Comprehensive and Detailed Explanation:
Operating Room (OR): ASHRAE Standard 170, Section 7.4.1, requires ORs to use laminar (unilateral) downward airflow from non-aspirating diffusers over the surgical table (20 ACH minimum, not 12). This minimizes contamination of the sterile field.
Patient Room: Table 7.1 specifies 6 ACH total (2 outdoor) with mixed airflow, not unilateral downward flow, for general ventilation and comfort.
Option Analysis:
A: Incorrect-Patient rooms use mixed airflow, not unilateral.
B: Incorrect-ORs require 20 ACH, not 12, and focus on laminar flow, not just dilution.
C: Incorrect-Patient rooms require 6 ACH, not 12.
D: Correct-unilateral downward flow is the primary OR design intent.