Instructions

HD32.3 - 8 - V1.4

From PMV comes a second index called PPD (Predicted Percentage of Dissatisfied) which calcu-

lates in percentage the “dissatisfied” beings in relation with precise microclimatic conditions.

ISO 7730 regulation suggests the PMV use in presence of the following environments with vari-

ables variations that influence the thermal balance:

• Energetic waste = 1 ÷ 4 met

• Thermal impedance by clothing = 0 ÷ 2 clo

• Wet bulb temperature = 10 ÷ 30°C

• Medium radiant temperature = 10 ÷ 40°C

• Air speed = 0 ÷ 1 m/sec

• Vapour pressure = 0 ÷ 2,7 kpa

So, PMV is an index suitable to the evaluation of working environments with moderate microcli-

mate such as houses, schools, offices, laboratories, hospitals, etc.; it’s useful in detecting limited

degrees of thermal discomfort in the people in this environment.

ISO7730 regulation suggests PPM values between + 0,5 and - 0,5 for the thermal comfort state and

to these values correspond a percentage of dissatisfied about the thermal conditions (PPD) less than

10% (see the following table).

Table 1: thermal environment evaluation scale

PMV PPD % THERMAL ENVIRONMENT EVALUATION

+3 100 Hot

+2 75,7 Warm

+1 26,4 A little bit warm

+0,85 20 Acceptable thermal environment

-0,5 < PMV < +0,5 < 10 Thermal well-being

-0,85 20 Acceptable thermal environment

-1 26,8 Cool

-2 76,4 Cold

-3 100 Very Cold

For the calculation of PMV and PPD indexes, it’s necessary to know:

• The working charge (energetic waste);

• The thermal impedance of clothing.

The working charge can be calculated using the following measurement units:

kcal/h (1 kcal/h = 1.163 Watt): with this unit is expressed the medium power per hour supplied

during the working activity;

MET (1 MET = 58.15 Watt/m

): with this unit is expressed the total power per hour supplied by a

being during the working activity divided for the body surface of the being.

Thermal impedance of the clothing is measured in CLO;

1 CLO = thermal gradient of 0.18 °C on a 1 m

area crossed by 1 kcal/h thermal flow

The following tables can help to establish the thermal impedance values of the clothing and the

working rate (metabolism).