تجزیه و تحلیل هزینه کربن و چرخه عمر از اقدامات بهره وری انرژی در ساختمان های تجاری جدید

Energy efficiency in new building construction has become a key target to lower nation-wide energy use. The goals of this paper are to estimate life-cycle energy savings, carbon emission reduction, and cost-effectiveness of energy efficiency measures in new commercial buildings using an integrated design approach, and estimate the implications from a cost on energy-based carbon emissions. A total of 576 energy simulations are run for 12 prototypical buildings in 16 cities, with 3 building designs for each building-location combination. Simulated energy consumption and building cost databases are used to determine the life-cycle cost-effectiveness and carbon emissions of each design. The results show conventional energy efficiency technologies can be used to decrease energy use in new commercial buildings by 20–30% on average and up to over 40% for some building types and locations. These reductions can often be done at negative life-cycle costs because the improved efficiencies allow the installation of smaller, cheaper HVAC equipment. These improvements not only save money and energy, but reduce a building’s carbon footprint by 16% on average. A cost on carbon emissions from energy use increases the return on energy efficiency investments because energy is more expensive, making some cost-ineffective projects economically feasible.

Building energy efficiency has come to the forefront of political debates due to high energy prices and climate change concerns. Improving energy efficiency in new commercial buildings is one of the easiest and lowest cost options to decrease a building’s energy use, owner operating costs, and carbon footprint. This paper uses life-cycle costing and life-cycle assessment with extensive building cost databases, whole building energy simulations, state level emissions rates, and statewide average utility rates to determine the energy savings and cost-effectiveness of energy efficiency improvements, the resulting carbon emissions reduction, and the impact a cost on carbon would have on energy efficiency investment decisions. The results of this analysis show that conventional energy efficiency technologies such as thermal insulation, low-emissivity windows, window overhangs, and daylighting controls can be used to decrease energy use in new commercial buildings by 20–30% on average and up to over 40% for some building types and locations. Although increasing energy efficiency usually increases the first costs of a building, the energy savings over the service life of the building often offset these initial higher costs. The first costs can be lower for the more efficient building design because, through integrated design, the improved efficiency reduces the size of the heating and/or cooling system required to meet the peak heating and/or cooling loads. The building type, local climate, and study period impact the financial benefits from energy efficiency improvements. The longer the study period, the greater the energy savings from energy efficiencies and the lower the life-cycle costs for more energy efficient building designs. The local climate impacts the appropriate integration of said improvements and the resulting savings from energy efficient designs. Energy efficiency varies by building type because of inherent design differences (e.g., number of stories, amount of glazing, and process loads). The cost-effective energy efficiency improvements not only save money, but also reduce a building’s carbon footprint. Carbon footprints are reduced by an average of 16% across all building types and sizes for a 10-year study period. These reductions are greater in buildings located in states that use large amounts of coal-fired electricity because of the large amounts of carbon dioxide emitted through coal combustion. A cost of carbon emissions is added to the building owner/operators energy costs based on the amount of energy use and type of fuel source. An additional cost on carbon increases the relative cost-effectiveness of energy efficiency improvements and potential carbon emissions reduction in new commercial buildings. Many energy efficiency measures are cost-effective without climate change policy, and should be implemented regardless of carbon restrictions. However, a cost on carbon results in a greater adjusted internal rate of return on energy efficiency investments, and makes energy efficiency projects more attractive relative to alternative investments. The change in cost-effectiveness is most prevalent in regions of the country that rely heavily on coal-fired power generation.

There are five conclusions from this analysis that are relevant to the current debate over energy efficiency investments in buildings. First, conventional energy efficiency measures can be used to reduce energy use by 20–30% on average without any significant alterations to the building design. These results give credence to the cost-effectiveness of building to meet ASHRAE Advanced Energy Design Guide’s recommendations. Second, the group of energy efficiency measures recommended in the LEC for the building types studied are life-cycle cost-effective for some building types and locations regardless of study period length. This result contradicts recent research using the flawed simple payback method that found it cost-ineffective to improve energy efficiency by 30%.21 The key difference is that the integrated design approach taken in this analysis allows the HVAC system to be appropriately sized based on the heating and cooling loads of the design. Third, the investor’s time horizon determines the cost-effective building design for many building type-location combinations. Much of the realized costs of a building are overlooked when the future costs of operating and maintaining the building are not taken into account. As the study period length increases, more building type-location combinations find it cost-effective to adopt the most energy efficient building design alternative, with the greatest change occurring between the 1–10-year and 10–25-year study periods. Fourth, these energy efficiency investments reduce the carbon footprint of the building by as much as 32% over a 10-year study period. The largest carbon reductions occur in states with the greatest energy reductions and states that rely heavily on coal-fired electricity generation, while states with large amounts of alternative energy use realize much smaller reductions. Finally, the introduction of a cost on carbon increases the rate of return on energy efficiency investments across all locations and building types, often turning the LEC into the most cost-effective choice. The greatest incentives to reduce energy use occur in the same states that use the most electricity from coal-fired generation. The results lead to several implications of interest to government decision-makers. Investments in building energy efficiency measures recommended by whole building energy simulations are often cost-effective and have competitive annual investment returns in many areas of the United States, while improving efficiency and lowering a building’s impact on climate change. A cost on carbon emissions further increases the return on investment for energy efficiency improvements, improving the business case by increasing the likelihood that the energy efficiency investments will be the best investment alternative. These increases in return on investment are greatest in states that have the largest carbon emission rates.