Geothermal/Heat pump control question

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

  1. geoxne

    geoxne Active Member Forum Leader


    Now I am confused. After rereading this thread from the beginning you say you will have one zone. Later on you mention 3 or more zones.

    You are going to get conflicting opinions regarding controlling your system anyway. Conflicting information from you will compound that.

    Can you please clarify?
  2. chuck767

    chuck767 New Member

    OK, sorry for the confusion on my part. Let me try to explain my zones. I have one zone pump supplying three different manifolds. The main manifold has no valves on the 5 individual loops. Another manifold has 4 Mr. Pex thermal actuator valves, two valves controlled by one wall stat and the other two valves controlled by another wall stat. The last manifold has only one valve controlled by a wall stat.
    The central area of 1800 sq ft, uses the main manifold and the manifold with only one valve one it.
    So would this be considered one zone or 4 zones?
  3. geoxne

    geoxne Active Member Forum Leader

    Here you are describing a Master/Slave zone control system sometimes used before the advent of electronic pump/zone relay controls (circa 1950s) and in retrofits to "fix" overheated areas. Your central area (1800 sq ft) would be the Master. The three other zones with valves would be the Slaves. As described, the Master zone tstat turns on the pump. The Slave zone tstats will open their respective valves. The Slave zones will only get heat if the Master zone is calling for heat and the pump is running. This is not a very good control design for lack of a zone valve on the central area (1800 sq ft) manifold.

    The 2 stage ODR control should operate the HP to maintain the calculated temperature of the buffer tank only.
    The zone control should open the appropriate zone valves and turn on the zone side pump based on tstat signals.
  4. chuck767

    chuck767 New Member

    [QUOTE=" This is not a very good control design for lack of a zone valve on the central area (1800 sq ft) manifold.[/QUOTE]

    Let me further explain the logic of the control design.
    The central area will always be heated to 72 deg. The slave area with one valve is a master suit area which by design is always set at 68 deg. The other two slave areas will, 90% of the time, be set at 60 deg and then never to exceed 72 deg.
    Do you think this type of control design will give me what I'm looking for. If so can I use the 261 and a wall stat in the central area?
  5. geoxne

    geoxne Active Member Forum Leader

    It will work if-
    -The output of the Slave radiant loops meets or exceeds individual Slave zone loads at design system temperatures.
    -You accept the fact that response to raising setpoints in the Slave zones will be very slow (maybe even days) unless your Master zone is designed to run constant or near constant with proper ODR settings (this is not a bad thing, allowing the HP to operate at the lowest possible load temps for efficiency).
    -The zone side pump is sized properly.
    In this design the Master zone tstat only has to turn on the zone side pump with a relay if needed. The 261 with proper settings only controls the temp in the buffer.

    My question is why? For the price of a zone valve on the Central area manifold? Or does existing piping exclude the possibility?
    Last edited: Sep 3, 2014
  6. chuck767

    chuck767 New Member

    I really don't know why it was set up this way. The company that did the design/install chose to do it this way. I was trying to understand how the stat for the central area was going to connect to the 261 (the installer hadn't hooked it up yet). It now sounds like it just needs to be wired to the master zone pump.

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