Exam HFDP Topic 1 Question 3 Discussion

Actual exam question for ASHRAE's HFDP exam
Question #: 3
Topic #: 1
Which of the following represents the MINIMUM allowable area of non-aspirating diffuser required for a 400 sq. ft. (37.16 sq. m) Class C Operating Room with 1,267 CFM (598 L/s) air supply?

Suggested Answer: B Vote an answer

Comprehensive and Detailed Explanation:
Class C OR Requirements: ASHRAE 170, Table 7.1, requires 20 ACH minimum, but diffuser sizing uses face velocity (25-35 fpm per Section 7.4.1).
Calculation: At 35 fpm (max recommended), Area = CFM / Velocity = 1,267 / 35 # 36.2 sq. ft.
Verification: 1,267 CFM over 36.2 sq. ft. = 35 fpm, meeting laminar flow criteria.

by Emily at Dec 18, 2025, 09:05 AM

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