impact_model.rb

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

 

      		
    

    

      
        

          
        

        
Automobile impact model



This model is used by the Brighter Planet CM1 web service to calculate the impacts of an automobile, such as energy use and greenhouse gas emissions.

      		
      
        

      		
    

    

      
        

          
        

        
Timeframe



The model calculates impacts that occured during a particular time period (timeframe).
For example if the timeframe is February 2010, an automobile put into use (acquisition) in December 2009 and taken out of use (retirement) in March 2010 will have impacts because it was in use during January 2010.
An automobile put into use in March 2010 or taken out of use in January 2010 will have zero impacts, because it was not in use during February 2010.



The default timeframe is the current calendar year.

      		
      
        

      		
    

    

      
        

          
        

        
Calculations



The final impacts are the result of the calculations below. These are performed in reverse order, starting with the last calculation listed and finishing with the greenhouse gas emissions calculation.



Each calculation listing shows:



    

  • value returned (units of measurement)
    • 

  • description of the value
    • 

  • calculation methods, listed from most to least preferred
    • 





Some methods use values returned by prior calculations. If any of these values are unknown the method is skipped.
If all the methods for a calculation are skipped, the value the calculation would return is unknown.

      		
      
        

      		
    

    

      
        

          
        

        
Standard compliance



When compliance with a particular standard is requested, all methods that do not comply with that standard are ignored.
Thus any values a method needs will have been calculated using a compliant method or will be unknown.
To see which standards a method complies with, look at the :complies => section of the code in the right column.



Client input complies with all standards.

      		
      
        

      		
    

    

      
        

          
        

        
Collaboration



Contributions to this impact 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.

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

      		
    

    

      
        

          
        

        

      		
      
        
          

      		
    

    

      
        

          
        

        
Carbon (kg CO2e)



The automobile’s total anthropogenic greenhouse gas emissions during active subtimeframe.

      		
      
        
          committee :carbon do

      		
    

    

      
        

          
        

        
Sum co2 emission (kg), ch4 emission (kg CO2e), n2o emission (kg CO2e), and hfc emission (kg CO2e) to give kg CO2e.

      		
      
        
            quorum 'from co2 emission, ch4 emission, n2o emission, and hfc emission', :needs => [:co2_emission, :ch4_emission, :n2o_emission, :hfc_emission],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                characteristics[:co2_emission] + characteristics[:ch4_emission] + characteristics[:n2o_emission] + characteristics[:hfc_emission]
            end
          end
          

      		
    

    

      
        

          
        

        
CO2 emission (kg)



The automobile’s CO2 emissions from anthropogenic sources during active subtimeframe.

      		
      
        
          committee :co2_emission do

      		
    

    

      
        

          
        

        
Multiply fuel use (l) by the automobile fuel co2 emission factor (kg / l) to give kg.

      		
      
        
            quorum 'from fuel use and automobile fuel', :needs => [:fuel_use, :automobile_fuel],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                characteristics[:fuel_use] * characteristics[:automobile_fuel].co2_emission_factor
            end
          end
          

      		
    

    

      
        

          
        

        
CO2 biogenic emission (kg)



The automobile’s CO2 emissions from biogenic sources during active subtimeframe.

      		
      
        
          committee :co2_biogenic_emission do

      		
    

    

      
        

          
        

        
Multiply fuel use (l) by the automobile fuel co2 biogenic emission factor (kg / l) to give kg.

      		
      
        
            quorum 'from fuel use and automobile fuel', :needs => [:fuel_use, :automobile_fuel],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                characteristics[:fuel_use] * characteristics[:automobile_fuel].co2_biogenic_emission_factor
            end
          end
          

      		
    

    

      
        

          
        

        
CH4 emission (kg CO2e)



The automobile’s CH4 emissions during active subtimeframe.

      		
      
        
          committee :ch4_emission do

      		
    

    

      
        

          
        

        
Multiply fuel use (l) by the automobile fuel ch4 emission factor (kg CO2e / l) to give kg CO2e.

