Read air temperature change through the coil, load breakdown, and bypass-factor sensitivity to check AHU heat balance.
Parameters
Airflow
m³/min
Air volume through the AHU.
Inlet dry-bulb
°C
Air temperature at coil inlet.
Coil surface temperature
°C
Effective coil surface temperature.
Bypass factor
-
Fraction of air that does not fully contact the coil.
Results
—
Outlet temperature
—
Sensible load
—
Approach
—
Contact efficiency
AHU coil temperature sketch
Sensible load breakdown
Bypass factor sensitivity
Model and equations
$$T_{out}=T_c+BF(T_{in}-T_c),\quad Q=\rho c_p \dot V (T_{in}-T_{out})$$
Bypass factor is a simple measure of how closely air approaches coil surface temperature. Latent load and dew point require a psychrometric model.
How to read it
The schematic shows air approaching the coil surface temperature.
The load view shows whether airflow or temperature difference dominates.
The BF curve shows outlet-temperature rise as coil effectiveness drops.
Learn AHU Heat Balance by dialogue
🙋
When reading AHU Heat Balance, where should I look first? Moving Airflow changes both the plots and the result cards.
🎓
Start with Outlet temperature, but do not treat the number as the whole answer. Use AHU coil temperature sketch to confirm the assumed state, then read Sensible load breakdown for the distribution or trend. The schematic shows air approaching the coil surface temperature.
🙋
I can see why Airflow changes Outlet temperature. How should I judge the influence of Inlet dry-bulb?
🎓
Move Inlet dry-bulb in small steps and watch Sensible load. That reveals which term is controlling the result. Bypass factor is a simple measure of how closely air approaches coil surface temperature. Latent load and dew point require a psychrometric model. A single operating point is not enough; sweep the realistic scatter range.
🙋
What is Bypass factor sensitivity for? It feels like the ordinary curve already tells the story.
🎓
Bypass factor sensitivity is for finding boundaries where the condition becomes risky or margin collapses quickly. The load view shows whether airflow or temperature difference dominates. In First-pass AHU coil capacity checks, the important question is often what happens after a small change, not only the nominal value.
🙋
So if Outlet temperature is within the target, can I accept the condition?
🎓
Treat this as a first-pass review. It helps with Diagnosing insufficient outlet temperature on existing units and Estimating sensible load after airflow changes, but final decisions still need standards, measured data, detailed analysis, and vendor limits. The BF curve shows outlet-temperature rise as coil effectiveness drops.
Practical use
First-pass AHU coil capacity checks.
Diagnosing insufficient outlet temperature on existing units.
Estimating sensible load after airflow changes.
FAQ
Start with Outlet temperature and Sensible load. Then use AHU coil temperature sketch to confirm the assumed state and Sensible load breakdown to read distribution or bias. The schematic shows air approaching the coil surface temperature
Move Airflow alone, then move Inlet dry-bulb by a comparable amount and compare the change in Outlet temperature. Bypass factor sensitivity shows combinations where margin or performance changes quickly.
Use it for First-pass AHU coil capacity checks. Instead of trusting a single point, widen the input range and check whether Outlet temperature keeps enough margin before moving to detailed analysis.
Bypass factor is a simple measure of how closely air approaches coil surface temperature. Latent load and dew point require a psychrometric model. Final decisions still require standards, measured data, detailed analysis, and vendor limits.