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
Vertical temp difference should not exceed __?
3 grade C
Cold feet syndrome
comfortable air temp , but feet is in contact with cold surface
Comfort parameters inside air-conditioned space:
Relative humidity: 30-60%
Air velocity: 0.15 - 0.25 m/s
Dry bulb temp: 21-24 grade C
In naturally ventilated space where temperatures are higher, a person is more comfortable at higher air velocities
Cooling
removing heat (energy) from space will reduce the temp
Heating
adding heat (energy) to space will increase temp
Modes of heat transfer:
Convection
Radiation
Conduction
Humidification
add moisture to air by means of steam, water sprays or ultrasonic humidifiers
De-humidification
remove moisture from air by means of sub-cooling & reheating / chemical process (desiccant wheels)