      		
      
        
            quorum 'from fuel use and automobile fuel', :needs => [:fuel_use, :automobile_fuel],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                characteristics[:fuel_use] * characteristics[:automobile_fuel].ch4_emission_factor
            end
          end
          

      		
    

    

      
        

          
        

        
N2O emission (kg CO2e)



The automobile’s N2O emissions during active subtimeframe.

      		
      
        
          committee :n2o_emission do

      		
    

    

      
        

          
        

        
Multiply fuel use (l) by the automobile fuel n2o emission factor (kg CO2e / l) to give kg CO2e.

      		
      
        
            quorum 'from fuel use and automobile fuel', :needs => [:fuel_use, :automobile_fuel],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                characteristics[:fuel_use] * characteristics[:automobile_fuel].n2o_emission_factor
            end
          end
          

      		
    

    

      
        

          
        

        
HFC emission (kg CO2e)



The automobile’s HFC emissions during active subtimeframe.

      		
      
        
          committee :hfc_emission do

      		
    

    

      
        

          
        

        
Multiply fuel use (l) by the automobile fuel hfc emission factor (kg CO2e / l) to give kg CO2e.

      		
      
        
            quorum 'from fuel use and automobile fuel', :needs => [:fuel_use, :automobile_fuel],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                characteristics[:fuel_use] * characteristics[:automobile_fuel].hfc_emission_factor
            end
          end
          

      		
    

    

      
        

          
        

        
Energy (MJ)



The automobile’s energy use during active subtimeframe.

      		
      
        
          committee :energy do

      		
    

    

      
        

          
        

        
Multiply fuel use (l) by the automobile fuel energy content (MJ / l) to give MJ.

      		
      
        
            quorum 'from fuel use and automobile fuel', :needs => [:fuel_use, :automobile_fuel] do |characteristics|
              characteristics[:fuel_use] * characteristics[:automobile_fuel].energy_content
            end
          end
          

      		
    

    

      
        

          
        

        
Fuel use (l)



The automobile’s fuel use during active subtimeframe.

      		
      
        
          committee :fuel_use do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise divide distance (km) by fuel efficiency (km / l) to give l.

      		
      
        
            quorum 'from fuel efficiency and distance', :needs => [:fuel_efficiency, :distance],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                characteristics[:distance] / characteristics[:fuel_efficiency]
            end
          end
          

      		
    

    

      
        

          
        

        
Distance (km)



The distance the automobile travelled during active subtimeframe.

      		
      
        
          committee :distance do

      		
    

    

      
        

          
        

        
Multiply annual distance (km) by the fraction of the calendar year in which timeframe falls that overlaps with active subtimeframe to give km.

      		
      
        
            quorum 'from annual distance', :needs => [:annual_distance, :active_subtimeframe],
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics, timeframe|
                characteristics[:annual_distance] * (characteristics[:active_subtimeframe] / timeframe.year)
            end
          end
          

      		
    

    

      
        

          
        

        
Annual distance (km)



The distance the automobile would travel if it were used for the entire calendar year in which timeframe falls.
Note that this will be more than the actual distance traveled if the automobile was not in use for the entire calendar year (if either acquisition or retirement occurs during the calendar year in which timeframe falls).

      		
      
        
          committee :annual_distance do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise divide weekly distance (km) by 7 and multiply by the number of days in the calendar year in which timeframe falls to give km.

      		
      
        
            quorum 'from weekly distance and timeframe', :needs => :weekly_distance,
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics, timeframe|
                (characteristics[:weekly_distance] / 7 ) * timeframe.year.days
            end
            

      		
    

    

      
        

          
        

        
Otherwise multiply daily distance (km) by the number of days in the calendar year in which timeframe falls to give km.

      		
      
        
            quorum 'from daily distance and timeframe', :needs => :daily_distance,
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics, timeframe|
                characteristics[:daily_distance] * timeframe.year.days
            end
            

      		
    

    

      
        

          
        

        
Otherwise divide daily duration (seconds) by 3600 (seconds / hour) and multiply by speed (km / hour) to give km.
Multiply by the number of days in the calendar year in which timeframe falls to give km.

