There are two methods for estimating emissions from the use of heat transfer fluids. The choice of methods will depend on the availability of activity data on the use of heat transfer fluids, and is outlined in the decision tree (see Figure 6.2, Decision Tree for Estimation of FC Emissions from Heat Transfer Fluids, and see Section 1.5 of Chapter 1, Choosing between the Mass-Balance and Emission-Factor Approach).
Tier 1 is appropriate when company-specific data are not available on heat transfer fluids. It is the less accurate of the two methods for estimating emissions from losses of heat transfer fluids. The method, unlike the Tier 2 method, gives an estimate of aggregate emissions - a weighted average emission across all liquid FCs that is expressed as the mass of C6F1410. The calculation relies on a generic emission factor that expresses the average
10 In the absence of GWP estimates, the appropriate GWP for C6F14 has been used as a proxy (to derive the default emission factor). (See the Inventory of U.S. Greenhouse Gas and Sinks: 1990-2003, the footnote to Table 4-58, page 166. (U.S. EPA, 2005))
aggregate emissions per unit of silicon consumed during semiconductor manufacturing. The formula is shown in Equation 6.12.
Tier 1 method for estimation of total FC emissions from heat transfer fluids
FCliquid, total = total FC emissions as expressed as the mass of C6F14, Mt C6F14
EFi = emission factor (aggregate FC emissions per Gm2 of silicon consumed during the period expressed as the mass of C6F14 (See Table 6.2.)), Mt C6FM/Gm2
Cu = average capacity utilisation for all semiconductor manufacturing facilities in the country during the period, fraction
Cd = design capacity of semiconductor manufacturing facilities in the country, Gm2
There is one Tier 2 method for estimating actual emissions from the use of each FC fluid. This method is a massbalance approach that accounts for liquid FC usage over an annual period. It is appropriate when company-specific data are available. Over the course of a year, liquid FCs are used to fill newly purchased equipment and to replace FC fluid loss from equipment operation through evaporation. The Tier 2 method neglects fluid losses during filling new or existing equipment or when decommissioning old equipment (which is reasonable for these costly fluids).11 Inventory compilers should obtain from companies the chemical composition of the fluid(s) for which emissions are estimated. The method is expressed in Equation 6.13.
Tier 2 method for estimation of FC emissions from heat transfer fluids
FC, = P • [/,t-1(/) + Pit(l)- Nht(l) + Rt(l)-Iu(l)-Di t(l)]
FCi = emissions of FCi, kg p, = density of liquid FCi, kg/litre
Ii,t-i(l) = the inventory of liquid FCi at the end of the previous period, litres
Pit(l) = net purchases of liquid FCi during the period (net of purchases and any returns), litres
Nit(l) = total charge (or nameplate capacity) of new installed, litres
Rit(l) = total charge (or nameplate capacity) of retired or sold equipment, litres
Iit(l) = inventory of liquid FCi at end of the period, litres
Dit(l) = amount of FCi recovered and sent offsite from retired equipment during the period, litres
11 Prices for heat transfer fluids vary from $55 - 130/litre. 3M, a manufacturer of a popular heat transfer fluid estimates that a vintage 2 000 manufacturing plant may loose 1 900 litres/year via evaporation. Manufactures of testing equipment that use heat transfer fluids report loss rates of approximately 30 litres/year/system for newer designs that reduce evaporative losses and 50 litres/year/system for older designs.
Decision tree for estimation of FC emissions from HT fluid loss from electronics manufacturing
Estimate emissions using the Tier 2 method.
Collect liquid FC use data from companies.
Estimate emissions using the Tier 1 method.
1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees
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