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Abstract:： underground space, the strategic space resources of cities, creates space of leisure shopping, parking, civil air defense works for human. However, compared with ground buildings, the environment quality of underground space is a bottleneck to the development of underground construction. Now, mechanical ventilation and artificial lighting ，causing high expense of energy consumption , are widely employed to improve the air environment of underground buildings, which goes against the concept of sustainable development and ecological buildings.
Key words: underground space；natural ventilation and lighting；energy saving；regional design
First: The urgency of the development of underground space
With the speedup of urbanization and the tension of land supply, the full use of underground space is highly valued to enhance land utilization ratio, preserve farm land, expand infrastructure capacity, abate downtown density and to improve urban ecology. Nowadays, the development depth of underground space has reached around 30m, and it is estimated that the development of 1/3 underground space equals to the capacity of the whole city ground buildings. All in all, the full use of underground space possesses favorable environmental, social, and economical benefits.
Second: The problems of underground space environment
1, The insufficiency of underground ventilation and lighting. Because of the location of underground space, problems such as light dimness, kinds of disagreeable odor, a mass of harmful gases volatilized by building materials, metope mold caused by humidity often occur.
2, High-pitched noise and lack of vitality of underground environment. In underground space environment, same sounds can not be absorbed, thus echoes appear, especially the mingled noise of metro and crowds which make people feel disturbing. Meanwhile, because of the isolation with natural environment, the visual effect of underground landscape planning is comparatively not so satisfying that the rigid and grim feeling of underground environment even makes people feel unbearable.
Third: Analysis of energy consumption of underground buildings
The main energy consumption of underground buildings includes daylighting, air conditioning and motive power. According to the measurement of energy consumption, the maximal consumption lie in August of high cooling load and February of high heating load. The biggest share of annual consumption is lighting, occupying 45 percent .then air conditioning of 44 percent, elevator and other consumption occupying 11percent. It is thus clear that the consumption of lighting and air conditioning take up huge proportion in that of underground buildings. It is estimated that new wind energy occupies 25 to 38 percent of China's energy consumption of air conditioning, which could be higher in underground buildings. Thus, natural lighting and ventilation make a big difference in energy saving of underground buildings. In order to create a natural environment of energy saving and comfort, and to meet people's psychological and physiological demands, the following building types can be used in the design of underground space:
1 Effective design methods of natural daylighting.
1.1 Courtyard Style
Natural daylighting of courtyard style is appropriate for underground buildings of small scales. Under this style, various functions of underground buildings are arranged centering on the courtyard. Meanwhile, extensive glass windows are set up on the envelop enclosure adjacent to the courtyard to get scenery and sunshine. Dayligting method of courtyard style is widely adopted in small-scale buildings of culture and entertainment.
1.2 Windowed Style
Windowed style is suited to underground buildings of lesser depth with square or g greenbelt on the ground. In this building type, sunshine of could get to the room through skylights of high-efficiency daylighting. Skylights can be adopted underground buildings, especially public and industrial buildings such as the exhibition buildings and industrial premises, etc.
1.3 Style of Underground Atrium
Underground atrium is an effective approach to improve the environment of underground works of great depth. The top of atrium can be composed of various space net racks and daylighting glass. Plants can also be cultivated in atrium to decorate the landscape to form rich inner space. Thus, underground buildings of multilayer usually obtain natural light and landscape effect through the share of atrium.
1.4 Style of Submerged Plaza
For extensive space in cities, part of ground usually sink to certain height to make the change of space pattern and form compound space of multi level。At the same time, it can also provide mass of natural light for underground building around the square.
2. Natural Ventilation
The reality that underground space is relatively airtight leads to people's pessimistic view on the quality of air environment of underground construction. Thus, it is indispensable to enhance natural ventilation in order to create a spacious environment of better air cleanliness, proper temperature and current speed. Natural ventilation is closely related with construction design. Plane layout, the installation of ventilation shaft and the selection of cowl all affect the effectiveness of natural ventilation, and these elements also play a significant role in improving the indoor air quality and saving energy.
2.1Plane Layout
Plane layout has a close relation with the wind path organization of the natural ventilation, and the design of plane layout will have a direct impact on the efficiency of natural ventilation. The key point for the design of wind channel is to lead the fresh air into the underground construction in order to discharge the air after making an exchange with the indoor air, which requires the architects to try their best to keep the wind channel unblocked to reduce blind angle so as to avoid air short-circuit when arranging the plane of underground construction.
