a. None: No exhaust air is recirculated.
       b. Exhaust Air Recirculation 20%: 20% Exhaust air is recirculated along with fresh             air to maintain indoor comfort.
       c. Exhaust Air Recirculation 40%: 40% Exhaust air is recirculated along with fresh              air to maintain indoor comfort.
       d. Exhaust Air Recirculation 60%: 60% Exhaust air is recirculated along with fresh               air to maintain indoor comfort. 

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