Jeff, you are correct, that's why I'm starting with adding a mixing valve to my current system. that way I can track what the max and min water temp needed for my home. I plan to install 4 temp sensors (Hot water in from boiler and return to boiler. Mixed water supply to and return from floor)

https://images-na.ssl-images-amazon....OL._SY400_.jpg
Cheapie hand control knob jobber, max outlet temperature is around 60 degC:
https://www.amazon.com/dp/B01MS3X57O...a-351414738935
Dude diesel has lots of solenoid valve choices for cheap:
http://www.dudadiesel.com/valves.php

Ok, so when your heading demand increases, your system cannot satisfy the increase in demand? You are hinting at an outdoor reset or setpoint type of PID control to auto adjust your supply water temperature. Again, this works very well with a big fat slab. With a hanging pipe or staple up system, you don't have the "thermal mass flywheel" to level out the heat supplied to your zones, nor the higher thermal efficiency of direct contact conduction that heat spreaders provide.

If your floor isn't radiating enough heat, it needs to be made to do so before you start reducing your heat source. Once it can " burn you out" of your heating zones, then the duty cycle or source temperature can be lowered.

Tekmar has some awesome stuff to look at in their support section:
http://www.tekmarcontrols.com/suppor...oor-reset.html
From the linked page, just browse around the related topics to get a good picture of the how and why this stuff works.

thanks Jeff. I looked at the valves and found a 4 way that might work, but they want way to much for the motor and control, about $800.

Oh I never said the tekmar stuff was inexpensive. Quite the contrary. Caleffi and uponor are comparable brands of the same type of equipment. If I was s building scientist or architect trying to heat and cool my bio-dome or skyscraper, I would consider using something along these lines. I was referring to the training and support materials and literature these guys provide, because that's how the super pros do it.

If I was going to make something like that, I would probably use one of the 3 way valves and adjust it by hand or use an outdoor reset valve if I wanted a set it and forget about it type of rig. There are lots of ways around the barn, so to speak, and some ways are much more economical than others. Using "bang bang" valves (zero pressure solenoid) and anti water hammer bladders is most likely the cheapest way to do it. Not so smooth and quiet though.

I did read some of the literature. I will get a 4way valve and see if I can use a stepper motor to set the temp

https://www.supplyhouse.com/Taco-I07...nsor-5203000-p

These work great

Those taco odr valves are the bee's knees. They're the automatic version of the knob jobbie I linked to before. They don't care about what kind of heat source you have, so for an intermittent source like solar or wood fired boiler, they work like magic.

so how does the outdoor reset work?

https://s3.amazonaws.com/s3.supplyho..._PROD_FILE.pdf

There are some details to study, basically outdoor reset makes the heating water hotter as the temperature outside goes lower.

4 dip switches set up temperature limits & a rotary sets the ratio.

In example, with outdoor reset ratio rotary set to 1.0
When the outdoor temperature drops by say 20* then the system water is increased by 20*

A well insulated house may use a .4 ratio & a poorly insulated house may need 1.4 ratio

You start with an educated guess & then fine tune by trial & error