Environmental Impacts[LINK]

Typically when a new building technology is evaluated the energy performance of a baseline building is compared to the energy and life-cycle costs of alternatives to determine cost-effectiveness. But what if the lowest energy or life-cycle cost alternative is not the cleanest or lowest environmental impact? By calculating environmental impact, designers can compare alternatives not only in terms of their energy performance but also their environmental performance—working towards a more sustainable design (Liesen 1997; Stroot, Nemeth, and Fournier 1996). Environmental impacts are quantified, in part, by modeling the amount of emissions and in EnergyPlus this is done using the input objects “EnvironmentalImpactFactors,” “FuelFactors,” and “Output:EnvironmentalImpactFactors.”

Based on emissions factors entered by the user, EnergyPlus calculates the mass or volume of thirteen different pollutants: CO${}_2$ (carbon dioxide), CO (carbon monoxide), CH${}_4$ (methane), NO${}_x$ (nitrogen oxides), N${}_2$O (nitrous oxide), SO${}_2$ (sulphur dioxide), PM (particulate matter), PM${}_{10}$ (particulate matter 10>PM${}_{10}$>2.5 microns), PM${}_{2.5}$ (particulate matter<2.5 microns), NH${}_3$ (ammonia), NMVOC (non-methane volatile organic compounds), Hg (mercury), and Pb (lead) as well as water consumed through evaporation in thermo- and hydro-electric generation and high- and low-level nuclear waste from nuclear electricity generation for on- and off-site energy production. Note that while these comprise the largest proportion of pollutants, more than one hundred other pollutants are emitted from fossil fuel combustion or electricity generation. Much of the information compiled here for fossil fuel combustion comes from AP-42 Compilation of Air Pollutant Emission Factors (EPA 1998a, 1998b, 1996). For more information on pollutants, see the U.S. Environmental Protection Agency (EPA) Clearinghouse for Inventories & Emission Factors (www.epa.gov/ttn/chief/efinformation.html).

EnergyPlus models energy performance of on-site fossil fuels and purchased electricity (generated from a variety of fuels including natural gas, oil, gasoline, diesel, coal, hydroelectric, nuclear, wind, solar power, and biomass). The energy performance calculated by EnergyPlus is converted into a mass or volume of pollutants emitted. From a baseline building, alternative energy and pollution saving technologies can be explored, and the energy savings and pollution reduction can be calculated. Figure 1 and Figure 2 illustrate a comparison of two buildings simulated using Chicago weather data in EnergyPlus and the calculated pollutant levels (based on U.S. national average pollutants) (Crawley 2003).

To calculate the mass or volume of each pollutant, consumption is multiplied by an emissions factor for each fuel (natural gas, electricity, fuel oil, diesel, or coal). In future versions, users will be able to schedule how the emissions factors by time of day, month, season and year. For electricity, the mix of generation fuel sources—whether utility, state or regional—is used to adjust the emission factors. If a user has emissions factors specific to the building site and equipment, these can be entered directly. There are no default emissions factors.

Types of Pollutants[LINK]

EPA categorizes pollutants as either Criteria Pollutants or Hazardous Pollutants. Criteria pollutants are the six substances for which EPA has set health-based standards, including carbon monoxide (CO), nitrogen oxides (NO${}_x$), sulfur dioxide (SO${}_2$), and particulate matter (PM10 and PM2.5), ozone (O${}_3$), and lead (Pb). Because ozone is created in atmospheric photochemical reactions of volatile organic compounds, ammonia, and other substances rather than direct building-related energy emissions, we do not calculated ozone emissions in EnergyPlus. But we do include ozone precursors: methane (CH${}_4$), non-methane volatile organic compounds (NMVOC), and ammonia (NH${}_3$). Hazardous pollutants are substances that are known or suspected to cause serious health problems such as cancer. We include typical hazardous substances associated with energy production and use including lead (Pb) and mercury (Hg). We also include CO${}_2$ (carbon dioxide) since it is largest greenhouse gas in terms of impact.

