Friday, 27 July 2012

Comfort (I)

I would like to continue with the environmental comfort discussion, trying to answer the following question:

-) Which indices should be studied for the environmental comfort?

There are two index called PMV (Predicted Mean Vote) and PPD (Planned Percentage of Dissatisfied). Let us try to understand them.
From materials by E. Moretti , we can read:

     "" The PMV (Predicted Mean Vote) is a mathematical function that depends on: clothing, air temperature, activity, mean radiant temperature, air velocity, humidity.
     

It represents the average grade given by a large sample of people residing in the same environment, expressing their thermal sensation through a psychophysical scale that ranges from a value of +3 (very hot) to -3 (very cold) through intermediate situations in which the 0 corresponds to neutrality.
     The PMV is related experimentally to PPD (Planned Percentage of Dissatisfied) (%), a parameter that expresses the number of people who would be dissatisfied of climatic conditions.
     PPD = 100 - 95exp [- (0.03353 + 0.2179 PMV4 PMV2)] ""
I finish this post bringing the graph of relationship between PDD and VMP. From barcol-air.nl read:
""There is a fixed relation Between the PMV and PPD value. When the PMV value is Between the recommended -0.5 + 0.5 and the PPD will be lower than 10%. The percentage dissatisfied in this model will never be lower than 5%.""

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