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Thermal Comfort Modeling
Transcript of Thermal Comfort Modeling
Thermal Environment Contributing Factors refers to temperature and humidity Thermal Comfort "The condition of the mind that perceives and expresses satisfaction with the thermal environment" P.O. Fanger Worked as a professor at Syracuse University and the Technical University of Denmark
An expert in the field of indoor environments
His research on thermal comfort still defines the standard for predicting indoor thermal environments
Developed the Predicted Mean Vote (PMV) Model and the Predicted Percentage Dissatisfied (PPD) Index Cecilia Escobar
LA 816 What is the Predicted Mean Vote (PMV) Model? The PMV Model was developed to predict thermal comfortability amongst large user groups in a given space.
However, the model is only 80-90% accurate
Gender, culture, age make it impossible for evey person to agree on what temperature levels make an environment thermally comfortable. The American Society for Heating, Refrigerating, and Air Conditioning (ASHRAE) Inc. Conducted multiple studies, experiments, lab tests to acquire large amounts of statistical data
Adopted Fanger's research and developed the ASHRAE Standard 55 - Thermal Environmental Conditions for Human Occupancy
Developed the thermal sensation scale.
Quantifies a person's thermal sensation at a given time in a neutral environment. +3
cold ASHRAE Thermal Sensation Scale Six Contributing Factors There are six factors identified by ASHRAE that dictate a person's thermal comfort
Humidity How Fanger applied these factors Ccombined the four environmental variables to the two personal variables Environmental Variables:
Radiant Temperature Personal Variables:
Clothing Insulation After he combined the environmental variables with the personal variables, Fanger developed an index for the PMV Model that directly correlates with The ASHRAE Thermal Sensation Scale. hot
-3 Fanger's Research Extensive Research on the body's physiological processes
Heat Balance Thermoregulation The body's ability to maintain a constant temperature, despite exterior thermal conditions Shivering to warm up Sweating to cool down Fanger's PMV Model will only operate under consistent neutral conditions. Sweating and shivering are not included in the six contributing factors in dictating thermal comfort as identified by ASHRAE Therefore, the PMV Model is unusable in predicting the environment for a space in which the users will be expected to shiver or sweat to regulate temperature. Fanger emphasized that a person's thermoregulatory system will create a heat balance despite the person's perception of thermal comfort. Therefore, Fanger studied thermoregulation and heat balance only when thermal comfort sensation amongst a large group of people was in a neutral state. Thermal Comfort vs. Thermal Sensation Thermal Satisfaction/Comfort: Refers to how "acceptable" the thermal environment is for an occupant. Thermal Sensation: The temperature perceived by an occupant, despite his or her satisfaction level with the thermal environment. Fanger's PMV Model -0.036M PMV= (0.303e +0.028)L PMV= Predicted Mean Vote The Predicted Mean Vote refers to the predicted vote correponding to the PMV Index (Thermal Sensation Scale) M = Metabolic Rate L= Thermal Load Thermal Load is the sum of the six key factors that contribute to thermal sensation (air speed, air temperature, radiant temperature, clothing insulation, metabolic rate, humidity) To reach the numbers used in the PMV Model, Fanger first conducted a series of preliminary equations that correspond to the six contributing factors. The numbers above a result of the preliminary equations. * M= Metabolic Rate Metabolic rate refers to how quickly the body converts chemical energy into heat for a given activity.
The ASHRAE 55-2004 Standard incorporates a list of several daily tasks and their corresponding typical metabolic rates.
According to ASHRAE, as Metabolic Rate increases above 1.0 Met unit, the evaporation of sweat becomes a factor in determining thermal comfort.
the PMV Model does not fully incorporate this aspect, and should not be used in situations where metabolic rates are expected to elevate beyond 2.0 Met units for the majority. The PPD Index Fanger's intention was to create a comfort equation, the PMV Model, that would predict conditions where most occupants would feel thermally satisfied.
The prediction of dissatisfied occupants cannot be ignored
Thus, the development of the Predicted Percentage Dissatisfied (PPD) Index
predicts the percentage of thermally dissatisfied people in a given thermal environment The PPD Index PPD= 100-95 x exp (-0.03353PMV - 0.2179 PMV ) 4 2 The PPD acts as a function of the PMV Model
PPD increases for PMV values other than zero (neutral)
The PMV Model and the PPD Index form a U-shaped relationship 100 represents the total percentage of a group of occupants
95 refers to the percentage of occupants subtracted from 100, and the PMV model is applied to account for the percentage of people who will be dissatisfied ASHRAE Adoption of Fanger's models ASHRAE has concluded acceptable comfort conditions for summer and winter seasons using Fange'rs Model. Winter
20-23 Celsius Summer
23-26 Celsius ASHRAE has made Fanger's Model the basis for predicting environmental conditions that will satisfy most occupants in a given space Key Points PMV Model is able to predict thermally acceptable conditions for 80-90% of users in a space PMV Model is practically unusable in a space expected to house occupants that will exceed 2.0 Met units on an average day. (perfect for office design) PPD Index acts as a function of the PMV Model and they have a U-shaped relationship Works Cited "ASHRAE 55-2004 Thermal Environmental Conditions
for Human Occupancy." ANSI/ASHRAE Standard 55-2004. Atlanta: ASHRAE, 2004 Print. Charles, Kate. Institute for Research in Construction.
National Research Council Canada. Fangers Thermal Comfort and Draught Models. Ottawa: 2003. Web. Olesen, B.W. "Thermal Comfort." Diss. Print. Pike-Paris, Ann. "Indoor Air Quality: Part I - What it is."
Pediatric Nursing 30.5 (2004):430-3. Proquest Research Library. Web. 9 Oct. 2012. Sherman, Max. "A Simplified Model of Thermal Comfort."
Energy and Buildings. 8. (1985): 37-50. Print.