Relative Humidity
The ratio of actual moisture in the air to the maximum it can hold at that temperature.
What is relative humidity?
The temperature measured with a standard thermometer exposed to air.
What is dry bulb temperature?
On the psych chart, dry bulb temperature lines run in this direction.
What is vertical?
The process of lowering dry bulb temperature without changing moisture content.
What is sensible cooling?
A 55°F leaving air temperature is commonly used in this type of HVAC system.
What is a standard comfort cooling / VAV system?
If air temperature increases but moisture content stays the same, relative humidity will do this.
What is decrease?
This temperature reflects the cooling effect of evaporation and is always lower than dry bulb (unless saturated).
What is wet bulb temperature?
Lines of constant humidity ratio run in this direction.
What is horizontal?
The process of removing moisture from air.
What is dehumidification?
If outside air is 95°F DB / 78°F WB, the high wet bulb indicates a high this.
What is latent load / moisture content?
At 100% relative humidity, the air is said to be this.
What is saturated?
The temperature at which condensation begins when air is cooled at constant pressure.
What is dew point?
The curved upper boundary of the psychrometric chart represents this condition.
What is the saturation curve (100% RH)?
This factor describes the ratio of sensible heat to total heat in a space.
What is sensible heat ratio (SHR)?
Reheat is often required in VAV systems because air is overcooled to remove this.
What is moisture / latent heat?
In comfort cooling, typical indoor design relative humidity is kept between these values.
What is 45%–60%?
When dry bulb and wet bulb temperatures are equal, the relative humidity is this.
What is 100%?
Moving left horizontally on the psych chart represents this process.
What is sensible cooling?
A space with high people load will typically have a lower SHR because of increased this.
What is latent load?
A DOAS system primarily handles this type of load.
What is latent load (ventilation moisture load)?
Two spaces both read 50% RH. The warmer space actually contains this compared to the cooler one.
What is more moisture (higher humidity ratio)?
Dew point is a direct indicator of this air property (independent of dry bulb).
What is moisture content / humidity ratio?
A cooling coil process typically moves air down and left on the chart, representing these two changes.
What is cooling and dehumidification?
Oversized cooling equipment often causes poor humidity control because it does this.
What is short cycling (does not run long enough to dehumidify)?
In Fort Lauderdale summer design conditions, the latent load is typically this relative to sensible load.
What is high / significant / often comparable?