New Infloor Radiant Heating System - Questions

Discussion in 'HVAC Heating & Cooling' started by tuffcalc, Jan 10, 2018.

  1. tuffcalc

    tuffcalc New Member

    Joined:
    Jan 10, 2018
    Location:
    Ontario
    Hi everyone,

    New around here. Hoping someone can help a newbie out.

    I'm building a new home (basement, ground level and upstairs). I'm having infloor radiant heating installed on each floor. The HVAC company has designed a system with these specs.

    1. 17 zones
    2. 17 Tekmar 561 thermostats
    3. 3 Tekmar 306V Zone Valve Controls
    4. 3 Groundfos Alpha2 circulators (one circulator per floor)
    5. 1 Lochinvar Knight boiler

    My question is this - if the Tekmar 306v can only control one circulator when a zone calls for heat, how are the other circulators wired up so they also turn on when the respective zones they serve call for heat?
     
  2. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    With 17 mostly low-thermal mass zones and NO BUFFER TANK (??), you're in danger of short-cycling the boiler silly on zone calls, into low as-used efficiency and an early grave. If it has a thermally massive hydraulic separator (like a Boiler Buddy or similar it might be OK, but any system that it micro-zoned to the nth (in this case 17th) degree this is an issue that has to be designed-for.

    You have three Tekmar 306Vs, and three pumps, one per zone controller. Each 306V turns on it's dedicated pump whenever any one of it's zones are calling for heat. If the Alpha2s are programmed for constant pressure or auto-adapt it will bump up the power to maintain proper flow when more than one zone on that controller is calling for heat.
     
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  4. tuffcalc

    tuffcalc New Member

    Joined:
    Jan 10, 2018
    Location:
    Ontario
    Hi Dana,

    Yes I'm aware there is risk for short-cycling due to the many zones. We are not installing a buffer tank. Here is the thought process:

    1. We've chosen the second smallest Lochinvar knight boiler (WHN086) that has a 10:1 turndown ratio, so on the lowest fire it will put out 8,500btu.
    2. If there is a heat demand more than one zone should be calling. Some of the zones are also very large (e.g., 1000sq ft. or more).
    3. The RoomResponse function on the Tekmar 306 will tell the boiler what setpoint to fire at. In low demand situations the setpoint should be very low (less than 100f?) which would force longer run times. Couple this with, ideally, more than one zone calling.

    On paper it should work and keep the boiler from cycling. We will see how it works out in practice.
     
  5. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    The min fire INPUT of the WHN086 is 8500BTU/hr.

    It's min-fire output in condensing mode is ~8000 BTU/hr.

    That definitely helps, but some of those zones are likely to have incredibly little thermal mass. Even a 5 gallon electric water heater (unpowered) employed as the hydraulic separator would be able to tame it, should it short cycle on you.
     
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    While you can put multiple loops on one controller, depending on the tubing size utilized, you generally don't want any single loop to be more than about 200' long.
     
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