Need help with DIY pool solar design

[davestew]

The solar heat is plumbed into the pool plumbing. I have not checked the exact temp. of the collector water as there is no simple way to do that. I assume it is fairly hot as the pool is warming up, although it still needs some tweaking, hence why I ordered a flow meter to check flow heading into the collectors.

Dave

[Naptown]

How hot is the water coming out very hot or just a few degrees above the inlet?
Does the return to the pool come out above the water line or does it tie back into the pool returns?

[davestew]

Hello everyone.

Well, my solar heating system is up and running and seems to be working ok. I had to replace my 3/4hp pump, so I put in a Pentair Intelliflo; amazing pump. I am waiting for a flow meter to arrive to I can test the flow into the solar collectors, but in the meantime I have a question. There are no leaks on the roof from any of the connections, unions, etc., but I am getting air bubbles from the return in the pool. Also, I can hear the water gurgling in the hot return pipe on the roof. Any idea why? There is plenty of flow on the cold supply to the roof (you can feel it in the pipe), but have much less flow and gurgling on the hot side. Is that just the way it is after coming out of the coil collectors?

Any ideas?

Thanks,
Dave

[LucMan]

Here are some more online calculators that may help.

http://wea-inc.com/calc-frm.htm

[davestew]

Looks like I just found my answer (although he doesn't mention the siphon effect):
"WHAT ABOUT SOLAR SYSTEMS? When a pool has a solar system mounted on the roof, a two speed pump may not be the answer. This is because the rise to the roof creates 10 ft or more of static lift, and that number does not change when you put a pump in low speed and reduce the flow through the system. With a solar system, it is often better to use a smaller single speed pump, such as a 3/4 HP pump that will give you adequate lift at all times."

Hmmm...

[russ]

It is not really a guess but an engineering calculation - try this calculator

Flow DP calculator http://www.pipeflowcalculations.com/pressuredrop/

[Naptown]

Once the system is filled and purged the head will go down due to the siphoning effect. How far down is anyone's guess and if the pump has enough power to pump on low speed this will reduce head even further. Now controlling the pump will take some thought.

[davestew]

Read the information at the URLs I provided for you for starters.

I have read that information. In fact, the one site is where I got the info. to base my design. Nowhere have I been able to find more specific information on two speed pumps. Basically, I need to know if the siphon effect of the water coming off the roof will cancel the total head of the water being pumped on the roof, so I can see if low speed on a two speed pump would be sufficient (based on the pumps performace curves) to circ. the water through the system. I understand that the total head of the rest of the system (pipe friction, collectors, fittings, etc.) would have to be overcome by the pump on either low or high speed.

[Naptown]

Sorry I saw where you were after I posted.

[davestew]

Why would I be replacing the collectors, because I don't have a vacuum break? In any case, it doesn't freeze here. January temps average around 25c/13c high/low (77F/56F), and the sun is still pretty hot during the day.

[russ]

Read the information at the URLs I provided for you for starters.

[Naptown]

dynamic head would be lower in 3/4 and there will be some siphoning effect to the collector. I hope it does not freeze there or you will be removing or replacing your collectors every year.

[davestew]

Thanks for all the info. I just have one more question regarding the pump. I am thinking of upgrading the pump to a two speed pump to save energy. Once the water is flowing through the system and collectors on the roof, would the low speed on a two speed pump be sufficient to circulate the water given the siphon effect of the water coming back down? It would be great if I could run the pump longer (to produce chlorine through my salt generator) and still have an efficient flow through the solar collectors all while saving energy....

Also, I've a lot of the coil type collectors use 1/2" polypropylene pipe. Do you think it's better to use 1/2" or 3/4" for flow, heat gain, etc.?

Thanks,
Dave

[russ]

If the total flow is 25 gpm then you need to consider two separate sections -

1) For the coils (5 each) you would use 5 gpm

2) For the common piping you would use the 25 gpm

You will probably have to balance the flow using valves - add the drop across these into the calculation.

[Naptown]

use one collector