Psychrometrics and Humidity Control Flashcards
7 cards from real 313D practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Psychrometrics and Humidity Control flashcards as text
What is the Apparatus Dew Point (ADP) of a cooling coil?
Answer: The effective average surface temperature of the coil at which moisture condenses
ADP is the effective mean surface temperature of a cooling coil — the theoretical temperature at which the coil would saturate leaving air if bypass factor were zero.
How does dehumidification occur in a typical residential split-system air conditioner?
Answer: Warm humid air is chilled below its dew point over the evaporator coil, causing moisture to condense on the coil
When warm humid air contacts the cold evaporator coil (below the air's dew point), water vapor condenses on the coil surface and drains away, reducing indoor humidity.
Under what condition are dry-bulb and wet-bulb temperatures equal?
Answer: When air is at 100% relative humidity (fully saturated)
At 100% relative humidity no evaporation occurs from a wet wick, so the wet-bulb thermometer reads the same temperature as the dry-bulb thermometer.
What is humidity ratio (specific humidity) as used in HVAC psychrometrics?
Answer: The mass of water vapor per unit mass of dry air, expressed in lbs/lb or grains/lb
Humidity ratio (W) is the actual mass of water vapor per unit mass of dry air — an absolute measure of moisture content independent of temperature.
A large wet-bulb depression (big difference between dry-bulb and wet-bulb temperatures) indicates what about the air?
Answer: The air is relatively dry with low relative humidity
A large wet-bulb depression means significant evaporation is occurring from the wet wick, which only happens when the surrounding air has a low relative humidity.
What are the primary negative effects of high indoor relative humidity on occupants?
Answer: It promotes mold growth, makes occupants feel warmer, and can cause respiratory irritation
High indoor humidity fosters mold and mildew, makes occupants feel hotter because perspiration evaporates more slowly, and can aggravate asthma and allergies.
On a standard psychrometric chart, which property is represented on the horizontal (x) axis?
Answer: Dry-bulb temperature
The horizontal axis of a psychrometric chart represents dry-bulb temperature, the fundamental measured air temperature read by a standard thermometer.