      		
      
        
            quorum 'from daily duration, speed, and timeframe', :needs => [:daily_duration, :speed],
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics, timeframe|
                characteristics[:daily_duration] / 3600.0 * characteristics[:speed] * timeframe.year.days
            end
            

      		
    

    

      
        

          
        

        
Otherwise use the size class annual distance (km).

      		
      
        
            quorum 'from size class', :needs => :size_class,
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics|
                characteristics[:size_class].annual_distance
            end
            

      		
    

    

      
        

          
        

        
Otherwise use the automobile fuel annual distance (km).

      		
      
        
            quorum 'from automobile fuel', :needs => :automobile_fuel,
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics|
                characteristics[:automobile_fuel].annual_distance
            end
          end
          

      		
    

    

      
        

          
        

        
Weekly distance (km)



The average distance the automobile is driven each week.



Use client input if available.

      		
      
        
          

      		
    

    

      
        

          
        

        
Daily distance (km)



The average distance the automobile is driven each day.



Use client input if available.

      		
      
        
          

      		
    

    

      
        

          
        

        
Daily duration (seconds)



The average time the automobile is driven each day.



Use client input, if available.

      		
      
        
          

      		
    

    

      
        

          
        

        
Automobile fuel



The automobile’s fuel type.

      		
      
        
          committee :automobile_fuel do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise use the make model year automobile fuel.

      		
      
        
            quorum 'from make model year', :needs => :make_model_year,
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                characteristics[:make_model_year].automobile_fuel
            end
            

      		
    

    

      
        

          
        

        
Otherwise use the average automobile fuel.

      		
      
        
            quorum 'default',
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics|
                AutomobileFuel.fallback
            end
          end
          

      		
    

    

      
        

          
        

        
Speed (km / hour)



The automobile’s average speed.

      		
      
        
          committee :speed do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise look up the United States average automobile city speed (km / hour) and automobile highway speed (km / hour).
Calculate the harmonic mean of those speeds weighted by urbanity to give km / hour.

      		
      
        
            quorum 'from urbanity', :needs => :urbanity,
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                1 / (characteristics[:urbanity] / Country.united_states.automobile_city_speed + (1 - characteristics[:urbanity]) / Country.united_states.automobile_highway_speed)
            end
          end
          

      		
    

    

      
        

          
        

        
Fuel efficiency (km / l)



The automobile’s fuel efficiency.

      		
      
        
          committee :fuel_efficiency do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise look up the make model year fuel efficiency city (km / l) and fuel efficiency highway (km / l).
Calculate the harmonic mean of those fuel efficiencies, weighted by urbanity, to give km / l.

      		
      
        
            quorum 'from make model year and urbanity', :needs => [:make_model_year, :urbanity],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                1.0 / (
                  (characteristics[:urbanity]         / characteristics[:make_model_year].fuel_efficiency_city) +
                  ((1.0 - characteristics[:urbanity]) / characteristics[:make_model_year].fuel_efficiency_highway)
                )
            end
            

      		
    

    

      
        

          
        

        
Otherwise look up the make model fuel efficiency city (km / l) and fuel efficiency highway (km / l).
Calculate the harmonic mean of those fuel efficiencies, weighted by urbanity, to give km / l.

      		
      
        
            quorum 'from make model and urbanity', :needs => [:make_model, :urbanity],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                1.0 / (
                  (characteristics[:urbanity]         / characteristics[:make_model].fuel_efficiency_city) +
                  ((1.0 - characteristics[:urbanity]) / characteristics[:make_model].fuel_efficiency_highway)
                )
            end
            

      		
    

    

      
        

          
        

        
Otherwise look up the size class fuel efficiency city (km / l) and fuel efficiency highway (km / l).
Calculate the harmonic mean of those fuel efficiencies, weighted by urbanity, to give km / l.
Multiply by hybridity multiplier to give km / l.