2.2 Setup of Ventilation Shaft
The atrium of the underground construction can generate greenhouse effect after shined by the sun and generate high pressure to discharge air. Therefore, the atrium can be served as ventilation shaft. The inlet ventilation shaft should surround the atrium which is served as exhaust air passage according to the wind path organization of natural ventilation, and the part of inlet ventilation shaft tuyere should consider the effect of ground surroundings as to avoid the places polluted by air and install air cleaning devices(for example, installing a cooling device in the interior of the tuyere to help the air sink will contribute to letting the air in), besides, the tuyere should take full advantage of air pressure to instill inlet hood or outlet hood according to the request.
3.To Create Comfortable Transitional Spac
The entrance of underground space is the transitional space between the ground space and underground space，its design will have a direct impact on people's psychological feelings. Nowadays, it is common to use stairs, escalators or transparent glass as the canopy at the entrance，so natural light can penetrate through the canopy into the channel. Thus, this eliminates the discomfort when people go into the underground from the surface, and at the same time, creates a comfortable and pleasant environment.
4. To Select Proper Illumination and Light Source
Our country has promulgated Standards for Architectural Lighting Design and Standards for Architectural Illumination Design, which requires that different lighting requests are respectively practiced according to different constructions and room and places of different purposes. The degrees of illumination design of residential buildings, public buildings, industrial buildings and public areas all have a standard degree, their designs should be implemented strictly by standards.
5、To Build Comfortable Acoustic Environment.
Underground space has a better ability in the isolation with ground noise and is hardly affected by the ground noise. The inner noise mainly comes from some machinery device, such as sewerage pump, drainage pump, supply-water pump, air conditioner, etc.。 So we must take the noise produced by these equipments into consideration and take effective measures to reduce the noise.
6、To Bring in Exquisite Landscaping
To bring landscaping into underground space can increase the ground sense and is helpful for the natural transition from underground space to ground or outside space. Meanwhile, it promotes spatial limit and separation, reduces people's psychological badness reaction, improves the environment of underground space and satisfies people's psychological need of returning to nature.
四 Summary
The application of underground construction is widely used, especially in countries with exhausted energy such as China. Emphasis on energy problems require architects to take energy-efficient design as an important part in design stage , to optimize the design plans and apply new techniques, new materials, new arts and new equipments. Meanwhile, authorities concerned should make powerful polices to increase the restraint of energy saving and emissions reduction, to reduce building consumption farthest while ensure the environmental comfort .
Key words: underground space；natural ventilation and lighting；energy saving；regional design
First: The urgency of the development of underground space
With the speedup of urbanization and the tension of land supply, the full use of underground space is highly valued to enhance land utilization ratio, preserve farm land, expand infrastructure capacity, abate downtown density and to improve urban ecology. Nowadays, the development depth of underground space has reached around 30m, and it is estimated that the development of 1/3 underground space equals to the capacity of the whole city ground buildings. All in all, the full use of underground space possesses favorable environmental, social, and economical benefits.
Second: The problems of underground space environment
1, The insufficiency of underground ventilation and lighting. Because of the location of underground space, problems such as light dimness, kinds of disagreeable odor, a mass of harmful gases volatilized by building materials, metope mold caused by humidity often occur.
2, High-pitched noise and lack of vitality of underground environment. In underground space environment, same sounds can not be absorbed, thus echoes appear, especially the mingled noise of metro and crowds which make people feel disturbing. Meanwhile, because of the isolation with natural environment, the visual effect of underground landscape planning is comparatively not so satisfying that the rigid and grim feeling of underground environment even makes people feel unbearable.
Third: Analysis of energy consumption of underground buildings
The main energy consumption of underground buildings includes daylighting, air conditioning and motive power. According to the measurement of energy consumption, the maximal consumption lie in August of high cooling load and February of high heating load. The biggest share of annual consumption is lighting, occupying 45 percent .then air conditioning of 44 percent, elevator and other consumption occupying 11percent. It is thus clear that the consumption of lighting and air conditioning take up huge proportion in that of underground buildings. It is estimated that new wind energy occupies 25 to 38 percent of China's energy consumption of air conditioning, which could be higher in underground buildings. Thus, natural lighting and ventilation make a big difference in energy saving of underground buildings. In order to create a natural environment of energy saving and comfort, and to meet people's psychological and physiological demands, the following building types can be used in the design of underground space:
1 Effective design methods of natural daylighting.
1.1 Courtyard Style
Natural daylighting of courtyard style is appropriate for underground buildings of small scales. Under this style, various functions of underground buildings are arranged centering on the courtyard. Meanwhile, extensive glass windows are set up on the envelop enclosure adjacent to the courtyard to get scenery and sunshine. Dayligting method of courtyard style is widely adopted in small-scale buildings of culture and entertainment.
