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Summer confort solutions in Mediterranean areas
WREC 1996
SUMMER CONFORT SOLUTIONS IN MEDITERRANEAN AREAS
Helena COCH and Rafael SERRA School of Architecture of Barcelona, U.P.C. Av. Diagonal n ° 649, 08028 Barcelona, Tel. 34 3 401 64 21, Fax. 34 3 401 64 26
ABSTRACT The climate of Mediterranean countries is characterized by its complexity. Rapidly changing conditions mean that both cold and heat can be a problem. In architectural practice the design solutions that must be applied in buildings are complex. Solutions for summer comfort in Mediterranean areas also reflect this complexity. The causes of summer discomfort will be described and some examples of solutions against these will be showed and analized.
KEYWORDS Comfort. Summer comfort. Cooling.
INTRODUCTION Regions with a complex climate, such as the Mediterranean countries and other areas of the world with similar climates, are characterized by the diversity of situations that occur through the year. These variable climatic situations require the local architecture to display great flexibility in order to cope with periods of both excessive cold and oppressive heat. Moreover, such climates have the peculiarity that changes can happen rapidly at any time of year, requiring a correspondingly rapid response from the architecture. Although for the sake of simplicity we shall limit ourselves here to the case of excessive heat, the alternation of conditions makes for a specially complex situation. In a short period conditions can go from dry heat to humid heat, from wind to calm, or from drought to downpours. Consequently, the solutions architecture provides to overcome climatic difficulties are similarly complex, often resorting to the use of radically different solutions depending on the type of climatic situation occurring at each moment. The more conventional approaches, in many cases developed from air conditioning technology, base their analysis of the climatic behaviour of buildings on the interior and exterior air temperatures, and propose environmental solutions based on this. in fact, this is an oversimplification and leads to frequent errors in the design of both the building itself and its mechanical installations. 128
WREC 1996 THE PROBLEM OF HEAT EXCESS In Mediterranean climates, and probably also in other hot climates, the problem of heat excess in architecture is a function of solar radiation, humidity and air temperature, in that order. Intense solar radiation for long periods does not only contribute indirectly to heating the air but, more importantly, also heats the built masses of the building, which in these areas tends to consist of heavy masonry. As a result it is common to find worse environmental conditions indoors than outdoors. The resulting comfort temperature is very high due to the internal radiation imean radiant temperature), even if the air temperature is not particularly high. It is cases such as these that demonstrate the truth of the unfortunate paradox that some buildings "work worse than the climate". A similar phenomenon occurs with the humidity of the air. Frequently, although not always nor in all regions, conditions along Mediterranean coasts are characterized by high humidity combined with relatively high temperatures. It is widely known that thermal comfort zones get narrower as humidity increases, to the extent that at times one can go from feeling cold to feeling hot w i t h o u t any possible intermediate feeling of balance. This fact, which we consider to be underestimated in conventional comfort studies, is in fact an important factor for comfort in buildings in such climates. Here too it is true to say that the outside climate is often more comfortable than the interior of the building, where in many cases there are elements that release humidity. Finally, the temperature of the air is also important, in conjunction with the above parameters. In conditions of dry heat, daytime temperatures can exceed 35 or even 40 degrees Celsius. In such conditions, the exterior becomes uninhabitable and interiors are cool refuges in which inertia enables the temperature of the air to be controlled, although when night falls that same air becomes unbreathable.
129
WREC 1996
STRATEGIES AGAINST HEAT Using the above to analyse the most suitable strategies, the architecture should: 1)
Control the entry of solar radiation, with the following measures: 1.1)
Totally blocking the entry of direct sunlight through openings, particularly on the east and west elevations and through the roof.
1.2)
Controlling and optimizing the entry of diffuse radiation through openings on any elevation, not only directly from the sky but also from sunlight reflected off exterior surfaces. It must be remembered that light is heat, and that therefore any excess of light indoors will be detrimental.
1.3)
Avoiding the entry of reemitted long-wave radiation, both that originating from exterior surfaces heated by the sun and entering the building through its openings and also that produced by the energy stored in the walls of the building. Both kinds can be noticeable at night, long after the sun has set.
These three strategies against radiation should be used together; 1.2) or 1.3) are of little use if the others are not implemented.
2)
Control the humidity of the air in the interior, by: 2.1)
Efficient, controllable ventilation to expel excess humidity in conditions of humid heat.
2.2)
Ventilation in combination with humidification of the air (evaporative cooling) in conditions of dry heat.
These two strategies are conceptually contradictory; again, it is essential, therefore, to find flexible solutions in those cases in which both climatic phenomena are likely to occur. 2.3)
3)
Controlled ventilation using previously cooled air, by means of conduits installed underground and/or conveying air from cooler exterior zones.
