Sensible and Latent Heat
The difference between heat you can measure with a thermometer and heat that removes moisture from the air.
What it is
Sensible heat
Heat that changes the temperature of a substance. A thermometer senses it, which is where the name comes from.
Latent heat
Heat that changes the state of a substance without changing its temperature, such as water vapor condensing on a cold coil.
Total capacity is the sum of the two. A cooling coil removes sensible heat by lowering air temperature and latent heat by condensing moisture out of the air.
Why it matters
A system can hit the thermostat setpoint and still leave a house clammy if it is not removing enough latent heat. Oversized equipment short cycles, satisfies temperature quickly and never runs long enough to dehumidify.
Sensible heat ratio = sensible capacity / total capacityA typical residential cooling coil runs a sensible heat ratio around 0.7 to 0.8 in a mixed climate.
How it works
Latent removal only begins when the coil surface is below the dew point of the air passing over it. Higher airflow raises coil temperature and shifts capacity toward sensible. Lower airflow drops coil temperature and shifts capacity toward latent, until the coil gets cold enough to freeze.
| Change | Sensible capacity | Latent capacity |
|---|---|---|
| Increase airflow | Up | Down |
| Decrease airflow | Down | Up until icing |
| Higher indoor humidity | Slightly down | Up |
| Oversized equipment with short runtimes | Met quickly | Poor |
How to diagnose it
Measure indoor relative humidity during a long cooling run
Above roughly 55 percent while cooling suggests poor latent removal
Measure wet bulb and dry bulb entering and leaving the coil
The enthalpy difference shows total capacity, not just sensible
Verify airflow per ton against the manufacturer target
Excess airflow is a common cause of humidity complaints
Check runtime per cycle
Very short cycles rarely dehumidify well
Where it is used
Equipment selection, blower speed setup, humidity complaints and dehumidifier sizing all depend on separating sensible from latent load.
Practice & Mastery
- Questions2
- Quiz1
- Sensible and Latent Heat Troubleshooting Scenarios2
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