supply temp ver: return temp


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Old 04-09-10, 10:46 PM
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supply temp ver: return temp

I have a small staple up under floor radiant heating system.
Right now 8 zone manifold that I am using 5 zones, will be adding 3 more zones in the near future.
I am running supply temp of 140deg F (it actually runs at 137 / 138deg F)
The return temp is between 126 and 128deg F, so it runs between 8 to 10deg F cooler.
Is this a good ratio?

Thanks for any info.
 
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Old 04-10-10, 03:19 PM
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I don't see how it could be any better but wait for some other opinions.
 
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Old 04-11-10, 10:50 PM
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Thats good suppose to really be 15 degree TD try lowering the water tempa little possability your short cycling.
 
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Old 04-12-10, 04:51 AM
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5 zones of heating only extract 10-12 degrees from the supply water? Either you're over-pumped or under-radiated. A smaller pump might save you some money, but I wouldn't bother if your 3 future zones are large enough to bring you closer to a 15°-20° ∆T.
 
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Old 04-12-10, 04:52 AM
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Return temp is not 'supposed' to be anything except what it was designed to be at design load.

So, if you designed the system for a 10F drop, which is common for several flavors of radiant systems, then at design cold load conditions, it should be in that ballpark. At temperatures higher than design load, the drop will be a bit less.
 
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Old 04-12-10, 06:02 PM
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Delta T is dependent on water temperature and flow. The Delta-T will be lower with cooler water and increase as water temperature increases. Flow also changes with water temperature.
This is one reason for the increased interest in variable speed pumps measuring Delta-T or Delta-P.
 
 

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