Air Conditioning Repair Heat Load Calculations and System Sizing 2 — Questions and Answers
Question 1: What type of heat gain is caused by heat transferring through walls, roofs, and floors due to a temperature difference?
- Solar heat gain
- Conductive heat gain (Correct answer)
- Latent heat gain
- Internal heat gain
Correct answer: Conductive heat gain
Conductive heat gain occurs when heat flows through solid building materials from a warm exterior surface to a cooler interior, governed by the material's U-value and the temperature difference.
Question 2: In the northern hemisphere, windows facing which direction typically contribute the greatest solar heat gain during summer afternoons?
- North
- East
- South
- West (Correct answer)
Correct answer: West
West-facing windows receive direct sunlight during the afternoon when outdoor temperatures are at their highest, resulting in the greatest peak solar heat gain.
Question 3: What does the latent heat load in an air conditioning system represent?
- Heat generated by lighting and appliances
- Heat that must be removed to lower air temperature
- Moisture that must be removed from the air (Correct answer)
- Heat transferred through the building envelope
Correct answer: Moisture that must be removed from the air
Latent heat load is associated with moisture (water vapor) removal from the air; removing latent heat does not lower air temperature but reduces relative humidity.
Question 4: ASHRAE design outdoor conditions used in load calculations are based on which statistical criteria?
- The absolute hottest temperature ever recorded locally
- The average high temperature in the hottest month
- A temperature exceeded only 1% of annual hours (Correct answer)
- The temperature at solar noon on the summer solstice
Correct answer: A temperature exceeded only 1% of annual hours
ASHRAE design conditions represent outdoor temperatures that are exceeded only 1% (or 2.5%) of all annual hours, providing a statistically reliable but not absolute worst-case design point.
Question 5: How does uncontrolled air infiltration affect a building's cooling load?
- It has no measurable effect on the cooling load
- It adds both sensible and latent load by introducing unconditioned outdoor air (Correct answer)
- It only affects the heating load, not the cooling load
- It reduces the load by diluting indoor heat sources
Correct answer: It adds both sensible and latent load by introducing unconditioned outdoor air
Infiltration introduces hot, humid outdoor air through gaps and cracks in the building envelope, adding both sensible heat (temperature) and latent load (moisture) that the AC system must handle.
Question 6: What is the primary purpose of an ACCA Manual D calculation?
- Determining residential heating and cooling loads
- Calculating the correct refrigerant charge
- Designing and sizing the duct distribution system (Correct answer)
- Selecting thermostat setpoints for efficiency
Correct answer: Designing and sizing the duct distribution system
ACCA Manual D is the industry standard for residential duct system design, providing methods to size ducts so that the correct amount of conditioned air reaches each room.
Question 7: In a residential load calculation, what category includes heat generated by occupants, lighting, and household appliances?
- Conductive heat gain
- Solar heat gain
- Internal heat gain (Correct answer)
- Infiltration heat gain
Correct answer: Internal heat gain
Internal heat gain accounts for heat produced by sources inside the conditioned space, including people, lighting fixtures, and appliances such as ovens and electronics.
Air Conditioning Repair Heat Load Calculations and System Sizing 2
What type of heat gain is caused by heat transferring through walls, roofs, and floors due to a temperature difference?