APPLICATION OF COMFORT REQUIREMENTS IN ARCHITECTURE The average climate data for each month can be compared with the required comfort

levels in order to detect the difference between the existing and desirable conditions.

Initially, this may take the form of a simple comparison: temperatures above, below or within the established comfort zone.

The second step is to detect the design characteristics that promote a favourable modification of the external conditions, for example, the use of solar radiation when temperatures are below the comfort range or the use of air movement when above the zone.

Olgyay (1963) was one of the pioneers to establish this link in graphic form in his wellknown diagramme, showing three zones: the outdoor conditions of climate, the comfort zone and zones that indicate appropriate bioclimatic design strategies when

‘climate’ is outside the ‘comfort zone’. The diagramme (Olgyay, 1960 and Olgyay, 1995), presented in Appendix 2 of this thesis uses the coordinates of dry bulb temperature on the vertical axis and the relative humidity on the horizontal axis to define the bioclimatic zones.

Only a few years later, Givoni (1970) proposed a variant of this concept using a psychrometric diagram, with dry bulb temperature on the horizontal scale and absolute humidity on the vertical scale. A number of zones can be added to these graphs to indicate conditions that require different bioclimatic design resources. Watson (1980), Szokolay (1990) and other authors have proposed modifications based on the same concepts and graphic presentation. Givoni recommends the use of the maximum values as indicators of bioclimatic design strategies.

Fanger (ISO, 1998) established the comfort conditions for different insulation values of clothing and levels of physical activity. The four environmental variables used in this scale are the dry bulb temperature, the relative humidity, the mean radiant temperature and the relative air velocity.

The result is expressed as a comfort level on a 7-point scale, from -3, cold, to +3, hot, called the Predicted Mean Vote, PMV. This is shown to be related to the proportion of the population dissatisfied with the thermal conditions, PPD Proportion of the Population Dissatisfied.

Although Nicol and Humphreys (2001) have expressed strong criticisms of the Fanger scales, this index, incorporated in the international standard ISO-EN-1994, has found wide acceptance.

4.3.1. Requirements for comfort conditions.

Izard and Guyot (1980) present seven environmental conditions required for thermal comfort, based on a proposal by Millar-Chagas and Vogt (1970), incorporating studies by Fanger and Givoni.

• Thermal equilibrium of the body, maintaining a stable and constant deep body temperature. This condition is achieved when the PMV developed by Fanger (1998) is between -1/2 and + 1/2.

• An average skin temperature of 33° C, without high or low extremes, avoiding the sensation of hot or cold in the extremities.

• Maximum transpiration rates of 100 gms / hour, to avoid excessive water loss from the body.

• Absence of sensible transpiration, to avoid a sensation of wet skin or drops of sweat that cause discomfort.

• Conditions of thermal equilibrium and skin temperature maintained with normal metabolic activity, avoiding shivering or other involuntary movements or the need to change the level of physical activity.

• Air humidity sufficiently high to avoid irritation of the eyes, throat or lungs, with a water vapour pressure of at least 10 mm hg.

• Relative humidity below 80 % in order to prevent the possibility of surface condensation and possible mould growth on surfaces with a temperature slightly below air dry bulb temperature.

In addition to the seven basic conditions proposed by Izard and Guyot (1980), three additional requirements for comfort can be added in the framework of this thesis, which stresses variations in temperature:

• Avoid excessive temperature asymmetries of surface temperatures, or large differences between the mean radiant temperature and the air temperature.

• Control the maximum air velocity according to the type of activity to avoid excessive local cooling of the skin or discomfort due to the physical action of the wind, for example moving the hair.

• Avoiding sudden changes, especially in air temperature, Fanger (personal communication) recommends a maximum change rate of 1° C in one hour to avoid a sensation of discomfort. These rates of change are known as ‘ramps’.

It is important to consider that these conditions are not rigid limits and that they may require adjustments according to the activities, expectations, climatic conditions and cultural contexts.

