impact_model.rb

Copyright © 2010 Brighter Planet. See LICENSE for details. Contact Brighter Planet for dual-license arrangements.

 

      		
    

    

      
        

          
        

        
Meeting carbon model



This model is used by Brighter Planet’s carbon emission web service to estimate the greenhouse gas emissions of a meeting (e.g. a conference).



Timeframe and date



The model estimates the emissions that occur during a particular timeframe. To do this it needs to know the meeting’s date. For example, if the timeframe is January 2010, a meeting that occurred on January 11 2010 will have emissions but a meeting that occurred on Febraury 1 2010 will not.



Calculations



The final estimate is the result of the calculations detailed below. These calculations are performed in reverse order, starting with the last calculation listed and finishing with the emission calculation. Each calculation is named according to the value it returns.



Methods



To accomodate varying client input, each calculation may have one or more methods. These are listed under each calculation in order from most to least preferred. Each method is named according to the values it requires. If any of these values is not available the method will be ignored. If all the methods for a calculation are ignored, the calculation will not return a value. “Default” methods do not require any values, and so a calculation with a default method will always return a value.



Standard compliance



Each method lists any established calculation standards with which it complies. When compliance with a standard is requested, all methods that do not comply with that standard are ignored. This means that any values a particular method requires will have been calculated using a compliant method, because those are the only methods available. If any value did not have a compliant method in its calculation then it would be undefined, and the current method would have been ignored.



Collaboration



Contributions to this carbon model are actively encouraged and warmly welcomed. This library includes a comprehensive test suite to ensure that your changes do not cause regressions. All changes should include test coverage for new functionality. Please see sniff, our emitter testing framework, for more information.

      		
      
        
require 'conversions'

module BrighterPlanet
  module Meeting
    module ImpactModel
      def self.included(base)
        base.decide :impact, :with => :characteristics do

      		
    

    

      
        

          
        

        

      		
      
        
          

      		
    

    

      
        

          
        

        
Carbon (kg CO2e)



The meeting’s total anthropogenic greenhouse gas emissions during timeframe.

      		
      
        
          committee :carbon do

      		
    

    

      
        

          
        

        
If date falls within timeframe multiply each fuel use by the fuel’s emission factor and sum to give kg CO2e. Otherwise carbon is zero.

      		
      
        
            quorum 'from fuel uses, electricity emission factor, date, and timeframe', :needs => [:natural_gas_use, :fuel_oil_use, :electricity_use, :district_heat_use, :electricity_emission_factor, :date],
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics, timeframe|
                date = characteristics[:date].is_a?(Date) ? characteristics[:date] : Date.parse(characteristics[:date].to_s)
                if timeframe.include? date
                   (characteristics[:natural_gas_use] * Fuel.find('Pipeline Natural Gas').co2_emission_factor) +
                   (characteristics[:fuel_oil_use] * Fuel.find('Distillate Fuel Oil No. 2').co2_emission_factor) +
                   (characteristics[:electricity_use] * characteristics[:electricity_emission_factor]) +
                   (characteristics[:district_heat_use] * Fuel.find('District Heat').co2_emission_factor)
                else
                  0
                end
            end
            

      		
    

    

      
        

          
        

        
Default emission

      		
      
        
            quorum 'default' do

      		
    

    

      
        

          
        

        
Displays an error if the previous method fails.

      		
      
        
              raise "The emission committee's default quorum should never be called"
            end
          end
          

      		
    

    

      
        

          
        

        
Electricity emission factor (kg CO2e / kWh)



A greenhouse gas emission factor for the meeting’s electricity use including transmission and distribution losses.

      		
      
        
          committee :electricity_emission_factor do

      		
    

    

      
        

          
        

        
Divide the eGRID subregion electricity emission factor (kg CO2e / kWh) by 1 minus the eGRID subregion eGRID region loss factor to give kg CO2e / kWh.

      		
      
        
            quorum 'from eGRID subregion', :needs => :egrid_subregion,
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:egrid_subregion].electricity_emission_factor / (1 - characteristics[:egrid_subregion].egrid_region.loss_factor)
            end
            

      		
    

    

      
        

          
        

        
Divide the state electricity emission factor (kg CO2e / kWh) by 1 minus the state electricity loss factor to give kg CO2e / kWh.

      		
      
        
            quorum 'from state', :needs => :state,
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:state].electricity_emission_factor / (1 - characteristics[:state].electricity_loss_factor)
            end
            

      		
    

    

      
        

          
        

        
Otherwise divide the U.S. average electricity emission factor (kg CO2e / kWh) by the U.S. average electricity loss factor to give kg CO2e / kWh.

      		
      
        
            quorum 'default',
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do
                EgridSubregion.fallback.electricity_emission_factor / (1 - EgridSubregion.fallback.egrid_region.loss_factor)
            end
          end
          

      		
    

    

      
        

          
        

        
Natural gas use (m3)



The meeting’s natural gas use.