Carbon Equivalent[LINK]

The Intergovernmental Panel on Climate Change has studied the effects on the relative radiative forcing effects of various greenhouse gases. This effect, called Global Warming Potential (GWP), is described in terms of the Carbon Equivalent of a particular greenhouse gas. This equivalent is based on a factor of 1.0 for carbon. This group of gases includes carbon dioxide (CO${}_2$), carbon monoxide, nitrous oxide, methane, halocarbon emission, hydrofluorocarbons (HFC), perfluorocarbons (PFC), and chlorofluorocarbons (CFC). For building energy use, the main gases of concern are carbon dioxide, carbon monoxide, methane, and nitrous oxide. Although carbon monoxide has a relatively short life, CO emissions into the atmosphere may have a significant impact on climate forcing due to chemical impact on CH${}_4$ lifetime, and tropospheric O${}_3$ and CO${}_2$ photochemical production normally reacts to produce carbon dioxide, but it can’t be ignored since it is produced in incomplete combustion and the carbon remains to interact as CO${}_2$ Yet there is no agreement on its carbon equivalent (IPCC 2001). The carbon equivalent of carbon dioxide, methane, and nitrous oxide are calculated and then multiplied by their GWP on a 100 year time frame. The Carbon Equivalents of the following gases have been determined and used in the program are shown in the following table.

The resulting carbon equivalents by fuel type are shown in the output of the program along with the individual gas pollutants.

Fossil Fuel Emissions Factors[LINK]

Emission factors for on-site fossil fuel consumption are based on Section 1.4 Natural Gas Combustion in EPA (1998a) Table 2 shows the greenhouse gas and precursors and criteria pollutant emissions factors for natural gas. Similar emissions factors are shown for residual fuel oil (No. 4 and No. 6 fuel oil) [Table 3], distillates (No. 1 and No. 2 fuel oil) [Table 4], residential oil furnace [Table 5], LPG (butane and propane) [Table 6], gasoline and diesel [Table 7], and coal [Table 8] in the indicated tables. Note that a zero for a pollutant in the table may mean that no data were available, not that there are no emissions of that pollutant.

Off-Site Electricity Generation Emissions[LINK]

While estimating emissions from on-site fossil fuel combustion can be fairly straight-forward, emissions from off-site electricity is more challenging. How the electricity is generated, i.e., from gas, oil, coal, nuclear, renewable sources (wind, PV) or hydroelectric, and the mix of generation determines the resulting level of emissions. While data are available at utility and even power plant level (from the sources cited), data are shown here for United States national- and state-level average emissions from electricity generation. Table 9 provides average greenhouse gas and precursors and criteria pollutant emissions factors for the entire United States from electricity generation. Table 10 provides average electricity emissions factors by state, for greenhouse gas and precursors, and Table 11 for criteria pollutant emission factors. These two tables also include a ratio of heat input to electric output (efficiency of electricity generation) including distribution and transmission losses to allow calculation of source energy.

As mentioned in the introduction to this section, EnergyPlus also calculates water consumed through evaporation in thermo-electric and hydro-electric generation. Torcellini, Long, and Judkoff (2004) provide data on average water consumption by generator type by state. These data are summarized in units suitable for EnergyPlus in Table 9, for national and state average water consumption for thermal-electric, hydro-electric, and Table 10 for weighted total electricity generation.

Other Energy-Related Pollutants and Sources of Other Information[LINK]

EnergyPlus (with user entered-data) will also calculate high- and low-level nuclear waste from electricity generation. Few utilities now provide data on nuclear waste resulting from electricity generation and no US national or state-level data are yet available (this will be added as data become available). Two Illinois utilities regularly report nuclear waste in terms of pounds per kWh or MWh for high-level waste and cubic feet per kWh or MWh for low-level waste. For these two utilities, high level nuclear waste values range from 0.0042 to 0.01 lb/MWh (7000 to 16000 g/MJ); low-level nuclear waste ranges from 0.0001 to 0.0002 ft${}^3$/MWh (0.01 to 0.02 m${}^3$/MJ) depending on relative proportion of nuclear as compared with other electricity generation sources.

