Which is exceeding the installation cost of insulation material. Beyond a certain thickness, incremental cost will exceed the savings, which means; additional thickness of insulation is not economical anymore. The optimum insulation thickness is achieved when the saving start to drop as the thickness material is increased. The optimum thickness for fiberglass-urethane is found to be 0,048 m. the optimum thickness for other insulation material are tabulated in table 5.
The result suggest that fiberglass-urethane is the most economic saving up to $71,773 in 20 years) among other insulation materials. If we see the thermal conductivity (see table 5). Perlite has the highest thermal of an insulation materials. Higher the thermal conductivity of an insulation material means lower thermal resistance; therefore the thickest thickness is required to be used in order to get optimum thermal insulation. The thickness of insulation material is an important part of designing of building since thick insulation material will reduce the space of building significantly.
Thermal transmission in a certain material depends upon the thermal property ( in this case the thermal conductivity) and the thickness of that material. The lower value thermal conductivity is the less thermal transmission will be. Similarly, the thicker insulation material is the less thermal transmission will be. Therefore, there should be a relationship between the thermal conductivity and optimum thickness for every insulation material. However, to our knowledge this relation has not been found yet. In this study we find that the relationship between the thermal conductivity (k) and optimum thickness (xopt) is non-linear and obeys a polynomial function of xopt=a+bk+ck2, where a= 0.0818, b=-2.973, and c=64.6. This relationship will be very important in the future since we will be able to estimate the optimum thickness of insulation material easily (without doing a long analysis) just by knowing its thermal conductivity only.