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# Delta T and hot spots tiedand and loop placement/direction

Member Posts: 659
So Hotrod explained why a low 10-15 delta T in radiant design is more about uniform panel temp than, whats going on in the boiler room which is how i thought was stupidly thinking about it. My house being 85% hard wood floor im particularly concerned with surface temp and yes humidity. So now Im imagining how Im placing the loop entry along coldest walls and its dropping its heat fastest as soon as it enters the room but still has a long journey it must need to start hot enough to create a over hot spot to overcome this? On the other hand if i make the coldest wall the end of the loop and the water hot and fast enough to make it to the end almost the same temp then it can drop its delt T just before it measured. Of course im a bit unclear on the physics of is it possible to heat the space without dropping much Deta T until the end is that a contradiction. And is it even true that what we think of as cold walls actually translate into cold heat sinks as far as the tubing is concerned, or is the heat transfer we are trying to compensate for happening above the loop level. In other words the loop indeed has a bit more heat to drop as it enters the room on the cold wall and less as it leaves on the warm, but its really exchanging heat at almost the same rate at the floor level the greater exchange rates are happening a couple feet higher and more diffused into the total rooms heat rather than panels heat.

• Member Posts: 659
obviously Im not seriously considering reversing flow to enter the cold wall but want to understand why we do what we do.Of course i get the simple answer enter at the cold wall with hottest water because its the coldest wall dummy.
But whats the the delta T if it was actually measured as it enters and exits room whats the panels delta T hows that change with reverse flow. Because in a sense we want that DT10 because we want that panel to be close to DT10 does that panel in reality have a higher DT? would the panel DT be more uniform say with a water DT 5 and reverse flow? not dropping its heat till last second
• Member Posts: 14,785
You can select different tube layouts depending on the results you want 1, 2, or 3 way serpentine, counterflow spiral, and counterflow serpentine are a few of the common layout methods.

A room with two exterior walls you might use 2 way serpentine, or 3 way with 3 exterior walls.

There was even some discussion, and attempts of starting away from the exterior walls a few feet on low, single digit, BTU/ sq ft applications, like super insulated homes, to try and keep "warm" surfaces in the areas where you walked or would sit.
When a design shows 80° supply on design day, it's tough to provide "warm" floors all heating season

Several of the earliest "twin tube" radiant products RadiantRoll and TwinTran used a counterflow concept where the flow on the twin, attached tubes was in opposite directions.

Many agreed that counter flow, tight mat type, 200 foot loop length layout provided the most consistent temperature across the panel. It sure felt like the slab was all the same temperature. That was long before infrared cameras were readily available so I don't have any documentation of that, other than my hands and feet.

Modern Hydronic Heating, 3rd edition has about 90 pages in chapter 10 that explains all the thermodynamics and science behind tube circuit length, spacing, layout pattern, etc. It a great read if you want to dig in that deep.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 9,514
If you end your loop along exterior walls it could actually benifits a condensing boiler. Getting the extra temp drop along an exterior wall would send cooler return water to the boiler. The extra drop would never be noticed 6" from the wall.

However I would hope that if this is a new build extra detail to sealing, and insulation would not cause such a drop.
• Member Posts: 659
Hotrod im going through sieggys book now its been a few years since i skimmed it thanks
Gordy yes its closed cell foam and triple pane windows im just over thinking a bit.
• Member Posts: 14,785
Gordy yes its closed cell foam and triple pane windows im just over thinking a bit.

Yeah, don't trip over dollars to pick up dimes.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 9,514
In your situation keystone with a well thought out design, and envelope. Delta, and type of loop layout is not a huge deal.

Delta is quite manageable with proper pump selection, and loop control.
• Member Posts: 659
was thinking these ecm pumps but they dont seem to come in stainless except multi thousand dollar wilos
• Member Posts: 9,514
Why SS?
• Member Posts: 2,565
Ditto , why stainless ?
You didn't get what you didn't pay for and it will never be what you thought it would .
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