Occasionally we get a call from a client that says the solar heated water coming out of their pool jets does not feel very hot. Our response is pretty simple: “Good!”
It’s not that we are being dismissive. If you feel a large temperature difference in the heated water coming from the solar panels, that usually means the flow rate is too low. The best way to heat a pool is a large amount of water heated a small amount each pass through the solar panels.
It’s all about flow rate!
A typical solar panel holds under 4 gallons of water and the optimum flow rate is over 4 gallons per minute. That means water molecules in the solar panel have less than 60 seconds to heat up. You shouldn’t expect it to get much warmer than the pool water that enters them.
And that’s a good thing.
The reason is that solar panels perform best when there is a large difference in the surface temperature and the water temperature inside. This is called Delta T, or the difference in temperature. Heat us transferred more quickly when there is a bigger difference. If you allow water to move slowly through the solar panels it get’s hotter, but the solar panel’s ability to transfer heat to the water diminishes quickly.
Don’t Slow Down Your Flow Rate!
We have seen people slow down their flow rate by closing off valves or reducing variable speed pump speeds. It may seem counterintuitive, but that strategy is counterproductive!
Flow x Temperature Rise = BTUs Delivered
What we want to do is deliver maximum BTUs (British Thermal Units) to the water. You can do that by increasing temperature rise or flow. As we mentioned previously, temperature rise is greater when flow is greater. So you deliver more total BTUs when you increase the flow rate!
Since all we want to do is deliver the most heat, you should focus on increasing flow and not worry so much about the temperature of the water coming out of the jets. It will take time, but solar panels will heat your pool more efficiently this way.