Regulate the temperature of the air in the interior, using: 3.1)
High inertia in the interior and the outside walls, in climatic conditions with acute temperature fluctuations, usually associated with dry heat.
3.2)
Reduced ventilation during the hottest part of the day; particularly important in the same cases as the point above.
3.3)
Insulation between interior and exterior in the outside walls, thus avoiding the transmission of heat from air to air during the hottest periods.
This group, particularly the last strategy mentioned, is of secondary importance in comparison with the two previous groups, and it is meaningless to apply them without first having dealt with radiation in all cases and humidity in most of them. 130
WREC 1996 ARCHITECTURAL SOLUTIONS The above strategies can take the shape of very different architectural solutions according to local circumstances as regards climate, sociology, the available construction technology, cultural tradition, etc.. We therefore do not intend to make an exhaustive list of them, but the following is a selection of those which best illustrate the wisdom that can be attained within popular architecture. A)
Protection from the sun by means of external barriers (vegetation, overhangs, jalousies, lattices)
B)
Protection from the sun by means of blinds (Mediterranean blind)
C)
Protection from the sun by means of white finishes on outside walls (cold selective surfaces)
D)
Protection from the sun by means of ventilated air chambers (double roofs)
E)
Cross-ventilation with continuous openings
F)
Generated ventilation with chimneys, solar chambers or wind conduits
G)
Treated ventilation with wet surfaces
H)
Ventilation with underground conduits
I)
Partial sinking of the building underground
J)
Opaque, mobile surfaces to block openings
K)
Insulation in the outside walls
131
WREC 1996 All the above systems can be combined, and sometimes need to be to function efficiently. This is the case with cross-ventilation, which must be employed in conjunction with blinds or jalousies over the openings to prevent sunlight from entering. It is also true of treated ventilation with wet surfaces or underground conduits, which requires air in motion, generated by some other system of ventilation. As well as these specific systems, there are some particularly interesting multipurpose solutions which are able to cover a number of strategies through a single system. "Intermediate spaces" fall into this category.
CONCLUSIONS By way of conclusion to all the above, we consider that the architecture of areas with a Mediterranean climate will always reflect the difficulties created by the complexity of this type of climate. However, we also believe that this architecture has sufficient resources at its disposal to provide satisfactory solutions for the environmental functioning of buildings without the need to use costly (as regards energy and the environment) artificial solutions for environmental control.
132
SUMMER CONFORT SOLUTIONS IN MEDITERRANEAN AREAS
Helena COCH and Rafael SERRA School of Architecture of Barcelona, U.P.C. Av. Diagonal n ° 649, 08028 Barcelona, Tel. 34 3 401 64 21, Fax. 34 3 401 64 26
ABSTRACT The climate of Mediterranean countries is characterized by its complexity. Rapidly changing conditions mean that both cold and heat can be a problem. In architectural practice the design solutions that must be applied in buildings are complex. Solutions for summer comfort in Mediterranean areas also reflect this complexity. The causes of summer discomfort will be described and some examples of solutions against these will be showed and analized.
KEYWORDS Comfort. Summer comfort. Cooling.
INTRODUCTION Regions with a complex climate, such as the Mediterranean countries and other areas of the world with similar climates, are characterized by the diversity of situations that occur through the year. These variable climatic situations require the local architecture to display great flexibility in order to cope with periods of both excessive cold and oppressive heat. Moreover, such climates have the peculiarity that changes can happen rapidly at any time of year, requiring a correspondingly rapid response from the architecture. Although for the sake of simplicity we shall limit ourselves here to the case of excessive heat, the alternation of conditions makes for a specially complex situation. In a short period conditions can go from dry heat to humid heat, from wind to calm, or from drought to downpours. Consequently, the solutions architecture provides to overcome climatic difficulties are similarly complex, often resorting to the use of radically different solutions depending on the type of climatic situation occurring at each moment. The more conventional approaches, in many cases developed from air conditioning technology, base their analysis of the climatic behaviour of buildings on the interior and exterior air temperatures, and propose environmental solutions based on this. in fact, this is an oversimplification and leads to frequent errors in the design of both the building itself and its mechanical installations. 128
WREC 1996 THE PROBLEM OF HEAT EXCESS In Mediterranean climates, and probably also in other hot climates, the problem of heat excess in architecture is a function of solar radiation, humidity and air temperature, in that order. Intense solar radiation for long periods does not only contribute indirectly to heating the air but, more importantly, also heats the built masses of the building, which in these areas tends to consist of heavy masonry. As a result it is common to find worse environmental conditions indoors than outdoors. The resulting comfort temperature is very high due to the internal radiation imean radiant temperature), even if the air temperature is not particularly high. It is cases such as these that demonstrate the truth of the unfortunate paradox that some buildings "work worse than the climate". A similar phenomenon occurs with the humidity of the air. Frequently, although not always nor in all regions, conditions along Mediterranean coasts are characterized by high humidity combined with relatively high temperatures. It is widely known that thermal comfort zones get narrower as humidity increases, to the extent that at times one can go from feeling cold to feeling hot w i t h o u t any possible intermediate feeling of balance. This fact, which we consider to be underestimated in conventional comfort studies, is in fact an important factor for comfort in buildings in such climates. Here too it is true to say that the outside climate is often more comfortable than the interior of the building, where in many cases there are elements that release humidity. Finally, the temperature of the air is also important, in conjunction with the above parameters. In conditions of dry heat, daytime temperatures can exceed 35 or even 40 degrees Celsius. In such conditions, the exterior becomes uninhabitable and interiors are cool refuges in which inertia enables the temperature of the air to be controlled, although when night falls that same air becomes unbreathable.
