Cool Roof Coatings on Industrial Buildings : An Energy Study of Reflective Coatings

Abstract: To evaluate the effect of cool roof coatings containing Expancel® thermoplastic microspheres on industrial buildings, a warehouse was built-up in the computer simulation software IDA-ICE. The warehouse was modelled in line with ASHRAE 90.1. 2004 ”Energy Standard for Buildings Except Low-Rise Residential Buildings”. Four different cases were set up where the coating of the roof was the only variable. Two coatings containing Expancel® microspheres - one white and one red coating were compared to the same white coating without Expancel® microspheres and the ”base case” where there is no coating at all. The same circumstances were also implemented in a practical laboratory test using a model warehouse with a detachable roof. Four interchangeable roofs with different roof coatings constitute the various cases in the laboratory tests. A ”sun” consisting of statically mounted IR light bulbs were constructed, as well as a cooling system to measure the difference in cooling effect (maintaining a constant indoor temperature) between the different cases as a result of the change in insolation. The results of the computational simulations show that for a warehouse placed in Houston, Texas about 50 MWh in combined heating and cooling energy can be saved yearly between the best and the worst case, a reduction of 6.2%. Changing the geographic placement of the warehouse to Tepic, Mexico the corresponding savings were determined to 83 MWh or 13.5%. A way of determining the yearly savings in heating and cooling amount for the warehouse with a generic roof coating, only knowing the SRI value of the coating, was developed. It was determined that for every unit-increment of the SRI value the yearly savings for the warehouse placed in Houston, Texas were 718 kWh and 0.1%. The corresponding savings for the warehouse placed in Tepic, Mexico were determined to be 1252 kWh and 0.22%. The laboratory tests showed that the indoor temperature of the model warehouse decreased by close to 16°C between the best and the worst case.