I am working on a HVAC project where lizard in going inside the electrical unit and causing wire damage and short circuit. I need to find some solution to detect or repel lizard before any catastrophic situation. Since lizard are cold blooded species, I cannot use IR head index measurement methods or PIR sensor. Also, lizard are very small creature so method need to be foolproof.

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    $\begingroup$ An obvious "low-tech" answer would be something like wire mesh to prevent the lizards getting in, but maybe I'm missing something here... $\endgroup$ – alephzero Jun 5 '18 at 9:43
  • $\begingroup$ Would this be better on the Biology SE? Seems to be more about Lizards, thhan HVAC systems? $\endgroup$ – Jonathan R Swift Jun 5 '18 at 9:53
  • $\begingroup$ It's difficult to make something foolproof as fools are so ingenious... $\endgroup$ – Solar Mike Jun 5 '18 at 10:08
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    $\begingroup$ cold-blooded animals still have temperature gradients. Further, are you implying it's acceptable for warm-blooded animals to invade your space? $\endgroup$ – Carl Witthoft Jun 5 '18 at 17:48

A camera with provided lighting (IR is okay) within the duct (area where no stray moving objects should appear) would be perfectly okay for detection. Lizards aren't invisible. Now, stopping the lizards might be trickier.

I think though, that the best approach would be to make the intakes/exhausts to face downwards and grease the walls - or include a T-shape section, with a service hatch on the short downwards facing segment, thoroughly greased. Detection no longer required.

  • $\begingroup$ Looks like a better idea, need to see if it is possible in practical situation. $\endgroup$ – Prasan Dutt Jun 5 '18 at 11:05
  • $\begingroup$ You should add more detail on the setup to be protected. It's different when it's a device within building with pipe/duct access, different if it's an outdoor cabinet, or if it's an open standalone device. $\endgroup$ – SF. Jun 5 '18 at 11:13
  • $\begingroup$ Greasing the intake seems like it would only work for a limited time before dirt and other stuff got in the grease and you probably don’t really want that in your outside air intake. As for the downward opening, that makes sense and what is preventing the use of a standard bird screen (or insect screen if the lizards are very small)? $\endgroup$ – Secundus Dec 2 '18 at 19:38
  • $\begingroup$ @Secundus: The grime won't be a problem as long as the surface remains something the lizard can't reliably climb. Some (geckos) have fantastically adhesive pawpads, but all the adhesion in the world won't help if the surface beneath doesn't have enough cohesion. The problem with insect screen is that dust (esp. fibrous) accumulating will obstruct the air flow. $\endgroup$ – SF. Dec 3 '18 at 6:57
  • $\begingroup$ You don't have to go with a fine mesh screen like a normal insect screen; you just need to make sure the screen is small enough to keep out the lizards. For what it's worth, having a very low velocity at the screen (larger duct where screen is than the rest of the intake) will minimize the amount of fibrous particles that stick to the screen. If the lizards are that big of a problem, having the screen cleaned once a year or so as a maintenance item beats replacing equipment. $\endgroup$ – Secundus Dec 10 '18 at 16:13

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