Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.

Are Nest Thermostats capatible with Vitodens 100 & ODR

satwar
satwar Member Posts: 24
Nest has a very good write-up of their True Radiant feature, to help level out the swings in room temperature due to the slow response of my cast iron radiators. At the same time the boiler is running with ODR and adjusting SWT accordingly. Is there a possibility of these two control systems might not work well together ?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 17,037
    They would not work together at all. The ODR should be setting your circulating water temperature so that the circulating pump is running all the time. The radiators should be at a constant temperature, just warm enough to keep the rooms comfortable.

    If that is not happening, then the ODR curve needs to be adjusted so that it does.

    The Nest will turn the whole system off and on and off and on and off and on...completely defeating the ODR and the modulation (if you have it) of the boiler.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ChrisJ
    ChrisJ Member Posts: 11,968
    edited April 2017
    @Jamie Hall Is any ODR nearly that accurate?
    What about solar gain?
    People being in the rooms, cooking, wind, opening doors?

    I assumed all ODR systems still used an indoor thermostat to cycle the system, they just did so much slower?
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • heathead
    heathead Member Posts: 160
    If the ODR is set right you don't need a thermostat. Some will set up a simple thermostat to turn off the boiler if the room gets too hot. It justs acts as overheat protection. That being said the best system for the Viessmann Boiler is a Viessmann thermostat/room sensor. It shifts the outdoor reset curve based upon the indoor temperature feedback. Very useful if you have a wood stove or high infiltration/heat loss on a windy day. The key is it is not on and off but Shifts the system Heating Curve in the boilers computer that then changes the boiler supply temperature from that indoor sensor. Does the 100 now offer the ODR is is that just on the 200?
    Gordydelta T
  • Jamie Hall
    Jamie Hall Member Posts: 17,037
    Quite true -- there are many variables which can throw them off, and that is why an indoor thermostat is always part of the equation for a setup with ODR. But a well-calibrated one in a reasonably tight structure should be very very close most of the time. I just don't see where a Nest would fit into the picture to any advantage.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    delta T
  • ChrisJ
    ChrisJ Member Posts: 11,968
    Ok
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • satwar
    satwar Member Posts: 24
    Thank you for the helpful comments.

    I'm not aware of a Viessmann thermostat for controlling the vitodens 100. The Vitodens 100 has basic ODR and does not have advanced ODR which can adjust for building heat Loss, as with the Vitodens 200.

    The nest thermostat was running the old heating system very well with True Radiant, but it was time upgrade from a non-condensing to a condensing hydronic boiler. The installer hooked up the existing two wires from the thermostat to the new furnace, but I don't know the details of how this was done.

    From what I see, The Vitodens 100 runs as follows:
    (1) The thermostat calls for heat and the circulators and burner start up
    (2) The SWT starts to slowly climb in response to the low fire of the modulating boiler
    (3) The burner cuts off to keep water temperature under control but the circulators continue to run
    (4) If the room temperature rises above the set=point then the thermostat trips both the burner and the circulators
    (5) If the room temperature does not rise above the set-point and the water has cooled down the burner starts up again.
    (6) As the outdoor temperature decreases the burner firing rate increases and the water temperature increases

    The room temperature remains very stable, my radiators are always warm, and I disabled the evening setback because it takes too long for the house to recover with the low heating curves being used now. When I was using the high heating curves set by the factory, the burner was always on full fire when heat was called for and could easily recover from evening setback.

