This methodology enables greenhouse gas emissions produced by Combined Heat and Power (CHP) facilities to be attributed to electricity and steam production respectively. The methodology originates from the WRI Greenhouse Gas Protocol worksheet Allocation of Emissions from a Combined Heat and Power (CHP) Plant (version 1.0).
Combined Heat and Power facilities produce both heat and electricity as outputs for consumption. The emissions produced in generating heat and electricity ultimately represent emissions attributable to the eventual energy consumer. The allocation of CHP facility emissions to specific quantities of energy consumed in the form of either heat (steam) or electricity is complicated however, and depends on (1) the emissions of the entire facility; (2) the ratio in which heat and electricity are produced; and (3) the efficiencies with which heat and electricity are produced from fossil fuel combustion (which is not typically the same). It is therefore usually necessary to allocate disproportionate quantities of the plant emissions to electricity users and heat users respectively.
This methodology provides an allocation of plant emissions to both steam and electricity outputs and derives unit emissions factors - i.e. measures of emissions intensity - for both steam and electricity production. The latter can be used by consumers of CHP steam or electricity for calculating the emissions attributable to specific consumed quantities.
Although CO2 is the primary greenhouse gas emitted during the combustion of fossil fuels, CH4, and N2O emissions also occur during the combustion process. The approaches described here can be applied equally to the allocation of CO2, CH4, N2O or CO2e emissions related to the purchase or sale of electricity or steam from a CHP facility. This methodology only deals in attributing the specified total plant emissions - whether CO2, or otherwise - to steam and electricity outputs.
The allocation of facility emissions to either steam or electricity production is dependent on the relative efficiencies in which each is produced. This methodology provides default efficiency factors for two scenarios: UK and US based facilities.
Activity data required
In order to allocate facility emissions to both steam and electricity production, total facility emissions and steam and electricity outputs must be provided. In addition, efficiency factors for steam and electricity production can be specified (as decimal percentages, i.e. 0-1) if facility specific data is available - otherwise US/UK typical default values are provided by the methodology.
If required, quantities of steam and/or electricity consumed can also be specified, in which case the corresponding emissions can be calculated.
Calculation and Results
The methodology uses the proportions of heat and electricity produced - together with their respective efficiency factors - to apportion the total facility emissions appropriately across heat and electricity outputs. These emissions are then converted to a per unit energy basis.
The quantities returned represent facility emissions and emissions intensities for steam and electricity production and emissions attributable to specified quantities of steam and/or electricity consumed.
This methodology requires an independent measure of total CHP facility emissions. Such emissions - typically associated with fuel combustion - can be calculated using the Greenhouse Gas Protocol (ultimately IPCC) methodology for stationary fuel combustion.