Primary/Secondary with Mod-Cons Part IV

Mike T., Swampeast MO

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

Why?

Why do I have the feeling that this is going to go somewhere else?

Mike T., Swampeast MO

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

thats interesting

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

Uni R_2

Buddha says

Everything must stay in harmony. Flow gentler...

Mike T., Swampeast MO

Again, PLEASE look for errors, stupid or otherwise.

Those with "Siggy software" have no problem. Do you find the same results?

Uni R_2

Actually....

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

NO!

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

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...