IEA (2003) contains carbon dioxide (CO${}_2$) emissions factors for electricity generation by country and region. Carbon dioxide (CO${}_2$) is responsible for over 60% of the anthropogenic greenhouse effect (UNEP 2002). Because only limited greenhouse gas emissions factors and data (other than CO${}_2$) is available for other countries, an interim method for estimating emission factors would be to compare the CO${}_2$ emission factor for the particular country from IEA (2003) and match it to the state with the closest CO${}_2$ emission factor in Table 10—using the other emissions factors for that state. Since the Kyoto Protocol (UNFCCC 1997) requires each country to report emissions of the major greenhouse gases [carbon dioxide (CO${}_2$), methane (CH${}_4$), and nitrous oxide (N${}_2$O)] as well as ozone-depleting substances [hydrofluorocarbons (HFC), perfluorocarbons (PFC), and sulphur hexafluoride (SF${}_6$)] and all energy consumption in their annual ‘national communication’, more complete emission factors for a larger number of countries should become available over the next few years. More information and other resources for calculating emissions factors are available in IPCC (2000, 1997).

References[LINK]

Crawley, Drury B. 2003. “Impact of Climate Change on Buildings,” in Proceedings of the CIBSE/ASHRAE International Conference 2003, September 2003, Edinburgh, Scotland. London, England: CIBSE.

Intergovernmental Panel on Climate Change. 2001. Climate Change 2001: The Scientific Basis. Cambridge: Cambridge University Press.

Intergovernmental Panel on Climate Change. 2000. Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories, Paris, France: IPCC/OECD/IEA.

Intergovernmental Panel on Climate Change. 1997. Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories, J.T. Houghton, L.G. Meira Filho, B. Lim, K. Treanton, I. Mamaty, Y. Bonduki, D.J. Griggs and B.A. Callender (editors). Paris, France: IPCC/OECD/IEA.

International Energy Agency. 2003. CO${}_2$ Emissions from Fuel Combustion 1971-2001 (2003) – 2003 Edition. Paris, France: IEA.

Liesen, Richard J. 1997. Atmospheric Pollution Prediction in a Building Energy Simulation Program, April 1997, BLAST Support Office, Department of Mechanical Engineering. Champaign, Illinois: University of Illinois.

Stroot, Peter J., Robert J. Nemeth, & Donald F. Fournier. 1996. Pollution Reduction Through Energy Conservation, REEP Model. Champaign, Illinois: U S Army Construction Engineering Research Laboratory.

Torcellini Paul A, Nicholas Long, and Ronald D. Judkoff. 2004. “Consumptive Water Use for U.S. Power Production,” in ASHRAE Transactions, Volume 110, Part 1. Atlanta, Georgia: ASHRAE.

United Nations Environment Programme. 2002. Climate Change Information Kit. Châtelaine, Switzerland: UNEP.

United Nations Framework Convention on Climate Change. 1997. Kyoto Protocol to the United Nations Framework Convention on Climate Change. Bonn, Germany: UNFCCC.

U.S. Department of Energy. 2004. Monthly Energy Review. Washington, DC: Energy Information Administration, U S Department of Energy.

U.S. Department of Energy. 2002. Updated State-level Greenhouse Gas Emission Coefficients for Electricity Generation 1998-2000. April 2002, Energy Information Administration, Office of Integrated Analysis and Forecasting, Energy Information Administration. Washington, DC: U.S. Department of Energy.

U.S. Environmental Protection Agency. 2003a. eGRID Emissions and Generation Resource Integrated Database, May 2003, Washington, DC: U.S. Environmental Protection Agency.

U.S. Environmental Protection Agency. 2003b. AirData, Tier Emissions Report - Criteria Air Pollutants, 1999 data, May 2003. Washington, DC: U.S. Environmental Protection Agency.

U.S. Environmental Protection Agency. 1998a. Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I: Stationary Point and Area Sources, Chapter 1 External Combustion Sources, Supplement D, July 1998. Research Triangle Park, North Carolina: U. S. Environmental Protection Agency.

U.S. Environmental Protection Agency. 1998b. Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I: Stationary Point and Area Sources, Chapter 1 External Combustion Sources, Supplement E, September 1998. Research Triangle Park, North Carolina: U. S. Environmental Protection Agency.

U.S. Environmental Protection Agency. 1996. Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I: Stationary Point and Area Sources, Chapter 1 External Combustion Sources, Supplement B, October 1996. Research Triangle Park, North Carolina: U. S. Environmental Protection Agency.