Human thermal comfort Flashcards
How does ASHRAE describe human thermal comfort?
The state of mind that express satisfaction ruth the surrounding environment.
Describe the key parameters that define human thermal comfort.
Air temperature: depending on the temperature of the air surrounding us we can either feel too hot, too cold or satisfied with the temperature. The range of comfortable air temperatures varies based on individual preferences, clothing insulation, and activity levels.
Relative air humidity: Relative humidity is the ratio of the actual amount of moisture in the air to the maximum amount of moisture the air can hold at a given temperature. Maintaining an appropriate relative humidity level helps prevent dry or overly humid conditions, which can affect comfort.
Mean radiant temperature: Temperature: Mean radiant temperature refers to the temperature of surfaces that emit or absorb thermal radiation, such as walls, ceilings, and windows. Radiant temperature can influence how warm or cool occupants feel, even if the air temperature is within the comfort range.
Air velocity (air movement): Air velocity or air speed refers to the movement of air in the indoor environment. Proper air movement can help distribute heat evenly and enhance comfort. Excessive draft or stagnant air can lead to discomfort.
CLO value (insulation): Clothing insulation is a measure of the insulating properties of the clothing worn by occupants. The type and thickness of clothing affect how the body loses or retains heat, influencing comfort.
Metabolism rate: Metabolic rate represents the rate at which the human body generates heat due to physical activity and metabolism. It is typically expressed in metabolic equivalent (MET) units. Higher metabolic rates (e.g., due to physical exertion) may require lower air temperatures for comfort.
Explain the terms “Met” and “Clo” in the context of human thermal comfort. Which units are met and clo expressed in?
Met
Metabolism = the internal heat production
Unit for activity level
1 met = one person sitting still on a chair = 58W/m2
Clo
Clothing = thermal insulation
Clo-value is a measurement of the thermal resistance of a piece of clothing or the total thermal resistance of the entire clothing set worn by a person.
The clothing has huge impact on heat transport to and from the body
1 clo = “full suit”: pants, shirt, jacket = 0,155m2K/W
Explain the terms “air temperature”, “mean radiant temperature”, “operative temperature” and “equivalent temperature”.
Air temperature
The average temperature of the air around us. In an indoor setting, this means that the air volume in a room is considered “well mixed” 0 that the same conditions are valid at every point in the air volume
Mean radiant temperature
The average temperature of the surrounding surfaces, taking ino account their view factors
Operative temperature
The mean value of the air temperature and the mean radiant temperature
Equivalent temperature
A concept that includes air temperature, mean radient temperature, vlothing, activity and air velocity
Explain the terms “Actual Mean Vote (AMV)”, “Predicted Mean Vote (PMV)”, “Actual Percent Dissatisfied APV)” and “Predicted Percent Dissatisfied (PPD)”.
Actual mean vote (AMV)
How real people assess the thermal comfort at a specific point in time and place, this is a measurement on a scale from -3 to 3
Predicted mean vote (PMV)
A prediction of the perceived occupant thermal comfort in a room based in a calculation including the impact factors defined earlier: air temperature, mean radiant temperature, relative humidity, air velocity, metabolic rate and clothing. Value between -3 and 3.
Actual percent dissatisfied (APD)
How many of the actual people in a room are dissatisfied with the thermal comfort at a specific point in time and place - because they perceive it as too cold or too warm.
Predicted percentage dissatisfied (PPD)
What percentage of occupants in a room would be dissatisfied with the thermal comfort, either by perceiving it as too cold or too warm.
Describe the term “occupied zone” using a simple sketch.
0,1 m över golvet
1 m från fönster och dörrar (windows and external doors)
2 m hög
0,6 m från vägg (exterior wall)
Explain (using a graph) the relationship between Predicted Percent Dissatisfied (PPD) and Predicted Mean Vote (PMV). What is the lowest achievable PPD-value and why can lower PPD-levels not be achieved?
The PPD value can never be 0 because of individual differences in the thermal comfort perception, with different words, people don’t think exactly the same.
People can have different thermal comfort perception because of:
Deviation in metabolic rate at equal levels of activity
Different in body surface/volume ratio
Healt - genreal fitness, disease, stress, tiredness
Gender
Age
Acclimatization
Expectations!
How does the International Society of Indoor Air Quality and Climate (ISIAQ) define the term “Indoor Air Quality (IAQ)”, and how does the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) define the term “Acceptable Indoor Air Quality (IAQ)?
ISIAQ define the term Indoor air quality (IAQ):
“An indicator of the types and amount of pollutants in the air that might cause discomfort or risk of adverse effects on human or animal health, or damage to vegetation.”
ASHRAE define the term “Acceptable indoor air quality (IAQ):
“ Air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a substantial majority (80% or more) of the people are satisfied.