    I decided to see what I could do about increasing energy efficiency by reducing the RMT by operating on a lower heating curve. I am currently in the process of reducing the heating curve to 2.0 compared to 4 1/4 set as the factory default. It looks good so far but I've run out of winter weather

    The fundamental difference in our approaches seems to be the type of thermostat hooked up to the Vitodens 100. I'd appreciate any information you have, because your control strategy is much simpler than my approach.
  • gschallert
    gschallert Member Posts: 170
    The 100 can't be "tweaked" as you know so the best way to optimize is to lower the preset curve setting until the house is barely maintaining your desired temp with constant circulation. My in-laws just had this model installed last fall and I optimized the setup and dialed in the curve for them over the holidays when we visited. The installer had left it at the default settings. The Nest is a total waste of money with this type of setup, you only need a cheap digital Honeywell for high temp shutoff. No setbacks, just leave the thermostats set to the room temp you want and ODR will take care of it. Which setting works best will actually vary from shoulder seasons to design temps and your specific heat loss v. emitter capacity. Dec-Feb they ran with ODR on "3" and I had him turn it back to "2" in March.
    Canucker
  • GW
    GW Member Posts: 4,302
    Couple issues: not sure if the lil Vito has a c terminal.Of course you could always set up a transformer and relay, send signal to the space heat terminals

    Also, I'd be curious to see the Nest arm wrestle the Vitodems.as to see which one is smarter. Seems like an awkward conflict of technology

    Gary
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
    Canuckerdelta T
  • Jamie Hall
    Jamie Hall Member Posts: 17,037
    Awkward conflict of technology is a mild way of putting it, Gary! The two represent completely different approaches to controlling heating.

    I don't really have a problem myself with the Nest -- or other "smart" thermostats -- controlling heating which is very quick to respond and which is inherently either on or off -- such as forced air or, possibly, electric baseboards. I do have a problem with gadgets of that sort which are part of the Internet of Things, but simply there because the security associated with them is somewhere between ghastly and abysmal -- and that's a philosophical thing.

    But I simply can't see their application to heat which is slower to respond -- steam, most hot water, and certainly radiant -- where if it is correctly set up the best approach from the standpoint of theory is the outdoor reset (and keep in mind I'm a steam guy!) and modulating combustion (it is set up properly to maintain efficiency). Add in a few more sensors than just temperature -- wind speed and solar gain come to mind as obvious -- and one could really have a nifty system, seems to me.

    On the other hand, there is a lot to be said in terms of simplicity and reliability for a plain vanilla thermostat and nicely calibrated pulse modulation of the heat source to keep the thermostat happy.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • satwar
    satwar Member Posts: 24
    Gschallert,

    Your comments give me hope, that I am heading in the right direction. I'm a little confused with your comment about setting the thermostat and leaving the rest to ODR. Are you referring to setting a high limit on the thermostat, when you say setting the thermostat ?
  • satwar
    satwar Member Posts: 24
    Jamie,

    Quote
    there is a lot to be said in terms of simplicity and reliability for a plain vanilla thermostat and nicely calibrated pulse modulation of the heat source to keep the thermostat happy.

    Can you explain how to practically achieve this ?
  • Gordy
    Gordy Member Posts: 9,514
    If outdoor reset is properly adjusted the thermostat becomes nothing more than a high limit switch. The thermostats duty then is to shut down the heating system when internal gains have overheated the space.

    It takes quite a while to tweak a reset curve. Usually easiest done when usage patterns are the same, and deffinetly no setting back.

    It sounds like you are close if the house can not recover from setback. Which is counter intuitive to ODR.
    delta TCanucker
  • Jamie Hall
    Jamie Hall Member Posts: 17,037
    satwar said:

    Jamie,

    Quote
    there is a lot to be said in terms of simplicity and reliability for a plain vanilla thermostat and nicely calibrated pulse modulation of the heat source to keep the thermostat happy.

    Can you explain how to practically achieve this ?

    Pulse modulation simply refers to modulating average output by going from full fire to off with the timing set so that the average firing rate is what is needed. On most steam systems, this is done with a combination of the thermostat and a pressure controller on the boiler; the thermostat controls how long a heating call (on pulse) is needed and how long to wait for the next call (off pulse). On hot water systems, the same sort of thing is accomplished with the aquastat on the boiler turning the burners on and off as required to maintain the proper circulating water temperature.

    The trick is to optimize the length of the on and off cycles, and one can get into rather heated debates as to the best way to do that.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England