HVAC Load Calculations Flashcards
6 cards from real HVAC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 HVAC Load Calculations flashcards as text
What does the 'R-value' of insulation represent in a load calculation?
Answer: Thermal resistance (opposition to heat flow)
R-value measures a material's resistance to heat flow; higher R-values mean better insulation and lower conductive heat gain or loss through the building envelope.
In HVAC load calculations, what unit is typically used to express cooling capacity in the US residential market?
Answer: BTU/hr (British Thermal Units per hour)
Residential cooling capacity in the US is expressed in BTU/hr, with one ton of refrigeration equal to 12,000 BTU/hr.
Which condition defines the 'heating design load' in a Manual J calculation?
Answer: ACCA/ASHRAE 99% winter design dry-bulb temperature
The heating design load is based on the ASHRAE 99% heating design temperature, meaning outdoor conditions are at or above this temperature 99% of the heating season hours.
What effect does increasing window area on the south-facing wall have on the cooling load in a US building?
Answer: Increases cooling load due to greater solar heat gain
Larger south-facing windows allow more solar radiation to enter the space, directly increasing the sensible cooling load that the air conditioner must overcome.
A building's 'thermal envelope' in load calculation terms refers to:
Answer: All conditioned-to-unconditioned boundary surfaces (walls, roof, floor, windows, doors)
The thermal envelope is the boundary separating conditioned interior space from the outdoors or unconditioned areas, and includes all surfaces through which heat can transfer.
Why is it important to perform a Manual J load calculation rather than using a rules-of-thumb method (e.g., 1 ton per 600 sq ft) for equipment sizing?
Answer: Manual J accounts for local climate, insulation, windows, occupancy, and orientation for an accurate system size
Manual J produces an accurate load based on the specific home's construction, orientation, climate zone, and usage, preventing the oversizing or undersizing that rules-of-thumb commonly cause.