I didn't want to derail a previous thread, so I started this one.
I said:
"What I did (and don't recommend) is long loops.
The reason pros
push parallel loops, is splitting your flow down parallel loops reduces
fluid velocity in each loop. Reduced velocity results in less pumping
resistance."
and joe.ami said:
"Understand there is more than one way to skin
this cat. Tubulent flow helps extract btu's with less loop in the
ground, but if you have enough loop you can reduce velocity and collect
adequate btu's with laminar flow. That would offset much of the pump
expense created by extra long loops."
Now, I'm no expert, and I've seen this come up before, so I wanted to make sure I understand this. For simplicity, I will only use the heating cycle for description. The theory is that if the coolant moves fast enough, it will be more turbulent in flowing down the pipe. That this will cause the loop to be more efficient, as the temperature of the coolant will be more even in cross section, thus gaining more BTU's per inch of pipe, than a slower speed run, where friction on pipe walls would cause the fluid in the center to move faster than the fluid on the edge. This would result in a temperature gradient within the pipe cross section. Have I got this right?
The worst conductor in the ground loop is the plastic pipe, so anything that increases the temperature differential on each side of that insulating barrier is a good thing for our purposes. Let's throw some numbers out there.
Head loss is from: http://www.engineeringtoolbox.com/pressure-loss-plastic-pipes-d_404.html
If our GSHP calls for 8 GPM (number chosen for simplicity of working the chart)
If this all goes down one 1600' 3/4" loop, that is 9 GPM. Head loss is 201.6 feet.
If it splits between 2-800' 3/4" loops, at 4 GPM, head loss is 56 feet
If it splits between 4-400' 3/4" loops at 2 GPM head loss is 16 feet.
Increasing pipe size changes the numbers entirely, use the chart.
This is just the head loss of the loops, not including any header, bends, antifreeze type or other loss that links to the total pumping power needed.
A quick Googling shows:
http://www.geo-flo.com/downloads/Magna_benefits_flyer.pdf for an optimized comparison of pumping cost. Optimized for their purposes, of course.
http://ca.grundfos.com/content/dam/GCA/Data%20Sheets/Small%20UP/UP_26-99_F_BFC_0311.pdf a flow/head chart for a UP 26-99 pump.
http://ca.grundfos.com/content/dam/GCA/Data%20Sheets/Small%20UP/UP_26-116_F_BF_0311.pdf
An ideal loop field would only use 1 tiny pump to achieve all the flow necessary. A 26-99 pump is the smallest I'm aware of, in regular use. So our example above would use 1 26-99 pump for 4-400' loops, 2 26-116 pumps for 2-800' loops, and a pumper truck from the local fire dept for the single loop (slight exaggeration
). Again, this is just the loops, and disregards other head loss.
That's my pie in the sky ideal scenario. In the real world, ground loops are pricey, land is not always available, and we all have to make tradeoffs. Raising fluid speeds makes the loops more efficient per foot. How much more efficient? Is there an online calculator?
I'm new here, and not trying to call anyone out. I'm just a geek trying to make sure I understand this. I also want to clarify concepts and the basis for calculations for the folks who are doing their due diligence before choosing a system/installer. The more we know, the better our decisions.