Room Climate Components

Figure 1
The comfortableness is an important factor for the well being and good health of anyone. How comfortable it is for a person depends to a great extent on the quality of the room climate. The room climate is of considerable importance because we stay on average two-third of our life in living rooms and offices. Air temperature, surface-temperature of floor, ceiling and walls, humidity and air movement are major factors for the comfortableness of human beings as shown in Figure 1.

(When measuring the thermal indoor climate, it is important to remember that you do not feel the room temperature, you feel the heat loss from your body. The parameters that must be measured are those which affect the energy loss of your body)
The above factors determine the heat transfer from our body to the surrounding environment, which is mainly related to the room air temperature as shown in Figure 2 and Figure 3. The main thermal comfort variables are:
1) Temperature (air, radiant, surface) , 2) Relative Humidity,  3) Air velocity  4) Activity 5) Clothing

To maintain thermal comfort two conditions must be fulfilled.
  1)  the skin temperature and the body's core temperature should be thermal neutral.
  2)  the body's energy balance: the heat produced by the metabolism should be equal to the amount of heat lost from the body (depends on physical activities).

Figure 2
Relative humidity 30 to 70 %
Air movement from 0 to 0.2 m/s
Similar temperature of all surrounding faces (H. Reiher & W. Frank)
Figure 3
average surface temperature of the
surrounding faces from 19.5 to 23 °C
Air movement from 0 to 0.2 m/s
(F.P. Leusden &H. Freymark)

Thermal comfort is highly subjective. However, based on the physical parameters it is possible to evaluate comfort conditions. The PMV value (Predicted Mean Vote) indicates whether people feel hot or cold. This temperature is affected by both the average annual climate and seasonal fluctuations within it.
Figure 4

Predicted Percentage Dissatisfied is an index that predicts the percentage of thermally dissatisfied people. The symmetrical PPD distribution is expressed as a function of the Predicted Mean Vote. When PMV is zero, PPD is 5% meaning that even under the best conditions, not everyone is satisfied with the condition of mean neutrality. 2.5 percent are uncomfortably cold and 2.5 percent are uncomfortably warm. We see that it is not possible to satisfy everyone, even within a perfectly controlled climate environment.    Figure 5 displays PPD as a function of PMV.

Table 1
Hot -3
Warm -2
Slightly warm -1
Neutral 0
Slighly cool 1
Cool 2
Cold 3

Figure 5

When PMV is either +1.5 or -1.5, as shown by the table, the Predicted Percentage Dissatisfied is about 50% (actually, 51.5%). On the other hand, this means that nearly one-half of the people are satisfied.When PMV is ±2.0, then about 75 percent of people are dissatisfied. From the opposite viewpoint, this means that about 25 percent of people are still comfortable.