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Primary/Secondary with Mod-Cons Part IV

Attached are the revised full-load system, such at half load (defined as 1/2 the full-load btu/sq.ft output) and a flow diagram.

Only major change to the full-load system was in the master suite where I dropped the plus carpet and considered hardwood with large area rugs (hopefully not too large if wool ;0) I also found two relatively minor errors--one in delta-t for one zone (I used half), the other in the total gpm requirements (I forgot to re-total after the change in the garage).

You'll have to tell Acrobat to rotate the flow diagram--sorry.

Personally, I consider 50% load to be a reasonable representation of true <I>outdoor design condition <B>maintenance</B></I> load for a RFH home with loss based on Manual-J. Literature and studies from Danfoss and others [seems] to validate this assertion.

<B>Actual</B> supply temp requirements in the "high temp" zones vary from 97°F to 109°F. The garage (now assumed 62°F ambient) still causes problems however as its supply requirement drops to a mere 70° with 81°F required for the bulk of the basement.

I did my best to normalize output of the zones (both in high and low temperature groups) to the same supply temp. This is an attempt at a snapshot of what would happen if ALL zones called simultaneously <I>just to maintain their desired settings</I>. Obviously, this CAN'T happen for any length of time as some zones (especially the garage) are relatively over-supplied with heat when all supply temps are equal.

I do ask that you pay particular attention to the flow diagram. Please check for errors. I've done my best to double- and triple-check, but sometimes stupid things pass me by...

Note that not only is the system supplying significantly more energy than required to <I>maintain</I> all zones, but that it is IMPOSSIBLE for the boiler (with fixed flow) to produce this condition--the output is EVEN GREATER if the supply temperature <I>at the low-loss header</I> is to be maintained.

Next, I'll re-design with flow-setters in an attempt to design for flow more in line with requirements. Of course there will still be that pesky little problem of zone delta-t dropping by approximately 50% as load drops by 50% with flow remaining constant...


  • Uni R_2
    Uni R_2 Member Posts: 589

    Why do I have the feeling that this is going to go somewhere else?
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    If by "somewhere else" you mean the fallacy of trying to maintain a reset curve target in a multi-zoned system with fully fixed flow you have an idea where I'm going...

    I already said that I suspect such is impossible. This is just the first step. I'll try to improve but I seriously doubt it will get much better...

    Please prove me wrong.

  • jp_2
    jp_2 Member Posts: 1,935
    thats interesting

    so, you are suggesting that ALL radiant floor systems are being oversized by 50%?

  • Uni R_2
    Uni R_2 Member Posts: 589
    Buddha says

    Everything must stay in harmony. Flow gentler...
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Again, PLEASE look for errors, stupid or otherwise.

    Those with "Siggy software" have no problem. Do you find the same results?
  • Uni R_2
    Uni R_2 Member Posts: 589

    I would guess that it is a factor of 5 to 10 times as inefficient as they could and should be. The circs won't be as reliable so why would a manufacturer risk their name putting them out there? This may very well be the case here. This change increases their complexity severalfold yet this is all to save $20 to $25 a year? And worse yet, more service calls that are lost time charges.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928


    I'm suggesting that ALL systems no matter how well designed are oversized in the range of 40% - 55% based on the ability to maintain desired setpoint in normal conditions.

    Manual-J and all other WELL DESIGNED "heat requirement" calculations provide the necessary and required uncertainty factor to include reasonable occupant desires. ZERO need to increase above!!!

  • Weezbo
    Weezbo Member Posts: 6,232
    with that general idea in mind...

    just how much leeway are you suggesting we use for the ability of a homeowner to control a zone other than by a specific set point control when they wish to change the setpoint temps while they are in"The Zone" ? :)

    is the 72 degree F a hoped for designe point that will allow the change to cover the anomalies of the particularly eccentric?

    if the 85 % thing is true then there seems to be 15 percent of some somewhat "different " individuals that seem to have their own particular take on comfort...

    do you recall the 40 zone home i posted a while back.....the Lady of the home dials zones up and down and curiously seems to have no set pattern of just what or where she will be next..:) i hope you do not find that offensive or derogatory ,..shes just a bit different...
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