Heads Up

According to a case study recently released by the Polyisocyanurate Insulation Manufacturers Association (PIMA), Washington, D.C., increasing the thickness of polyiso roof insulation significantly reduces energy costs while providing a positive rate of return on the cost of installation.The purpose of the case study, conducted by Energy Services Provider Group (ESPG), an independent energy analysis firm in Maryland, was to measure the economic and environmental effects of additional thickness of polyiso roof insulation, over the minimum code requirement. Building energy costs were calculated for buildings in seven U.S. cities: Boston, Chicago, Los Angeles, Dallas, Seattle, Denver, and Atlanta.The study demonstrated that increasing the thickness of polyiso roof insulation not only provides a positive rate of return on the cost of installation but also reduces energy costs and harm to the environment.MethodologyThe study examined two types of facilities: a retail building and an elementary school. A “model” of each facility, based on a statistical database of 25 years of energy simulations, was referenced. The current ASHRAE 90.1-1999 standards for roof insulation were used as the baseline for the minimum roof insulation requirements.This database defined the typical retail building as a single-story, 100,000-square-foot structure (two-to-five length/width ratio) with 30-percent glazing. The structure was cooled to 78 degrees F. in the summer and heated to 72 degrees F. in the winter. Unoccupied temperatures were maintained at 90 degrees F. in summer and 55 degrees F. in winter.This database also defined the typical elementary school as a single-story 65,000-square-foot structure (two-to-five length/width ratio) with 30-percent glazing. The structure was cooled to 75 degrees F. in the summer and heated to 72 degrees F. in the winter. Unoccupied temperatures were maintained at 90 degrees F. in summer and 60 degrees F. in winter.Results: Retail BuildingsGenerally, the study found that increasing the insulation thickness by 1-inch or more:• Provides a significant rate of return to users for the financial investment of installing additional polyiso insulation.• Reduces the costs to facilities on average $2,500 per year.• Reduces CO2 emissions by thousands of pounds, SO2 emissions by thousands of grams, and NOx emissions by thousands of grams per year.Results: Elementary SchoolsIn each city, except for Los Angeles, the ASHRAE specified minimum insulation value equates to 2-inches of polyiso roof insulation. In Los Angeles, the ASHRAE specified minimum insulation value equates to 1-inch of polyiso roof insulation. The study concluded that the environmental impact of these energy savings in elementary schools equates to significant reductions in CO2 , SO2 , and NOX emissions. Due to the unoccupied summer months, the overall energy savings for elementary schools is low. However, the savings in operating costs and energy use are still significant. In addition, users receive a positive rate of return on their investment (see chart).POLYISO IN ELEMENTARY SCHOOLSCityASHRAE 90.1-1999 ThicknessENERGY COST SAVINGS**/ IRR (%)
INTERNAL RATE OF RETURNBostonR15, 2.5"3"3.5"4.8"$954/ 13.2 $1641/ 12.1 $2086/ 4.6ChicagoR10, 1.5"3"3.5"4.8"$357/ 9.2 $1002/ 9.6$1957/ 5.6L.A.R15, 2.5"2"2.5"4.8"$2608/ 35.7$3800/ 32.6$5297/ 13.5DallasR15, 2.5"3"3.5"4.8"$918/ 12.6$1559/ 11.5$2661/ 7.1SeattleR15, 2.5"3"3.5"4.8"$955/ 13.2 $1581/ 12$2363/ 5.9DenverR15, 2.5"3"3.5"4.8"$748/ 10$1174/ 8$2041/ 4.4AtlantaR15, 2.5"3"3.5"4.8"$903/ 12.4$1515/ 11.1$2575/ 6.8**Energy cost savings values listed above represent the reduction in cost per year for increasing the thickness of polyiso roof insulation over the ASHRAE required listed in the previous column.