Calculating energy-saving potentials of heat-island reduction strategies

<p>We have developed summary tables (sorted by heating- and cooling-degree-days) to estimate the potential of heat-island reduction (HIR) strategies (i.e., solar-reflective roofs, shade trees, reflective pavements, and urban vegetation) to reduce cooling-energy use in buildings. The tables provide estimates of savings for both direct effect (reducing heat gain through the building shell) and indirect effect (reducing the ambient air temperature).</p><p>In this analysis, we considered three building types that offer the most savings potential: residences, offices, and retail stores. Each building type was characterized in detail by Pre-1980 (old) or 1980⁺ (new) construction vintage and with natural gas or electricity as heating fuel. We defined prototypical-building characteristics for each building type and simulated the effects of HIR strategies on building cooling- and heating-energy use and peak power demand using the DOE-2.1E model and weather data for about 240 locations in the US. A statistical analysis of previously completed simulations for five cities was used to estimate the indirect savings. Our simulations included the effect of (1) solar-reflective roofing material on building (<em>direct effect</em>), (2) placement of deciduous shade trees near south and west walls of building (<em>direct effect</em>), and (3) ambient cooling achieved by urban reforestation and reflective building surfaces and pavements (<em>indirect effect</em>).</p><p>Upon completion of estimating the direct and indirect energy savings for all the locations, we integrated the results in tables arranged by heating- and cooling-degree-days. We considered 15 bins for heating-degree-days, and 12 bins for cooling-degree-days. Energy use and savings are presented per 1000 ft² of roof area.</p><p id="">In residences heated with gas and in climates with greater than 1000 cooling-degree-days, the annual electricity savings in Pre-1980 stock ranged from 650 to 1300 kWh/1000 ft²; for 1980⁺ stock savings ranged 300–600 kWh/1000 ft². For residences heated with electricity, the savings ranged from 350 to 1300 kWh/1000 ft² for Pre-1980 stock and 190–600 kWh/1000 ft² for 1980⁺ stocks. In climates with less than 1000 cooling-degree-days, the electricity savings were not significantly higher than winter heating penalties. For gas-heated office buildings, simulations indicated electricity savings in the range of 1100–1500 kWh/1000 ft² and 360–700 kWh/1000 ft², for Pre-1980 and 1980⁺ stocks, respectively. For electrically heated office buildings, simulations indicated electricity savings in the range of 700–1400 kWh/1000ft² and 100–700 kWh/1000 ft², for Pre-1980 and 1980⁺ stocks, respectively. Similarly, for gas-heated retail store buildings, simulations indicated electricity savings in the range of 1300–1700 kWh/1000 ft² and 370–750 kWh/1000 ft², for Pre-1980 and 1980⁺ stocks, respectively. For electrically heated retail store buildings, simulations indicated electricity savings in the range of 1200–1700 kWh/1000 ft² and 250–750 kWh/1000 ft², for Pre-1980 and 1980⁺ stocks, respectively.</p>