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outdoor reset with trv's

I'm seting up my first outdoor reset system.
I am using thermostatic rad. valves and constant circulation .
i was given a penn/johnson a350r (it's new)
my questions are thus, does this unit connect to the TT of the boiler control?
can it accept an inside temp sensor or do i use a regular thermostat for that purpose .
if i'm to use a therm. for inside temp how do i wire it in to the system .

thank you


  • carol_3
    carol_3 Member Posts: 397

    I think the idea with a thermostatic rad valve is that it's the thermostat and valve all in one--thus no separate thermostat. Any other opinions on that anyone?
  • hydronicsmike
    hydronicsmike Member Posts: 855
    I am with you Carol...

    First to answer the initial question, you do not need to add a thermostat to a TRV system...But it is commonly done with an Indoor Air Sensor.

    It is often recommended by Europeans and many controls offer the feature.

    Using a single Indoor Air Sensor in Multi-Zone Systems for Indoor Temperature feedback is not neccessarily ideal, in my opinion. The supply water temperature is then always regulated based on Outdoor and Indoor Air condition.

    There has been times where a zone or more can not get satisfied, as the Indoor Air Sensor sits in a room that is satisfied and has therefore lowered the supply water temperature. At the same time, a zone trying to recover or being exposed to a greater heat loss may then not get the temperature it needs.

    Its always the same when guys use single Indoor Air Temperature Sensors in Multi Zone Systems. Where to put the Indoor Air Sensor, I often ask?? I am always told to put it into the 'coldest room'. Well, where is that room?? Whether it is in Europe or North America (or elsewhere, I would suspect) the sun always comes up in the East and goes down in the West. Would it not appear that my coldest area in the building (or highest requirement) may be moving with the sun?? Heat Gains, Shaded areas??

    None the less, I have seen it done and it worked many times. But I have also seen it underheat zones.

    Anyways, sorry to be a little off topic here, but it is commonly done and there may be a small chance that the thermostat that is referred to, is actually an Indoor Air Sensor.

    Best Regards.

  • Dennis Bellanti_2
    Dennis Bellanti_2 Member Posts: 36

    It has been some time since I have used the Johnson control so they may have changed the control since I last used one. I believe there is not a connection that will read an indoor sensor... only outdoor.

    The idea behind using non-electric T-stats and zone valves with constant circulation is pretty basic and works amazingly well. Non electrics modulate. When your outdoor reset control is really dialed in for that particular building, you will be creating the same amount of heat in the boiler at the same rate that the building is losing it. (This is a perfect application for a modulating boiler.) When the control is set properly (takes a few trips back to the job to get it fine tuned)the zone valves will always be in some state of open, spoonfeeding just the right amount of heat into the zone. This setup will provide a temperature variance in the rooms of only 1/2 degree! Very steady comfort.

    The main thermostat is only there as a switch to turn the pump on. It gives the homeowner an easy way to control the whole system... no flow no heat. It is important the you use a pressure activated bypass valve downstream from the pump so that when the zone valves are mostly closed the excessive flow has somewhere to go. It doesn't matter where you put it so long as it is downstream from the pump. If you need a resource for the bypass valve contact the Oventrop importer, Pieter DeHaan at Heatlines (603)437-1667.
  • Dennis Bellanti_2
    Dennis Bellanti_2 Member Posts: 36

    The beauty of this system is it's simplicity. Don't make more out of it than necessary. It will work great.
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