Sacramento - Energy Savings Analysis

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Sacramento has a May through September cooling season. Most residential buildings are one story and commercial buildings are low-rises. Air conditioning saturation in the Sacramento Metropolitan Statistical Area (MSA) is high with a total air conditioned roof area in 1998 of 648 million (M)ft² residential, 37 Mft² office, and 50 Mft² retail.

Modeling Methodology

The Department of Energy's Lawrence Berkeley National Laboratory (LBNL) analyzed the energy savings potential (direct and indirect effects) of heat island reduction measures on cooling energy use in Sacramento. Determining direct energy impacts involved modeling the effects from placing eight mature deciduous shade trees around residential buildings, eight shade trees around office buildings, and four shade trees around commercial buildings to provide 10% summertime (April - October) transmittance and 90% transmittance for the remainder of the year.

In addition, determining direct impacts involved modeling the effects from increasing solar reflectance – or albedo – on residential and commercial roofs from 0.2 to 0.5 and 0.6, respectively, using an infrared emittance of 0.9, to calculate savings. (Emittance is the percentage of energy a material can radiate away in the form of heat.) This modeling was performed using DOE-2 building energy software, which is an advanced computer program that simulates hourly building energy use.

LBNL modeled the indirect impacts by analyzing the ambient cooling from the placement of four or eight shade trees per building and from the reduced rooftop temperatures due to the albedo changes discussed above. LBNL captured these indirect effects by using the Colorado State Urban Meteorological Model (CSUMM). The CSUMM outputs were used to modify the typical meteorological year 2 data, which were fed into the DOE-2 building energy model.

Modeling Results

LBNL calculated the following annual results for the total Sacramento MSA:

$26M energy savings in 1997 dollars ($46M in annual electricity savings less a 43% natural gas deficit);
486 megawatts peak power avoided (84% from residential, 7% from office, and 9% from retail); and
92,000 tons of carbon emissions reduced.

For more information see the full report: 3 Cities Report (PDF, 61 pp., 344 KB).

Sacramento - Energy Savings Analysis

Pilot Cities

Modeling Methodology

Modeling Results

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