Keeping supply temps consistant

Yes, I can put 130 * into my slab or in floor radiant and then overnight the temp drops to 80*, I haven't figured this out either. Turned my back up propane boiler on, it's a condensing boiler, it runs up to 160 shuts off for far too long with. 30* delta t, and can't keep the system hot enough.

Some mixing valves are very not accurate on either side of the center temp. So a 80-120 holds its best at 100. Then there are those that cannot handle a wide Delta T spread between supply and return. So anymore than a 25-30 degree spread and that can't hold the set point. And finally the third type of three way mixing valve that can't handle to low or to high GPM flow. So if the bumblebee doesn't hold steady, it can be an issue. I prefer to use a very high quality mixing valve , 3 or 4 port for these applications. No $100-160 options here. JMO

Taco i valve-setpoint, tekmar mixing valve 710-712 , stadler-viega ,aka Viessman mixer. 3 or 4 way. Esbe, Calefi high flow not point of use. Yes these cost more , but the reliability , control , cV or flow and long term cost will be better than the unibody cartridge style.

The honey wells flow isn't so good. Beyond 4 GPM, I don't like them. Any more and the head is so much you have to increase pump size. A 007 won't even do a full 4gpm unless headers are big enough. And then too much pump can cause to high of pressure differential in some piping cases.

Don't run out and buy something before you know what's going on for sure, but it's an easy test if you can try cheaply. I will say this, if you had a high volume or low headloss mixer, it would be one thing you could eliminate if the problem was there. One method I have used for testing is pulling the cartridge (when possible) and using the service valves to control temp. Just like adjusting a differential boiler bypass. Now you have plenty of flow and no head loss factors.

Then just don't get the power head for ODR. That Honeywell valve is stable to 5 maybe 6 GPM, after that the pipe with the least head will overcome the other, whether it's the supply or return. Also if the DT is smaller than 30 degrees between boil supply and mix set point it won't hold as you are seeing. The flow just makes it worse. This is what I was trying to describe, if you want to set a mix temp and forget about it, the tekmar 710-711-712 are the way to go. I have had lots of trouble with the valve style you have. The ones I mentioned will have all these specs listed.

Now you have 9 loops, what size pex? Do you have flow meters on the loops? Add up the GPM flow if you do. Your Honeywell cV is 3.5-3.9 , the taco 1/2" set point mix valve is 3.9 for example. So that 1/2" taco flows as good or better than the AM102. The taco set point valve works like an injection circ would with a tekmar or Viessman injection controller. Monitoring temp and maintaining within 2 degrees for example. The tekmar,Esbe or viega are manual, just turn butterfly lever and forget it.

I think I can honestly add something here. I have a Groundfoss mixing valve. It is supposed to close at 140 completely and it does, but sometimes when the water gets hot again it doesn't open back up. This causes the boiler to get to high temps, like 170 and even higher a few times. The first 2 years I thought the thermostat was in backwards, so took the thermostat out and tried to turn it around but wouldn't work. It has to be sticking but only sticks when I start a cold fire. It is closed then and sometimes stays closed till I bypass it. Sometimes @ 170-180 it opens by itself though. Very strange. It never gets stuck in open, just closed position.

BHetrick10 said:

So my supply drops in my Garn between my burns from 165 to 110 give or take. I got my mixing valve set with my IR gun at 110 when supply was around 135. Seems mixing valve cant hold a tight tolerance at all, prob about +/- 7. I got a bumble be pump set up on a 20* DELTA T. So the problem is my supply will drop the whole way to 103 sometimes less then my return goes to 83. So know i am essentially cooling my slab down.

mix valve is honeywell am102r

whats everyone else do?

Click to expand...

Most thermostatic mix valves have a spec sheet that tells operating condition required. The key for radiant mixing is the "min, temperature difference between the hot in and the mixed temperature". If it falls below the 27° noted on this brand (similiar for most brands) the accuracy starts to get wonky. There is only so much you can do with a tiny wax cartridge type of valve

If you need accurate temperature control over a wide range, a motorized mix valve is a better choice.

Also the flow limitations need to be considered with thermostatic mix valves. These valves were really designed for DHW mixing. They can and will work for radiant mixers but you need to be aware of the limitations.