Overview of air conditioning design for large space buildings?

This paper outlines the load characteristics, air conditioning air volume and air change number, air conditioning method and airflow organization and related issues in the design of air conditioning systems for large space buildings, and elaborates on the cooling and heating sources of air conditioning and energy saving issues.

Keywords: large space, load characteristics, airflow organization, air-conditioning mode, energy saving

Preface:

Since the 20th century, along with the needs of human survival and development, countries competing for the construction of large-scale public **** building movie theaters, theaters, gymnasiums, exhibition halls, airports and terminals, high-rise buildings, such as atriums, etc., the construction of the building within the building is increasingly attracting interest and concern. and attention. In order to give full play to the functions of these buildings and create a quality environment, HVAC technology must also continue to progress. Traditional large-space buildings have fewer structural and functional changes and have accumulated a wealth of experience in engineering. Modern large-space buildings with strange shapes and large dimensions, relying on traditional experience is difficult to meet the requirements in all aspects, and it is necessary to use computer simulation to make design predictions. The following is a brief overview of the air conditioning design of large space buildings.

I. Characteristics of large space buildings

(1) The height of large space is high. This is the main reason for the formation of temperature gradients.

(2) Large spaces have a large ratio of exterior wall area to floor area (Figure 1). This creates an external interface that has a strong influence on the natural convection of the interior space and tends to create a downward airflow around it in winter.

(3) The volume of space occupied per capita in the residence area is large (Figure 1). It is good from a hygienic point of view and a smaller number of air changes can be used.

(4) Multi-functional use requirements. Requirements for air conditioning to meet the multi-environment, flexible control

Two, load characteristics

Various large-space buildings do not have the same proportion of compliance factors. Figure 2 represents the differences between them.

Three, air-conditioning air volume and the number of air changes

Air-conditioning air volume can be determined according to the following factors: 1. hot and cold load handling requirements; 2. indoor cleanliness maintenance; 3. the number of air changes to ensure that the 4. to meet the requirements of the regulations. 1, 2, 3 can be determined by conventional calculations, but 3 sometimes lack of experience in practice as a basis. For conventional movie theaters and halls, the per capita volume is relatively consistent. Through the indoor load calculation and air supply temperature difference from the per capita air volume is similar, the corresponding number of air changes are generally between 4 to 6 times /, but for the complexity of the body type, space size irregularities, the residence of the high density of the occasion, these indicators are not necessarily applicable. For example, in the case of sports buildings, the maximum number of air changes is 4.5 times /, the minimum is 1.2 times /. This is due to: 1. such buildings are huge, the number of people in the arena is small; 2. the design of the load handling and calculation of different considerations, and thus there is a calculation to determine the number of air changes have a greater difference. But as long as you take effective airflow organization, even if the number of air changes is small, can also meet the requirements of air conditioning.

Four, air-conditioning, airflow organization and related issues

1. Air-conditioning and airflow organization on the indoor environment and the impact of the load.

Air conditioning using different forms of air conditioning or airflow organization has a great impact on the distribution of indoor temperature in the vertical direction (as shown in Figure 3). In addition, the method of air-conditioning supply and return air also has a great influence on the load rate (as shown in Fig. 4, a study by Hiroyuki Miyagawa), so the airflow organization and load calculation are interrelated in the design.

2. Application of air-conditioning and induced ventilation in the residence area (work area).

For the general air conditioning and airflow organization of the cinema, venue, etc., due to the limited height, generally use a comprehensive air conditioning method, supplemented by a more conventional form of airflow organization. However, the indoor temperature stratification phenomenon of high space is very serious. Practice has shown that different layered air conditioning can be used in different occasions to achieve. The basic principles of air conditioning for the residence area (work area) are: (1) when supplying cold, the cold air is only sent to the work area. In addition to the use of outdoor air or return air to separate the formation of the upper part of the non-air-conditioned rooms, or to meet the needs of fire smoke exhaust. (2) in the heating, air temperature difference should be small, and should be sent to the work area. When possible, combined with radiant heating. After taking these measures, the air-conditioning load can be reduced by 30% to 40%. The use of induction (induction sealing of the induction ratio and 4 ~ 5 times), so that the upper and lower temperature distribution can be uniform. For large space air conditioning, the most important thing is the control of airflow.