4.3.2. Energy and Bioclimatic Zoning.

The differences between climatic variables and the conditions required for comfort in each month of the year can indicate the bioclimatic design resources appropriate for each location. The Mahoney Tables (Koenigsberger et al, 1970) present a detailled and quantitative methodological sequence to satisfy this objective.

In a further stage of analysis, this method, or similar approaches, can be applied to identify geographic zones where the same bioclimatic design resources can be applied.

Equally important is the possibility to detect change these design resources as climate conditions vary. In this way bioclimatic zones can be defined to show the geographical distribution of climate factors that affect building design, and relate these to relevant design guidelines. One example is the Argentine Standard for Bioclimatic zones IRAM 11603 (1970, 1999), which establishes 6 zones and 13 sub zones for the country. The standard ABN (2003) establishes zones for Brazil and the ChN Standards defines the zones for Chile. These bioclimatic zones are closely related to three factors that affect

climate and climate variation: latitude, height above sea level and distance from the sea or continentality. This last factor indicates the impact of the moderating thermal capacity of the sea, in comparison with the large landmass in the interior of the continents.

The Mahoney Tables characterise the general climatic impact in relation to comfort using the indicators of aridity and humidity. Evans (1999) suggested adding a third indicator of coldness.

These three indicators can be related to the three extreme corners of the psychrometric chart; cold, hot-humid and hot-dry. This approach is clearly related to the relationship with the comfort zone and the search for passive strategies to modify existing conditions and approach comfort.

Another approach arises from the increasing concern about the use of fossil fuels to achieve comfort with artificial conditioning systems. This preoccupation, starting in the decade of the 70’s, relates to the use of energy resources and the environmental impacts, especially those related to climate change. In this case the zoning is related to potential energy demand, indicated by the degree-days for each locality. The Argentine IRAM Standard (IRAM 11.603, 1999) incorporates the use of degree-days to define climatic zone limits. The need to search for a more sustainable habitat has its roots in the environmental, social and economic concern for achieving a built environment compatible with existing and future needs and resources.

In this context, the definition of bioclimatic zones was developed in order to identify appropriate design measures for natural conditioning that promote comfort and well being according to the climatic region. While the strong impacts of globalised influences, with architectural images and technological changes tend to encourage a built environments more dependant on energy, new approaches must be developed to contribute to a more sustainable development.

4.4. CONCLUSIONS

In this chapter, an outline of the study of thermal comfort is presented, with special reference to the application in the field of building design. Two different approaches to thermal comfort are identified; on the one hand the concepts based on detailed climate chamber studies, characterised by Fanger and the PMV method and the other based on subjective responses by building occupants, exemplified by the approach of Humphreys and Nichol. The application of thermal comfort to the study of regional architectural responses is introduced in this chapter in order to provide the background to the specific studies of bioclimatic zoning, presented in the next chapter.

CHAPTER 5. BIOCLIMATIC ZONING

5.1. INTRODUCTION

This chapter presents studies on bioclimatic zoning and examples developed in different regions of Latin America in order to detect the state of advance, the methods adopted and the levels of thermal moderation achieved. A selection of examples is included in this context, based on the following factors:

• A general lack of thermal standards and bioclimatic requirements for buildings, compared with Europe and North America, showing the need to improve this aspect of development of the man-made environment.

• The wide range of climates found in the region, extending from the equatorial region to colder high latitudes, allowing a wide range of bioclimatic requirements to be analysed. The range of altitudes and distance from the sea also widens the climatic variation, as commented in previous sections.

5.1.1. Approach to bioclimatic zoning.

Bioclimatic zoning allows geographical areas with similar climatic conditions to be identified, where architectural design with specific natural conditioning strategies can promote thermal comfort, reduce energy demand for heating and cooling, as well as reducing environmental impacts.

This panorama of the advances and implementation of bioclimatic zoning provides a critical analysis of the current state of development and application.

