Garn and mixing valves

A bit uncertain here - sounding like you don't have an HX between the Garn & the rest of the system?

I likely can't offer much more, no experience with mixing valves.

I have a Garn 2000 and I run tank temperature water right into the house and it works fine. In the house the water is distributed to 2 furnaces, DHW & in floor heat. At the moment only the 2 furnaces are on operation. DHW is coming this summer and floor heat this week. I just did get the system online in the past week, so I'm still working out some bugs

If the water is 170° it heats fast, if the water is 130° it heats slower.

Edit: The thermostats control the temperature of the house, so water temp isn't really critical to functional. I'll know more after the next cold snap.

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Without knowledge of your system layout and definitive goal, kinda tough to respond accurately. But, I will explain my current concern. I too am happy with the boiler in use and a slightly discouraged with the end results in the home particularly the temperature swings. My intention is to add a mixing valve actuator to a previously installed 3-way mixing valve (Tekmar valve). The actuator (Armatur LK 130) has an outdoor reset program with indoor input too. For $510 US, you could go with the two items at the following links, or, use your Taco valve and get a controller and actuator that mates to it. The Armatur unit is also available without the indoor input for $350 US.

https://store.tarmusa.com/products/lk130-smart-control?variant=18921520646

https://store.tarmusa.com/collectio.../lk-840-thermomix-3-way-valve-3-4-male-thread

Best of luck in getting the results you would like to see. My plan includes the LK 130 and a 3-way that looks like this:

Pics of the current mix valve/ circ plumbing would help. Any mix valve needs to be sized correctly to the flow rate, not pipe size to have control. My Garn has 1-1/4 near boiler piping, the belimo mix valve has 3/4 inch ports, a cv of 4.7, but requires 10 gpm to work properly, a Grundfos 15/58 on med speed works for this application. The valve is controlled by a 0-10vdc signal generated from a Tekmar outdoor reset module. The Tekmar controller generates a 0-10 signal representative of the outdoor reset temp required, that signal is input into a Eurotherm pid controller as a remote setpoint, then looks at the actual supply temp, calculates the difference and creates a output for the belimo mix valve. This is a example of proportional control, and results in very little error if tuned properly.
There are other control strategies that such as pulse width modulation, floating point that work more on the average temp between the highs and lows that are represented by manufacturers of outdoor reset controlls.
Generally modulating a valve will give better control than modulating circ speed.
Are you looking to control a backup heat source as well or just the Garn?

Bill, are you using a flat plate, if so what side of it is the mix valve on, where is the supply temp sensor located, how is your backup heat source plumbed, series or parallel?

Who did the install of your system? The thermostatic valve is plumbed to serve what purpose? Is it for boiler protection (keep cold water from returning to the boiler)?

The Garn is not under pressure, yes. Maybe you should consider a plate exchanger at the Garn with the house side pressurized. There are several members here who use Garns, maybe they will be jumping into this thread.

I see @TCaldwell is already here, he is quite experienced with the Garn units. Best of luck in reaching your goals.

When I was setting up my Garn Heaterman did not recommend a mixing valve. In his words "a Garn can not be shocked with cold return water"

He did advise to run at slab heat with a plate heat exchanger.

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Look into the tekmar 356 with outdoor reset. It runs a pump on the garn to my heat exchanger, (on/off, it just brings whatever water is in the garn to an exchanger).

another pump on the house side of the exchanger is used to hit my 'target mix temp' based off the outdoor reset temp.

It also runs a variable speed pump for all my house zones. Works great and I get good heat out of my garn down to 80-90F

There are other ways to run it, but I like the exchanger because i'm always sending warm water back to the Garn.

I have a 50 plate hx at the Garn. With a new taco 0015e pump.

I have no experience with the 356, but any control that modulates a cap start circ like a taco, is at a disadvantage to a 3 way valve. The 356 will send a 0-10 vdc signal to the circ that won’t start rotation until 2 vdc, essentially you’ve lost the first 20 percent of control, a contributor to hunting. This might not even be noticed in some applications and doubtful you’d catch it unless you monitor temps.

A few bullet points....

* If you're looking for maximum control over water temp, I've always had best results with a motorized mixing valve of some type.
The Taco i-series...not so much. Bellimo or Tekmar mainly. Viessmann makes an excellent stand alone motorized valve also but big $$.

* Best control is to mix at point of use and run high temp water from the boiler to that location. Especially true in cases where the supply run is on the long side or tube diameter is inadequate.

* Any mix valve will "hunt" when temperature supplied to the valve drops below required water temp.
Most will bypass a certain amount of the return back into the supply even when supply temp is lower than demand.
You just plain need to keep the supply temp up.

* A Garn absolutely does not need a mixing device of any kind for "boiler protection". Water temp in the Garn should however always be maintained above 120*. Higher if the fuel is on the "green side" of dry.

I'm surprised you guys have better luck with valves, my tekmar 356 and grundfos injection are always spot on.

Early on I tried a taco ivalve for setpoint control behind my Garn, as heater man said, not so much luck. Currently I have a belimo mix valve, they call it a characterized control valve, it is programmed at the factory in ct., including stroke speed and input voltage range to match the output signal of a independent controller.
I agree with heaterman on the point of accuracy is generally better at point of use and probably in a pressureized environment.
Having said that I installed mine between the Garn and the flat plate in the Garn barn, thus mixing at the Garn, sending only the low outdoor reset temp water underground to the house, this works well also.
Some things to consider with stand alone valves, you also need a controller like a Tekmar 423 that provides a outdoor reset signal to the valve, I think Honeywell makes a controller also that has adjustable control parameters, Tekmar has their own proprietary control algorithm. The adjustability is needed the farther away you get from the point of use.
The integrated valve controllers like the LK brand Tarm USA sells are used by a member named sparky. He could give a assessment.

Bill in IL said:

Sounds like I may need to rethink my strategy a bit then. No mixing valve and just pump directly to the house. I am slightly concerned now that I will ruin the stratification in the tank pumping at my target rate especially on warmer days. I have always figured for 10 gpm flow to get 100 k Btu at 20 deg drop. I will give it a try and see how it goes.

Thanks heaterman the stove has been working great.

Click to expand...

I am thinking that slowing your circ down while removing your mixer, might have the same effect on stratification as your present faster circ flow but using a mixer?

Bill, your probably tired of seeing my posts, one more thing to consider weather you choose mix valve or circ, if your primary loop from the Garn is plumbed with closely spaced t’s to a zone manifold, the supply sensor placement will depend what you see. If the sensor is on the supply pipe leaving the mix valve it will be accurate as to valve performance. If the sensor is down stream of the closely spaced t’s you will get a less stable reading because some mixing happens in those t’s as zone calls start and stop.
That’s all I got!