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Title: Inclusion of cool roofs in nonresidential Title 24 prescriptiverequirements

Roofs that have high solar reflectance (high ability toreflect sunlight) and high thermal emittance (high ability to radiateheat) tend to stay cool in the sun. The same is true of low-emittanceroofs with exceptionally high solar reflectance. Substituting a cool rooffor a non-cool roof tends to decrease cooling electricity use, coolingpower demand, and cooling-equipment capacity requirements, while slightlyincreasing heating energy consumption. Cool roofs can also lower citywideambient air temperature in summer, slowing ozone formation and increasinghuman comfort.DOE-2.1E building energy simulations indicate that use of acool roofing material on a prototypical California nonresidential (NR)building with a low-sloped roof yields average annual cooling energysavings of approximately 3.2 kW h/m2 (300 kW h/1000 ft2), average annualnatural gas deficits of 5.6 MJ/m2 (4.9 therm/1000 ft2), average annualsource energy savings of 30 MJ/m2 (2.6 MBTU/1000 ft2), and average peakpower demand savings of 2.1 W/m2 (0.19 kW/1000 ft2). The 15-year netpresent value (NPV) of energy savings averages $4.90/m2 ($450/1000 ft2)with time-dependent valuation (TDV), and $4.00/m2 ($370/1000 ft2) withoutTDV. When cost savings from downsizing cooling equipment are included,the average total savings (15-year NPV+equipment savings) rises to$5.90/m2 ($550/1000 ft2) with TDV, and to $5.00/m2 ($470/1000 ft2)without TDV.Total savings range from 1.90 to 8.30 $/m2 (0.18 0.77 $/ft2)with TDV, andmore » from 1.70 to 7.10 $/m2 (0.16 0.66 $/ft2) without TDV,across California's 16 climate zones. The typical cost premium for a coolroof is 0.00 2.20 $/m2 (0.00 0.20 $/ft2). Cool roofs with premiums up to$2.20/m2 ($0.20/ft2) are expected to be cost effective in climate zones 216; those with premiums not exceeding $1.90/m2 ($0.18/ft2) are expectedto be also cost effective in climate zone 1. Hence, this study recommendsthat the year-2005 California building energy efficiency code (Title 24,Part 6 of the California Code of Regulations) for NR buildings withlow-sloped roofs include a cool-roof prescriptive requirement in allCalifornia climate zones. Buildings with roofs that do not meetprescriptive requirements may comply with the code via an"overall-envelope" approach (non-metal roofs only), or via a performanceapproach (all roof types).« less
Authors:
; ; ;
Publication Date:
OSTI Identifier:
928326
Report Number(s):
LBNL--52849
Journal ID: ISSN 0301-4215; ENPYAC; R&D Project: 000000; TRN: US200815%%842
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: Energy Policy; Journal Volume: 33; Related Information: Journal Publication Date: 2005
Research Org:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org:
USDOE; Pacific Gas and Electric
Country of Publication:
United States
Language:
English
Subject:
32; 36; AIR; CALIFORNIA; CAPACITY; CLIMATES; ELECTRICITY; ENERGY CONSUMPTION; ENERGY EFFICIENCY; HEATING; NATURAL GAS; OZONE; PEAK LOAD; PERFORMANCE; POWER DEMAND; REGULATIONS; ROOFS cool roofs solar reflectance thermal emittance Title 24DOE-2