Pool Hydraulics-Solar heating. I want to do the right way first.

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math question. I have 50' of 2" poly heading up to my roof (12'). The plan is to have a manifold to branch 6 1/2" (.6"id) poly pipe each 500' long. Then back to a manifold, back 50' through the 2" poly. The total id of the 6 poly pipes is 3.6". I understand that there is loss from friction because of the increased interior surface area... What are your thoughts on this setup? Thanks!
 
Smaller diameter results higher head loss. Larger diameter results lower head loss.

Yes, the larger pipe has more surface area but because it is a larger diameter, the same GPM results in lower water velocity which in turn reduces head loss. Also since head loss is proportional to the water velocity squared, head loss is actually inversely proportional to pipe diameter^4. Double the diameter and the head loss goes down by a factor of 16.
 
mas985 said:
Smaller diameter results higher head loss. Larger diameter results lower head loss.

Yes, the larger pipe has more surface area but because it is a larger diameter, the same GPM results in lower water velocity which in turn reduces head loss. Also since head loss is proportional to the water velocity squared, head loss is actually inversely proportional to pipe diameter^4. Double the diameter and the head loss goes down by a factor of 16.
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Holy! I read that a few times and cant fully wrap my head around it. Is the answer, yes 6-1/2" pipes would be OK because water velocity would be reduced because of the larger collective diameter of the pipes? In school I counted 9 fingers. 0, 1, 2, 3...9. What do you mean you don't count zero?
 
I found a dramatic error in the math I have done. a 2" id pipe has a surface area of 3.14sq''. the surface area od a 1/2" pipe .6''id is .28sq". I would need just over 11 1/2" pipes to not create a bottle neck. I am going to use six 250' 1/2" pipes in parallel for each collector. 2 collectors. I also figured out a cheapish way to automate the valve to turn on and off the flow to the solar heater. Stay tuned. Thanks!
 

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Air locks generally do not happen with pumps and plumbing. However, you can get situations where the panels will not prime properly (complete air evacuation) without enough flow rate. And if the head loss in the plumbing is too high, then the flow rate may not be sufficient for priming.
 
I'm planning on using municipal water supply to prime the system at the start of each season.
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Are you sure you want do it that way? It is far easier to prime the panels with the pool pump. But does that mean that the panels are not self draining? Given your climate, I would think self draining would be far easier and safer.
 
mas985 said:
Are you sure you want do it that way? It is far easier to prime the panels with the pool pump. But does that mean that the panels are not self draining? Given your climate, I would think self draining would be far easier and safer.
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I'm planning on 2 collectors each with 200' x 6 of poly pipe round and round. I have no idea how I could make that self draining. A disadvantage I see is if the collectors drain every time the pump is off the pump would need to prime them. I am planning on blowing them out at the end of the season when the pool gets closed. I figure it'll take all day to winterize pool and outdoor sprinklers. Does anyone know how to make a poly coil self draining? Thoughts?
 
I have been using black poly coils for the last three years.
Basically just blow as much water out as I can, the pipe can take a bit of stress, but 90% of the water out there is lots of room for the ice to expand, have yet to have troubles with freeze up out here in the west, Alberta.
When I first started out I used a small Intex pump to circ, my panels are on the ground so head pressure wasn't a big deal, I also used to run a check valve to prevent them from draining. Since I have gone to a 2500 gph 3/4 hp pump dedicated to my heating circuit I haven't worried about the panels draining back as the pump just pushes the air out when it starts up.
Next year I plan on adding more coils and running a large header to feed all my coils individually, coil length will be around 100', each coil will have an isolation valve on the feed. Then to balance the system I will buy a temp sensing device/gun for about 50$, then adjust the valves so I get even output temps on the pipe, just in case anything decides to take a short circuit on me.
The last few years I have been using an old heat/cool thermostat mounted inside the enclosure I have my coils running in, this controls the operation via a 24 volt transformer and 24 volt valve. Having two heating circuits one solar and another a heat exchanger my "heating" pump runs whenever my filtering pump 1 hp doesn't, so I cycle the solar with a t stat and the heat exchanger circ pump with a timer.
One important thing I did learn here and poolside this year is sq footage is very important, my coils/exchanger worked good on my 16' pool last year not so good this year with a 24' pool, more square footage to come next year.
 
scottpanek said:
I'm planning on 2 collectors each with 200' x 6 of poly pipe round and round. I have no idea how I could make that self draining. A disadvantage I see is if the collectors drain every time the pump is off the pump would need to prime them. I am planning on blowing them out at the end of the season when the pool gets closed. I figure it'll take all day to winterize pool and outdoor sprinklers. Does anyone know how to make a poly coil self draining? Thoughts?
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Ok, I understand now. In that situation, I would probably do the same.
 
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