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Old 10-09-12, 12:07 PM   #1
Daox
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Default Low head loss hydronic floor heating

We have an excellent thread on DIY hydronic floor heating here. Admittedly I haven't read all of it, but there is tons of good information in there.

One topic I haven't seen come up in the discussion much is minimizing head loss in a hydronic system. I'm curious why low head loss hydronic heating isn't a larger topic. I realize that hydronics requires much less energy to move its heat around vs a conventional gas furnace, but it seems like it can be further optimized. I see many images of people heating a room with a single loop of 1/2" pex as illustrated below:




However, if one were to route the plumbing in many parallel lines, the head loss would be significantly reduced.





In a properly designed system, the two hydronic floors would both recieve the same flow rate, same thermal transfer and heating abililty. However, the second floor would require a substancially smaller pump to achieve the same flow rate. This means less electricity consumed and more efficient operation.

I think that the only downside here would be all the tees and connections you'd need to make within the floor.


Lets take a look at an example to see what kind of gains could be made. In this example, we'll look at putting hydronic heating into a 10'x10' room.

With a single run of 1/2" pex with 6" spacing, this would require about 170 feet of pex. At a flow rate of 1 gpm (total guess, sorry, I haven't done any calculations for hydronic floor flow rates yet, it might be too high or too low), we'll have a pressure head of 6.6 inches of water.

With a parallel setup of 1/2" pex with 6" spacing, this would also require 170 feet of pex. However, now we have a 1/2" headers on each end of the room and 18 parallel run lines of 1/2" pex. We would like to keep that 1 gpm flow rate. This means we have 1 gpm through the headers, and .055 gpm through each parallel line. The pressure head of this system turns out to be .39 inches of water for the 9 or so feet of header tubing. Pressure head for the parallel lines is a bit more tricky because the flow rate is so low (1gpm / 18 lines = .055 gpm). I haven't been able to find any head loss charts that go anywhere near this low. However, I took the 1 gpm rating and divided it by 18 to get a rough idea (actual head loss will be lower) which gives us .23 for the parallel lines. You then add these together for a whopping .62 inches of water.

.62 inches of water vs 6.6 inches of water to do the exact same thing to the exact same room. Add in a bunch of tees and crimp/cinch clamps.

Besides having trouble finding a pump small enough to give us the required flow rate at this rediculously low pressure head, does anyone else see any major problems? Ideas and thoughts are quite welcome.

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