Building Physics 1: Thermodynamics Concepts Flashcards
(24 cards)
What are some individual factors influencing thermal comfort?
Clothing, activity, age, gender, health, adaptation
What temperature does the human thermoregulatory system attempt to maintain?
37.2 deg C
How is heat lost from occupants (with percentages)?
Radiation (45%), convection (30%), evaporation (25%), conduction (negligible)
What are some environmental factors influencing thermal comfort?
Dry bulb temperature, air velocity, area of exposed skin
What is convection?
The heat transfer between a surface and adjacent fluid by the flow of fluid from one place to another, induced by temperature
What is convective heat transfer?
Controlled by dry bulb temperature (wet bulb temperature is humidity), air velocity, and area of exposed skin. Air movement perceptible at 0.2-0.25m/s. Effect of air movement depends on air temperature
What is radiation?
The transfer of thermal energy through matter or space by electromagnetic waves, thus no transfer medium required
What is radiative heat transfer?
Occurs between skin/clothes and surfaces seen by body (more significant surfaces are windows, hot or cold panels, and services), mean radiant temp used to quantify surface temperatures
What is evaporative heat loss?
Moisture lost from body via perspiration or exhalation, all heat loss above 29 deg C is evaporation, significantly reduces above relative humidity of 70%
What is conduction?
The direct flow of heat through a material resulting from physical contact
What is relative humidity?
Vapour pressure: saturation temperature at same dry bulb temperature
What is the mean radiant temperature, tr?
Measure of radiation heat transfer taking place between various surfaces
What is the dry resultant temperature, tres?
A simplified measure of thermal comfort that combines air temperature, mean radiant temperature, and air speed to assess how warm or cool a person feels
What are the roles of ventilation?
Supplying oxygen, removing contaminants, controlling humidity, controlling air velocity, controlling heat
What is ventilation rate?
Describes the volume (or mass) flow rate of air in and out of a room
What other terms can ventilation requirements be specified in?
Area of open windows (rapid ventilation), area of opening (trickle ventilation), performance of fan or stack (extract ventilation)
What is enthalpy?
e total heat content of a sample with reference to 0 deg C (J)
What is specific enthalpy?
Enthalpy per unit mass (J/kg)
What is Fourier’s Law?
The negative gradient of temperature and the time rate of heat transfer is proportional to the area at right angles of that gradient through which the heat flows
What is thermal resistance?
The ratio of the temperature difference between the twof aces of a material to the rate of heat flow per unit area
What are some examples of convective heat transfer processes?
Forced convection (forced air from fan), natural convection (buoyancy-driven flow), boiling (hot plate), condensation (water droplets)
What is Newton’s Law of Cooling?
The rate of heat loss of a body is directly proportional to the difference the temperatures between the body and its environment
What is the Stefan-Boltzmann Law?
Describes the intensity of the thermal radiation emitted by matter in terms of that matter’s temperature
What is emissivity?
The ratio of a material’s emissive power to that of a black body
