Advances in Building Energy Research

Volume 2

Mat Santamouris

• Publisher: Routledge
• Year: 2013
• Print ISBN:
  9781844073894
• eBook ISBN:
  9781136572463
• Topic: Architecture
• Subtopic: Architecture General

'Several high quality scientific journals are published in the area of building energy and indoor/outdoor environment; however, one has been missing. Advances in Building Energy Research fills the gap. I recommend ABER to all technical libraries, research institutes and universities. It should also be used by construction companies and those manufacturing building materials and building products.'
Professor Olli Sepp nen, President of REHVA (Federation of Heating and Air-conditioning Associations)

'Advances in Building Energy Research is a unique index. It will be an inexhaustible resource for energy related sciences and a continuous inspiration for architects around the world.'
N. Fintikakis, Architect and Director of UIA-ARES WP (Architecture and Renewable Energy Sources)

Advances in Building Energy Research (ABER) offers state-of-the-art information on the environmental science and performance of buildings, linking new technologies and methodologies with the latest research on systems, simulations and standards. As stringently reviewed as a journal but with the breadth of a book, this annual volume brings together invited contributions from the foremost international experts on energy efficiency and environmental quality of buildings. Spanning a broad range of technical subjects, this is a 'must have' reference on global developments in the field, suitable for architects and building engineers, environmental engineers, industry professionals, students, teachers and researchers in building science, technical libraries and laboratories.

1

Evolution of Cool-Roof Standards in the US

Hashem Akbari and Ronnen Levinson

Abstract

Roofs that have high solar reflectance and high thermal emittance stay cool in the sun. A roof with lower thermal emittance but exceptionally high solar reflectance can also stay cool in the sun. Substituting a cool roof for a non-cool roof decreases cooling electricity use, cooling power demand and cooling equipment capacity requirements, while slightly increasing heating energy consumption. Cool roofs can also lower the citywide ambient air temperature in summer, slowing ozone formation and increasing human comfort.

Provisions for cool roofs in energy efficiency standards can promote the building-and climate-appropriate use of cool roofing technologies. Cool-roof requirements are designed to reduce building energy use, while energy-neutral cool-roof credits permit the use of less energy-efficient components (e.g. larger windows) in a building that has energy-saving cool roofs. Both types of measures can reduce the life-cycle cost of a building (initial cost plus lifetime energy cost).

Since 1999, several widely used building energy efficiency standards, including ASHRAE 90.1, ASHRAE 90.2, the International Energy Conservation Code and California’s Title 24 have adopted cool-roof credits or requirements. This chapter reviews the technical development of cool-roof provisions in the ASHRAE 90.1, ASHRAE 90.2 and California Title 24 Standards, and discusses the treatment of cool roofs in other standards and energy efficiency programmes. The techniques used to develop the ASHRAE and Title 24 cool-roof provisions can be used as models to address cool roofs in building energy efficiency standards worldwide.

▪ Keywords – cool roofs; solar reflectance; thermal emittance; solar reflectance index; building energy efficiency standards; ASHRAE 90.1; ASHRAE 90.2; California Title 24; International Energy Conservation Code (IECC); Leadership in Energy and Environmental Design (LEED); Energy Star; Florida Building Code (FBC); Revised Ordinances of Honololu (ROH); City of Chicago Energy Conservation Code

INTRODUCTION

Roofs that have high solar reflectance (high ability to reflect sunlight: spectrum 0.3–2.5µm) and high thermal emittance (high ability to emit thermal radiation: spectrum 4–80µm) stay cool in the sun. The same is true of roofs with lower thermal emittance but exceptionally high solar reflectance. Roofs that stay cool in the sun by minimizing solar absorption and maximizing thermal emission are hereafter denoted ‘cool roofs’.

BENEFITS OF COOL ROOFS

Low roof temperatures lessen the flow of heat from the roof into the building, reducing the need for space cooling electricity in conditioned buildings. Since building heat gain through the roof peaks in mid to late afternoon, when summer electricity use is highest, cool roofs can also reduce peak electricity demand. Prior research has indicated that savings are greatest for buildings located in climates with long cooling seasons and short heating seasons, particularly those buildings that have distribution ducts in the plenum (Akbari, 1998; Konopacki and Akbari, 1998; Akbari et al, 1999).

Cool roofs transfer less heat to the outdoor environment than do warm roofs (Taha, 2001). The resulting decrease in outside air temperature can slow urban smog formation and improve human health and outdoor comfort. Reduced thermal stress may also increase the lifetime of cool roofs, lessening maintenance and waste (Akbari et al, 2001).

Earlier studies have measured daily air-conditioning energy savings and peak-power demand reduction from the use of cool roofs on buildings in several warm weather climates, including California, Florida and Texas. Cool roofs on non-residential buildings typically yielded measured summertime daily cooling energy savings and peak-power demand reductions of 10 to 30 per cent, though values have been as low as 2 per cent and as high as 40 per cent (see Table 1.1) (Konopacki et al, 1998). For example:

...

TABLE 1.1 Cool-roof energy savings measured in six California non-residential buildings

	(A) DAVIS MEDICAL OFFICE	(B) GILR0Y MEDICAL OFFICE	(C) SAN JOSE RETAIL STORE	(D) SACRAMENTO OFFICE	(E) SACRAMENTO MUSEUM	(F) SACRAMENTO HOSPICE
Roof

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• List of Figures and Tables
• List of Acronyms and Abbreviations
• 1 Evolution of Cool-Roof Standards in the US
• 2 A Review of Innovative Daylighting Systems
• 3 Physically Based Modelling of the Material and Gaseous Contaminant Interactions in Buildings: Models, Experimental Data and Future Developments
• 4 The Application of Urban Climate Research in the Design of Cities
• 5 Solar Air Conditioning: A Review of Technological and Market Perspectives
• 6 Experimental Methods in Ventilation
• 7 A Review of Optical Properties of Shading Devices
• Index