hot water heating system problem?
Posted in Plumbing Talk
namakan asked:
Working on solving a hydronic heating problem at a friends new garage. Its a heated slab and the guys that installed the slab, also laid in the PEX tubing and did it very wrong. They were told to keep the loops less than 240′ (1/2″ pex) well being given three 500′ rolls they laid in 3 loops 500′ long. Big problem is that my buddy and I were gone that day and the slab was poured and finished when we returned late that night. Each loop will have 51′ head loss at 3 GPM. Any suggestions on salvaging this mess? circ pumps in series? One big pump? trying to solve this for hundreds not thousands.
Evan
Working on solving a hydronic heating problem at a friends new garage. Its a heated slab and the guys that installed the slab, also laid in the PEX tubing and did it very wrong. They were told to keep the loops less than 240′ (1/2″ pex) well being given three 500′ rolls they laid in 3 loops 500′ long. Big problem is that my buddy and I were gone that day and the slab was poured and finished when we returned late that night. Each loop will have 51′ head loss at 3 GPM. Any suggestions on salvaging this mess? circ pumps in series? One big pump? trying to solve this for hundreds not thousands.
Evan
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Miriam
According to the attached source, the drop at 3 gpm is 12.2 psi per 100 feet, and at 2 gpm is 5.8 psi per 100 feet. So it works out that 500 feet of PEX at 2 gpm has the same head loss as 240 feet of PEX at 3 gpm.
One option is to use the original pump as designed. If the pump were to supply each loop at 2 gpm, you would nominally have 2/3 of the design heating, except that the fluid takes 50% longer to circulate through the loop, so it has longer to give up its heat. Thus the 2/3 is actually higher. On top of that, the pump will run farther up its curve to pump more than 2 gpm (but less than 3 gpm) through the loops, so that the 2/3 value increases even closer to the design value. And finally, the heat source typically is sized 50% larger than the steady-state design heat load, so that it has the ability to bring a cold slab up to temperature without taking forever.
Considering those three factors, I anticipate that your system will perform well without making any changes.