In 1990, the residential, commercial and institutional buildings sector was responsible for roughly one-third of global energy use and associated carbon emissions both in the Annex I countries and globally. In that year, buildings in Annex I countries used 86 EJ of primary energy and emitted 1.4 Gt C, accounting for about 75% of global buildings energy use (112 EJ, with associated emissions of 1.9 Gt C). However, the share of primary energy use and associated emissions attributable to Annex I countries is projected to drop; the IS92a scenario projects that global buildings-related emissions from Annex I countries will be about 70% in 2020 and slightly over 50% in 2050.

Greater use of available, cost-effective technologies to increase energy efficiency in buildings can lead to sharp reductions in emissions of CO2 and other GHGs resulting from the production, distribution and use of fossil fuels and electricity needed for all energy-using activities that take place within residential, commercial and institutional buildings. The buildings sector is characterized by a diverse array of energy end uses and varying sizes and types of building shells that are constructed in all climatic regimes. Numerous technologies and measures have been developed and implemented to reduce energy use in buildings, especially during the past two decades in Annex I countries.

Table 1 outlines measures and technical options to mitigate GHG emissions in the buildings sector, and provides a brief description of the climate and environmental benefits as well as economic and social effects (including costs associated with implementation of measures), and administrative, institutional and political issues associated with each measure. Tables 2 and 3 provide estimates of global and Annex I, respectively, emissions reductions associated with both energy-efficient technologies and the energy-efficiency measures. The estimates for the reductions from energy-efficient technologies are based on studies described in the SAR, using expert judgment to extrapolate to the global situation and to estimate reductions in 2020 and 2050, because most of the studies in the SAR estimate energy savings only for 2010. The estimates for the reductions from energy-efficient technologies captured through measures are based on expert judgment regarding policy effectiveness. These two categories of reductions "potential reductions from energy-efficient technologies" and "potential reductions from energy-efficient technologies captured through measures"-are not additive; rather, the second category represents an estimate of that portion of the first that can be captured by the listed measures.

and cooling systems, lighting and all plug loads, including office equipment) and reducing heating and cooling energy losses through improvements in building thermal integrity (SAR II, 22.4.1, 22.4.2). Other effective methods to reduce emissions include urban design and land-use planning that facilitate lower energy-use patterns and reduce urban heat islands (SAR II, 22.4.3); fuel switching (SAR II, 22.4.1.1, Table 22-1); improving the efficiency of district heating and cooling systems (SAR II, 22.4.1.1.2, 22.4.2.1.2); using more sustainable building techniques (SAR II, 22.4.1.1); ensuring correct installation, operation and equipment sizing; and using building energy management systems (SAR II, 22.4.2.1.2). Improving the combustion of solid biofuels or replacing them with a liquid or gaseous fuel are important means for reducing non-CO, GHG emissions. The use of biomass is estimated (with considerable uncertainty) to produce emissions of 100 Mt C/yr in CO2-equivalent, mainly from products of incomplete combustion that have greenhouse warming potential (SAR II, Executive Summary).

The potential for cost-effective improvement in energy efficiency in the buildings sector is high in all regions and for all major end uses. Projected energy demand growth is generally considerably higher in non-Annex I countries than in Annex I countries due to higher population growth and expected greater increases in energy services per capita (SAR II, 22.3.2.2). Although development patterns vary significantly among countries and regions, general trends in Annex I countries with economies in transition and non-Annex I countries include increasing urbanization (SAR II, 22.3.2.2), increased bousing area and per capita energy use (SAR II, 22.3.2.2, 22.3.2.3), increasing electrification (SAR II, 22.3.2.2), transition from biomass fuels to fossil fuels for cooking (SAR II, 22.4.1.4), increased penetration of appliances (SAR II, 22.3.2.3), and rising use of air conditioning (SAR II, 22.4.1.1). For simplification, the authors assume that by 2020 urban areas in non-Annex I countries will have end-use distributions similar to those now found in Annex I countries, so that energy-saving options and measures for most appliances, lighting, air conditioning and office equipment will be similar for urban areas in both sets of countries. The exception is heating which is likely to be a large energy user only in a few of the non-Annex I countries, such as China (SAR II, 22.2.1, 22.4.1.1.1). In addition, it is assumed that the range of cost-effective energy-savings options will be similar for Annex I and non-Annex I countries by 2020.

