Balancing loop flow - Radiant Hydronic Residential

wmwinn

Just a general question regarding water flow balancing of loops. I understand the need to reduce flow rate for shorter loops and keep maximum flow rate for the longest loop within a given manifold design.



All of my PEX tubing is contained within concrete slab on grade. What about loops that travel under carpeted rooms versus ceramic tile? I'm noticing a large difference in delta temperature between these, even though the flow rates have been balanced. Input-Output of only 10 degrees for carpet - while measuring 25 for the tile. My theory is that the carpeting acts as a "blanket" to insulate the heated water, not allowing as much thermal transfer to the foundation as compared to the tile loops.



Here's my question. To help heat the carpeted rooms better, should I reduce the flow rates for those loops further to slow down the water even more? It seems weird to reduce the flow rate in hopes of increasing heat transfer.



Any advice or help would be appreciated! Thanks,

- Mark -

Gordy

Insulation

Is there any under the slab.

wmwinn

Insulation under slab

That's a good question. I have many photos during construction. What should I look for?

Jamie Hall

The question about flow rate

isn't really about heat transfer, but delta T.  The heat transfer rate to the slab -- and therefore the space above it -- is strictly a function of the temperature of the water in the tubing.  However, as heat is transferred out of the water, the water temperature drops and tubing farther down the line gets less heat because of the lower temperature.  The difference isn't that marked, but it is surely there.  The amount the temperature drops, though, is related to the flow rate.  More flow, less drop.



So... if you want more heat in the space, you need more heat transfer from the tubing.  Therefore you need higher temperatures in the tubing.  A greater flow rate will do that -- the average temperature across the loop as a whole will be greater.  The delta T, however, will be less.



The reason for the lower delta T with the carpet is that carpet is a remarkably good insulator, so the space can't extract as much heat from the water as the floors with tile.  If you want to increase the delta T in the areas with carpet, you will have to reduce the flow rate.

SWEI

Construction photos

Look for a shot just before the slab was poured, or early in the process of pouring it.