Solar system question

[AZAA]

(I composed this post earlier but I can't find it, so sorry if this is a double post)
I mentioned being very grateful for the help I've received here and look forward to the day when I can help others.
Anyway...I have an 8 section (about 26' total) Solocol solar heater for my small 5850 gallon pool. I just replaced my pump with a new TriStar VS 900. There is an automatic valve that diverts water thru the system based on the available sunshine, and the pump changes speed when this occurs. I'm new to all this and have been unsure of the pump speed required to get the most out of my solar heater. I don't know how to figure how many GPM the pump pushes at any given speed or if that is even a valuable statistic. How can the optimum speed be determined to get the maximum benefit? Is pushing a lot of water quickly thru the tubes better, or is a slower "trickle" better for heating up the water? Thanks (again) in advance.

 

[CRUSH-IT!]

if you have an infrared thermometer like for checking temp of an ac register or manifold on a car then put some shade on a portion of your inflow and outflow pipes for the solar and get the temp. (so you get water temp not sunbaked pipe temp.) this will tell you how much the water temp changes each time it goes through. "generally" the smaller the difference the more efficient the panel absorption. One can get really carried away with this because more flow gives less difference (delta t) and costs more electricity. On a hot day here in florida I am doing just fine with a temperature difference less than ten or so degrees. I hope that this is helpful.

 

[CRUSH-IT!]

You don't want your water coming down at 120 degrees.

 

[AZAA]

Thanks! Where am I sampling water from with this IR thermometer? I would think the water passing thru the pipes would be moving too fast for the sun to have an effect on the water within. Perhaps the sun is having an effect on the thermometers themselves? The 10 degrees you mention; is that the difference between the inflow and outflow pipes? If 10 is good why isn't 20 better (assuming it not higher than your 120 maximum)? I guess my question is; this time of year the return water is about 80 degrees. Not enough to raise the pool to the 85 degrees I prefer. Is there anything I can do with pump speed to increase that return temp?

 

[jimmythegreek]

Theres a balance of speed and gain. Most panels want 5 to 7.5 gpm and even up to 10. There are charts for flow that account for pipe size amd panel sizes. Alot of solar powered pools have single speed pumps amd they work fine. In the end it's almost the same if you are in the flow range. Warmer water slower into the pool is about the same as not as warm mixing the pool temo water faster. Same btus in the end really. When the sun is low slower is better as you will get higher temps. Maybe not enough for this time of year. Regardless you need enough flow to shut the PRV so that is a minimum threshold.

 

[CRUSH-IT!]

I agree with all of the above. if the flow through the panels is in range then you are fine. in theory the faster the flow through the panel the more efficient they work. In practice however if your flow is adequate you gain almost nothing by doubling it. You are at the point of limited returns. Almost without exception, the cooler your water returns the more efficient your panels are working. What matters is not the temp difference between the water coming down and your desired temp. what matters is the difference between your intake temp and solar return temp. If it is goin up it its heating. If you slow flow too much you may get uneven perfusion of your panels. You will heat your pool to 85 faster with 80 degree return water than with 90 degree water. This may seem counter intuitive. If your water comes down at 90 you are super heating a very small flow. You are better off heating more flow to a lesser degree. if you have enough sun you will get there. Don't forget bubble wrap does a helluvalot if the air is cold. most heat loss is evaporative.

Are your panels plumbed according to manufacturers diagram?

Is the flow in manufacturers range?

Pray for sun.

I hope this is helpful

 

[AZAA]

Thank you both very much. It is indeed counterintuitive that less warm water will heat the pool faster than warmer water but I have no problem accepting this from you both.
I'm probably pumping an adequate amount of water for the system to work efficiently. I'm new to this whole pool thing and was probably overthinking it. Again, thank you both for taking the time to help me.

 

[jimmythegreek]

Dont forget a solar cover on the pool. Without it you will lose as you gain

 

[AZAA]

Yep, thanks. It's on every night and a lot of the days during the cooler months.