      		
      
        
            quorum 'from size class, hybridity multiplier, and urbanity', :needs => [:size_class, :hybridity_multiplier, :urbanity],
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics|
                (1.0 / (
                  (characteristics[:urbanity]         / characteristics[:size_class].fuel_efficiency_city) +
                  ((1.0 - characteristics[:urbanity]) / characteristics[:size_class].fuel_efficiency_highway)
                )) * characteristics[:hybridity_multiplier]
            end
            

      		
    

    

      
        

          
        

        
Otherwise look up the make year fuel efficiency (km / l).
Multiply by hybridity multiplier to give km / l.

      		
      
        
            quorum 'from make year and hybridity multiplier', :needs => [:make_year, :hybridity_multiplier],
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics|
                characteristics[:make_year].fuel_efficiency * characteristics[:hybridity_multiplier]
            end
            

      		
    

    

      
        

          
        

        
Otherwise look up the make fuel efficiency (km / l).
Multiply by hybridity multiplier to give km / l.

      		
      
        
            quorum 'from make and hybridity multiplier', :needs => [:make, :hybridity_multiplier],
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics|
                characteristics[:make].fuel_efficiency * characteristics[:hybridity_multiplier]
            end
            

      		
    

    

      
        

          
        

        
Otherwise look up the United States average automobile fuel efficiency (km / l).
Multiply by hybridity multiplier to give km / l.

      		
      
        
            quorum 'from hybridity multiplier', :needs => :hybridity_multiplier,
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics|
                Country.united_states.automobile_fuel_efficiency * characteristics[:hybridity_multiplier]
            end
          end
          

      		
    

    

      
        

          
        

        
Hybridity multiplier (dimensionless)



A multiplier used to adjust fuel efficiency if we know the automobile is a hybrid or conventional vehicle.

      		
      
        
          committee :hybridity_multiplier do

      		
    

    

      
        

          
        

        
Check whether the size class has hybridity multipliers for city and highway fuel efficiency.
If it does, calculate the harmonic mean of those multipliers, weighted by urbanity.

      		
      
        
            quorum 'from size class, hybridity, and urbanity', :needs => [:size_class, :hybridity, :urbanity],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                drivetrain = (characteristics[:hybridity] == true) ? :hybrid : :conventional
                city_multiplier    = characteristics[:size_class].send(:"#{drivetrain}_fuel_efficiency_city_multiplier")
                highway_multiplier = characteristics[:size_class].send(:"#{drivetrain}_fuel_efficiency_highway_multiplier")
                
                if city_multiplier and highway_multiplier
                  1.0 / ((characteristics[:urbanity] / city_multiplier) + ((1.0 - characteristics[:urbanity]) / highway_multiplier))
                end
            end
            

      		
    

    

      
        

          
        

        
Otherwise look up the average size class hybridity multipliers for city and highway fuel efficiency.
Calculate the harmonic mean of those multipliers, weighted by urbanity.

      		
      
        
            quorum 'from hybridity and urbanity', :needs => [:hybridity, :urbanity],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                drivetrain = (characteristics[:hybridity] == true) ? :hybrid : :conventional
                urbanity = characteristics[:urbanity]
                fuel_efficiency_multipliers = {
                  :city => AutomobileSizeClass.fallback.send(:"#{drivetrain}_fuel_efficiency_city_multiplier"),
                  :highway => AutomobileSizeClass.fallback.send(:"#{drivetrain}_fuel_efficiency_highway_multiplier")
                }
                1.0 / ((urbanity / fuel_efficiency_multipliers[:city]) + ((1.0 - urbanity) / fuel_efficiency_multipliers[:highway]))
            end
            

      		
    

    

      
        

          
        

        
Otherwise use a multiplier of 1.0.

      		
      
        
            quorum 'default',
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do
                1.0
            end
          end
          

      		
    

    

      
        

          
        

        
Hybridity (boolean)



True if the automobile is a hybrid vehicle. False if the automobile is a conventional vehicle.



Use client input, if available.

      		
      
        
          

      		
    

    

      
        

          
        

        
Size class



The automobile’s size class.



Use client input, if available.

      		
      
        
          

      		
    

    

      
        

          
        

        
Urbanity (%)



The fraction of the total distance driven that is in towns and cities rather than highways.
Highways are defined as all driving at speeds of 45 miles per hour or greater.

