p.2
Classification of Climates
What is the primary focus of climate classification?
To categorize different climate types based on specific criteria.
p.2
Importance of Climatic Design
Why are climatic elements important in building design?
They influence the design decisions to ensure comfort and efficiency.
What is psychrometry?
The study of the properties of air and water vapor mixtures.
p.2
Psychrometric Properties
How can psychrometry be used in air-conditioning?
To evaluate air properties and describe air-conditioning processes.
p.3
Classification of Climates
What is the main problem in cold climates for building design?
Lack of heat (under heating) or excessive heat dissipation.
p.3
Classification of Climates
How does the temperate/moderate climate affect heating and cooling?
It has seasonal variations between underheating and overheating, but neither is very severe.
p.3
Classification of Climates
What is the primary issue in hot-dry (arid) climates?
Overheating, with dry air allowing for effective evaporative cooling.
p.3
Classification of Climates
What characterizes the diurnal temperature variation in hot-dry climates?
There is usually a large diurnal (day-night) temperature variation.
p.3
Classification of Climates
What complicates overheating in warm-humid climates?
Very high humidities restrict the evaporation potential.
p.17
Psychrometric Processes
What is the formula for mass flow rate of supply air?
Q_s = m_a C_pa (T_R - T_S)
p.10
Psychrometric Properties
How is dew point temperature related to evaporation?
It is the temperature at which evaporation and condensation occur at the same rate.
p.15
Psychrometric Processes
What does AM/BM represent?
The ratio of the mass flow rates A and B.
What does cloud cover measure?
The fraction of the sky hemisphere covered by clouds, ranging from 0 (clear sky) to 1 (total cover).
p.4
Importance of Climatic Design
What is one key objective of climatic design?
To reduce energy cost of a building.
p.10
Psychrometric Properties
What is dew point temperature (T dp)?
The temperature at which water vapor in air condenses into liquid water at constant pressure.
p.13
Psychrometric Processes
What happens during the cooling process in psychrometrics?
The dry bulb temperature decreases, and moisture may condense out of the air.
p.9
Psychrometric Properties
What does moisture content (w) represent?
The vapour content of air, given in grams or kg of water vapour per kg of moist air.
p.9
Psychrometric Properties
How is wet-bulb temperature (T wb) measured?
By a hygrometer or a sling psychrometer.
p.14
Psychrometric Processes
What is the apparatus dew point (ADP)?
The temperature at which air becomes saturated with moisture in a cooling system.
p.4
Importance of Climatic Design
What does climatic design optimize in buildings?
Architectural design (passive) and building services systems (active).
Where can climatic data for Hong Kong be found?
Typically published by meteorological stations.
p.7
Thermal Comfort Variables
What are the four environmental variables that directly affect thermal comfort?
Temperature, humidity, solar radiation, and air movement.
p.10
Psychrometric Properties
What is specific volume (v)?
The reciprocal of density, measured in m³/kg.
p.17
Outdoor Design Conditions
What are the room design conditions (Rs) for summer?
20 – 25.5 °C dry bulb; 40 – 70% RH
p.17
Outdoor Design Conditions
What is the minimum supply air temperature (Sc) in relation to room temperature?
8 °C lower than room temperature.
p.18
Air Conditioning Systems
How is the cooling coil load calculated?
Cooling coil load = m_a Δh = 0.7(57 – 32.5) = 17.15 kW.
How is precipitation measured?
Total amount of rain, hail, snow, or dew measured in mm per unit time.
p.14
Psychrometric Processes
What is adiabatic cooling?
Cooling that occurs without heat transfer, often achieved through evaporative cooling.
p.11
Psychrometric Properties
What does the wet bulb thermometer measure?
The temperature of evaporative cooling.
p.9
Psychrometric Properties
How is dry-bulb temperature (T db) measured?
By a thermometer with consideration of air movement.
p.9
Psychrometric Processes
What indicates a status point on the psychrometric chart?
A pair of dry-bulb temperature (T db) and wet-bulb temperature (T wb).
p.7
Outdoor Design Conditions
Why is rainfall data sometimes needed in climatic design?
For designing drainage systems and assessing the level of precipitation.
How is sunshine duration measured?
Using a sunshine recorder that burns a trace on a paper strip, expressed as hours per day or month.
What are the main climatic elements measured by meteorological stations?
Temperature, humidity, air movement, and precipitation.
p.18
Air Conditioning Systems
What role does the fan play after dehumidifying the air?
Acts as a sensible air heater.
p.13
Psychrometric Processes
How does heating affect the psychrometric properties of air?
It increases the dry bulb temperature while potentially decreasing relative humidity.
p.14
Psychrometric Processes
What is sensible cooling?
