Using the Oak Ridge National Laboratory Cool Roof Calculator

Using the Oak Ridge National Laboratory Cool Roof Calculator (http://web.ornl.gov/sci/buildings/tools/cool-roof/) estimate the design of your roof, a/c conditioner and heating system efficiency in order to maximize the net savings compared to a black roof. Assume summertime cooling and wintertime heating (electricity) costs of $0.20/kWh. Explain how changes in R-value, SR and IE influence your net savings.

Solution

ANSWER : Using Oak Ridge national laboratory cool roof calculator,

   Infrared emittance, IE (HIGH=90; AVG=60; LOW=10) [%] = 10

   Air conditioner efficiency (Coefficient of Performance) (HIGH=2.5; AVG=2.0; LOW=1.5) = 2.5

If electricity, wintertime cost (HIGH=0.20; AVG=0.10; LOW=0.05) [$/KWh] = 0.20

            (Electric heat pump: HIGH=2.0; AVG=1.5)   (Electric resistance: 1.0) = 0.5

Net savings compared to black roof :

We will get maximum net savings with lowest R-value, SR & IE values.

By keeping R value lowest and SR & IE values as maximum, we can increase net savings in Cooling but Heating savings will be in negative due to which Net savings will be in negative.

Conclusion : Lowest Values of R,SR & IE will give us maximum net savings.