Separate circulating temperatures for zones on same radiant manifold

RascalOrnery

Hey All, I have a 5 zone manifold supplying 4 zones under wood flooring and 1 zone under tile flooring.

The degree difference between the two desired is between 5 and 10 degrees, currently I have them all the same, the tile is a tinge warm and the wood a tinge cold so I'm not seeing a drastic need for major difference between the two zones. It should be noted that these is supplemental heat only (for warm toesies) and is not controlled by a thermostat.

What is the best way to allow for individual mixing for the tile floor? I don't see anyway to do this without having a separate circulator for the tile zone, which is OK. But beyond that I'm scratching my head a little, this is the best I could come up with.

Basically since the whole system is thermostatically consistent through a mixing valve, a proportional valve to throttle flow will in turn control temperature. My thought was a slight choke to the supply from the main circulator and in return force the zone circulator to take on some of the return, but is it possible the main circulator will just overpower the zone circulator? Where do I go from here?

Maybe I'm really overthinking this and I just just the flow meter to reduce the flow to the zone via the manifold??

Jamie Hall

If you want to have different circulating temperatures in the two zones, you really need to have two separate mixing valves — and, correspondingly, two pumps pulling from the mix valve outlets. However, if there is a balance valve on the supply to the tile zone, you could try running the whole thing warmer and just throttling the flow to the wood floor zone. That may or may not work… depends as much as anything on how the wood floor piping is laid out.

hot_rod

If required SWT are within 8-10° of one another, no need to add a second mix station. Trying to adjust loop temperature by chocking flow may cause the end of the loop to run too cool.

Residential radiant loops design around a 10- 15° temperature droop across the loop.

Here is a look at how that plays out.

RascalOrnery

I'm a little confused, I think we all agree that choking the flow may help some areas to have the proper floor temp but at the price of some being too low.

What's the normal strategy to determining flow rate? I would imagine there's a lot of variables but I would think circuit lengths would have rough start points for flow rates to achieve somewhat uniform outputs, like the longer the run the faster the flow, but by how much and how little for short runs?

Why would the setup I sketched fail?

DCContrarian

"What's the normal strategy to determining flow rate?"

First you determine how much heat you want out of a zone. Then you decide what temperature drop you want between the sent water and returning water. The heat output (in BTU/hr) is equal to the temperature drop (in F) times the flow rate (in GPM) times 500.

From your description it sounds like you'd rather target a specific floor temperature rather than a heat output. If that's the case, the heat output (in BTU/hr) is equal to the difference between the room temperature and the floor temperature times the square footage of the floor, times 2.