HVAC Ventilation Design 4 — Questions and Answers
Question 1: What is the typical CO2 setpoint used in demand-controlled ventilation systems as an indicator of adequate ventilation?
- 400 ppm (outdoor ambient level)
- 700 ppm above outdoor levels (≈1,100 ppm) (Correct answer)
- 2,000 ppm total
- 5,000 ppm total
Correct answer: 700 ppm above outdoor levels (≈1,100 ppm)
A common DCV setpoint is 700 ppm above outdoor ambient (roughly 1,100 ppm total), which ASHRAE 62.1 associates with providing approximately 15 cfm per person.
Question 2: In a hospital, which area requires the highest number of air changes per hour (ACH) according to ASHRAE 170?
- Patient room
- Corridor
- Operating room (Correct answer)
- Waiting room
Correct answer: Operating room
Operating rooms require a minimum of 20 ACH total air (with at least 4 ACH outdoor air) per ASHRAE 170 to control surgical site infection risk.
Question 3: What is the purpose of a transfer air pathway between spaces in a ventilation design?
- To supply conditioned air directly to a space without ductwork (Correct answer)
- To allow air to flow from a less critical zone to a more critical zone
- To balance pressure between supply and return plenums
- To recirculate exhaust air back to the air handler
Correct answer: To supply conditioned air directly to a space without ductwork
Transfer air (via grilles, door gaps, or ducts) allows a space to receive ventilation air that passes through from an adjacent space, reducing the need for dedicated supply runs.
Question 4: When designing natural ventilation using stack effect, the driving force is created by:
- Wind pressure against the building facade
- Temperature and density differences between indoor and outdoor air (Correct answer)
- Mechanical exhaust fans at the roof
- Pressure differentials from neighboring buildings
Correct answer: Temperature and density differences between indoor and outdoor air
Stack effect is driven by the buoyancy difference between warmer, less-dense indoor air and cooler, denser outdoor air, creating airflow through low inlets and high outlets.
Question 5: Which ASHRAE standard governs ventilation requirements specifically for healthcare facilities?
- ASHRAE 55
- ASHRAE 62.1
- ASHRAE 170 (Correct answer)
- ASHRAE 90.1
Correct answer: ASHRAE 170
ASHRAE 170 'Ventilation of Health Care Facilities' sets specific ACH, pressure relationships, filtration, and humidity requirements for hospitals and clinics.
Question 6: What is the correct pressure relationship between a hospital isolation room (airborne infection isolation) and the adjacent corridor?
- Isolation room is positive relative to corridor
- Isolation room is negative relative to corridor (Correct answer)
- Isolation room and corridor are at equal pressure
- Pressure varies based on patient condition
Correct answer: Isolation room is negative relative to corridor
Airborne infection isolation (AII) rooms are maintained at negative pressure relative to the corridor to prevent infectious airborne particles from escaping the room.
Question 7: Which ventilation design method uses tracer gas measurements to quantify how effectively fresh air reaches the breathing zone?
- Blower door testing
- Age-of-air measurement (Correct answer)
- Pitot tube traversal
- Smoke pencil testing
Correct answer: Age-of-air measurement
Age-of-air (or mean age of air) measurements using tracer gases like SF6 or CO2 quantify how long air takes to reach the breathing zone, indicating ventilation effectiveness.
HVAC Ventilation Design 4
What is the typical CO2 setpoint used in demand-controlled ventilation systems as an indicator of adequate ventilation?