HVAC Ventilation Design 2 — Questions and Answers
Question 1: According to ASHRAE 62.1, what is the minimum outdoor air ventilation rate for an office space occupied at 5 people per 1,000 sq ft?
- 5 cfm per person
- 10 cfm per person (Correct answer)
- 15 cfm per person
- 20 cfm per person
Correct answer: 10 cfm per person
ASHRAE 62.1 specifies 10 cfm per person as the minimum outdoor air rate for office occupancies under standard conditions.
Question 2: What does the term 'ventilation effectiveness' describe in HVAC design?
- The ratio of supply air to return air
- How efficiently outdoor air reaches the breathing zone (Correct answer)
- The efficiency of the air handler fan
- The percentage of recirculated air in the system
Correct answer: How efficiently outdoor air reaches the breathing zone
Ventilation effectiveness (Ev) measures how well the outdoor air delivered to a space actually reaches the occupants' breathing zone.
Question 3: A demand-controlled ventilation (DCV) system uses which sensor to modulate outdoor air intake?
- Humidity sensor
- CO2 sensor (Correct answer)
- VOC sensor
- Temperature sensor
Correct answer: CO2 sensor
DCV systems use CO2 sensors as a proxy for occupancy level to dynamically adjust outdoor air supply and reduce energy waste.
Question 4: What is the primary purpose of an energy recovery ventilator (ERV) compared to a heat recovery ventilator (HRV)?
- ERV recovers heat only; HRV recovers both heat and moisture
- ERV recovers both heat and moisture; HRV recovers heat only (Correct answer)
- ERV filters air; HRV recovers heat
- ERV is for cooling climates; HRV is for heating climates
Correct answer: ERV recovers both heat and moisture; HRV recovers heat only
An ERV transfers both sensible heat and latent moisture between exhaust and supply airstreams, while an HRV transfers sensible heat only.
Question 5: Which ventilation strategy introduces 100% outdoor air and exhausts 100% of return air, with no recirculation?
- Mixed-air system
- Once-through system (Correct answer)
- Recirculating system
- VAV system
Correct answer: Once-through system
A once-through (100% OA) system uses no return air recirculation, making it ideal for spaces like laboratories and hospitals with contamination concerns.
Question 6: In a multi-zone VAV system, the 'critical zone' is defined as the zone that:
- Has the highest cooling load
- Requires the highest fraction of outdoor air relative to supply air (Correct answer)
- Is farthest from the air handler
- Has the lowest thermostat setpoint
Correct answer: Requires the highest fraction of outdoor air relative to supply air
The critical zone is the zone with the highest outdoor air fraction (Zp), which drives the system-level outdoor air correction calculation.
Question 7: What ventilation design approach is most appropriate for a commercial kitchen exhaust hood?
- Dilution ventilation
- Local exhaust ventilation (Correct answer)
- Displacement ventilation
- Natural ventilation
Correct answer: Local exhaust ventilation
Local exhaust ventilation captures contaminants (grease, heat, combustion gases) at the source before they can disperse into the occupied space.
HVAC Ventilation Design 2
According to ASHRAE 62.1, what is the minimum outdoor air ventilation rate for an office space occupied at 5 people per 1,000 sq ft?