SIMULATION OF ENVIRONMENTAL IMPACTS OF COMMERCIAL BUILDING SYSTEMS Ayat Osman 1 and Robert Ries 1 Department of Civil and Environmental Engineering, University of Pittsburgh Pittsburgh, PA, USA ABSTRACT Hourly energy simulation was used in combination with a life cycle assessment framework to model the environmental effects of energy consumption in buildings. The energy efficiencies and environmental impacts resulting from the construction and operation of alternative technnologies for providing space and water heating, cooling, and electrical power for equipment and lights in commercial buildings is evaluated. The analysis shows that building load characteristics are one of the main factors affecting the selection of technologies and operational strategies to limit the environmental impacts of building energy systems. INTRODUCTION The Energy Information Administration (EIA) of the Department of Energy estimates that commercial buildings in the United States consume 5.6 EJ of energy for space and water heating, cooling, and lighting, of which 2.1 EJ is natural gas (about 37%) (USDOE 1995). In addition, commercial buildings consume 2.5 EJ of electricity that results in 8.3 EJ of primary energy use, 0.2 EJ in fuel oil, and 0.6 EJ in district heating. This results in a total annual energy expenditure of $70 billion. The EIA also estimates that 92% of future generation capacity, including distributed generation, will be fueled with natural gas, and that distributed generation and fuel cells are expected to represent 3.5% of new generation capacity added by 2020 (EIA 2000). In commercial buildings in the United States, natural gas is recognized as the principal fuel for space and water heating, with electricity, principally generated off- site, used for cooling loads, lighting needs, and equipment. However, natural gas-fired equipment can also be used for on–site power generation in buildings. On–site generation is often co–generation, the combined production of both electrical (or mechanical) energy and thermal energy. Two–thirds of the primary energy used by conventional electric power plants is lost, largely as heat. In contrast, co– generation systems, or combined heat and power (CHP), recapture much of the otherwise wasted thermal energy and use this energy for a variety of purposes, such as space or water heating. Gas-fired cogeneration systems are an attractive option from both an environmental and an energy efficiency standpoint. On–site co–generation could make natural gas the dominant primary energy source for commercial buildings in the United States. The analysis of the results from the current study demonstrated a) a framework that supports decision– making regarding system selection and operational strategies to limit environmental impact; b) the importance of a life cycle assessment framework, illustrated by the analysis of primary energy use, global warming potentials, acidification potentials, and tropospheric ozone potential; and c) the importance of building load characteristics for the analysis of CHP scenarios. SIMULATION AND LIFE CYCLE ASSESSMENT Study Description The goal of this study was to evaluate natural gas- fired technologies for heating, cooling, and electrical energy generation in commercial buildings and compare these systems based on their primary energy consumption and emissions. The natural gas-fired cogeneration technologies studied were solid oxide fuel cell (SOFC), microturbine, and internal combustion engine (ICE). These systems were compared to current practice, i.e., large utility-scale power generation, electric chillers, and gas boilers. Both average U.S generation mix and high efficiency natural gas combined cycle (NGCC) power generation were investigated. Three basic operational strategies were considered in this study: baseline, thermal load following, and electrical load following. Baseline cases refer to when U.S. average electric generation mix or NGCC were used to satisfy the electric load of the building, and the heating demand was satisfied by gas boilers. An alternative scenario substituted gas-fired absorption chillers for electric chillers. In thermal load following cases (TLF), cogeneration systems were operated to meet the thermal energy use of the building, consisting of mainly space and water heating, as well as absorbtion cooling in summer months. The cogenerated electricity was used to meet part or all of the electric energy use of the building. Eighth International IBPSA Conference Eindhoven, Netherlands August 11-14, 2003 - 979 - - 987 -