5 This section is based on SAR II, Chapter 22, Mitigation Options for Human Settlements (Lead Authors: M. Levine, H. Akbari, J. Busch, G. Dutt, K. Hogan, P. Komor, S. Meyers, H. Tsuchiya, G. Henderson, L. Price, K. Smith and Lang Siwei).

• Global energy use and emissions values are based on IS92 scenarios. 7 Tables 2 and 3 include only carbon emissions resulting from the use of fuels sold commercially. They do not include the large quantities of biomass fuels used in developing countries for cooking. Fuel switching from biomass fuels for cooking to sustainable, renewable fuels such as biogas or alcohol in developing countries can reduce these emissions (SAR II, 22.4.1.4).

14

Other Effects

-Similar to those from

mandatory energy

efficiency standards

The largest potential energy savings are for building equipment. Cost-effective energy savings for these end uses vary by product and energy prices, but savings in the range of 10-70% (most typically 30-40%) are available by replacing existing technology with such energy-efficient technologies as condensing furnaces, electric air-source heat pumps, ground-source heat pumps, efficient air conditioners, air-source or exhaust air heat pump water heaters, efficient refrigerators, horizontal axis clothes washers. heat pump clothes dryers, kerosene stoves, compact fluorescent lamps, efficient fluorescent lamps, electronic ballasts, lighting control systems, efficient computers, variable speed drives and efficient motors (SAR II, 22.4) (see Table 1).

Residential buildings are expected to account for about 60% of global buildings energy use in 2010, falling to 55% by 2050. Based on this ratio. IS92a scenarios indicate that residential buildings will use energy that produces 1.5 Gt C in 2010, 1.6 Gt C in 2020, and 2.1 Gt C in 2050, while commercial buildings will be responsible for emissions of 1.0 Gt C in 2010. 1.1 Gt C in 2020, and 1.7 Gt C in 2050. Based on information presented in the SAR, the authors estimate that efficiency measures with paybacks to the consumer of five years or less have the potential to reduce global residential and commercial buildings carbon emissions on the order of 20% by 2010, 25% by 2020 and up to 40% by 2050, relative to a baseline in which energy efficiency improves (see section of Table 2 entitled "Potential Reductions from Energy-efficient Technologies").

requirements by an estimated 25% in new buildings relative to those built in the late 1980s (SAR II, 22.4.1.1.1). Although large commercial buildings tend to be internal load-dominated, important energy savings opportunities also exist in the design of the building envelope (SAR II, 22.4.2.1.1). Considerably larger cost-effective savings are possible for new buildings than for existing ones (SAR II, 22.5.1). Since most of the growth in building energy demand is expected to be in nonAnnex I countries and a large percentage of this will be new buildings, there are significant opportunities to capture these larger savings if buildings are designed and built to be energyefficient in these countries (SAR II, 22.4.1).

Overall, based on information presented in the SAR and on expert judgment, the authors estimate that improvements in the building envelope (through reducing heat transfer and using proper building orientation, energy-efficient windows, and climate-appropriate building albedo) have the potential to reduce carbon emissions from heating and cooling energy use in residential buildings with a five-year payback (or less) by about 25% in 2010, 30% in 2020 and up to 40% in 2050, relative to a baseline in which the thermal

17

integrity of buildings improves. Heating and cooling are about 40% of global residential energy use and are expected to decline somewhat as a proportion of total residential energy. For commercial buildings, improvement in the thermal integrity of windows and walls with paybacks of five years or less have lower potential to reduce global carbon emissions, because only about 25% of energy use is due to heating and cooling, and reductions in these loads are more difficult in commercial than residential buildings (see section of Table 2 entitled "Potential Reductions from Energy-efficient Technologies"). Most of these reductions will occur only in new commercial buildings, as retrofits to the walls and windows of existing buildings are costly.

Footnotes are the same as those for Table 2, except for.