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Post by matt3552 on Nov 25, 2010 9:53:07 GMT -6
I'm heating a 1150 sq. ft. slab on grade new cabin in Minnesota. Its insulated very well. I'm using a Takagi jr boiler, 1'' manifolds with five 265' loops. I am wondering how many gpm I should have in each loop?
thanks, matt
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Post by Christopher on Nov 29, 2010 9:59:26 GMT -6
Matt,
I'm not sure. Did anyone do a heat loss or a radiant design for you? That would tell you what the gpm for each zone would be. Without working up a full design and allowing our software to calculate it, I would have no idea.
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Post by matt3552 on Dec 24, 2010 10:23:34 GMT -6
Yes, I had one done but they figured it out for 7/8 pex and I am using 1/2" They came up with 34500 btu's/hr with tubing output of 50000
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Post by Watts Radiant on Dec 28, 2010 10:00:20 GMT -6
Yes, I had one done but they figured it out for 7/8 pex and I am using 1/2" They came up with 34500 btu's/hr with tubing output of 50000 Hey Matt- You can use the following formula to figure out GPMs as needed: GPM = BTU / (500 x ΔT) In this case, assuming you designed for a 20 degree delta T: GPM = 50,000 / (500 x 20) = 5GPM Now that's the GPM for the entire zone, so if you have 5 circuits, then that would be 1GPM for each circuit. As a side note, the GPM required for the zone is not dependent on the type of tubing or manifold, it's only dependent on the design. However, to figure out your pump specs (pressure drop), you do need to know the type of tubing, circuit length, and GPM requirements. -MDR |
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Post by matt3552 on Dec 29, 2010 7:45:42 GMT -6
Thank you very much for the info.
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Post by matt3552 on Nov 20, 2011 11:06:19 GMT -6
I got my system running for my cabin and it seems to be working well. Here is what i ended up installing: a 120a quietside boiler, a 15-58 grunfos 3 speed pump on high, five 270' loops 10" spaced with a watts five branch manifold. It is closed loop series piped in 3/4. I think I messed up though. I installed the pump on the supply side of the boiler in between the expansion tank and the boiler. When the pump comes on, the pressure gauge (in between the pump and boiler) drops 7 psi. Is this normal or should I move the pump on the other side of the tank? I am running 5/8 gpm through each loop 95deg. leaving and 74 coming back.
thanks matt3552
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Post by Christopher on Nov 21, 2011 11:29:31 GMT -6
You will want to have your pump on the supply side of the boiler, but it needs to be on the other side of the expansion tank.
What is happening, basically, is that the point where the expansion tank connects is called the point of no pressure change. The pressure cannot change there. Since your pump is pointing right at that, and it can't change that pressure, it ends up dropping pressure on the other side to make the water circulate. This could cause air to get sucked into the system, and then your pump will cavitate.
Once your pump is on the other side of the expansion tank, it can then properly raise the pressure upward on that side, since it's no longer pushing at the point of no pressure change.
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Post by matt3552 on Nov 21, 2011 18:55:58 GMT -6
Thanks for the info, I will move the pump to the other side of the expansion tank
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Post by matt3552 on Jan 27, 2012 6:54:30 GMT -6
System is running and heating pretty good. I think I might try a different pump to get my gpm a little higher. I might go to a grundfos ups26-99 on medium speed. I got 5/8 gpm per loop right now and would like to get between 3/4 and 7/8. I got my first couple of nat. gas bills and I am pretty happy with the price.
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