3. The overall choice of air supply method for large space.

Different nature of the public **** building and people stay, the overall consideration of the air supply method has the following principles: stay for a long time and high comfort requirements of the occasion, such as theater auditoriums, religious churches, classrooms, etc., regardless of the size of the appropriate use of the roof vents; stay for a long time but not too high comfort requirements of the occasion, such as gymnasiums, indoor baseball stadiums, large workshops, suitable for the use of the roof vents and horizontal vents. Ceiling vents and horizontal vents; for short stays in the occasion, such as the airport hall, foyer, etc., it is not suitable for the use of ceiling diffuser and upward air supply.

4. Specific measures for each type of building.

(1) theaters, concert halls, venues 1. In general, are used in low-speed ducts all-air approach. In order to regulate the load, there is also the use of variable air volume regulation. From the point of view of indoor air distribution, there are dilution type and replacement type. The traditional up-flow down-flow method is a dilution type, and the uniform down-flow up-flow method is a replacement type. Load intensity is recommended to use the replacement method. 2. Airflow organization: up to send back, the side of the send back, the rear nozzle air supply, down to send back. The above occurs with the use of, generally several ways of integrated application. 3. With a reasonable system partition to ensure the uniformity of the temperature distribution in the field. General audience hall according to the plane and vertical direction can be divided into 3 ~ 5 zones. According to the characteristics of the hall there is a temperature gradient, the use of multiple AHU or in the system branch with a temperature control device to control the air supply unit.4. Reasonable design of the stage air conditioning system. Can be installed on both sides of the stage under the catwalk air supply pipe, down to the side stage to send air. Can be set up under the bridge in front of the air duct, down to the wind, directly to the performance area, or the use of spherical rotary air outlet from both sides of the stage to the center of the wind. Can also be set up along the curtain between the flat high type duct downward air supply. In addition, the stage must set up an independent air supply and return system in order to regulate the pressure.

(2) sports competition tube and multi-functional hall 1. Meet the residence area air-conditioning: can be used to cover the audience side of the jet, equivalent to the local air conditioning seat air-conditioning in large stadiums are also used in the application. From the energy-saving point of view, for the super-large competition venues, not necessarily set up air-conditioning system in the stadium. For the strict requirements of the competition venue, you can use the bleachers around the stadium to the field of air supply. 2. airflow organization practices: change the direction of air supply to meet the required jet trajectory, to adapt to the different requirements of winter and summer. Change the number and location of air supply outlets to control the corresponding air-conditioned areas. 3. Utilize sensible airflow. From the energy saving and thermal comfort of the two contradictory unity, large stadiums can be used to strengthen the field airflow velocity to meet the requirements of comfort, when the summer can be appropriate to increase the indoor temperature. 3. High-speed jet system. To prevent the formation of severe temperature gradients in large spaces. Caused by hot air in the upper part of the stagnation, in recent years, multi-functional halls, gymnasiums using systematic or monolithic induced nozzle is particularly widespread.

(3) atrium 1. Closed atrium: temperature fluctuations in the atrium is small, generally can be in the comfort temperature zone, that is, in the zero energy consumption zone. Can only consider exhaust ventilation (summer) and radiant floor heating (winter), not necessarily set up the air conditioning system. Can also be set in the lower part of the atrium according to the actual load of air conditioning air supply system, with horizontal air supply to isolate the upper and lower air conditioning. 2. open atrium: usually in the lower part of the air conditioning air supply direct control, but also in the center of the activities directly set up with the coordination of air conditioning and building air supply devices and in the interface of the atrium in each layer of the air supply. Because of the atrium of the body type is different, the location and climate is different, the function is also different, in the design, should be carried out in advance model experiments and computer simulation calculations.

On the membrane structure of sports buildings, swimming competition hall, artificial ice rinks, airport passenger hall air conditioning due to its specificity, there is a special literature, here due to space limitations will not be elaborated.

Fifth, the air conditioning of large space building heat and cold source

Conventional heat and cold source, electric or thermal (such as gas) compression chiller (or heat pump), absorption chiller, direct-fired chiller and water heater units can be used for large space buildings. From the point of view of cooling and heating should be considered: when the region has a sufficient scale of regional cooling and heating facilities, can be utilized to provide cold and heat; in the basic way of cooling and heating should be used as much as possible on the heat pump and cold storage and heat storage technology; in some occasions, the gas engine heat pumps is also a very reasonable way of energy. In addition to energy composite - composite energy application is also worth noting the tendency. The use of two energy sources, such as electricity and gas (or oil), to a certain extent, not only can realize the city energy supply in the electricity and gas peaks and valleys between the balance, and in the energy price can choose the occasion, the operating costs can have a moderating effect.