129
WREC 1996
STRATEGIES AGAINST HEAT Using the above to analyse the most suitable strategies, the architecture should: 1)
Control the entry of solar radiation, with the following measures: 1.1)
Totally blocking the entry of direct sunlight through openings, particularly on the east and west elevations and through the roof.
1.2)
Controlling and optimizing the entry of diffuse radiation through openings on any elevation, not only directly from the sky but also from sunlight reflected off exterior surfaces. It must be remembered that light is heat, and that therefore any excess of light indoors will be detrimental.
1.3)
Avoiding the entry of reemitted long-wave radiation, both that originating from exterior surfaces heated by the sun and entering the building through its openings and also that produced by the energy stored in the walls of the building. Both kinds can be noticeable at night, long after the sun has set.
These three strategies against radiation should be used together; 1.2) or 1.3) are of little use if the others are not implemented.
2)
Control the humidity of the air in the interior, by: 2.1)
Efficient, controllable ventilation to expel excess humidity in conditions of humid heat.
2.2)
Ventilation in combination with humidification of the air (evaporative cooling) in conditions of dry heat.
These two strategies are conceptually contradictory; again, it is essential, therefore, to find flexible solutions in those cases in which both climatic phenomena are likely to occur. 2.3)
3)
Controlled ventilation using previously cooled air, by means of conduits installed underground and/or conveying air from cooler exterior zones.
Regulate the temperature of the air in the interior, using: 3.1)
High inertia in the interior and the outside walls, in climatic conditions with acute temperature fluctuations, usually associated with dry heat.
3.2)
Reduced ventilation during the hottest part of the day; particularly important in the same cases as the point above.
3.3)
Insulation between interior and exterior in the outside walls, thus avoiding the transmission of heat from air to air during the hottest periods.
This group, particularly the last strategy mentioned, is of secondary importance in comparison with the two previous groups, and it is meaningless to apply them without first having dealt with radiation in all cases and humidity in most of them. 130
WREC 1996 ARCHITECTURAL SOLUTIONS The above strategies can take the shape of very different architectural solutions according to local circumstances as regards climate, sociology, the available construction technology, cultural tradition, etc.. We therefore do not intend to make an exhaustive list of them, but the following is a selection of those which best illustrate the wisdom that can be attained within popular architecture. A)
Protection from the sun by means of external barriers (vegetation, overhangs, jalousies, lattices)
B)
Protection from the sun by means of blinds (Mediterranean blind)
C)
Protection from the sun by means of white finishes on outside walls (cold selective surfaces)
D)
Protection from the sun by means of ventilated air chambers (double roofs)
E)
Cross-ventilation with continuous openings
F)
Generated ventilation with chimneys, solar chambers or wind conduits
G)
Treated ventilation with wet surfaces
H)
Ventilation with underground conduits
I)
Partial sinking of the building underground
J)
Opaque, mobile surfaces to block openings
K)
Insulation in the outside walls
131
WREC 1996 All the above systems can be combined, and sometimes need to be to function efficiently. This is the case with cross-ventilation, which must be employed in conjunction with blinds or jalousies over the openings to prevent sunlight from entering. It is also true of treated ventilation with wet surfaces or underground conduits, which requires air in motion, generated by some other system of ventilation. As well as these specific systems, there are some particularly interesting multipurpose solutions which are able to cover a number of strategies through a single system. "Intermediate spaces" fall into this category.
CONCLUSIONS By way of conclusion to all the above, we consider that the architecture of areas with a Mediterranean climate will always reflect the difficulties created by the complexity of this type of climate. However, we also believe that this architecture has sufficient resources at its disposal to provide satisfactory solutions for the environmental functioning of buildings without the need to use costly (as regards energy and the environment) artificial solutions for environmental control.
132