Changing approaches and zoning criteria are identified in different periods, according to the levels of implementation in the countries of the region. The first studies of zoning were developed to identify the design characteristics for the bioclimatic design of low cost housing, based on the techniques developed by Olgyay (1970). Studies undertaken by the Institute for Housing Research in Argentina (1965) also analysed the regional variations of vernacular housing and conventional construction methods in order to detect different responses to climate.

Various attempts to detect regional building design requirements were related with the vegetation and climatic zones such as Thornthwaite or Köppen Geiger (Kendrew, 1961) based on specific climatic variables or indicators.

However, the growth and distribution of certain types of vegetation depends to a large extent on the rainfall regime, a variation that is less important for bioclimatic building requirements, as this section will show.

Table 5.1. Criteria, indicators and meteorological data for bioclimatic zoning.

Criteria Indicator Meteorological data Criteria for summer

Comfort in summer.

Design day, typical summer day.

Temperature exceeded in ‘n’ days per year, with relative humidity values.

Use of thermal inertia

Average thermal swing in summer.

Maximum and minimum temperature in months with hot temperatures.

Minimize a / c Simulation of annual energy demand for refrigeration.

Hourly temperature, relative humidity and diffuse and global solar radiation data.

Solar protection

Air velocity in months with high temperatures and RH.

Direction and frequency of air movement in months with high temperatures and relative humidity.

Solar radiation, wind speed and hourly temperatures on days with clear skies.

Criteria for winter Minimize use of conventional energy resources.

Heating degree-days. Average monthly temperatures

(approximate) or hourly temperatures for each day of a typical design year or test reference year, TRY.

Minimum design temperature for a cold day in winter,

Use of solar gains in winter

Solar angles that provide favourable radiation.

Latitude for solar geometry and average hourly temperatures for each month.

Use of passive solar systems.

Favourable solar radiation in cold months.

Distribution of solar radiation intensity in each month.

Hourly temperatures on a design day for winter.

Other climatic criteria related to sustainability Control of soil

erosion.

Rainfall regime. Design values for maximum rainfall in 1 hour or 24 hours.

Use of rainwater. Demand according to climate and offer to rainfall.

Average and minimum expected monthly rainfall and monthly temperatures.

Indoors air quality.

Potential for natural conditioning.

Temperature, relative humidity and hourly solar radiation during a typical design year.

Natural lighting. Natural light levels. Latitude, days with cloudy sky in winter or detailed illuminance data.

Use of vegetation.

Rainfall regime related to temperature.

Average and minimum monthly rainfall according to average monthly

temperatures.

5.1.2. Zoning criteria.

The bioclimatic zoning has also been developed to establish the geographical distribution of thermal qualities of walls and roofs, necessary to achieve adequate levels of thermal comfort, efficiency in the use of energy resources and avoidance of condensation.

These requirements need specific criteria to establish maximum admissible thermal transmittance values, considering two fundamental data (IRAM, 1996):

• Number of annual degree days: indicator of the heating demand according to the duration and severity of periods below the indoor comfort level

• Minimum design temperature: used to establish thickness of insulation required to avoid internal surface condensation.

The development and distribution of the bioclimatic zones depend on the criteria adopted, related to the different climatic variables, as indicated in Table 5.1.

5.1.3. Zoning examples.

The climatic variations over the earths surface are a result of a series of factors: latitude, height above sea level, continentality or distance from the coast and barrier effects caused by mountain ranges, such as the Andes. In some countries, one factor may be dominant while in others different factors may be critical.

In the countries of Central America, for example, with limited extension in the North-South direction, the principal variations are due to height, with secondary effects due to the barrier effect on the central mountain range that produces climatic differences on the eastern and western coasts. In the Andes countries of Colombia, Ecuador and Peru, height above sea level is also the dominant factor in climatic variation. In Uruguay, the most critical climatic variations are those due to distance form the coast, with a significant increase in the daily thermal swing as distances increase. In Argentina, Brazil and Chile, with large extensions in the north-south direction, the variation due to latitude is more important, though differences of continentality, height and barrier effects are also evident. These three countries have the largest variations of latitude found in the world. The resulting bioclimatic zones are analysed in the following section.