow through the brazed plate from the boiler in order to maintain a set temperature to the loops on the other side of the plate. Works great to reduce flow through thermal storage systems.... and excellent with an alpha pump.

cheers

 

[benjamin]

Now that I've figured out what Piker meant, I agree, that's the best way to do it.

On the other hand, you have it running right now without a tempering valve, you're planning to replace the boiler with a heat exchanger, do you really need a tempering valve here?

Assuming the pump is moving enough water, that slab is a pretty good sized load, your open system won't exceed boiling, so you're not going to get high temperature water out of the heat exchanger except for the little bit that's contained in the hx when the pump is off. I'd say keep it simple with as little flow restriction as possible.

 

[welderboyjk]

Piker, do you have a make/model # for such a valve?

 

[Piker]

Piker, do you have a make/model # for such a valve?

http://verwarming.danfoss.com/PresentationFiles/1691_ravv.pdf

cheers