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Grundfoss Mixer Miser

hr
hr Member Posts: 6,106
they are mainly an injection pump. Not to be used a system pump. Really shouldn't have anything to do with the wall stat?

Maybe just adjust the curve up a notch for additional heat output.

What temperature did the heat loss design call for? What temperature is the Mixi actually supplying to the zone?

Is the space, or home,warm and comfortable? If the stat is hovering around 1° of setpoint that's not a bad thing?

Ideally a radiant system would be constant circ, whereas that Miximiser is matching the injection output to the actual room load. Sounds like your system is running close to that.

hot rod



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Comments

  • Ragu
    Ragu Member Posts: 138
    Grundfos Mixer Miser

    Has anybody used these? They are an injection pump with an integral Tekmar outdoor reset. I've got three of them out there. As the room approaches set point temp, the pump slows down (I assume to avoid overheating). The problem is that it takes FOREVER to achieve that last portion of a degree to satisfy the t'stat(which only has a 1 degree differential). These are all radiant slabs. Same action from contol regardless of curve setting. No info from Grundfoss. Tekmar says proprietary property of Grundfoss. Is this thing a wannabe hybrid?
  • Ragu
    Ragu Member Posts: 138
    Mix Miser

    Background...system is piped P/S, slab pump on constant circ, house is comfy for HO, system is o.k. until outdoor temps drop below 20 degrees. EG: outside temp 10 degrees, inside temp drops 1 degree ( from 70 to 69), boiler and/or system circs come on, water injects at 140, after awhile drops to 130, eventually hovers around 115 FOREVER. Note: at 1 degree drop in room temp, slab has dropped 8-10 degrees. Honeywell aquastat on Buderus set at 175 (for indirect); built in differential (I don't like). Also t'stat controls the whole show, which I don't like. Rehau design program calls for 104 degree mean fluid temp. My gut says to avail myself of that boiler full of hot water to pee into slab during t'stat off times in order to keep slab from dropping 8-10 degrees before t'stat goes through 1 degree differential. With t'stat running the show, nothing gets injected,because system circs and outlet powering Mixmizer are only powered upon a call for heat from t'stat. This is wired per Rep's specs, and I think I'm missing something. When there finally is a call for heat, boiler has a long run time. Slab and house are new and excellent insulation to both. Minimal infiltration. I think i'm not correct on my control strategy?? Could use feedback.
  • hr
    hr Member Posts: 6,106
    Clear a few thing up

    on top you say slab pump is on constant circ? But lower down you say the the t-stat calls the system pump and miximiser on. Maybe we are calling the circs differently. Got a drawing or pics?

    If the design (Rehau)calls for 104° at design, and the Mixi is supplying 115° FOREVER, it sounds more like a distribution problem?

    What is the supply to the zone and the return from the zone on cold days? This delta t will tell you how much heat is left behind in the slab.

    Also the Rehau design should spell out a delta t that the zone was designed around. Is the measured delta t close to the designed?

    Get a couple Azel dual digital thermometers and start collecting some actual, hard data.

    You could push the Mixi to setpoint, but kind of defeats the reset ability of the control.

    Why not run the zone pump constant circ and have the t stat call on the Miximiser? Of course the primary pump needs to run whenever the Mixi does to assure it sees adequate boiler temperature. Is it?

    Also check to see what primary loop temperature the Mixi was designed to. It may be as simple as boosting the boiler aquastat 5 degrees or so. If it shuts down at 175 currently, at a 20 degree delta t you may be too low on the bottom side to provide the Mixi with enough temperatures to do it's thing.

    Lots of temperatures to watch and record.

    Does the mixi have a flowsetter or balance valve to run it up it's curve and balance that injection flow?

    That's your homework assignment for today :)

    hot rod

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  • Ragu
    Ragu Member Posts: 138
    mixmizer

    Hi
  • Ragu
    Ragu Member Posts: 138
    mixmizer

    Hi
  • Ragu
    Ragu Member Posts: 138
    Miximizer

    Thanks for help. Have drawings but will have to get assistance to send as Attachments. It's a partial primary loop. No flowsetter on Mixer, but ball valves before and after. Slab pump on const. circ. Constant power to Mixer, BUT, when TT calls, it pulls in primary pump, 24 volt trans. to Mixer and TT on boiler. (DRAWINGS!). Documented readings from the file: Outdoor temp 20, Tstat set 72, differential 1, stat calls at 71, slab surface 76, curve .3, slab supply 130, slab return 90, 6 hours boiler run time ends up with slab supply 120, slab return 100, slab surface 83, stat off 72, Rehau mean delta T 20, Rehau mean fluid 104. Thanks.
  • hr
    hr Member Posts: 6,106
    First off

    you really need a way to balance that VS Miximiser. Here are 3 options

    http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,7879,00.html

    Also if the floor surface is 83° and it cannot meet the load on design, or near design days, you may need supplemental heat. The design program generally will notify you of "close calls" or floor panels that may not meet the load. RadiantWorks spits out a warning in red type. Also the amount of the shortfall (btu/hr.) to design the supplemental to.

    You may choose push that floor surface to 85, but this temperature can start to get uncomfortable, depending on the rom and type of floor coverings. Tile and concrete feels too hot to me at 85°. No one wants sweaty feet on their radiant system.

    Sounds like so real life measurements will show some simple adjustments are all that is needed. Simmer down that injection pump with some balance first so it can track and react better. You may have a yoyo effect going on as the VS circ "hunts" for the sweet spot :)

    hot rod

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  • Weezbo
    Weezbo Member Posts: 6,232
    Ragu, i have not used a mix master...however no problem

    i savey constant circulation ...the trick to some engines is that they rev like crazy and arent going anywhere so the trick is to put a balanced flow ahead of them or give them something to overcome...a very simple pointer i would suggest is mix down the water ahead of the variable speed ...so that it must work for a living...like us..if we arent working we dont like it much..neither do pumps..
  • Ragu
    Ragu Member Posts: 138
    Mixermizer

    Thanks a bunch HR and Weez; I'll get a throttling device in there and watch the performance. Something was off the wall there, but I had no idea what it was. See ya youse guys.
  • hr
    hr Member Posts: 6,106
    Ragu invest in

    a copy of Siggy's HDS available at www.hydronicpros.com. It has an injection module that will give you all the required design, flow requirements, and balance info you need. i think you can still try a demo at his site.

    hot rod

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