Research has shown that when summer temperatures hit 45 degrees centigrades, the surface temperature of your brick tiled roof gets heated upto 65 degrees. This heat penetrates through the mud and RCC lintel and makes it way into your room.
Studies under above conditions show that the heat entering into your room through the RCC lintel is anywhere between 40 to 50 Btu per hour per square foot of your ceiling / roof area, depending on various factors like thickness of the RCC slab, mud mixture and brick-tiles.
Now if your bedroom has a size of 15 foot x 15 foot, then it will have ceiling area of 225 square feet.
Knowing the square feet of your room's roof, you can now calculate the number of BTUs/hr entering your room through the ceiling.
225 x 45 = 10,125 BTUs/ hour.
Remember that the heat entering the room through the walls, windows, gaps below the doors, electrical appliances running in your room like TV and fridge, bulbs, which emit heat, and the number of persons occupying the room, etc is apart from the 10,125 BTUs/hr calculated above. Lets assume that this heat is around 1500 BTUs/hr. (this is a very low figure assumed). The total heat gained in this case will rise to 10125+1500= 11,625 BTUs/hr.
Now If you choose to install a 1.5 ton Inverter AC in this room, it will hardly come onto the low amperage consumption as while it will be removing 18,000 BTUs/hr from your room, there will be 11,625 BTUs/hr of heat coming into your room. In this situation, the Inverter AC will continue to work like a standard AC consuming 8 or 9 amperes of current.
Now this is where man made insulations come into use. A one inch thick pink Jumbolon board has an average R value of 5, while a 1 inch thick layer of polyurethane foam has an average R value of 6. The R value is a factor which reduces heat flowing through that material.
As an example if 1000 BTUs/hr of heat is being transmitted, a one inch thich Jumbolon will reduce the heat 5 times. So 1000/5 = 200 BTUs/hr.
Similarly a layer on 1 inch thick polyurethane will reduce the heat transfer by 6 times. 1000/6 = 166 BTUs/hr.
Now if you choose to install two inches of Jumbolon which will now have a total R value of 10, on the roof of your bedroom where 10,125 BTUs/hr were entering through the ceiling, it will reduce the heat 10 times. 10,125/10 = 1012 BTUs/hr.
Now instead of 10,125 BTUs, you will only have 1012 BTUs/hr entering into your room. Your total heat gain into your room will be reduced to 1012+1500 = 2512 BTUs/hr.
Now in the very same bedroom, you can install a 1 ton Inverter or even a 1 ton Standard AC which removes 12,000 BTU/hr of heat from your room. The Inverter AC will now quickly reach the set temperatures and then go into a almost sleep mode (low comsumprion mode) as it will be facing heat load of 2512 BTUs instead of 11625 BTUs/hr.
This will reduce your electric bills considerably.
I hope that with he above examples, you will know how important is insulation and what it can do for you. One thing to note is that Polyurethane foam is the best insulation material available in the market. However with the passage of time, like 5 to 10 years, it begins to loose its R value, as it ages. The extruded polystyrene which is Jumbolon continously maintains its R value throughout the life of the building.
When I was planning to construct my home, I talked to the leading architects of lahore to design a Energy effiecient home for me. They all demanded a consultancy fee of Rs 10 lakhs to 15 lakhs. Unfortunately none of them could tell me what a BTU was. I decided to do the entire engineering myself. I only hired a computer literate draftsman for Rs 15,000 to do the drawings on a computer. I ended up building a home exactly I had dreamt of. Some one here very rightly pointed out that our architects and building contractors know nothing inspite of their Degrees!