Modeling the urban heat island effect's impact on residential heating and cooling loads in the United States from 1960-2010

Abstract

The urban heat island effect is a phenomenon wherein the dark, hard surfaces prevalent in heavily-developed urban areas absorb and re-radiate heat, leading to measurably higher air temperatures in urban areas than in surrounding rural areas. A primary consequence of the urban heat island effect is a shift in energy consumption patterns, as increased urban air temperatures lead to greater summertime air conditioning demand and lower wintertime space heating demand. This study takes a three-step approach to characterizing the historical extent of space conditioning demand in the United States, using these results to model residential space heating and cooling loads, and identifying the share of these quantities attributable to the urban heat island effect. First, daily average temperature records dating back to 1960 were compiled from 9,417 U.S. climate stations listed in NOAA’s Global Historical Climatology Network and converted into heating and cooling degree days. Individual climate stations were then cross-referenced with regional housing characteristics such as recommended insulation levels, housing square footage, space heating fuel types, and air conditioner unit types. Then, climate stations’ degree day tallies were used to model the total annual BTU or kWh demanded for space heating and air conditioning over a range of insulation levels and furnace and air conditioner efficiencies. Finally, modeled loads were averaged for climate stations inside and within a 50-mile radius beyond the boundary of the country’s 20 largest metropolitan areas (ca. 2010) and compared in order to determine the relative rise or fall in load due to the urban heat island effect. Results demonstrate: (1) a general warming trend from 1960-2010, expressed through a respective decrease and increase in heating and cooling degree days over time; (2) confirmation of the relative warming of urban areas, as they record more cooling degree days and less heating degree days than rural areas; and (3) a logical distribution of space heating and air conditioning loads for modeled homes with regards to geography. For the 20 largest metropolitan areas in 2010, the urban heat island effect was measured to reduce space heating demand by an average of 5.26-7.68 MMBTU and $91-$134 in associated expenditures, as well as increase air conditioning demand by 155-210 kWh and $16-$21 in associated expenditures. These figures suggest that the urban heat island effect has a larger impact on the bottom line for space heating than for air conditioning. By modeling individual households, these results possess a scalability that can easily be incorporated into future studies aiming to examine urban heat island-induced increases or decreases in energy expenditures, demand for electricity, natural gas, other space conditioning fuels, and/or greenhouse gas emissions for an entire city or country.