For those “Home Brew”, DIY pool automation types that are using Raspberry Pi micro-computers in their Swimming Pool Outdoor Control Panels (OCP) or in Swimming Pool Automation Enclosures or you are planning to in the future.
The following brand-new information may be of some use if Raspberry Pi cooling fans are of any interest or importance to you.
Looks like Sequent Micro-Systems is introducing a “smart” fan hat for the Raspberry Pi’s.
Definitely looks like it has some nice features.
Its own tiny 32-bit processor receives commands from Raspberry Pi through the I2C interface. A step-up power supply converts the 5 Volts provided by Raspberry Pi to 12 Volts, ensuring precise speed control. Using pulse width modulation, it powers the fan just enough to maintain a constant temperature of the Raspberry Pi processor.
More than one smart fan can be used within an automation stack.
The Smart Fan has its own command system, which can be downloaded from GitHub. You can control it from any program using the built-in command line system or from a Python script. A Node Red interface lets you set the processor temperature from the browser. The Smart Fan will implement a PID loop and adjust the fan's speed to keep the processor temperature you specified.

Additional information can be found in the links below.
sequentmicrosystems.com
Or can be pre-ordered it looks like for $5.00 less at the link below.
www.kickstarter.com
r.
The following brand-new information may be of some use if Raspberry Pi cooling fans are of any interest or importance to you.

Looks like Sequent Micro-Systems is introducing a “smart” fan hat for the Raspberry Pi’s.
Definitely looks like it has some nice features.
Its own tiny 32-bit processor receives commands from Raspberry Pi through the I2C interface. A step-up power supply converts the 5 Volts provided by Raspberry Pi to 12 Volts, ensuring precise speed control. Using pulse width modulation, it powers the fan just enough to maintain a constant temperature of the Raspberry Pi processor.
More than one smart fan can be used within an automation stack.
The Smart Fan has its own command system, which can be downloaded from GitHub. You can control it from any program using the built-in command line system or from a Python script. A Node Red interface lets you set the processor temperature from the browser. The Smart Fan will implement a PID loop and adjust the fan's speed to keep the processor temperature you specified.

Additional information can be found in the links below.

Smart Fan HAT: the best cooling solution for Raspberry Pi
The smart fan cooling for Raspberry Pi gives you full use of the GPIO pins. Stack your HATs on top of Pi and keep constant temperature

Or can be pre-ordered it looks like for $5.00 less at the link below.
Smart Fan: Ideal cooling solution for Raspberry Pi
Better than a heat sink, and allowing unlimited add-on cards, the Smart Fan will keep your Raspberry Pi running when things get hot.