Pasado, presente y futuro de Cuba según La Quincena

The Comfort Triangles, introduced in the previous sub-sections, was developed by a process of logical deduction, based on initial data of thermal comfort limits, using the reasoning sequence presented.

The first test of the utility and application of the Comfort Triangle Chart was it’s introduction as a bioclimatic analysis technique in the two subjects at graduate level, Introduction to Bioclimatic Design and Introduction to Solar Architecture, currently given at the Faculty of Architecture, Design and Urbanism, of the University of Buenos Aires, since 1984. It’s implementation, over a period of 22 years by approximately 10,000 graduate students who passed the subject, has shown it’s value as a bioclimatic design tool, especially in situations where the indoor or outdoor temperature swing is significant. In addition, the method was tested in postgraduate courses in universities of Argentina, Mexico, Panama, Ecuador and Chile, in Latin America as well as the United Kingdom and Spain.

This long testing process of the Comfort Triangles has provided relevant useful feed-back indicating the following aspects that need to be improved and adjusted:

• The difficulty of relating the outdoor temperature swing to the indoor temperature variation, or establishing Range Ratios RR proposed by Strickley (1978). A further response to this requirement is provided in Chapter 8 and the case studies in Part 4.

• The maximum allowable temperature swing of 10 degrees appears to be excessive and implies the need to change or adjust the clothing excessively during the day.

To solve the first difficulty, tests and measurements are required to establish RR values for buildings under real conditions. These measurements can then be used to calibrate the numerical simulation of buildings in order to verify the possible variations that can be achieved a favourable modification of the internal conditions. Thermal simulation can also be used to define the conditions that provide thermal comfort.

In this sub-section, the range of conditions that provide thermal comfort periodic heat flow are evaluated. As the previous chapter established, this evaluation can be achieved using physiological models such as that developed by Fanger (ISO, 1988) or surveys of thermal comfort based on subjective sensations in typical conditions based on the principle of adaptive comfort (Nicol and Humphreys, 2001).

The case studies with measurements in existing buildings, which are presented in Chapters 10 and 11, provide relevant data to show typical values of RR and average temperature increase of occupied buildings.

These are then used to indicate the possible modification of indoor conditions in both heavy and light buildings according to the bioclimatic design resources, relating climate, comfort and design.

7.5.1. Variation of body temperature.

The internal temperature of the human body is conventionally considered as fixed with a value of 36,4° C (Edholm, 1969). However, detailed measurements show a variation in temperature with a tendency to increase in the afternoon and decrease at night with a range that can extend between 36° and 37,5° C. Table 7.5 shows the full range of possible body temperatures.

Table 7.5. Range of human body temperatures, based on Edholm (1967).

Body temperature Conditions

20 - 30° C Hypothermia during surgery with total anaesthetic

< 36° C Hypothermia

36 – 38° C Temperature of the body at rest 37° C Average temperature

38 – 39° C Temperature with exercise

> 39,5° C Tolerated for limited periods 38 – 41° C Fever

40 – 42° C Hiperthermia

> 42° C Brain damage

> 45° C Death

The typical daily variation of 0,55° C allows the body to respond to the expected swing of environmental conditions although, in some cases, the variation can reach 1° C without producing discomfort. As the air temperature rises in the afternoon, the body temperature also rises slightly (Edholm, 1969).

The effect of this increase can then be estimated considering a typical body weight of 100 kg, with a thermal capacity of 3000 KJ/kgK, a 0,55° C increase of temperature over a three hour period, with a surface area of the body of 1,6 m2 and a surface resistance of 0,03 W/m2K. The result shows that the body can resist an air temperature increase of 2°

C over a three hour period without any additional adjustment than the normal variation of body temperature, assuming a reasonable rapid distribution of this temperature increase in the body, achieved with blood circulation.

This temperature variation also favours the work efficiency of the body (Edholm, 1967), achieving better muscular performance with slightly higher corporal temperatures. In spite of the clear evidence of body temperature variation, Fanger’s model, presented in the Annex of ISO Standard (1994) takes for granted a fixed temperature of 37° C, including a variation in the comfort range as a function of the PMV, Predicted Mean Vote that is considered comfortable for a range between 0,5 and -0,5.

To achieve steady outward heat flow, the maximum skin temperature is 3° C below the body temperature, with slight variations for differences in air movement, relative humidity and mean radiant heat:

• Sensible air movement permits higher skin temperatures.

• Low relative humidity also allows higher skin temperatures.

• High relative humidity requires lower skin temperatures, often achieved through transpiration and aided by air movement.

• Mean radiant temperatures above air temperature require lower skin temperatures for the same body heat loss.

As the air temperature drops, clothing is needed to provide additional insulation to control heat losses.

Based on Edholm (1968), Figure 7.6 was constructed to indicate the range of temperature and average temperature of the body required to achieve comfort, related to the skin temperature needed to dissipate metabolic heat. This demonstrates that the Comfort Triangles can also be used to analyse body temperature variations.

Figure 7.6. Thermal conditions of the human body:

Zone 1: Average variation at rest.

Zone 2: Maximum variation at rest.

Zone 3: Possible variation with high rates of physical activity.

Zone 4: Conditions of hyperthermia.

Zone 5: Conditions of hypothermia.

Line 6: Indicative skin temperature.

Arrow 7: Difference between body and skin temperature necessary to dissipate metabolic heat production.

Line 8: Range of comfortable air temperatures

Arrow 9: Difference between skin temperature and air temperature necessary to dissipate metabolic heat production.

Source: 1 – 6 Based on data from Edholm (1968).

7 – 9 Based on Figure 7.3

7.5.2. Skin temperature variation.

As Figure 7.6. indicates, the skin temperature should be lower than the body temperature in order to achieve a steady flow of heat to the surface, allowing the dissipation of metabolic heat.

12

10

8

6

4

2

0

Temperature swing

1 2

3

24 26 28 30 32 34 36 38 40 42 Average temperature ° C

4 5

6 7 8 9

Once again the range of skin temperatures considered comfortable can vary, though the total comfort range is 2 deg K, from 31° - 34° C. Above 34° C transpiration is likely to cause discomfort in humid climates, while temperatures below 30 are considered too cool. The possible variation according to Edholm (1968) is shown in Table 7.6.

Table 7.6. Examples of skin temperatures.

Skin temperature Conditions

35° C Excessive discomfort with sensation of heat

>34° C Intense sweating with high humidity 34° C Typical value for warm climates 33° C Typical value for temperate climates 32° C Typical temperature with cool climates 15° C Absolute minimum value; start of pain.

The values are for average skin temperature, as extremities can have wider swings, and are the first to suffer from chilblains, frost-bite and other consequences of extreme values.