Air Conditioning Repair Heat Load Calculations and System Sizing 1 — Questions and Answers
Question 1: What unit is commonly used to measure the cooling capacity of an air conditioning system?
- Watts
- BTU/hr (Correct answer)
- Horsepower
- Kilowatts
Correct answer: BTU/hr
BTU/hr (British Thermal Units per hour) is the standard unit used to express the cooling capacity of air conditioning equipment on nameplates and specifications.
Question 2: How many BTU/hr are equivalent to one ton of refrigeration?
- 6,000
- 9,000
- 12,000 (Correct answer)
- 18,000
Correct answer: 12,000
One ton of refrigeration equals 12,000 BTU/hr, which originated from the amount of heat needed to melt one ton of ice in 24 hours.
Question 3: What is ACCA Manual J used for in the HVAC industry?
- Selecting refrigerant recovery equipment
- Performing residential load calculations (Correct answer)
- Sizing commercial duct systems
- Calculating EPA refrigerant allowances
Correct answer: Performing residential load calculations
ACCA Manual J is the industry-standard method for calculating residential heating and cooling loads to properly size HVAC equipment.
Question 4: Which of the following factors does NOT significantly affect a building's cooling load?
- Window area and orientation
- Attic insulation levels
- Number of occupants
- Interior wall paint color (Correct answer)
Correct answer: Interior wall paint color
Interior paint color has a negligible effect on cooling load; exterior surface colors can affect solar absorptance, but interior colors do not meaningfully impact heat gain.
Question 5: What is the primary consequence of installing an oversized air conditioning system?
- Lower monthly energy bills
- Improved dehumidification performance
- Short cycling and poor humidity control (Correct answer)
- Extended equipment service life
Correct answer: Short cycling and poor humidity control
An oversized system reaches the thermostat setpoint too quickly, causing it to short cycle and run for insufficient time to remove humidity from the air.
Question 6: What does the Sensible Heat Ratio (SHR) indicate about an air conditioning system?
- The ratio of refrigerant charge to system capacity
- The proportion of total cooling capacity devoted to sensible versus latent heat removal (Correct answer)
- The efficiency rating of the compressor
- The ratio of supply air to return air volume
Correct answer: The proportion of total cooling capacity devoted to sensible versus latent heat removal
SHR is the ratio of sensible cooling (temperature reduction) to total cooling capacity, indicating how much of the system's capacity is used for temperature versus humidity removal.
Question 7: What is the recommended method for sizing a replacement air conditioner when no prior load data is available?
- Match the existing system's capacity exactly
- Install one size larger for added comfort margin
- Perform a proper Manual J load calculation (Correct answer)
- Apply the rule of 500 square feet per ton
Correct answer: Perform a proper Manual J load calculation
A proper Manual J load calculation is always the correct approach because existing equipment may have been incorrectly sized, and building conditions may have changed.
Air Conditioning Repair Heat Load Calculations and System Sizing 1
What unit is commonly used to measure the cooling capacity of an air conditioning system?