DEVELOPMENT AND APPLICATION OF THE METHOD

In this section of the Chapter, the original proposal for the definition of the comfort zone using the Comfort Triangles is compared with other methods to define the comfort limits. The two comfort approaches, based on climate chamber studies and questionnaires of occupants in buildings, represented by the Fanger comfort model (ISO, 1994) and the adaptive comfort model (Nicol and Humphreys, 2001), are presented in the following sub-sections.

7.6.1. Numerical simulations.

Fanger’s model (1996) establishes a thermal balance of the human body, balancing the metabolic heat production with the heat losses, according to the activity rate, the environmental conditions and the insulation value of clothing (ISO, 1994).

The program Comfort, written by the author in Quick Basic, uses the algorithms provided in the Annex of the ISO Standards (1998). It also calculates the intermediate values of the external surface area and temperature of clothing in order to calculate the heat exchange with the surrounding environment. This depends on the air temperature or dry bulb temperature, the relative humidity, the mean radiant temperature and the relative air velocity.

This has been used to calculate the range of comfort conditions, considering that the acceptable daily swing can be obtained by using a PMV, Predicted Mean Vote of comfort between -0.5 and +0,5 and an adjustment of clothing. Further possible methods of adjustment to variation in the environmental conditions include slight changes in the activity level and posture, though these were not included in the analysis of comfort ranges.

In the paper on the Comfort Triangles (Evans, 2003), the limits of the comfort zone were analysed for different levels of clothing using the Fanger´s model (1996). This exercise confirmed the need to adjust the form of the Comfort Triangles to take into

account the maximum possible adjustment of clothing during a typical working day.

Basically, the possibilities of comfortable clothing limit the acceptable thermal swing to 8 deg, a lower swing than originally proposed.

The revised form of the triangle was published as Figure 1 in Evans (2003), with a truncated apex to the triangle, reducing the maximum acceptable swing. The original proposal for night comfort also used this concept of the truncated triangle.

With this further test, the triangles were then adjusted and improved to respond to requirements of thermal comfort with periodic variation of temperatures. The resulting Comfort Triangles are shown in Figure 7.7. and apply to sedentary activities and rest in climates with average monthly temperatures up to about 27°C.

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Sedentary Ventilation Night comfort

Figure 7.7. Modified form of the ‘Comfort Triangles’, taking into account the limitations of clothing adjustment during the day.

7.6.2. Adaptive comfort.

An alternative approach to the definition of comfort, which can give different results from those obtained by Fanger’s method (Fanger,1973; ISO EN 7730, 1994) is the

‘adaptive comfort’ concept, arguing that the comfort zone depends in part on the temperatures that the user experiences in the same month (Nicol and Humphreys, 2001).

This approach is considered to be especially applicable for occupants of buildings without artificial cooling. In this case, the comfort zone can vary according to the monthly average outdoor temperature, or the average outdoor temperature in the previous 30 days.

An example of this approach, incorporated in ASHRAE Standard 55:2004 (Ashrae, 2004), shows the range of the comfort with an average that varies from 21°C to 27°C,

with a constant range of 8 degrees to satisfy 90 % of the population, shown in Figure 7.8. A slightly wider range is achieved when this proportion drops to 80 %.

Figure 7.8. The adaptive comfort zone, related to the average monthly temperature, according the ASHRAE Standard 55:2004 (2004).

Assuming a constant indoor temperature range for 90% satisfied, as shown in Figure 7.8, the comfort zone can be redrawn using the concept of the Comfort Triangles, to obtain the graph show in Figure 7.9.

Figure 7.9. The comfort zones proposed in the ASHRAE adaptive comfort standard (2004), compared with the Comfort Triangle for sedentary activity, shown in Figure 7.4.

The result is similar to the Comfort Triangles derived in the previous sections, though the extreme limits of comfort extend slightly further, from 17° to 31° C, instead of 18°

to 30° C. The maximum range of comfort is constant, while in the previous sections argued that the range decreases as the temperature drops.

Although the upper limit of the comfort range, which according to the ASHRAE Standard reaches 31°C, this only occurs when the average monthly temperature exceeds 30°C, a rare situation that seldom occurs even in very extreme climates. If average monthly temperatures above 30°C are excluded, there is a good agreement between the upper comfort limit in both approaches.

At the lower end of the comfort scale, the ASHRAE Standard implies a continuing drop in the comfort temperature when the average monthly temperature falls below 10°C.

This is not consistent with the findings of Humphreys (1981) who shows a levelling of the minimum comfort level when the average monthly temperature reaches 10° and a slight rise at very low average monthly temperatures.

Figure 7.10 shows that when the extreme climate conditions, corresponding to average monthly temperatures below 10° and above 30°C are excluded, there is a very good relationship between the comfort zone proposed in the previous section of this thesis and the comfort zone with adaptive comfort according the ASHRAE Standard (2004).

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Figure 7.10. The Comfort Triangle compared with the conditions for comfort established by the ASHRAE Standard 55:2004 for average monthly temperatures between 10 and 25º C.

7.7 ADDITIONAL APPLICATIONS OF THE COMFORT TRIANGLES