how can we cool our rooms by coal and wood

 

Coal and wood are types of fuels. They provide heat when burnt. Hence, they can be used to heat the room and not cool it.

 

However, wood and coal are poor conductors of heat. Hence, one can create a layer of wood and coal between the walls, thereby providing an insulating layer.

During summers, this layer will not allow heat to pass through the walls and keep the room cool.