HVAC HVAC Load Calculations 2 — Questions and Answers
Question 1: What does Manual S (ACCA) provide for HVAC technicians and designers?
- Duct sizing procedures
- Residential equipment selection based on Manual J loads (Correct answer)
- Ventilation rate requirements
- Commercial load calculation methods
Correct answer: Residential equipment selection based on Manual J loads
ACCA Manual S guides technicians in selecting properly sized heating and cooling equipment that matches the Manual J calculated loads within acceptable tolerance ranges.
Question 2: Which of the following is an 'internal gain' source that adds to the cooling load in a building?
- Exterior wall conduction
- Occupants, lighting, and appliances (Correct answer)
- Outdoor air infiltration only
- Ground-floor slab conduction
Correct answer: Occupants, lighting, and appliances
Internal gains from people, lights, and equipment add sensible and latent heat directly to the conditioned space, increasing the required cooling capacity.
Question 3: Solar heat gain through windows is accounted for in a cooling load calculation using which factor?
- R-value
- Solar Heat Gain Coefficient (SHGC) (Correct answer)
- U-factor
- Visible Transmittance (VT)
Correct answer: Solar Heat Gain Coefficient (SHGC)
The Solar Heat Gain Coefficient (SHGC) represents the fraction of solar radiation admitted through a window, used with peak solar intensity and window area to calculate solar load.
Question 4: In load calculations, 'infiltration' refers to:
- Purposeful outdoor air supplied by the ventilation system
- Uncontrolled air leakage into the building through gaps and cracks (Correct answer)
- Heat transfer through the foundation slab
- Duct air leakage to unconditioned spaces
Correct answer: Uncontrolled air leakage into the building through gaps and cracks
Infiltration is the unintended entry of outdoor air through envelope leaks, adding both sensible and latent load that must be included in Manual J calculations.
Question 5: What is the result of significantly oversizing an air conditioner based on load calculations?
- Better dehumidification and lower energy bills
- Short cycling, poor humidity control, and increased wear (Correct answer)
- Faster cool-down with no negative effects
- Longer compressor life due to less run time
Correct answer: Short cycling, poor humidity control, and increased wear
An oversized AC short-cycles (starts and stops frequently), never runs long enough to remove adequate moisture, causing high humidity, comfort complaints, and premature wear.
Question 6: Which ACCA manual is used for sizing and designing residential duct systems?
- Manual J
- Manual S
- Manual D (Correct answer)
- Manual N
Correct answer: Manual D
ACCA Manual D provides the methodology for designing residential duct systems, including trunk-and-branch and radial layouts, to deliver the required airflow to each room.
HVAC HVAC Load Calculations 2
What does Manual S (ACCA) provide for HVAC technicians and designers?