Geothermal/Heat pump control question

Discussion in 'Radiant Heating and Cooling' started by chuck767, Aug 18, 2014.

  1. chuck767

    chuck767 New Member

    Tekmar 261.JPG Tekmar-1  261.JPG Tekmar 261.JPG Tekmar-1  261.JPG
    Hi, new to this forum and new to Geothermal heating. I'm building a new house and installing a 5 ton Hydron Module Water-to-Water geothermal heating system with hydronic heat through in the floors utilizing a Boiler Buddy.

    I have a simple question. Can I use a Tekmar 261 control and still control the temperature in my home which has a single zone via a centrally located wall mounted thermostat?

    Is so, what terminals does the thermostat use?

  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    The thermostat would not connect to the Tekmar 261. The thermostat is now just being used to turn on the zone valve/pump.

    I don't think the 261 has compressor timeouts? Once thing to make sure is your are not short-cycling the heat pump with such a control. The heat pump itself likely has timeouts.
  3. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I would have you look at the Tekmar 406 house control.

  4. ACES-Energy

    ACES-Energy Member Industry Professional Forum Leader

    Look at the HBX eco-1000 as the hydron is 2-stage or you could use the cpu-500 and a time delay and consider the HBX THM-0100 t-stats!
  5. chuck767

    chuck767 New Member

    When you say, "I would have you look at the Tekmar 406 house control" are you saying the 406 is a better control for my system or are you saying the 261 will just not work for my system.
    Thanks for you inputs.
  6. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    The 406 is designed for geo applications.

  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    We use the tekmar 261 commonly, it controls 2 stages, has an outdoor reset, and usually controls the supply/buffer tank temperature. However, if you have a single zone,
    you would not need a buffer tank, the zone itself becomes the buffer tank. Then your wall thermostat could control the heatpump with the load side circulation, which would result in a very efficient system. This assumes that you have an efficient radiant floor, which might even eliminate the need for a tekmar 261 with an outdoor reset. If you can heat your house with 90F water, you don't need an outdoor reset.
  8. chuck767

    chuck767 New Member

    Thanks docjenser.

    I'm not sure if my system is considered one zone or not. I have one floor loop pump and three manifolds with loop valves on some of the loops on two of the manifolds. These valves are controlled via room stats.
    I do have a buddy boiler. Total heated area is 3000 sq ft.

    Do I connect my main wall stat to the "set point" terminals 3&4 on my Tekmar 261?
  9. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    No. not set point control for the radiant if you have an outdoor reset controller like the 261. If you have multiple zones controlled by wall thermostats, your flow requirements of each individual zone are different than the flow requirements of your heat pump. You need to connect the temp sensor going into the boiler buddy to terminal 15, that controls the buffer tank temp. Then all the zone thermostats turn on the valves to apply flow to the zones.
  10. chuck767

    chuck767 New Member


    I understand what you are saying.

    I'm not describing my system very well.
    9 of my 14 floor loops (200 ft each) don't have any valves controlled by stats. I was wanting one central wall stat to control those 9 loops. Where do I connect that stat on the 261 to do this?
    Thanks, sorry this is all new to me.
  11. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    again, the 261 is designed to control the supply temperature in a hydronic system, and not to be integrated with a room thermostat. The hydronic heating works by allowing flow to a zone, something the 261 usually not do. I am also not sure if I understand what you want. Turn your 9 loops on? What about the other 5 loops? Best to put a valve in the feed for the 9 loops, and have the room thermostat open that valve.
  12. chuck767

    chuck767 New Member

    The other 5 loops are off 2 of the manifolds. 2 off one manifold and 3 off the other. These loops are controlled via valves/stats in three different rooms. These temps always be lower than the centural area temp. I have 3 manifolds in total.

    So it sounds like you are saying I can't control the heat in the centural area of the house ( about 1800 sq ft) from a stat in that centural area connected to the 261.
  13. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Yes. In addition, the 261 has an outdoor reset. It beats the purpose to shut down the load side with a room thermostat.
  14. chuck767

    chuck767 New Member

    I see.
    So to change the temp in the central area I will need to do down to the mechanal room and adjust the 261.

    What is "an outdoor reset"?
  15. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Outdoor reset: Measures outdoor temperature and reduces the load supply temperature accordingly, so you save operational costs on warmer outside days.
  16. chuck767

    chuck767 New Member

    Thanks docjenser, I understand.

    If I user the Tekmar 406 could I then connect a wall stat to control temps to my 1800 sq ft central area? I really don't want to go to the mechanical room to tweek temps.
  17. geoxne

    geoxne Active Member Forum Leader

    I think you are failing to understand. The ODR control whichever you choose will control the HP to maintain the buffer tank to a temperature based on relationship with outdoor temp.

    A separate zone or pump control will turn on pumps and/or valves based on calls from thermostat. An end switch from this control can tell the ODR control that a demand is present. Usually with a HP buffer tank the demand should be constant with a jumper wire (Tekmar 261 terminals 1+2:Boiler Demand), so the tank can recover after a call.

    In a perfect world ODR controls, programmed with the right settings, don't need thermostats. However, with multizone systems the right settings for one zone might not work on the next. In this world, thermostat(s) are added to control individual zone(s) and their respective pump(s) and/or valve(s). This helps prevent overshoot when internal and solar gains interfere with the ODR curve.

    Make sure your system is designed for the lowest possible temperatures. That is where the savings are (approx one more COP for every 20f drop).
  18. chuck767

    chuck767 New Member

    OK, I think I got it now.
    Since I have three manifolds being fed by one pump, the central area (1800 sq ft) thermostat will control that pump. The three other rooms with valves (Mr Pex thermal actuator) on two different manifolds will be controlled via their stats. With this type of setup I can see that the other three rooms can never be warmer than the central area which is OK.
  19. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    yes, this might work, although usually not working well.

    It is better to have another zone valve installed, controlled by the central thermostat for the central zone. The pump comes on whenever one of the zones calls for heat. That way you have the temp in each zone the way you want it.
  20. geoxne

    geoxne Active Member Forum Leader

    Not OK. Wire ODR control with constant demand as mentioned in my previous post (Tekmar 261 terminals 1+2 jumpered) and as doc mentions above. Any zone that wants heat gets it, except when ODR control is in Warm Weather Shut Down. Typically WWSD temperature setting in my climate is around 60f, but yours will vary depending on how much internal gain, infiltration, and insulation you have. A separate zone/pump relay controller will handle pump and valves according to thermostat calls.
    Please consider a single properly sized variable speed pump and zone valves on zone side of buffer tank for efficient operation.
    Last edited: Sep 2, 2014

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