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Questions and Answers
What happens to relative humidity (RH) when moist air is totally dry?
What happens to relative humidity (RH) when moist air is totally dry?
Which line on a psychrometric chart represents saturated conditions?
Which line on a psychrometric chart represents saturated conditions?
On a psychrometric chart, which property is represented along the x-axis?
On a psychrometric chart, which property is represented along the x-axis?
What describes the region beyond the 100% relative humidity line on the psychrometric chart?
What describes the region beyond the 100% relative humidity line on the psychrometric chart?
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What does the scale for specific humidity represent on the psychrometric chart?
What does the scale for specific humidity represent on the psychrometric chart?
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What type of lines on the psychrometric chart depict wet-bulb temperature?
What type of lines on the psychrometric chart depict wet-bulb temperature?
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Which of the following expresses the degree of saturation of moist air?
Which of the following expresses the degree of saturation of moist air?
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How does dew point temperature relate to moist air properties on the psychrometric chart?
How does dew point temperature relate to moist air properties on the psychrometric chart?
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What does the term 'Dew Point Temperature' (DPT) refer to?
What does the term 'Dew Point Temperature' (DPT) refer to?
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Which of the following factors is NOT a property of moist air studied in psychrometry?
Which of the following factors is NOT a property of moist air studied in psychrometry?
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What does Relative Humidity (RH) indicate?
What does Relative Humidity (RH) indicate?
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Which temperature measurement is taken using a thermometer covered with a wet wick?
Which temperature measurement is taken using a thermometer covered with a wet wick?
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What does the psychometric chart visually represent?
What does the psychometric chart visually represent?
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Which property helps determine the energy requirements for cooling in an air conditioning system?
Which property helps determine the energy requirements for cooling in an air conditioning system?
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When conditions require dehumidification, what should be done concerning the cooling coil temperature?
When conditions require dehumidification, what should be done concerning the cooling coil temperature?
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What is the term for the volume of air occupied by a unit mass of moisture?
What is the term for the volume of air occupied by a unit mass of moisture?
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What does specific volume refer to in the context of air conditioning?
What does specific volume refer to in the context of air conditioning?
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Which of the following describes the degree of saturation?
Which of the following describes the degree of saturation?
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Relative humidity is defined as which of the following?
Relative humidity is defined as which of the following?
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What is the primary purpose of the psychrometric chart?
What is the primary purpose of the psychrometric chart?
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Which parameter is NOT considered a fundamental parameter in psychrometry?
Which parameter is NOT considered a fundamental parameter in psychrometry?
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What represents the dew point temperature in air conditioning?
What represents the dew point temperature in air conditioning?
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How is the specific humidity (humidity ratio) generally expressed?
How is the specific humidity (humidity ratio) generally expressed?
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Which equation can be used to find the partial pressure of water vapor?
Which equation can be used to find the partial pressure of water vapor?
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Study Notes
Principles of Environmental Control Part 1
- The atmosphere in and around buildings primarily contains air and water vapor.
- High moisture levels, especially combined with high temperatures, negatively affect both human and animal comfort and livestock production.
- Controlling atmospheric moisture is crucial for maintaining a suitable environment in farm buildings.
Psychrometric Charts
- Psychrometrics studies the properties and behavior of moist air under various conditions.
- Properties of moist air include dry-bulb temperature (DBT), wet-bulb temperature (WBT), humidity, and relative humidity (RH).
Psychrometric Charts (continued)
- Dry-Bulb Temperature (DBT): Measured by a standard thermometer, denoted by T, Tab, or DBT.
- Wet-Bulb Temperature (WBT): Measured by a thermometer with a wet wick or cloth over which air is moving at a velocity of 2.5-10 m/s.
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Dew Point Temperature (DPT): Measured by a thermometer when moisture in the air starts condensing, denoted by Tap or DPT.
- In dehumidification, cooling coil temperature must stay significantly below the DPT.
- DPT values are available in steam tables, linked to vapor pressure (Pv).
Psychrometric Charts (continued 2)
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Fundamental Parameters:
- Pressure (p): Total pressure of air (pa + Pv)
- Specific Humidity or Humidity Ratio (w): Ratio of vapor mass to dry air mass (w = mv/ma)
- Relative Humidity (RH): Ratio of current vapor pressure to maximum vapor pressure at the same temperature (RH = pv/ps).
- Enthalpy (h): Sum of dry air's enthalpy and water vapor's enthalpy.
- Specific volume: Volume of air per unit mass of dry air
- Degree of Saturation (μ): Ratio of humidity in a sample of air to its saturated level
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Carrier's Equation for Partial Pressure of Water Vapor (Pv):
- A way to calculate partial pressure of water vapor from data like dry bulb temperature and wet bulb temperature.
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Psychrometric charts graphically depict the interrelationships among moist air properties.
Psychrometric Charts (continued 3)
- Example Problem: Given dry-bulb temperature (30°C) and dew point temperature (14°C), calculate the humidity ratio if atmospheric pressure is 758 mmHg.
Psychrometric Processes
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Sensible Heating: Adding heat to raise air temperature without changing moisture content; occurs with a surface warmer than the air temperature.
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Sensible Cooling: Cooling air without altering moisture content, by passing air over a cooler surface.
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Cooling and Dehumidification: Cooling air to remove water vapor while making sure the cooling coil temperature stays below the air's dew point.
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Adiabatic Cooling (Cooling with Humidification): Cooling air by evaporating water, using water spray or surfaces.
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Heating and Humidification: Adding both heat and water vapor to the air, typically using heated water spray.
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Unitary Systems: Refrigeration and air conditioning components installed as packaged units directly in or near a conditioned space.
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Central Systems: The components are separately designed and installed. These are suitable for multiple-zone settings.
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Heat Pump Unit: A heat pump unit is an air conditioner able to reverse its refrigeration cycle, providing heating in place of cooling.
Comfort Air Conditioning
- Body Heat Loss Factor: The comfort level is correlated to heat loss. factors that influence such loss are temperature, humidity, air movement and the surrounding environment.
- Indoor Air Quality: Pure air quality is important for comfort and health. Contaminants, such as dust, smoke, or biological material, lower the air quality. Ventilation can clear these.
- Effective Temperature (ET): The temperature at which the person feels the same in saturated and unsaturated air.
Lab Activity No. 1
- Investigate and identify the ideal living conditions for at least five plant and livestock species.
- Include temperature (air and surroundings), humidity, wind speed, sunlight, precipitation, soil moisture and surrounding topography.
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Description
Explore the fundamental concepts of environmental control, focusing on atmospheric conditions in buildings. This quiz addresses the significance of moisture and temperature in maintaining comfort for humans and livestock. Understand psychrometric charts and the measurement of various air properties.
