I believe it's hot because one of the wall face sunlight during afternoon to evening. Heat trap in the wall will be released at night.

Have ventilation, use a suction fan to suck out hot air. Ventilation fan does not use much electric as air con.

if you have money to invest. The best bet will be an insulator. I got a contractor to build this some time ago.

On the wall that face sun light, they assembled a frame consisting of made of wood laid vertically. aluminium can be use as well. In the empty spaces, heat insulator can be placed. if not leave empty, air also can act as an insulator. Before you put up the wooded / gypsum / artificial concrete. You can have additional heat reflector pasted at the board facing inside to reflect heat.

Last time i did not do both heat reflector / physical insulator. Still the temperature reduce to an acceptable range.

The greenest way. Grow a tree to block of the afternoon sunlight.

If you were to put aircond do not put at the wall facing the afternoon sunlight. avoid placing the compressor at the same wall too,

Good luck!

---

Added on June 4, 2011, 10:53 amrefer here! http://en.wikipedia.org/wiki/File:Hallway_insulation.jpg

This post has been edited by akmis: Jun 4 2011, 10:53 AM