Theme 2 - Human Comfort Flashcards
Factors affecting human comfort
Personal
(Metabolic rate ‘‘met’’ / Clothing level ‘‘clo’’)
External
(Air speed ‘‘m/s’’ / Humidity ‘’% RH’’ / Mean radiant temperature ‘‘grade C’’ - air & radiant temp)
Factors needs to be in equilibrium for human comfort.
2 Methods of development comfort scales
Analytical
People & responses are monitored in temp controlled environment. Results are used to develop a predictive model based on highly controlled environments.
Behavioral
People are monitored in their normal environment & their responses are related to conditions they experience. Results are analyzed statistically in order to understand the interaction between people & buildings
2 Most common predictive comfort scales used
Predicted Mean Vote (PMV)
Predicted Percentage of Dissatisfied (PPD)
What causes discomfort?
Irrespective of temp, humidity, air velocity, direct solar radiation & heat radiation from facade
Predicted Mean Vote (PMV)
Thermal scale that runs from cold (-3) to hot (+3).
Original data was collected by subjecting large number of people to different conditions within a climate chamber & having them select a position on the scale that beat describes their comfort.
According to ASHRAE 55 the recommended acceptable PMV range for thermal comfort is -0.5 to +0.5 for an interior space.
Predicted Percentage of Dissatisfied (PPD)
The percentage of occupants that will be dissatisfied with thermal conditions.
This scale is a function of PMV given that further PMV is from neutral, the higher PPD.
ASRHEA 55 recommends an acceptable range as less than 10% persons dissatisfied for an interior space.
Metabolic rate (M)
Amount of energy used by human body per unit of time.
Energy is used to:
- Do work - pumping blood (internal process) & lifting objects (external work)
- Maintain internal body temp.
Metabolic Heat Rate (Rejected excess heat)
Metabolic rate minus energy to do work for specific period of time
Fuel + O2 = Energy + Heat
Food + Oxygen = Metabolic process (internal work & body temp) = external work + Rejected excess heat
What is the metabolic heat rate (heat output / unit area of skin) for an individual who is seated and at rest?
1 met = 58.2 W/m2
Depends on body mass & surface area
Ave male = 1.8 m2 & 70 kg
Ave female = 1,6 m2 & 60kg
Metabolic Rate is dependent on:
Age
Weight
Height
Hormones
Digestion
Explain why is M determined by adding clo Values for individual garments worn by a person
Clothing level affects a persons ability to reject heat or prevent heat loss to the environment
Terminal comfort
environmental condition where a persons body heat is in equilibrium with environment
Thermal comfort is dependent on:
Personal factors:
Activity level (Metabolic heat rate) & clothing
Environment factors:
temp (air/ radiant), humidity & air velocity
