VDECS stands vehicle diesel emission control system. There are technically three types of VDECS.
As you can recall from earlier discussions, the regulation requires you meet your fleet average targets each year. If you fail to meet a fleet average target you must then meet BACT. BACT is no longer required once you meet your final fleet average emission targets. Because you can meet BACT using a VDECS, and a VDECS will reduce you in-use emission rates it is therefore important keep in mind the implications VDECS retrofits have on your fleet average emission rates:
|Type of VDECS Installed||VDECS Factor|
|No VDECS Installed or Level 1 VDECS||1|
|Level 2 PM VDECS, not highest level||0.82|
|Level 2 PM VDECS, not highest level, with NOx Reduction||1 minus (0.18+(verified % NOx reduction divided by 170)|
|Highest Level PM VDECS||0.7|
|Highest Level PM VDECS with NOx Reduction||1 minus (0.3 + rerified % NOx reduction divided by 170)|
|NOx Reduction only||1 minus (verfied NOx reduction dividied by 170)|
When evaluating your options you have to keep these factors in mind. In the table below we show the reduction in emission rates for various emission reductions actions you can take.
|Type of VDECS Installed||Reduction in Emission Rate|
|Level 2 PM VDECS, not highest level||18%|
|Highest Level PM VDECS||30%|
|Highest Level PM VDECS with NOx Reduction||54%|
|Tier 1 to Tier 2 replacement/repower||39%|
|Tier 1 to Tier 3 replacement/repower||62%|
|Tier 1 to Interim Tier 4 replacement/repower||78%|
|Tier 1 to Final Tier 4 replacement/repower||96%|
|Tier 2 to Tier 3 replacement/repower||40%|
|Tier 2 to Interim Tier 4 replacement/repower||64%|
|Tier 2 to Final Tier 4 replacement/repower||93%|
For comparison purposes assume your fleet hp is evenly split Tier 1, Tier 2 and Tier 3 equipment. In order to meet your final fleet average targets your fleet average emission rate would have to be reduced by 65%. PM VDECS are not going to get you there, so you are going to have to use some combination of PM VDESC with NOx control and equipment/engine replacement with higher tier equipment to meet your final target.
For details on VDECS options see: Verification Procedure - Currently Verified