Why does temperature spike when humidity falls to "zero"?

[cassiadawn]

I left my hatching incubator running after my last hatch, and let the humidity tray run dry. Checked it tonight, and the temp in there was reading 114F! Added water back to the pan, and as soon as the humidity started to climb back out of the "low" range, the temperature dropped back down to about 98F.

Can someone explain what is happening here? I have three digital thermometers in there, all read within a couple degrees of each other - none should be giving a "wet bulb" reading. When I've got my humidity tray full of water and it's been closed up long enough to equalize, the hygrometers in there read about 75% and the thermometers are around 98-99F. I can't figure out why the dry, low humidity air temperature is so much higher (because, shouldn't the thermometers be reading the actual temperature regardless of humidity?)

 

[eggbert420]

I would start by checking the thermostat. Temps should not rise to 114º, no matter what the humidity is.

 

[blue eggs and hen]

Hi there! Just happened to stumble across this while I was looking for something else on the internet. I see this is an old thread, but I happen to know the answer, so I joined so I could answer you...

In this case, the humidity pan in the incubator is acting like a swamp cooler. Evaporation causes cooling. So as long as there is water to evaporate, there is a small cooling effect going on.

When the water runs dry, the cooling effect of evaporation stops, and the temperature inside the incubator runs away on you.