A5. PPD index establishes a quantitative predication of the number of thermally dissatisfied people. When the PMV-index has been determined, the PPD can be found from Figure A5: (a) (b) Predicted percentage of dissatisfied 80 60 40 30 20 08654 10 -2.0 -1.5 -1.0 -0.5 0 Figure A5 0.5 1.0 1.5 2.0 Predicted mean vote Discuss the function of PMV index with its thermal sensation scale. (3 Marks) Discuss why the PPD value cannot reach zero even when PMV = 0. (2 Marks)