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setpoint or outdoor reset??

stew_4
stew_4 Member Posts: 7
in THE MAIN WALL
howdy from the great white north (alaska). Been hearing different stories and suggestions from many different heating guys in the area reguarding setpoint and outdoor reset controls like the Tekmar or wirsbo promix setups. some good some bad. what are the benefits and down falls of each? which is the way to go considering our varying climate here? some days it can be -50 F and 2 days later it can be +40 F.

Thanks....Stew

Comments

  • jerry scharf_2
    jerry scharf_2 Member Posts: 414
    my take on outdoor reset

    I think outdoor reset is a good idea, but it's only part of the picture. Some people mistakenly think that outdoor reset replaces the thermostat/TRV/other room control. It doesn't, and in fact you have to make sure you run the outdoor reset such that the room control can still do it's job well (don't try for the perfect curve.)

    What outdoor reset buys you is more efficiency and more comfort. When the water setpoint is lowered on warm days, the emitters heat more slowly which makes it much more comfortable and easier to control. There is some efficiency gain with standard boilers, but this really shines with condensing/modulating boilers.

    One down side to outdoor reset is that it's more complex. You have to look at the entire system when setting it up rather than just the boiler or the thermostat. If you mess it up, you can have plenty of BTUs waiting in the boiler and not enough in the house.

    Another down side to outdoor reset is that it can mix badly with night-time setback. Because the water is cooler, it's ability to recover after setback can be much slower. This could also be an issue up your way with recovering from a no-heat situation. You really want full water temperature to drive the emitters at max output in this case.

    I hope this helps, jerry
  • hr
    hr Member Posts: 6,106
    Jerry has it

    I have outdoor reset issues every shoulder season around here. Daytime temperatures can be in the 60's or even 70's then 30- 40's at night. The outdoor reset controls can be slow to respond. And also overshoot a slab under this situation. I'm not sure there is a "fix" supplemental low mass emitters would trump a slab radiant in a wide temperature swing situation.

    Also not a good match if you want to keep some floor warming in the master bath in mild, or even summertime use. weather. There are plenty of times the WWSD prevents "warm floors"

    I've learned to add a seperate loop with a 3 way thermostatic for this type of application.

    All in all outdoor reset WITH an indoor feedback is a sweet, but not perfect, control logic. It may take some owner adjusting to make it suit their needs, wants, and desires.

    Teach your childern well :) And your customers, well! CSNY forever :)

    hot rod

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