Six, large space building energy efficiency

80s large space building in the energy-saving issues as long as the focus on energy saving and comfort aspects of concern. After entering the 90s, in addition to the above considerations, more attention to air-conditioned buildings on the earth's environment. Natural energy (sun, wind, rain, earth, etc.) should be fully utilized in order to maximize energy and resource savings and to reduce the load on the environment.

The traditional and proven means of utilizing energy are still applicable to large space buildings. In air-conditioning to reduce the design load (building design to match), the use of residence area air-conditioning, reasonable determination of the amount of air supply and fresh air, reduce the energy consumption of air and water delivery, the use of fresh air cooling, a reasonable combination of energy, the selection of high-efficiency refrigeration equipment and air terminal devices, cold storage and the use of low-level heat source, etc., are all important energy-saving measures. In the case of conditions, the following methods can be used:

(1) the building is covered with soil buried type will be made into a sunken gymnasium, that is, semi-underground, surrounded by a layer of soil, sound insulation, heat preservation, and improve the stability of the building is very favorable.

(2) the use of natural ventilation for no environmental noise interference in large space buildings, maximize the use of natural ventilation to improve the indoor environment and save energy consumption is the most reasonable. Nowadays, the roof can be opened and closed large-scale gymnasium completely realized this requirement.

(3) the use of soil heat stadium covers a large area, the use of its underground soil as heat storage material heat storage is very favorable. For example, in the hall buried under the ground coil, the use of cheap electricity at night by the cooling (hot) water, the coil will be the heat stored in the soil, during the day to take out for air-conditioning, and at the same time due to the underground heat storage, so that the floor of the role of radiation for cooling (hot). In addition, in order to reduce the new air load, the new air flow through a special piping trench for pre-cooling or preheating, indirectly using the heat of the soil (soil and air heat exchange).

VII, other issues

(1) system division

System division principles:

1. Large space building air volume is huge, from the plane, should be based on the orientation, area, zoning organization of air-conditioning systems, generally large and medium-sized gymnasiums are made of zoning.

2. On the basis of the above, according to the requirements of the upper and lower temperature uniformity, the possibility of multi-functional use, the difference in working hours to be divided into systems.

3. According to the specific situation can also be subdivided into systems, so that there is no large air ducts, but the water system is more complex.

(2) air handling issues

1. foreign air handling box from the 1970s are used in the surface heat exchanger, generally set up reheaters and humidifiers.

2. Air filtration should be emphasized.

3. The new air and exhaust air between the full heat exchanger to recover energy: this is an important measure to reduce the load on the cooling and heating devices, both to reduce the capacity of the device, saving initial investment, can reduce operating costs.

4. Directly according to the number of people to control the amount of fresh air into the system

5. For hot and dry areas, according to the analysis of meteorological conditions, some of the large space building can be used by direct evaporation or indirect evaporative cooler of the fresh air air air treatment system.

(3) fresh air pre-treatment

1. Fresh air cooled with deep well water and then mixed with the return air, there is a very good economy, and air treatment of well water used as refrigerator condenser cooling water, you can improve the working conditions of the refrigerator, when the application of well water is limited, it is not feasible.

2. According to the theater latent heat load, new air ratio, air conditioning and refrigeration dehumidification load, some areas of the United States use the new air pre-desiccant treatment, and then mix the return air and then air cooling treatment.

Conclusion:

With the progress of society, the people's pursuit of quality of life, in addition to the material life, the spirit, culture, sports, interest has become increasingly demanding, for which people look forward to more functional and reasonable quality of the environment of a comfortable public **** the construction of the activity space. The environmental facilities of these spaces also require new creations in terms of health, comfort, efficient use of energy and environmental protection of the earth. At the same time as the function of large space building countries are developing towards functional integration, in order to make full use of social resources, but also conducive to the operation of this type of building, that is, in the economy to support. Therefore, how the HVAC equipment to adapt to this need (for multi-functional flexible operation) is also a modern large space building design, operation and management are worth emphasizing the issue.

References

1. Fan Cunyan. Large space building air-conditioning design and engineering fact sheet. China Building Industry Press 2001.09.

2. East China Architectural Design Institute. High-rise public **** building design examples. China Construction Industry Press. 1997.04.

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