We are modeling a small fast food restaurant for LEED certification and need
clarification regarding LEED's Exceptional Calculation Method.

According to the Reference Guide, the Exceptional Calculation Method (ECM)
allows for the documentation of "any measures that cannot be adequately
modeled in a simulation program." It gives some examples that would warrant
an ECM including improvements to laboratory or kitchen exhaust systems.

Our building uses an improved kitchen exhaust hood that allows for a
reduction in exhaust airflow. The airflow reduction was calculated by the
hood manufacturer. Because this is a component of the HVAC system and
directly affects the sizing of the heating and cooling systems, our initial
Proposed model simulated the kitchen exhaust hood with the lower airflow, as
designed, without using an ECM. This seemed reasonable, as the exhaust hood
is a measure that can be adequately modeled by the software. The Baseline
model used a higher exhaust cfm that was determined by the hood
manufacturer, and the Appendix G fan power calculations.

The LEED reviewer's response was to use an ECM to document energy savings
associated with the hood. However, the dilemma we are encountering is that
Appendix G requires the Proposed model's HVAC system to be modeled as
designed. It also requires the outdoor air (hood makeup air) to be identical
in both models.

Below are some of the scenarios we've considered.

Option A.)
Proposed Model: Use the theoretical higher exhaust cfm, exhaust fan power as
designed, HVAC sizing and capacity as required for the additional exhaust
airflow.
Baseline Model: Use the same exhaust airflow as the Proposed, Appendix G fan
power and HVAC sizing and capacity.
ECM: Proposed Model re-simulated with the lower exhaust cfm as designed,
exhaust fan power as designed, HVAC sizing and capacity as designed, with
the energy savings provided in the LEED template.
Problems: This option does not allow the HVAC system of the Proposed model
to be modeled as designed. The increase in exhaust air increases the makeup
air requirement, thereby increasing the heating and cooling loads.

Option B.)
Proposed Model: Use the lower exhaust cfm as designed, exhaust fan power as
designed, HVAC sizing and capacity as designed.
Baseline Model: Use the same exhaust cfm as the Proposed, Appendix G fan
power and HVAC sizing and capacity.
ECM: Baseline Model re-simulated with the higher exhaust cfm, with the
energy increase provided in the LEED template.
Problems: From my understanding, an ECM is designed to show energy savings
for a particular measure rather than an energy increase to the Baseline for
not using the measure.

Does anyone have experience with a similar situation?

Thanks,

--
Karen