1.2 Windowed Style
Windowed style is suited to underground buildings of lesser depth with square or g greenbelt on the ground. In this building type, sunshine of could get to the room through skylights of high-efficiency daylighting. Skylights can be adopted underground buildings, especially public and industrial buildings such as the exhibition buildings and industrial premises, etc.
1.3 Style of Underground Atrium
Underground atrium is an effective approach to improve the environment of underground works of great depth. The top of atrium can be composed of various space net racks and daylighting glass. Plants can also be cultivated in atrium to decorate the landscape to form rich inner space. Thus, underground buildings of multilayer usually obtain natural light and landscape effect through the share of atrium.
1.4 Style of Submerged Plaza
For extensive space in cities, part of ground usually sink to certain height to make the change of space pattern and form compound space of multi level。At the same time, it can also provide mass of natural light for underground building around the square.
2. Natural Ventilation
The reality that underground space is relatively airtight leads to people's pessimistic view on the quality of air environment of underground construction. Thus, it is indispensable to enhance natural ventilation in order to create a spacious environment of better air cleanliness, proper temperature and current speed. Natural ventilation is closely related with construction design. Plane layout, the installation of ventilation shaft and the selection of cowl all affect the effectiveness of natural ventilation, and these elements also play a significant role in improving the indoor air quality and saving energy.
2.1Plane Layout
Plane layout has a close relation with the wind path organization of the natural ventilation, and the design of plane layout will have a direct impact on the efficiency of natural ventilation. The key point for the design of wind channel is to lead the fresh air into the underground construction in order to discharge the air after making an exchange with the indoor air, which requires the architects to try their best to keep the wind channel unblocked to reduce blind angle so as to avoid air short-circuit when arranging the plane of underground construction.
2.2 Setup of Ventilation Shaft
The atrium of the underground construction can generate greenhouse effect after shined by the sun and generate high pressure to discharge air. Therefore, the atrium can be served as ventilation shaft. The inlet ventilation shaft should surround the atrium which is served as exhaust air passage according to the wind path organization of natural ventilation, and the part of inlet ventilation shaft tuyere should consider the effect of ground surroundings as to avoid the places polluted by air and install air cleaning devices(for example, installing a cooling device in the interior of the tuyere to help the air sink will contribute to letting the air in), besides, the tuyere should take full advantage of air pressure to instill inlet hood or outlet hood according to the request.
3.To Create Comfortable Transitional Spac
The entrance of underground space is the transitional space between the ground space and underground space，its design will have a direct impact on people's psychological feelings. Nowadays, it is common to use stairs, escalators or transparent glass as the canopy at the entrance，so natural light can penetrate through the canopy into the channel. Thus, this eliminates the discomfort when people go into the underground from the surface, and at the same time, creates a comfortable and pleasant environment.
4. To Select Proper Illumination and Light Source
Our country has promulgated Standards for Architectural Lighting Design and Standards for Architectural Illumination Design, which requires that different lighting requests are respectively practiced according to different constructions and room and places of different purposes. The degrees of illumination design of residential buildings, public buildings, industrial buildings and public areas all have a standard degree, their designs should be implemented strictly by standards.
5、To Build Comfortable Acoustic Environment.
Underground space has a better ability in the isolation with ground noise and is hardly affected by the ground noise. The inner noise mainly comes from some machinery device, such as sewerage pump, drainage pump, supply-water pump, air conditioner, etc.。 So we must take the noise produced by these equipments into consideration and take effective measures to reduce the noise.
6、To Bring in Exquisite Landscaping
To bring landscaping into underground space can increase the ground sense and is helpful for the natural transition from underground space to ground or outside space. Meanwhile, it promotes spatial limit and separation, reduces people's psychological badness reaction, improves the environment of underground space and satisfies people's psychological need of returning to nature.
四 Summary
The application of underground construction is widely used, especially in countries with exhausted energy such as China. Emphasis on energy problems require architects to take energy-efficient design as an important part in design stage , to optimize the design plans and apply new techniques, new materials, new arts and new equipments. Meanwhile, authorities concerned should make powerful polices to increase the restraint of energy saving and emissions reduction, to reduce building consumption farthest while ensure the environmental comfort .