Greenhouse Gas Inventory
Net emissions in metric tons of carbon dioxide equivalent (MT CO2e).
Background & History
NOTE: for current information, please see the Emissions Update, published annually.
Anthropogenic emissions of carbon dioxide and other greenhouse gases are the dominant factor contributing to the rapid, unprecedented, and accelerating changes in the global climate that are occurring. An inventory of Clark University's greenhouse gas emissions is an important step in assessing the environmental impact of the campus and in identifying areas and activities with a high environmental impact that could be targeted for reduction.
The Clark University Environmental Sustainability task force completed a baseline multi-year greenhouse gas inventory in 2007 using the Greenhouse Gas Emissions Calculator developed by the nonprofit organization Clean Air Cool Planet. The calculator multiplies measures of energy use, agriculture, refrigerant use, and solid waste by emissions factors to determine the amount of metric tons of carbon dioxide equivalent (MT CO2e) added to the atmosphere by campus operations. The six greenhouse gases considered in this calculation are those included in the Kyoto Protocol: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFC), and sulfur hexafluoride (SF6). Of these six, CO2 (produced during the combustion of all fossil fuels) and HFCs (gases that are used in refrigerants and air conditioners) have been shown by this inventory to be the primary gases emitted on campus. CH4 and N2O emissions are primarily associated with agriculture, and PFCs and SF6 are primarily associated with industrial emissions not relevant to Clark.
The scope of this initial inventory includes greenhouse gas emissions for three calendar years, 2004 through 2006, derived from heat energy, generated electricity and heat, purchased electricity, solid waste, and refrigerants.
Performance of Baseline GHG Inventory
The major sources of greenhouse gas emissions are the operation of our steam heat boilers and the cogeneration plant, as well as the operation of power plants generating the electricity consumed on campus. Data on fossil fuel use in the operation of the boilers and the cogeneration plant, along with data on electricity consumption and estimates on the fuel mix used in generating electricity in this region, are converted in our emissions calculator into metric tons of carbon dioxide equivalent. Between 2004 and 2006, total (gross) emissions decreased by 9.6 percent, from 14,155 MT CO2e to 12,802 MT CO2e. The decrease is largely explained by reductions in thermal energy use throughout the period as well as the reduction in electricity consumption in 2006.
To understand the observed reduction in total emissions in greater depth, it is helpful to assess emissions by each source. This is made possible because the Greenhouse Gas Emissions Calculator allocates proportionally the emissions from the cogeneration engine to its two outputs, heat energy and electricity. The graph displays total electricity emissions (emissions from purchased electricity and cogen electricity) and heat emissions (from steam heat from the boilers and steam and hot water from the cogen engine). Refrigerants, while in the graph, were not considered in the analysis here given their relatively small impact.
Between 2004 and 2005, total emissions dropped by 2.6 percent. The reduction is the net result of a 15.2 percent reduction in heat emissions (1,562 MT CO2e) and a 25.5 percent increase in electricity emissions (930 MT CO2e). Heat emissions fell due to a 7.6 percent reduction in heat use in 2005. Heat emissions were also reduced due to a greater reliance on the boilers for heat in 2005 when the cogeneration engine was taken offline for six months. The boilers are more carbon efficient (averaging 229 lbs of CO2e per MMBtu) than the cogeneration plant with regard to producing heat (averaging 400 lbs of CO2e per MMBtu). This is because the waste heat boiler currently attached to the cogen engine is too small to capture the bulk of the exhaust heat. In other words, the heat benefit of the cogeneration plant in not maximized with the current setup. Electricity emissions increased as the result of a 5.0 percent increase in electricity consumption in 2005 and because more electricity was purchased while the cogeneration plant was offline. Purchased power is less carbon efficient (averaging 1 lb. CO2e per kWh) than the cogeneration engine (which averages .6 lb CO2e per kWh).
Between 2005 and 2006, total emissions dropped by 7.2 percent. The reduction is the net result of a 19.3 percent reduction in electricity emissions (885 MT CO2e) and a 0.6 percent increase in heat emissions (55 MT CO2e). Electricity emissions reduced due to the 2.5 percent reduction in electricity use in 2006 and because a greater portion of electricity came from the cogen engine. In 2005, 43 percent of the total electricity used on campus was generated by the cogen engine. In 2006, that percentage increased to 90 percent. In other words, the amount of carbon dioxide equivalent emitted to produce a kWh of electricity is reduced as the cogen engine is used more. Heat emissions increased slightly, despite using 6.6 percent less heat, because a greater amount of heat was supplied by the cogen engine rather than the boilers.
Based on the baseline inventory performance regular use of cogeneration in the current configuration contributes more greenhouse gas emissions than would occur if Clark purchased all of its electricity and used the boilers to generate all the needed heat. Although electricity generation through the cogen engine is more carbon efficient than electricity supplied through the grid for our region, the generation of steam heat and hot water during the last three years was far less carbon efficient than the on-campus boilers. While use of the cogen engine during this period has presented substantial financial savings, the underutilization of the waste heat effectively rendered the operation more carbon intensive.
Offsets and GHG Emissions Reduction Activity
In addition to capturing emissions data, the calculator highlights greenhouse gas offsets resulting from different activities. In 2006, the Clark Sustainability Initiative, a student group focused on environmental sustainability issues, coordinated Clark's first-ever student purchase of futures for renewable energy certificates (RECs) through the New England Wind Fund. Someday, these monies – currently in escrow – will deliver at least two hundred MWh of wind power onto the New England grid.
The manner in which Clark's solid waste is handled acts as an offset. The daily trash from campus is hauled to a Mass Burn Incinerator in Millbury, Mass. In this version of a waste-to-energy facility, the heat energy from the burning trash powers a turbine that produces electricity. The process produces less greenhouse gases per unit of electricity than a conventional, fossil fuel power plant. By routing the waste stream through such a system, 56 MT CO2e were offset in 2006. The slight decrease over time is the result of reductions in trash tonnage generated on campus.
By deducting the offsets from total emissions, we find the net emissions for the campus. These net emissions effectively capture the impact of both regular campus operations as well as emissions reduction measures.
During the period of 2004 through 2006, net greenhouse gas emissions fell from14,093 MT CO2e to 12,746 MT CO2e (9.6 percent). As discussed in the review of the Presidents Climate Commitment, the University's ultimate goal is to achieve climate neutrality, or zero net greenhouse gas emissions from campus activities.