      		
      
        
          committee :natural_gas_use do

      		
    

    

      
        

          
        

        
Multiply the census division meeting building natural gas intensity (m3 / m2 hour) by area (m2) and duration (seconds) / 3600 (seconds / hour) to give m3.

      		
      
        
            quorum 'from census division, area, and duration', :needs => [:census_division, :area, :duration],
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:census_division].meeting_building_natural_gas_intensity *
                  characteristics[:area] *
                  characteristics[:duration] / 3600.0
            end
          end
          

      		
    

    

      
        

          
        

        
Fuel oil use (l)



The meeting’s fuel oil use.

      		
      
        
          committee :fuel_oil_use do

      		
    

    

      
        

          
        

        
Multiply the census division meeting building fuel oil intensity (l / m2 hour) by area (m2) and duration (seconds) / 3600 (seconds / hour) to give l.

      		
      
        
            quorum 'from census division, area, and duration', :needs => [:census_division, :area, :duration],
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:census_division].meeting_building_fuel_oil_intensity *
                  characteristics[:area] *
                  characteristics[:duration] / 3600.0
            end
          end
          

      		
    

    

      
        

          
        

        
Electricity use (kWh)



The meeting’s electricity use.

      		
      
        
          committee :electricity_use do

      		
    

    

      
        

          
        

        
Multiply the census division meeting building electricity intensity (kWh / m2 hour) by area (m2) and duration (seconds) / 3600 (seconds / hour) to give kWh.

      		
      
        
            quorum 'from census division, area, and duration', :needs => [:census_division, :area, :duration],
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:census_division].meeting_building_electricity_intensity *
                  characteristics[:area] *
                  characteristics[:duration] / 3600.0
            end
          end
          

      		
    

    

      
        

          
        

        
District heat use (MJ)



The meeting’s district heat use.

      		
      
        
          committee :district_heat_use do

      		
    

    

      
        

          
        

        
Multiply the census division meeting building district heat intensity (MJ / m2 hour) by area (m2) and duration (seconds) / 3600 (seconds / hour) to give MJ.

      		
      
        
            quorum 'from census division, area, and duration', :needs => [:census_division, :area, :duration],
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:census_division].meeting_building_district_heat_intensity *
                  characteristics[:area] *
                  characteristics[:duration] / 3600.0
            end
          end
          

      		
    

    

      
        

          
        

        
eGRID subregion



The meeting venue’s eGRID subregion.

      		
      
        
          committee :egrid_subregion do

      		
    

    

      
        

          
        

        
Look up the zip code eGRID subregion.

      		
      
        
            quorum 'from zip code', :needs => :zip_code,
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:zip_code].egrid_subregion
            end
          end
          

      		
    

    

      
        

          
        

        
Census division



The meeting venue’s census division.

      		
      
        
          committee :census_division do

      		
    

    

      
        

          
        

        
Look up the state census division.

      		
      
        
            quorum 'from state', :needs => :state,
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:state].census_division
            end
            

      		
    

    

      
        

          
        

        
Otherwise uses an artificial census division representing U.S. averages.

      		
      
        
            quorum 'default',
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do
                CensusDivision.fallback
            end
          end
          

      		
    

    

      
        

          
        

        
State



The meeting venue’s state.

      		
      
        
          committee :state do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise look up the zip code state.

      		
      
        
            quorum 'from zip code', :needs => :zip_code,
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do |characteristics|
                characteristics[:zip_code].state
            end
          end
          

      		
    

    

      
        

          
        

        
Zip code



The zip code of the meeting venue.



Use client input, if available.

      		
      
        
          

      		
    

    

      
        

          
        

        
Area (m2)



The meeting venue’s area.

      		
      
        
          committee :area do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise use 1,184.5 m2 (the average size of meeting buildings in the EIA Commercial Building Energy Consumption Survey).

      		
      
        
            quorum 'default',
              :complies => [:ghg_protocol_scope_3, :iso, :tcr] do
                10_448.square_feet.to(:square_metres)
            end
          end
          

      		
    

    

      
        

          
        

        
Duration (seconds)



The meeting’s duration – the length of time the meeting facilities are in use. For example a two-day conference that runs 8 hours each day would have a duration of 57600.

      		
      
        
          committee :duration do

      		
    

    

      
        

          
        

        
Uses client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise use 28800 seconds (8 hours).

      		
      
        
            quorum 'default' do
              28800.0
            end
          end
          

      		
    

    

      
        

          
        

        
Date (date)



The day the meeting occurred.

      		
      
        
          committee :date do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise use the first day of timeframe.


      		
      
        
            quorum 'from timeframe',
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics, timeframe|
                timeframe.from
            end
          end
        end
      end
    end
  end
end