A process that reduces the temperature of air without changing its moisture content.
p.15
Psychrometric Processes
What does 'M is closer to B' imply about mass flow rates?
It means that the greater mass flow rate is from branch B.
p.15
Psychrometric Processes
What is the equation for mass flow rate at the branches?
m_M θ_M = m_A θ_A + m_B θ_B.
p.11
Psychrometry Overview
What is a sling psychrometer used for?
To measure humidity by comparing dry and wet bulb temperatures.
p.18
Psychrometric Processes
What does the point S_c represent?
It is determined based on the room ratio line (RRL).
p.13
Psychrometric Processes
What is the significance of understanding psychrometric processes?
They are essential for designing HVAC systems and ensuring thermal comfort.
What are the ways humidity can be expressed?
Relative humidity, absolute humidity, wet-bulb temperature, or dew-point temperature.
What aspects of air movement are indicated in climatic measurements?
Wind speed and direction.
What units are used to express precipitation?
Millimeters (mm) per unit time (day, month, year).
p.10
Psychrometric Properties
What does enthalpy (h) represent?
The heat content of unit mass of the atmosphere, in kJ/kg, relative to 0 °C dry air.
p.18
Psychrometric Properties
What is the formula for the sensible to total heat ratio?
Q_s / (Q_s + Q_L) = 5 / (5 + 1.2) = 0.806.
p.13
Psychrometric Processes
What occurs during the dehumidifying process?
Moisture is removed from the air, lowering its humidity level.
p.14
Psychrometric Processes
What does the contact factor measure?
How close the air will get to the coil dew point.
p.14
Psychrometric Processes
What does a rate of heat transfer of 0 kW indicate?
No heat transfer occurring between points A and B.
p.21
Psychrometric Processes
What does the process 1 to 2 show?
B. cooling and dehumidification.
p.8
Outdoor Design Conditions
What climatic conditions in Hong Kong necessitate outdoor air control?
High temperature and humidity.
What is psychrometry?
The study of moist air properties and their changing conditions.
p.14
Psychrometric Processes
What is dehumidification?
The process of removing moisture from the air.
p.15
Psychrometric Processes
What is the equation for gravitational mass flow rate at the branches?
m_M g_M = m_A g_A + m_B g_B.
p.19
Thermal Comfort Variables
Which of the following is not an important weather parameter in designing thermal conditions of a building?
D. Fraction of cloud cover
p.16
Air Conditioning Systems
What type of air conditioning system is described?
A constant volume, 100% fresh air system.
p.8
Outdoor Design Conditions
What is required for some buildings during winter in Hong Kong?
A little bit of winter heating.
p.18
Psychrometric Processes
How can the Coil ADP (pt X) be determined?
Based on a given contact factor.
p.4
Importance of Climatic Design
What type of environment does climatic design aim to provide?
A comfortable and healthy environment for people.
p.13
Psychrometric Processes
What are the main psychrometric processes?
Heating, cooling, humidifying, and dehumidifying.
p.11
Psychrometry Overview
What is the purpose of the handle in a sling psychrometer?
To swing the thermometers around at a constant speed for accurate readings.
p.3
Classification of Climates
How does the diurnal temperature variation in warm-humid climates compare to hot-dry climates?
The diurnal temperature variation is small in warm-humid climates.
p.9
Psychrometric Properties
What is saturation humidity?
The maximum amount of moisture air can support at a given temperature.
p.14
Psychrometric Processes
How is the bypass factor calculated?
By subtracting the contact factor from 1.
p.14
Psychrometric Processes
What is the formula for the rate of heat transfer from A to B?
Rate of heat transfer = 0.75(66 – 40.5) = 19.125 kW.
p.4
Importance of Climatic Design
How does climate affect buildings?
It has a major effect on building performance and energy consumption.
How is solar radiation recorded?
As continuously varying irradiance (W/m²) or as irradiance over the hour or day using an electronic integrator.
p.4
Importance of Climatic Design
What is meant by using 'natural energy' in climatic design?
Using natural energy instead of mechanical systems and power.
p.13
Psychrometric Processes
What are psychrometric processes?
Processes that involve the study of the thermodynamic properties of moist air.
p.11
Psychrometric Processes
What is the function of the cloth sleeve covering the thermometer?
To keep the bulb of the wet bulb thermometer soaked in water.
p.13
Psychrometric Processes
What is the effect of humidifying air in psychrometric processes?
It increases the moisture content and relative humidity of the air.
p.9
Psychrometric Properties
What is relative humidity (RH)?
The ratio (in %) of the partial pressure of water vapour in moist air to that in saturated air at the same temperature.
