Calculation sequence
Step-by-step method
- Define a boundary and identify every inflow and outflow once.
- Sum inflows and outflows separately.
- Calculate signed and percent imbalance and compare with the entered tolerance.
CommissioningIntermediateTAB
TAB Flow Reconciliation Calculator
Reconcile entered airflow streams and calculate the imbalance between inflow and outflow totals.
Why it matters: Flow reconciliation can expose missing branches, inconsistent test bases, leakage, and measurement uncertainty.
Calculated result
Engineering evaluation
Absolute airflow reconciliation imbalance (Bp)1.005 %
- Total airflow into boundary (Qin)
- 10,000 cfm
- Total airflow out of boundary (Qout)
- 9,900 cfm
- Signed airflow imbalance (B)
- 100 cfm
Engineering interpretation
The defined boundary has 10000 cfm in and 9900 cfm out, for a signed imbalance of 100 cfm and absolute reconciliation difference of 1.005%.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
Qin = Qs+Qo
Qout = Qr+Qe
B = Qin−Qout
Bp = |B|/((Qin+Qout)/2)×100
within entered criterion when Bp ≤ T
Current substitution
Qin = 10000+0 = 10000 cfm; Qout = 8500+1400 = 9900 cfm; Bp = 1.005%.
Equation legend
Inputs and calculated quantities
- Qs
- Supply airflow into boundary — cfm or m³/s
- Qo
- Additional outdoor/makeup airflow — cfm or m³/s
- Qr
- Return airflow leaving boundary — cfm or m³/s
- Qe
- Exhaust/relief airflow leaving boundary — cfm or m³/s
- T
- Entered reconciliation tolerance — %
- Bp
- Absolute airflow reconciliation imbalance — %
- Qin
- Total airflow into boundary — cfm
- Qout
- Total airflow out of boundary — cfm
- B
- Signed airflow imbalance — cfm
Applications
How this calculation is used
Building design
Define the intended airflow-balance boundary.
Construction
Review TAB summaries and branch relationships.
Commissioning
Calculate imbalance across a documented air-system or building boundary.
Quality controls
Assumptions and limitations
Assumptions
- Entered values represent the same stable operating condition.
- Measurements and reference values use consistent units and boundaries.
Limitations
- This is a screening and field-verification tool, not an automatic acceptance decision.
- Project criteria, manufacturer data, governing standards, and measurement uncertainty remain controlling.
Field use
Verification procedure
- Confirm the approved reference values and test boundary.
- Stabilize the system and record calibrated field measurements.
- Review calculation assumptions, uncertainty, and supporting evidence before disposition.
Common engineering mistakes
- Comparing readings taken at different loads, modes, or reference conditions.
- Treating a calculated status as proof of code, contract, or manufacturer compliance.
Technical basis
References and source standards
- ASHRAE Handbook—FundamentalsCurrent handbook chapters covering fluid flow, thermodynamics, psychrometrics, measurement, and engineering analysis; the project reviewer must verify the licensed edition used for approval.
- ASHRAE Commissioning ResourcesCommissioning-process context for defining test methods, acceptance criteria, evidence, and owner requirements.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement