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Old 04-06-2023, 06:20 PM   #1 (permalink)
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Designing a better (Best?) car cooling solution for when parked in the sun

This seems like such a simple concept that it never sat right with me that there aren't any really good solutions out there in the wild that I've seen or been able to find.

EDIT: I know of those cheap window units that are all over the internet, but they're absolute garbage and on top of being poorly manufactured, they're not well designed and not a good solution at all.

My modest proposal:

Use one or two small fans with efficient ducting to draw clean, cool air into the cabin, and exhaust hot air out. Have them run only when a sufficient temperature delta exists between the cabin and outdoors, and remain sealed off the rest of the time to prevent energy loss. Power them using either their own PV circuit, or from the vehicle's 12v system, with a PV and BMS to keep it topped up and prevent over-discharging.

The Materials:
  • 2x high-static-pressure 120mm 12v PWM fans from Noctua
  • 3D printed static turbines, louvers, and ducting (will design parametric library in OpenSCAD
  • MERV12/13 furnace air filter
  • Arduino or similar microcontroller
  • two remote temperature probes/thermistors
  • Some discrete electronics components
  • 5-watt 12-volt dash-top solar panel
  • possibly a clutch of 18650 cells and BMS
  • Drill/hole saw/sawzall

The plan:
  1. Cut hole size of fan on lower bulkhead behind the front seats, install fan to pull air in.
  2. Route ducting in from the underside of the car, with a slim enclosure for a small furnace air filter.
  3. 3d print slim ducting to run from an inlet just below the headliner, down the passenger B pillar, and out the bottom of the car, using another fan.
  4. Install inlet/outlet louvers that only open when the fans are running
  5. use remote temp probes with microcontroller to power the fans on conditionally when the inside temp reads 10 degrees higher than the outside temp, and the vehicle is off and stationary
  6. install solar charger for 12v system (was going to do that anyway...) and low voltage cutoff to fan system, OR, isolated system with 18650 batteries and solar charger/BMS.

Thoughts? ideas? Search didn't turn anything up, but has anyone done something like this before?


Last edited by SimplifyAndAddCoffee; 04-06-2023 at 09:31 PM..
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Old 04-06-2023, 06:42 PM   #2 (permalink)
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I'm sorry to say, but this has already been created.
If I find a link to the product, I'll post back.
Edit : There are several. Search for ' Solar powered cabin exhaust fan for cars '
I think your design is better though.
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Old 04-06-2023, 06:52 PM   #3 (permalink)
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Quote:
Originally Posted by Cd View Post
I'm sorry to say, but this has already been created.
If I find a link to the product, I'll post back.
Edit : There are several. Search for ' Solar powered cabin exhaust fan for cars '
I think your design is better though.
If you're referring to those window-mount units, they're absolute garbage and not worth the time or effort.
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Old 04-06-2023, 07:13 PM   #4 (permalink)
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Quote:
Thoughts? ideas?
What car? Why the underbody. A wheelwell might be more convenient.
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Old 04-06-2023, 09:27 PM   #5 (permalink)
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Quote:
Originally Posted by freebeard View Post
What car? Why the underbody. A wheelwell might be more convenient.
gen 1 insight,

Wheel well might work yes. Might be more prone to getting full of dirt though.

I need to get the car on a proper lift before I can really plan out exactly where it will go.
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Old 04-07-2023, 10:12 PM   #6 (permalink)
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You could use the existing HVAC blower, unless your "2x high-static-pressure 120mm 12v PWM fans from Noctua" are more efficient. Like most (all?) cars, the Insight has cabin air exit vents in the back, inside the rear bumper. They have rubber flaps to keep air (and exhaust) from going in, but open easily to let air out. Bring fresh air in, and the hot air will find its own way out.

For control, I would just have it come on when the interior temp is above whatever temp you want to avoid, with a low-voltage cutoff to protect whatever is powering it. Or if you had enough solar power to run it, you could just let it do its thing anytime there's enough sun.

I have a trio of Insights, so I'll give this more thought. It's something I've always wanted, but never got around to doing it. I'm not sure what is the best air inlet spot if not using the HVAC blower. I wouldn't want the inlet near the fuel tank, engine, or exhaust. The spare tire well is easy and accessible.
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Old 09-09-2023, 05:52 PM   #7 (permalink)
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Haven't scientists discovered that if you make a material that is reflective in visible and ultraviolet light yet dark in the infrared spectrum it will reflect the sun's light and radiate heat at the same time making it possible to be several degrees cooler than ambient temperatures? If you could paint the car with such a color and then make folding up sheets to go on all the glass possible, then you could have a cooler than ambient air temperature car sitting in direct sunlight.
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Old 09-09-2023, 06:35 PM   #8 (permalink)
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Quote:
Haven't scientists discovered that if you make a material that is reflective in visible and ultraviolet light yet dark in the infrared spectrum it will reflect the sun's light and radiate heat at the same time making it possible to be several degrees cooler than ambient temperatures?
No. It's a frequency band in IR that is dependent on the atmospheric gases opacity or reflectance or something.
Quote:
https://en.wikipedia.org › wiki › Atmospheric_window
Atmospheric window - Wikipedia
An atmospheric window is a range of wavelengths of the electromagnetic spectrum that can pass through Earth's atmosphere. Learn about the role of atmospheric windows in astronomy, remote sensing, telecommunications and other science and technology applications.
Currently, the coating is much thicker than paint and difficult to seal against the environment.
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Old 09-10-2023, 12:23 AM   #9 (permalink)
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Old 09-10-2023, 01:59 AM   #10 (permalink)
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They that do:

Air Conditioning isn't free... but we're close.

Making Infrared Cooling Paint From Grocery Store Items (w/Novel CaCO₃ Microsphere Synthesis)

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