## Poolside Chat Episode #38: Swimming Pool Solar Panel Flow Rates

This is Poolside Chat where every week we answer your questions on how to fix and maintain your swimming pool. Poolside Chat is presented by INYOPools.com, helping pool owners find the right parts since 2001. In today’s episode of Poolside Chat, Rob and Matt tackle another common swimming pool question:
• Can a variable speed pump operate a pool solar heater?

Can I run my variable speed pump on low speed while operating solar panels?

Inyo Forum

Each solar panel requires a water flow rate of three to five gallons per minute. So let’s say we average that out to four and you have eight panels. Multiply eight by four– 32 gallons per minute. So if your variable speed is producing 32 gallons per minute on low, you’re good. If not, you have to kick it up a little bit.

Yes and if you don’t know what your variable speed is putting out, you’ll probably want to put on a flow meter. You can either get a digital one or a little analog one, it has a little bead that floats, it tells you how much water is being put out. And you want to make sure that you put it after your solar panels so it’s an accurate reading.

## 9 thoughts on “Poolside Chat Episode #38: Swimming Pool Solar Panel Flow Rates”

1. Ron T. In PA says:

I have 1000 lineal feet of 5/8” black pipe coiled between a new steel roof and roof sheathing. I purchased a psi booster pump. Now basically my pool is my well. The new pump is self priming. It takes water from the pool to the 1000’ of pipe. This pump can boost psi 5 to 100 psi. I am trying to figure out if I should run pump entire time the sun is shining or force the water out quickly and let it recover, then repeat. Run constantly or intermittently. The 1000’ of pipe basically holds 38 gallons of water. I can set pump to empty that in about 2 minutes. If I shut down for 45 minutes the temperature raises roughly 12-14 degrees. Pushing 1 gallon per minute I gain 3-7 degrees. 3 gallons per minute I gain 2-5 degrees. Here’s my question, run constantly or periodically to get most heat increase. Somebody smarter than me has to figure this out.

2. Alan C says:

Where would the flow meter be installed? I would it would be after water is returned from panels and before entering pool returns? I have a Blue White F200 meter
Thanks
Alan C

1. I usually like to install mine right after the filter, so I can see any drops in flow rate being caused by a dirty filter media. Unless the instructions say specifically otherwise, you can place it on the main return.

3. WhyMeLord says:

Flow rate does effect heat transfer.

The best way to know is to measure the delta T temp (water out temp minus water temp in.) Optimum pump flow rate for greatest heat transfer is the biggest delta T number at the highest speed.

In theory one can (somewhat) control the end temperature by adjusting the pump speed.

1. Alan says:

Being practical, I would start the pump at the lowest RPM which will push water through the panels and measure the output temperature. That would be your maximum achievable temperature as the water has spent the most time in the panels possible.

I would then increase the pump RPM until the output temperature starts to drop. That would be the minimum time the water needs to stay in the pump to reach the maximum temperature. Or another way to say it, the maximum temperature at the maximum flow. And voila, done.

Then the question then becomes whether the flow is dependent on the temperature differential. i.e. hot days.

Now turn down the pump until it stops screaming at your neighbors. 😉

Alan

4. Paul says:

So, I’ve thought about this, and I guess my follow-up question is: What’s the harm of running the solar panels with too little flow? It seems like it will just cause the water to not change temperature as much or as quickly as it would if the flow rate were high enough.

In fact, I wonder if flow rate really affects the energy transfer that much… Clearly a very low flow rate will not transfer much energy (heat). Intuitively a very high flow rate will also not support much energy transfer. But I’d think a rather broad range of flow rates would have a relatively effective energy transfer.

Or am I just way off base?

1. Ron from the frozen North (Winnipeg) says:

The flow rate is nothing to be worried about. The slower the flow, the hotter the water. If the flow rate is too high, the water does not have a chance to warm up.
I use a very high tech system to establish the proper flow rate. I feel the return pipe from the solar panel grid.
If it’s too cold, I slow the flow , If its too hot I open up the flow.

2. Mike Claffy says:

Sounds right to me!

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