HVAC HVAC Load Calculations 1 — Questions and Answers
Question 1: Which industry standard manual is most widely used in the US for residential HVAC load calculations?
- Manual D
- Manual J (Correct answer)
- Manual N
- Manual S
Correct answer: Manual J
ACCA Manual J (Residential Load Calculation) is the ANSI-approved industry standard used to determine heating and cooling loads for homes.
Question 2: What does 'sensible heat' refer to in HVAC load calculations?
- Heat associated with moisture in the air
- Heat that causes a change in temperature without a change in state (Correct answer)
- Latent heat stored in refrigerant
- Heat generated by occupants
Correct answer: Heat that causes a change in temperature without a change in state
Sensible heat causes a measurable temperature change and is calculated using the formula Q = 1.1 × CFM × ΔT for air systems.
Question 3: In a Manual J calculation, what is the term for the maximum heat gain a building experiences, which determines the required cooling capacity?
- Design heating load
- Peak cooling load (Correct answer)
- Infiltration load
- Ventilation load
Correct answer: Peak cooling load
The peak cooling load (design cooling load) represents the maximum rate of heat gain at the design outdoor conditions and governs the selection of cooling equipment.
Question 4: Which factor accounts for heat transfer through walls, roofs, windows, and floors in a load calculation?
- Infiltration load
- Conduction (envelope) load (Correct answer)
- Internal gain load
- Latent load
Correct answer: Conduction (envelope) load
The conduction (envelope) load calculates heat flow through the building envelope using the formula Q = U × A × ΔT, where U is the assembly's thermal transmittance.
Question 5: What is the design temperature difference (ΔT) based on in a Manual J load calculation?
- The homeowner's comfort preference
- Outdoor design temperatures from ACCA or ASHRAE data minus indoor setpoint (Correct answer)
- Average annual temperatures for the region
- The equipment's rated operating range
Correct answer: Outdoor design temperatures from ACCA or ASHRAE data minus indoor setpoint
Manual J uses ACCA/ASHRAE outdoor design temperatures (typically the 99% heating or 1% cooling condition) minus the indoor design setpoint to calculate ΔT.
Question 6: Latent heat load in HVAC calculations is primarily associated with:
- Sunlight coming through windows
- Moisture removal (dehumidification) from the conditioned space (Correct answer)
- Heat conducted through the roof
- Duct heat gain
Correct answer: Moisture removal (dehumidification) from the conditioned space
Latent load accounts for the energy required to condense and remove moisture from the air, calculated using Q = 0.68 × CFM × ΔGrains.
HVAC HVAC Load Calculations 1
Which industry standard manual is most widely used in the US for residential HVAC load calculations?