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Studied by 88 peopleNoteStudied by 39 peopleNoteStudied by 6 peopleNoteStudied by 15643 peopleNoteStudied by 3 peopleNoteStudied by 3 peopleBRAC LECTURE 2: BASIC CONCEPTS
UNIVERSITY Inspiring Excellence
MECHANICAL SERVICES
DEPARTMENT OF ARCHITECTURE
BRAC UNIVERSITY
Course Code: MEE 344
Definition: Any liquid or frozen water falling from the atmosphere to Earth.
Forms of Precipitation:
Rain
Sleet
Snow
Relation to the Water Cycle:
Along with evaporation and condensation, precipitation is a major part of the global water cycle.
Formation:
Water vapor condenses into larger droplets in the clouds.
Heavy droplets fall to Earth.
Cold clouds may cause droplets to freeze into ice, leading to snow or hail based on temperature.
Most rain originates as snow high in the clouds.
Growth of Ice Crystals:
Cloud droplets can freeze spontaneously at temperatures below -40 °C or -40 °F.
Definition: Amount of water vapor in the air.
Water vapor is the invisible gaseous state of water.
Significance:
Indicates likelihood of precipitation, dew, or fog.
High humidity lowers sweating effectiveness by reducing moisture evaporation from skin.
Definition: Amount of water vapor in a unit volume of air (kg/m³).
Units:
SI: kilograms of water vapor (kg)
Imperial: pounds of water vapor (lbs)
Dependence:
Maximum mass of vapor varies with air pressure and temperature.
Effects on Comfort:
Higher absolute humidity makes outdoor environments feel hotter due to reduced sweat evaporation, thus decreasing cooling effects from evaporation.
Indicates the chance of dew, fog, or precipitation.
Definition: Ratio of current moisture in the air to the maximum moisture possible at the same temperature.
Comparison:
Unlike absolute humidity, relative humidity provides a comparative measure.
Ideal Range:
Ideal relative humidity for humans: 30% to 60%.
Over 60%: Ineffective perspiration, increased discomfort.
Under 30%: Thirst and dry skin issues.
Water Pressure:
Increases by 1 psi for every 2.31 feet of water depth.
Human Perception of Pressure:
Sea level pressure is 14.7 psi.
Pressure decreases on elevation.
Airplane Pressure:
Cabin pressure must be maintained for comfort.
Definition: Measurement of heat content, useful for determining heat requirements in processes.
Zero Point: Enthalpy of water = 0 at 32°F.
Function:
Indicates energy exchange between system and surroundings at constant temperature and pressure.
Components: Change in internal energy and work done.
Definition: Study of thermodynamic properties of moist air.
Psychrometric Charts:
Graphically represent psychrometric properties of air.
Allow HVAC engineers to analyze processes and solve practical problems without complex calculations.
Usage:
Understanding basic properties of air facilitates usage of psychrometric charts.
Knowing any two parameters allows the rest to be determined easily.
Construction Base:
Based on water vapor saturation data.
Open floor for inquiries regarding the lecture topics.
Acknowledgment for participation in the lecture.
NoteStudied by 88 peopleNoteStudied by 39 peopleNoteStudied by 6 peopleNoteStudied by 15643 peopleNoteStudied by 3 peopleNoteStudied by 3 people
Lecture 2 - Part 2
BRAC LECTURE 2: BASIC CONCEPTS
UNIVERSITY Inspiring Excellence
MECHANICAL SERVICES
DEPARTMENT OF ARCHITECTURE
BRAC UNIVERSITY
Course Code: MEE 344
Definition: Any liquid or frozen water falling from the atmosphere to Earth.
Forms of Precipitation:
Rain
Sleet
Snow
Relation to the Water Cycle:
Along with evaporation and condensation, precipitation is a major part of the global water cycle.
Formation:
Water vapor condenses into larger droplets in the clouds.
Heavy droplets fall to Earth.
Cold clouds may cause droplets to freeze into ice, leading to snow or hail based on temperature.
Most rain originates as snow high in the clouds.
Growth of Ice Crystals:
Cloud droplets can freeze spontaneously at temperatures below -40 °C or -40 °F.
Definition: Amount of water vapor in the air.
Water vapor is the invisible gaseous state of water.
Significance:
Indicates likelihood of precipitation, dew, or fog.
High humidity lowers sweating effectiveness by reducing moisture evaporation from skin.
Definition: Amount of water vapor in a unit volume of air (kg/m³).
Units:
SI: kilograms of water vapor (kg)
Imperial: pounds of water vapor (lbs)
Dependence:
Maximum mass of vapor varies with air pressure and temperature.
Effects on Comfort:
Higher absolute humidity makes outdoor environments feel hotter due to reduced sweat evaporation, thus decreasing cooling effects from evaporation.
Indicates the chance of dew, fog, or precipitation.
Definition: Ratio of current moisture in the air to the maximum moisture possible at the same temperature.
Comparison:
Unlike absolute humidity, relative humidity provides a comparative measure.
Ideal Range:
Ideal relative humidity for humans: 30% to 60%.
Over 60%: Ineffective perspiration, increased discomfort.
Under 30%: Thirst and dry skin issues.
Water Pressure:
Increases by 1 psi for every 2.31 feet of water depth.
Human Perception of Pressure:
Sea level pressure is 14.7 psi.
Pressure decreases on elevation.
Airplane Pressure:
Cabin pressure must be maintained for comfort.
Definition: Measurement of heat content, useful for determining heat requirements in processes.
Zero Point: Enthalpy of water = 0 at 32°F.
Function:
Indicates energy exchange between system and surroundings at constant temperature and pressure.
Components: Change in internal energy and work done.
Definition: Study of thermodynamic properties of moist air.
Psychrometric Charts:
Graphically represent psychrometric properties of air.
Allow HVAC engineers to analyze processes and solve practical problems without complex calculations.
Usage:
Understanding basic properties of air facilitates usage of psychrometric charts.
Knowing any two parameters allows the rest to be determined easily.
Construction Base:
Based on water vapor saturation data.
Open floor for inquiries regarding the lecture topics.
Acknowledgment for participation in the lecture.