So after some trial and err, I put this next system together.
It is very basic. It works on two physical principles that is amlost common sense : Capillary Effect and Evaporation.
Here's how : place a container under the hamster's Outhouse. Fill the container with some amount of water (but not flooding into the outhouse). Place a cloth over the outhouse and let the cloth half immersed in the tub of water. Dress the cloth nicely so that the outhouse is not totally sealed, leave some air gap for air circulation.
Picture 1 showed the outhouse with the setup. The outhouse is attached to the right side of the CT2 cage.
Picture 2 showed a closer look of the Outhouse with the cloth covered.
Picture 3 here reveal the Outhouse underneath the cloth. You can faintly see hammy tugs inside the outhouse.
Picture 4 showed the ambient air temperature. Again a high 32 degree Celcius (almost 90F).
Picture 5 showed the temperature on the surface of the outhouse under the wet cloth. A comfortable 28 degree Celcius (82 F).
How it works ? Firstly, the water in the tub travel up the cloth due to capillary effect. The cloth would be moisted by itself as long as there is water in the tub. Then as the water in the cloth slowly evaporates, the evaporation draws heat away from the cloth surface which in terms carry away the heat of the outhouse and the hammy got a pleasant stay within.
The beauty of this system is totally energy-free ! The hot weather actually provide the energy for cooling.
Updates :
Now, as nothing is perfect, this system still generate some amount of condensation (dews) under the out-house cover.
I tired a few variations of this system. The following seems to give a better result with no dews form in the outhouse and yet cooling enough (it passes the hammy's "cooling factor test" - which is measured as the duration that a hamster willing to sleep within the "cool-spot".)
Well, after all three attempts, why not carry on exploring other ways?
You bet ! So here's Take 4 - Bring in the Burner