looking for mixing valve
 

I currently have an underfloor heating system with a 10 gal hot water heater that I’m hope to convert to a GSHP system next summer. My current system is missing a mixing valve. At the timer the HVAC guy said I didn’t need one, the system has been working fairly well. I have the water set at 175°.
What I would like to do, is to use an Arduino to control a mixing valve. What I’m looking for is a motorized 4-way mixing valve. Hot water in from boiler and return to boiler. Mixed water supply to and return from floor. thank you

What's wrong with a mechanical thermostatic mixing value?

what changes the set point when the outside temp drops?

I see some holes in the story here, and details matter. Before anyone can recommend a system upgrade, the existing one needs described.

the system is: 10gal hot water heater set at 175° to an expansion tank to a temp/psi gage to the 4 zone manifold supply to the underfloor hanging 3 inches down back to the 4 zone manifold to the pump to a air trap back to the heater. what holes in my story do you see?

Lots on eBay! So many different flavors. You'll have to dig through the spec sheets.

Generally you purchase the valve body and actuator separate from each other. If you're trying to do this on a budget, it can take a lot of digging to find a cost effective pair.

The valve body choices are pretty obvious. The actuators are available in different voltages and modulating techniques.

Most on eBay are on/off control, no modulation.

Personally I like the floating actuators. Easy to control. Two pins: pulse one to close, one to close, and it'll hold its part-way position when power is removed.

You can get remote sensing mechanical thermostatic mixing valves.
I work in industrial automation and instrumentation.

Maybe the HVAC guy is correct, you don't need a mixing valve.
 

Just control the water heater temp our of the heater and run the water directly to the distribution manifold.

Ok, so you have a staple up or free hanging setup. That's not going to work real well with the lower water temperature that a heat pump provides. With the high water temperature you're using now, natural convection and radiation do a lot. These 2 effects go away drastically when you lower the loop water temperature.

With a solid slab, running a low temperature heating loop makes sense because of all of the thermal mass. With a thin floor, the heater pipes have to maintain direct contact with the surface they're going to heat. With most underfloor setups, this means heat spreaders. There's not much thermal mass, either. Lots of details to consider before you commit to a big system change.

that's what I do now but when the temp drop's from 25° during the day to 5° at night the water temp I have set does not keep up. that's way I'm looking at a mixing valve

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

outdoor reset:

“It changes the supply temperature in response to an ANTICIPATED change in demand indoors. I say "anticipated" because your house shell and insulation introduce a lag in demand.

If your system is digitally controlled it will try to keep calls for heat as long and as infrequent as possible regardless of the temp outside. The more closely your reset curve matches the actual loss, the longer and less frequent the calls for heat.

If your system is proportionally controlled (IE: TRV’s)
it will try to keep flow through the system as consistent as possible by ensuring that the temperature of the circulating water closely matches the heat being lost by the structure.”

This is a quote from an expert “Mike T., Swampeast MO”
On Heatinhelp.com

Why do you need a 4-port? You should easily be able to do this with a standard 3-port valve. Hot water goes in one inlet, return teed into the other inlet, and circulating pump for the zone on the mixed outlet port.

been looking into a 3 way as well.

You will not get anything close to 175*F from the GSHP?

New water to water heat pumps probably have controls built in for outdoor reset.

It's inefficeint to mix down the water from the heat pump, most likely the temp can be adjusted with a temp sensor connected to the GSHP.