No_11_November_1968 — Page 36

DRY BULB

TEMPERATURE

"F

2

ΠΙΟ

100-

R

VELOCITY OF AIR IN FT PER MIN.

GLOBE THERMOMETER

OR

8

8

10

8

30

06

50

60

CORRECTED EFFECTIVE (OR EFFECTIVE) TEMPERATURE *F

سليليسيا

لسالسا

120

rio

100

90

2

WET

BULB

8

TEMPERATURE 'F

80

60

50

40

30

Fig. 1. Chart for computing the Corrected Effective (or Effective) Temperature for sub- jects wearing normal indoor clothing and engaged in light work. To obtain the corrected effective temperature for a given set of environmental conditions draw a straight line from the appropriate wet bulb temperature mark on the right hand scale to the measured globe thermometer mark on the left hand scale; the required C.E.T. is then read off the C.E.T. scale at the point of intersection between the line on the grid corresponding to the mea- sured air velocity. The effective temperature (E.T.) is obtained in a similar manner except that the measured dry-bulb temperature is used instead of the globe thermometer reading.

order to permit him to adapt to heat. This, briefly, is the thermal comfort

zone.

Many attempts have been made to integrate all the four meteorological factors into a single index to indicate their combined effect on body thermal comfort. The Effective Temperature Scale, originally developed in 1923 in America for air-conditioning engineers, is still the most widely used. This empirically determined index is based on the hypothesis that different com- binations of temperature, humidity and air movement will induce like sensations of warmth or cold on the body.

Later, in its corrected form (Cor- rected Effective Temperature), radia- tion effect is included. Thus, one set of climatic conditions can be expressed as the equivalent of another. For ex- ample, 80°E.T. can be obtained from each of the combinations in table 2.

Fig. 1 reproduces the chart from which the Effective Temperature can be read off from different combina-

R.H. for summer cooling, and 70-72°F D.B. and 55-60% R.H. for winter heating.

Hong Kong's elements

Everyday experience tells us that the best time in Hong Kong, bio- climatologically speaking, occurs from late October through November. Dur- ing this time, the air temperature ranges from 70-75°F while relative humidity

―

is at its lowest for the year at below 70%. Sunny days and clear sky pro- duce a mean radiant temperature from the surrounding surfaces of a few de- grees above air temperature.

This set of conditions is equivalent to an effective temperature index of around 74°, right on the optimum range. At any other time of the year, it is either too hot, or too cold.

Everyday experience is clearly borne out in Fig. 2, which is an at- tempt at a "graphical diagnosis" of the Hong Kong climate. It shows at "bioclimatic chart" with wet- and dry- bulb temperatures as ordinate and ab- sicca. Relative humidity is represented by diagonal lines. The effective tem- perature based on 20 f.p.m. of air movement can be read off from these combinations and is indicated by curved downward strokes. Five day mean values of dry- and wet-bulb temperatures and relative humidity for 60 years based on Peacock's compil- ations are plotted against the pro- bable comfort zone.

1

It is seen readily that for most of

tions of dry and wet-bulb temperatures the year, with the exception of the and air movement.

Based on this scale, various research- ers have carried out experiments relat- ing to the thermal comfort zone in the tropics. Their results have been sum- marised by Kendrick". Though minor descrepencies exist, some general con- clusions can be drawn: The probable optimum comfort zone lies in the range 74-86°F D.B., 70-80°E.T. and between 30-70% R.H. A seasonal range of about 4-5°F between summer and and winter is also indicated.

No data is available for Hong Kong conditions, but the range coincides well with local air-conditioning engin- eers' design criteria: 78° D.B. and 55%

-

1) 80°F D.B. 80°F W.B. 2) 90 3) 100 4) 100

October and early November data, Hong Kong's climate departs consider- ably from the comfort zone. In order to achieve a climate-balanced design, the major climatic elements may be considered to bear the following im- plications. Temperature

The magnitude and range of dry- bulb temperature are criteria in design,

since it has been shown that most people would like to live in an environ- ment having a temperature range of about 65-70°F in winter and around 76-80°F in summer. Hong Kong's tem- perature data is about evenly located. above and below this preferred range

Table 2

-

100% R.H.

42

11

-

72

64

―

70

22

―

―

T

20f.p.m. air movement 20

20

500

34

Far East BUILDER, November 1968.