Effect of cool roofs on commercial buildings energy use in cold climates

• We simulated energy consumption for prototype office and retail buildings in cold-climates.
• The effect of snow on roofs was simulated.
• Cool roofs saved net annual energy expenditure in all climates.
• Accounting for the effect of snow, the winter penalties were reduced.
• Cool roofs reduced the peak electric demand for all buildings.

We used DOE-2.1E to simulate energy consumption for several prototype office and retail buildings in four cold-climate cities in North America: Anchorage, Milwaukee, Montreal, and Toronto. To simulate the effect of snow on the roof, we defined a function calculating the daily U-value and absorptivity of the roof. Cool roofs for the simulated buildings resulted in annual energy expenditure savings in all cold climates. In Anchorage, the simulated annual heating energy consumptions of the old retail building with a dark versus a cool roof (without snow) are 123.5 and 125.8 GJ/100 m2, respectively (a 2.3 GJ/100 m2 penalty for the cool roof). With snow, the heating penalties decreased to 1.2 GJ/100 m2, leading to an annual energy savings of 7 $/100 m2 of roof area. For an old retail building in Montreal and Toronto, a cool roof can save up to 62 $/100 m2 and 37 $/100 m2, respectively. For a new, medium-sized office building with natural gas heating fuel, a cool roof would save 4 $/100 m2 in Montreal, 14 $/100 m2 in Milwaukee and Anchorage, and 10 $/100 m2 in Toronto. Cool roofs can reduce the peak electric demand of the retail buildings up to 1.9 and 5.4 W/m2 in Toronto and Montreal, respectively.