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Radiant 3-way Mixing Valve Return Inlet Temp?

I am installing a couple of low-temp radiant zones, and was planning to use a 3-way mixing valve to temper down the supply to my desired temp. The valves I purchased are Taco 5000-HX's. They seem widely used for this purpose, and the manufacturers website even specifies "an ideal choice for a radiant heating system, whether in slab, over pours, or in joist bay heating installations."
Looking at the Instruction Sheet provided with the valves, I noticed they specify a "cold water inlet temperature between 39º-80ºF." Maybe I am mis-understanding, but if I have the valve outlet set at 120º for my radiant, with a 10-15º ∆T, won't the return water temp be 105º+ and way out of spec? I realize these valves are also used for tempering down domestic hot water, so maybe this specification doesn't apply to radiant? Will the valve still function as intended?
It also specifies a "Minimum Temperature Differential (between hot supply and outlet) of 10ºF." So should I assume that the valve will not function properly if set to 120º but my incoming water temp is below 130º?
Thanks in advance,
-Chris
Looking at the Instruction Sheet provided with the valves, I noticed they specify a "cold water inlet temperature between 39º-80ºF." Maybe I am mis-understanding, but if I have the valve outlet set at 120º for my radiant, with a 10-15º ∆T, won't the return water temp be 105º+ and way out of spec? I realize these valves are also used for tempering down domestic hot water, so maybe this specification doesn't apply to radiant? Will the valve still function as intended?
It also specifies a "Minimum Temperature Differential (between hot supply and outlet) of 10ºF." So should I assume that the valve will not function properly if set to 120º but my incoming water temp is below 130º?
Thanks in advance,
-Chris
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Comments
Also, what happens with outdoor reset and even lower supply temps?
Now if the valve does not have or see that exact differential it does continue to flow, but the mixed outlet will vary some as the valve hunts around for it's required delta.
The valve will maintain accurately if the boiler or source on the hot is 25- 27° warmer than the 20F you are looking for. So if you mix down to 120, you want 145 SWT.
Also be aware of the valves Cv, the gpm it will flow at a 1 psi drop. As you flow above say 2.3 gpm pressure drop goes up.
5 gpm would be about 11 feet of head in a 2.3 Cv valve.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
https://www.supplyhouse.com/Taco-I100T3S-1-1-3-Way-Setpoint-I-Series-Mixing-Valve-w-Sensor
So if you have one system (radiators) designed to run at 140* and staple up radiant that runs at 120*, is there such a mixing device that can handle this narrow differential?
This is a mixing valve that only has a 3*F differential requirement.
https://www.supplyhouse.com/Honeywell-Sparco-AM101-US-1LF-3-4-Sweat-Union-Mixing-Valve-LF?gclid=CjwKCAjwqML6BRAHEiwAdquMnYopkl-EdIdGBLvtc76Gwuo--AuTcYFDqca-f1EV1rwPQSmWz-fEhBoC3kYQAvD_BwE
Is there a better way to do this? How else do I control the temperature to my staple-up zones to protect my floors?
The valve can and will maintain a tight delta, maybe 3° with no problem, as long as it has the correct delta to work with. That is a thermostatic mixing valves main purpose in life, maintain a tight fixed output temperature. they are built and listed for that purpose.
If you want accurate control with any hot supply temperature, above the requirement of course, a motorized mixer is best.
Yes a manual valve could work, but once set it is good (accurate) for that one specific condition. As the load increases or decreases the temperature will be too warm, or two cold, it's called a "dumb" mixing device for that reason, it has no brain, either a motor or thermostatic motor
A smart mixing device can automatically respond and adjust to a specific condition.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
It needs a supply of cold water, lower than 120 of course, to mix down.
A 3 way thermostatic on a water heater for examples always has the incoming cold, say 55F to blend with the tank 140F to achieve 120F
On a hydronic application the only cold at the C port is the return water temperature.
If the valve is set at 120 and has that 25° differential between hot in and mixed out, plus a return colder that 120F it will maintain within plus or minus 2°
Here is a cutaway to show what happens inside a Caleffi 521, other brands are similar. This specific valve and many others cannot close the ports off 100%. Our 520 series will fail safe if it loses cold supply.
Notice the openings (light blue color) to the center on the H&C ports. One is up high, one down low. As one opens, it closes the other. The temperature sensed at the bottom Mix port is what opens and closes the windows. It cannot close one window less than it opens the other.
Some motorized valve has the ability to close ports off 100%, so that required differential is not as critical. If it is set at 120, and 120 is returning, then H port closes and it continues to circulate 120 until it drops in temperature to whatever differential is required and opens H port.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me