<a href=showthread.php?s=&postid=7296137#post7296137 target=_blank>Originally posted</a> by BigSkyBart
. Has anyone given an thoughts to the best circulator pump for this system? I would think that a pump designed for radiant heated flooring applications would be appropriate.
I think you are right Bart. The circulators for radiant heating are good little pumps and tend to run and run and run. There is one small issue that we should consider; plastic (type) tubing does not usually come with an oxygen barrier, to get it costs a little more. I am fairly certain the stuff in your home flooring has it. Without it there is a good chance that oxygen will permeate the tube wall and this would require the use of a bronze or stainless impeller.
Now with a salt water pump, you will pay more but they have plastic impellers, well everyone here knows that. I'm the rookie.
Pump selection . . . HP = GPM X Head (ft)/3960 X Efficiency. For a closed loop system head is calculated by the pressure drop per 100' of pipe. So if the PD was 3.5 PSI/100 feet of pipe you would convert PSI to feet of head at 2.31 feet for 1 PSI. You would need to add a few feet for valves (if any).
So if 3/4" pipe were used you would run say 4 GPM at a velocity of 3 FPS which is enough by far. This equates to 3.5 PSI/100 ft.
(Did I already do this or was I just thinking about it? Man I am tired)
H2OENG on a WAG I would agree with your 400 to 600 feet of pipe per ton. But we should check it.
Thermal conductivity is listed as Btu/h*ft*DegF.
Aluminum = 128, Cardboard (just for fun) = 0.04, Copper = 160, PEX = 0.219 (ouch), Aluminized PEX or PEX-AL-PEX (thanks) = 3.12. So per Square foot of surface area or pipe per degree differential you can determine how much piping is needed.
Compare;
3/4" has circumference of about 3" so that's 0.25 FT per LF. Say the water temp is 82 and the Earth is 60, you have a 22 Deg F temp diff. (I know there are variables here but I am tired so please don't yell at me. Please feel free to check and correct my math however)
PEX: 0.219*0.25*22 = 1.2 BTUH per LF If you have 1/2 ton you need 5000 LF
PEX-AL-PEX = 17.16 BTUH /LF so 349 LF
Copper: 880 BTUH/LF so less than 10 feet.
LESS THAN TEN FEET!!!!
hmmmm, copper is looking GOOD. However, I agree with you H2O that the Earth in that short of a space will heat up and not permit the heat to dissipate well enough. So what would happen is you would raise the temp of the Earth around that 10 feet of pipe to nearer the water temp then your transfer would drop off.
Well I got spanked on another thread for being a fan of PEX but looking at these numbers I think I deserved it. My money is now on copper in the ground, PEX where it's exposed and a ti coil in the sump.
PS, I am now very behind in my real work.
