Note: The information contained in this periodical weblog may be outdated. This was my personal weblog published before January 1, 2015. Since then I have been the co-owner and Principal Solar Designer at Florida Solar Design Group.

How Flow Rate, Pressure, and Energy are Affected by Solar Pool Heating

There is a common misconception that solar pool heating increases the energy needed to operate a pump. That is NOT true!

It’s true that solar pool heating systems will increase the back pressure on your pump. On a single speed pump, that means your flow rate will be reduced. However, it also means that your energy consumption will be reduced. Without having a degree in fluid dynamics, you make be wondering how a pump can use less energy if the pressure is increased! The short answer is that the pump is doing LESS work – it’s moving less water.

This is a simplistic explanation of how a pumps energy requirements relate to the flow rate and system pressure, but suffice it to say that at a constant pump speed, less flow means less energy consumed.

Here is a little video I put together to show a real system in action.

Now, since you are reducing the flow rate with solar pool heating on, you would need to run your pump for a longer period of time to achieve the same turnover/filtration of your pool water. The net result would be no energy savings or loss for the same turnover each day.

 

 

2 Comments

  1. Hi
    I would like to ask in the winter months, I use the pool solar panels to heat the hot tub. Since the winter months have less sun and ambient temp is less
    Is there a possibility that if the flow rate was slowed down the collectors may be quicker to heat?
    I just recently purchased a variable speed pump and maybe use the slower pump motor cycle to collect more heat?
    Thanks for your time.
    Pete

  2. Author

    Peter,

    I wrote a post on this very subject a few months ago. It’s a common misconception. See:
    http://www.solarsouthwestflorida.com/solar-pool-heater-optimum-flow-rate/

    Unfortunately, your concept of decreasing the flow rate is exactly opposite of what we want to see happen. As water gets heated in a solar pool heated panel, the efficiency of the panel (the ability to transfer heat to the water) decreases. What results in the best efficiency is a large relative difference from the panel surface temperature and the water temperature. That means colder water in the panel makes it more efficient, and that is achieved with a higher flow rate (to an extent).

    The manufacturer recommended flow rate for maximum annual yield is 4 gallons per minute per panel. Most manufacturers’ panels fall into a similar flow rate range.

    Good question – and thanks for asking!

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