HVAC Ventilation Design 3 — Questions and Answers
Question 1: What is the purpose of the 'uncorrected outdoor air intake' (Vou) calculation in ASHRAE 62.1's Ventilation Rate Procedure?
- To size the supply fan
- To determine outdoor air needed before accounting for system efficiency (Correct answer)
- To calculate exhaust fan capacity
- To size ductwork for return air
Correct answer: To determine outdoor air needed before accounting for system efficiency
Vou represents the total system outdoor air requirement before applying the system ventilation efficiency correction factor (Ev).
Question 2: A building with a high window-to-wall ratio in a mild climate is best suited for which passive ventilation strategy?
- Stack effect ventilation
- Cross ventilation (Correct answer)
- Earth tube ventilation
- Mechanical pressurization
Correct answer: Cross ventilation
Cross ventilation relies on wind-driven airflow through windows on opposite or adjacent walls, effective when openings are well-positioned and climate is mild.
Question 3: Which duct leakage class per SMACNA represents the tightest construction standard?
- Class 12
- Class 6
- Class 3
- Class 1 (Correct answer)
Correct answer: Class 1
SMACNA Class 1 (formerly Class A) allows only 1 cfm per 100 sq ft of duct surface at 1 inch w.g. and represents the most airtight construction.
Question 4: In displacement ventilation design, supply air is introduced at which location?
- High on the wall or ceiling
- Low on the wall or floor level (Correct answer)
- Through ceiling diffusers at high velocity
- Through return air grilles
Correct answer: Low on the wall or floor level
Displacement ventilation supplies cool, fresh air at low velocity near the floor, allowing it to rise naturally as it absorbs heat and contaminants from occupants.
Question 5: What is the ASHRAE 62.1 term for the ratio of outdoor air to total supply air at the zone level?
- Ventilation efficiency factor
- Zone outdoor air fraction (Zpz) (Correct answer)
- System ventilation efficiency
- Outdoor air correction factor
Correct answer: Zone outdoor air fraction (Zpz)
Zpz (zone outdoor air fraction) equals the zone outdoor airflow (Vbz) divided by the zone supply airflow (Vpz) and is used to calculate system-level efficiency.
Question 6: A garage ventilation system design must account for which primary contaminant?
- CO2 from occupant respiration
- Carbon monoxide (CO) from vehicle exhaust (Correct answer)
- Formaldehyde from building materials
- Radon from soil
Correct answer: Carbon monoxide (CO) from vehicle exhaust
Carbon monoxide from vehicle exhaust is the primary design contaminant in parking garages, and codes typically require CO sensors to trigger ventilation.
Question 7: Which factor does NOT directly affect the required outdoor air ventilation rate per ASHRAE 62.1 Ventilation Rate Procedure?
- Occupancy density (people per sq ft)
- Area of the space (sq ft)
- Ceiling height of the space (Correct answer)
- Occupancy category (office, gym, etc.)
Correct answer: Ceiling height of the space
The Ventilation Rate Procedure uses occupancy density and area-based rates by category; ceiling height is not a direct input, though it influences volume and air change calculations.
HVAC Ventilation Design 3
What is the purpose of the 'uncorrected outdoor air intake' (Vou) calculation in ASHRAE 62.1's Ventilation Rate Procedure?