For each of the two categories, the technologies are listed in the order of their potential impact in 2,050 according to IEA  for two global emission reduction scenarios: the ACT and Blue scenarios (Table7.1). The Blue scenario is the most aggressive in that it calls for 2,050 global CO2 emissions to be reduced to 50% of actual 2005 emissions. The ACT scenario would constrain 2,050 emissions at 2005 levels. The technologies are either aimed at enhancing end use efficiency or are new alternative building heating/cooling technologies. It is important to note that those high-efficiency appliances and heating and cooling technologies are currently commercial, although there is potential for even higher efficiencies assuming a focused, successful research program. Lack of incentive and higher initial costs are the primary reasons for the slow rate of utilization. This is in contrast to the power generation sector, which is constrained both by unavailable or undemonstrated technology and underutilized technology.
Due to slow building turnover, increasing the energy efficiency of existing building stock and maximizing energy efficiency of new buildings is essential in reducing total building energy use. This includes a concerted effort both in building systems, design and in selection/replacement of mechanical systems and appliances. The process is most efficient when comparing all building system components against each other, as commonly done in a building energy audit. Example tools for determining a building's energy use and potential energy savings can be found on the Department of Energy web page . To be truly effective, an integrated design approach is needed both during initial building construction and retrofitting to determine the most effective method of maximizing individual building efficiency. For example, a relatively simple aspect such as building siting (based on reference angle with the sun instead of the road) can greatly affect the available natural lighting and building cooling load requirement. This can allow for a reduction in both cooling needs and electrical lighting, which is a significant component of electricity use in buildings worldwide.
Immediate, off-the-shelf options exist for increasing the energy efficiency of residential and commercial buildings regardless of building age or type. The method resulting in maximum energy use reduction will vary by region, building type, etc., making a nationwide or global drive complex, likely relying on regional incentives and techniques. The IPCC  presents just such a regionally based technology recommendation to increase energy efficiency in buildings, including parameters such as cost effectiveness, technology stage, and appropriateness. An example of this regional dependence is the use of structural insulation panels in building design for
Table 7.1 Ref.  summarizes major building technologies capable of achieving significant global reductions in Gt CO, generation in the 2050 time frame. The technologies are divided into two categories: (1) heating and cooling and (2) appliances, which include lighting. The Blue column shows Gt of global CO, emission reductions in 2050. The Blue scenario calls for 2050 global CO, emissions from all sources to be reduced to 50% of actual 2005 emissions
Current state of the art
Blue 2050 impact
Technology RD&D priority and needs
Potential environmental impacts
Heating & cooling
Enhanced energy mgt. and high efficiency building envelope: insulation, sealants, windows, etc.
High efficiency building heating and cooling, including heat pumps Solar heating and cooling
First generation commercial
Lack of incentive, high initial costs, long building lifetime
Lack of incentive, high initial costs
High initial costs, availability of low cost efficient biomass heating systems
incremental improvements to lower cost and enhance performance
incremental improvements to lower cost and enhance performance Medium, focus on development of advanced biomass stoves and solar heating technology in developing countries
Less fossil fuel and nuclear power generation, and less on site fossil fuel combustion, yield reductions in coal & natural gas emissions, and nuclear wastes Same as above
Same as above
Appliances More efficient electric Commercial 4.5 appliances
More efficient lighting Commercial-systems compact fluorescent
Reduce stand-by losses Commercial from appliances, computer peripherals, etc.
Higher initial costs and lack of information to the consumer
Low/medium priority, incremental improvements to lower cost and enhance performance
Lack of incentive given higher initial costs
Medium, LED and OLED technology needs further development with aim of lowering initial cost
Lack of incentive Low from vendors and lack of knowledge form end-users
Less fossil fuel and nuclear power generation, yields reduction in coal & natural gas emissions, and nuclear wastes Same as above; however, mercury content of fluorescent bulbs could cause health and env. problems Less fossil fuel and nuclear power generation, yields reduction in coal & natural gas emissions, and nuclear wastes cold climates that are not as appropriate for use in warm climates. In fact, Levy et al.  projected a potential savings of 800 trillion British thermal units (TBTU) per year due to insulation retrofits in existing housing. In warmer climates however, it is projected that technology such as solar thermal water heaters are a much more appropriate way to conserve energy, as solar energy is more readily available. Technologies which use direct sunlight to reduce energy demand for heating water exist and are especially economical in temperate regions.
In new construction, primary barriers for use of energy efficient design may include concern over increased initial building cost (including a lack of incentives), designer lack of knowledge, owner specifications, owner lack of interest, and an unknown potential for energy savings via a detailed energy analysis. Building appliances are rarely replaced when a newer version is available due to initial cost of new equipment, and the long operating life of many existing household appliances. Often, building occupants are accustomed to a consistent energy bill and are put off by the high initial cost of appliance upgrade considering the effort required to quantify the effect it will have on the energy bill. Although initial costs can often be recouped in reduced energy bills in a reasonable time frame, this is not immediately obvious or important for consumers who are not responsible for the building energy bill, a frequent scenario in rental properties. Newly purchased appliances are not always used as a replacement for aging equipment either. A new refrigerator may provide a more efficient means of cooling food but the older system, if operable, may continue to be used for owner convenience . In fact, even when older appliances are discarded, increased energy efficiency may not be fully realized due to increase in new appliance use (termed the 'rebound effect') . Truly an integrated approach that results in a well informed consumer AND user is necessary to increase the energy efficiency of our household products.
It is important that every government incentive be thoroughly analyzed to ensure that the intended effects are realized. Young  found that individual incentives had to be tailored to individual population groups in order to be most effective. The success of incentives to increase the turnover of household appliances can range greatly depending on socioeconomic factors such as income. This drive towards increased building energy efficiency happens on multiple fronts. In the effort to reduce final building price, it is not uncommon for builders to begin the design process with a focus on minimizing initial design and construction costs. Standards and codes exist by regions that define the minimum requirements with which a building can be constructed. Changes in these codes are a means of leveling the field in regards to building construction and operation. If all buildings are kept to the same energy efficiency standard, there can be no one builder undercutting the competition by reducing the building efficiency or quality. This has also driven the development of high performance building standards and codes which allow perspective homeowners to compare similar buildings during the purchase process. For example the Energy Star for Homes label  and ASHRAE Standard 189.1 are straightforward metrics the normally uninformed buyer can use to compare all perspective properties against one another. More recently, federal dollars have been allocated to help U.S. homeowners and builders reduce the cost of building energy efficiency upgrades and new building construction . Incentives to buy Energy Star appliances allow consumers to upgrade their current systems for a reduced initial price. Similar programs provide homeowners incentives to install photovoltaic panels or passive water heating technology. Regardless of increased building efficiency, building energy use will continue to impact the energy needs of our nation.
The IPCC  discusses a number of co-benefits as potential outcomes of a reduced building energy use scenario including; reduction in local/regional air pollution, improved health (discussed in the following section), quality of life and comfort, improved productivity, employment creation, improved social welfare and poverty alleviation and energy security. Such benefits are useful incentives in regions where direct benefits may not be realized. Many of these benefits may be just as important as the anticipated side effects of global climate change.
A myriad of options exist for increasing energy efficiency in buildings across the United States. While the optimal mitigation technique is dependant on region and is often building specific, it is believed that a nation-wide concerted effort is needed to significantly reduce energy use in buildings.
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