HVAC HVAC Load Calculations

Question 1

Which industry standard manual is most widely used in the US for residential HVAC load calculations?

Accepted Answer

Manual J

Answer

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?

Accepted Answer

Heat that causes a change in temperature without a change in state

Answer

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?

Accepted Answer

Peak cooling load

Answer

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?

Accepted Answer

Conduction (envelope) load

Answer

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?

Accepted Answer

Outdoor design temperatures from ACCA or ASHRAE data minus indoor setpoint

Answer

Manual J uses ACCA/ASHRAE outdoor design temperatures (typically the 99% heating or 1% cooling condition) minus the indoor design setpoint to calculate ΔT.

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HVAC Practice Test

HVAC HVAC Load Calculations