      		
      
        
          committee :urbanity do

      		
    

    

      
        

          
        

        
Use the United States average automobile urbanity (%).

      		
      
        
            quorum 'default',
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do
                Country.united_states.automobile_urbanity
            end
          end
          

      		
    

    

      
        

          
        

        
Active subtimeframe (date range)



The portion of timeframe that falls between acquisition and retirement.

      		
      
        
          committee :active_subtimeframe do

      		
    

    

      
        

          
        

        
Calculate the portion of timeframe that falls between acqusition and retirement (date range).
If there is no overlap then we don’t know active subtimeframe.

      		
      
        
            quorum 'from acquisition and retirement', :needs => [:acquisition, :retirement],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics, timeframe|
                Timeframe.constrained_new characteristics[:acquisition].to_date, characteristics[:retirement].to_date, timeframe
            end
          end
          

      		
    

    

      
        

          
        

        
Acquisition (date)



The date the automobile was put into use.

      		
      
        
          committee :acquisition do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise use the first day of year (date).

      		
      
        
            quorum 'from year', :needs => :year,
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics|
                Date.new characteristics[:year].year, 1, 1
            end
            

      		
    

    

      
        

          
        

        
Otherwise use whichever is earlier: the first day of timeframe or retirement.

      		
      
        
            quorum 'default', :appreciates => :retirement,
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics, timeframe|
                [ timeframe.from, characteristics[:retirement] ].compact.min
            end
          end
          

      		
    

    

      
        

          
        

        
Retirement (date)



The date the automobile was taken out of use.

      		
      
        
          committee :retirement do

      		
    

    

      
        

          
        

        
Use client input, if available.

      		
      
        
            

      		
    

    

      
        

          
        

        
Otherwise use whichever is later: the last day of timeframe or acquisition (if we know it).

      		
      
        
            quorum 'default', :appreciates => :acquisition,
              :complies => [:ghg_protocol_scope_3, :iso] do |characteristics, timeframe|
                [ timeframe.to, characteristics[:acquisition] ].compact.max
            end
          end
          

      		
    

    

      
        

          
        

        
Make model year



The automobile’s make, model, and year.

      		
      
        
          committee :make_model_year do

      		
    

    

      
        

          
        

        
Check whether the make, model, and year combination matches any automobiles in our database.
If it doesn’t then we don’t know make model year.

      		
      
        
            quorum 'from make, model, and year', :needs => [:make, :model, :year],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                AutomobileMakeModelYear.find_by_make_name_and_model_name_and_year(characteristics[:make].name, characteristics[:model].name, characteristics[:year].year)
            end
          end
          

      		
    

    

      
        

          
        

        
Make year



The automobile’s make and year.

      		
      
        
          committee :make_year do

      		
    

    

      
        

          
        

        
Check whether the make and year combination matches any automobiles in our database.
If it doesn’t then we don’t know make year.

      		
      
        
            quorum 'from make and year', :needs => [:make, :year],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                AutomobileMakeYear.find_by_make_name_and_year(characteristics[:make].name, characteristics[:year].year)
            end
          end
          

      		
    

    

      
        

          
        

        
Make model



The automobile’s make and model.

      		
      
        
          committee :make_model do

      		
    

    

      
        

          
        

        
Check whether the make and model combination matches any automobiles in our database.
If it doesn’t then we don’t know make model.

      		
      
        
            quorum 'from make and model', :needs => [:make, :model],
              :complies => [:ghg_protocol_scope_1, :ghg_protocol_scope_3, :iso] do |characteristics|
                AutomobileMakeModel.find_by_make_name_and_model_name(characteristics[:make].name, characteristics[:model].name)
            end
          end
          

      		
    

    

      
        

          
        

        
Year



The automobile’s year of manufacture.



Use client input, if available.

      		
      
        
          

      		
    

    

      
        

          
        

        
Model



The automobile’s model.



Use client input, if available.

      		
      
        
          

      		
    

    

      
        

          
        

        
Make



The automobile’s make.



Use client input, if available.


      		
      
        
        end
      end
    end
  end
end