Why Heating & Cooling Coils are Essential in an AHU

Most HVAC discussions focus on temperature…

But real air conditioning is about temperature + humidity control and that is exactly where heating and cooling coils play a critical role.

What actually happens inside an AHU?

1. Heating Coil
   •Used in cold conditions
   •Raises air temperature to required supply level
   •Prevents coil freezing and maintains comfort
2. Cooling Coil
   •Uses chilled water (5–10°C)
   •Cools air below dew point
   •Removes moisture → controls humidity
   • The real function of the cooling coil
     It does two jobs simultaneously:
     1.Sensible cooling → reduces temperature
     2.Latent cooling → removes moisture
     Condition: Coil surface temperature < Air dew point
3. After cooling coil:
   Air is near saturation (90–100% RH)
   But with lower absolute humidity
   This is often misunderstood.

Why are both coils required?

•Heating coil → winter / reheat control
•Cooling coil → summer + dehumidification

Together they maintain: Comfort + Indoor Air Quality (IAQ)

Common mistake in systems

Overcooling air to remove moisture
Then reheating to maintain room temperature

→ Leads to simultaneous cooling & heating loss

Conclusion

If your AHU is controlling only temperature,
you are missing half the system performance

Real HVAC control = Dew point + Airflow + Coil performance