Environment 1 Flashcards
Heat
- The heating, cooling or lighting of a building is done by adding or removing heat energy
- Heat is the energy transferred between 2 materials as a result of the temperature differences between them
- In the UK, 47% of all GHG Emissions come from buildings
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Sensible Heat
- Sensible Heat is a function of temperature, eat capacity and mass
- Sensible Heat affects the temperature of a material, but not its volume or pressure
- Its measured in degrees celsuis
Latent Heat
- Latent Heat is the energy needed to cause a phase change in material e.g. freezing, melting, vapourising or condensing
- It is measured in Kilo Joules per Kilogram (KJ/Kg)
Radiant Heat
- Radiant Heat is the transfer of energy rom an emitting heat source to an object
- Warmth from the Sun is the most common example
- The amaount of radiation is inversely proportional to its wavelength
- The shorter the wavelength, the greater the energy content
Thermal Transfer
There are 3 key methods of Thermal Transfer:
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Conduction:
* If one object has a greater amount of molecular movement than the other, this more intense motion will be transferred to the cooler object - Convection:
- Convection is the form of heat transfer in liquids and gases
- As the volume of the gas increases with temperature, warmer areas have less mass than cooler areas- thus forcing the heat to rise
- Radiation:
- Radiation is heat energy in transit as electromagnetic waves
- A Thermogram measures infrared radiation emitted by objects an is exceptionally useful in identifying heat loss
Thermal Transfer:
Energy Matter Transmission
- Transmittance: When radiation passesthrough a building material
- Absorptance: When the radiation is absorbed and heats up the material
- Reflectance: When radiation reflects off of a surface
- Emittance: When radiation is given off by a surface
Thermal Transfer:
Heat Capacity
- Definition: The amount of heat required to raise the temperature of a material by 1°C
- Generally, heavier materials have higher Heat Capacities
- The greater the Heat Capacity of a building, the better suited it is to storing energy in the building envelope
Thermal Transfer:
Thermal Mass and Insulating Mass
Thermal Mass:
Materials with good Thermal Mass are those that can absorb heat, store it and then release it at a later time.
Insulating Mass:
Mass can be used to regulate heat; in hot, arid regions, thick walls are often used to insulate against heat.
Passive Solar Design:
The Greenhouse Effect
- Solar Radiation has a short wavelength, so it is easily transmitted through glass
- When it is reflected off of the internal surfaces it because Longwave Thermal Radiation
- Glass obstructs Longwave radiation so the heat becomes trapped
Passive Solar Design:
Principles
All passive solar heating systems have at least two elements:
- A Collector (Usually South-Facing)
- An Energy Storage or Temperature Mediating Element usually comprising of layers of thermal mass and insulation
Sun Spaces
Definition: A space intended to capture passive olar energy
Day Time Use: During the day, the Sun Space collects Solar Radiation and distributes heat to the rest of the building
Night Time Use: At night, the Sun Space must be sealed from the rest of the building. Heat is released by Thermal Mass and retained by Thermal Insulation
Passive Cooling
- Arid Zones: often exhibit high diurnal temperature swings prompting the use of thermal mass as a temperature regulator
- Tropical Zones: are much more reliant on ventilation for mitigation of heat
- Temperate Zones: sometimes require cooling in the summer months and also to mitigate solar gain from south glazing and internal gains
Passive Cooling:
Venturi Effect
Passive Cooling:
Bernoulli Effect
Passive Cooling:
Cooling Tower
