The quality of the internal environment of shopping malls is an important indicator that affects people's physical and mental health. Currently, some shopping malls have problems such as excessive temperature and poor air quality due to the increase in passenger flow. The author focuses on this problem The spring air-conditioning system operation of a shopping mall in Dalian was investigated and studied, and the annual operation of the air-conditioning system was further analyzed. A comparison of the full air system using combined air-conditioning units was proposed to control the internal environment of large and medium-sized shopping malls in Dalian and achieve energy saving. Reasonable and for reference by relevant engineering personnel in design and operation management.
Keywords: Fresh air operation in the transition season for air conditioning systems in large and medium-sized shopping malls
1 Introduction
In recent years, with the development of our country’s national economy, people’s living standards have With the increase in the purchasing power of the people, many large and medium-sized commercial buildings have been built, especially shopping malls in prosperous areas are relatively crowded. In order to create a comfortable shopping environment for customers, central air-conditioning facilities are generally installed in large and medium-sized shopping malls. However, many air conditioning systems cannot meet the requirements, and some shopping malls need to pay a high energy consumption price to make the indoor environment comfortable. At present, it is generally believed that large and medium-sized shopping malls use ceiling-type air conditioning systems or combined air-conditioning unit all-air systems. There are more than 20 large and medium-sized shopping malls in Dalian, of which eight use ceiling-type air-conditioning systems and more than ten use combined air-conditioning systems. Total air system for air conditioning units. This article investigates and studies a shopping mall that uses a combined air-conditioning unit with an all-air system to analyze which form of air-conditioning system is more reasonable for large and medium-sized shopping malls.
2 Shopping mall load characteristics
Shopping mall air conditioners are comfort air conditioners. The purpose of setting up is to create a comfortable shopping environment for customers, provide a good working environment for salespersons, and facilitate the sale of goods. store. The main characteristics of the shopping mall load are: large and medium-sized shopping malls have large inner areas, many people, and complex personnel structures. The personnel load and fresh air load account for the majority of the cooling load, while the building envelope load accounts for a small proportion. In order to ensure the lighting and advertising effects of shopping malls, shopping malls use many kinds of lighting equipment with high heating values ??(such as projection lamps, halogen lamps, etc.), resulting in a heavy lighting load. In winter, the heat load in the outer area is larger due to the load of the building envelope, while the inner area is less affected by the building envelope, and the personnel load and lighting load remain unchanged, so the heat load is very small, and it may even be cold. load. During the transition season, the outdoor temperature is lower than the indoor temperature. During this period, there is no cooling load on the building envelope. Fresh air can reduce the temperature in the mall.
3 Selection of air-conditioning methods in shopping malls
The choice of air-conditioning system for commercial buildings is related to its size, the plane structure and functional zoning of the building. Small shopping malls generally use split air-conditioning units, and large shopping malls usually use split air-conditioning units. There are three air conditioning methods in medium-sized shopping malls: fan coil plus fresh air system; ceiling air conditioning system; and combined air conditioning unit full air system.
3.1 Fan coil plus fresh air system
Fan coil plus fresh air system can save the use area, but the amount of fresh air is limited. For large and medium-sized shopping malls, it is difficult to use outdoor fresh air for ventilation. , which is not conducive to energy saving in transition seasons. The return air is filtered by the filter at the return air box of the fan coil suspended in the ceiling. The filter is easily blocked, and the cleaning workload is large and troublesome. Especially in summer, if the filter is not cleaned in time, it will cause return air. The air volume decreases, the condensation water increases, the drainage is poor, and the drip tray overflows. This humid condition is the best environment for germs to breed. It may also cause other germs and viruses to gather and grow, causing trouble and unnecessary management. losses. Due to limited installation space, fan coil units are inconvenient to repair and maintain. Not suitable for large shopping malls.
3.2 Ceiling air conditioner system
The ceiling air conditioner system is an air conditioning system developed in recent years. It can save the area of ??the machine room, reduce the building height, and save wind. Tube. The ceiling-mounted air conditioning unit is installed in the ceiling of the use space. The noise of the unit is not only transmitted through the air outlet, but also radiated directly. Therefore, the noise problem is a major problem for the ceiling-mounted air conditioning unit. Secondly, there are many water supply and return pipes, and the water pipes are installed in the suspended ceiling, which increases leakage and dripping.
The limited fresh air volume is also a major disadvantage of ceiling-mounted air conditioning units. Since there are many air ducts, water pipes and other pipes under the beams, the fresh air ducts are restricted, so the ceiling-mounted air conditioning system only has limited fresh air in the outer area.
3.3 The all-air system of the combined air-conditioning unit
The all-air system of the combined air-conditioning unit has a large capacity to handle heat and moisture loads; it can realize fresh air operation in the transition season; it has fewer water pipes , Reduce the phenomenon of water leakage; in winter, the supply air temperature can be adjusted by adjusting the proportion of fresh return air to solve the problem of excessive temperature in the inner area in winter; it can achieve higher cleanliness; it has the advantages of convenient operation management and maintenance. These advantages make it suitable for large and medium-sized shopping malls. However, due to the large area of ??the computer room, the large cross-section of the air duct, and the large space it occupies, some developers are reluctant to adopt this system form.
Based on the advantages and disadvantages of the three system forms, for large and medium-sized shopping malls with large internal areas, it is better to use a combined air-conditioning unit all-air system. It can not only solve the problem of overheating in the inner area in winter, but also make full use of fresh air during the transition season. It not only improves the indoor environment, but also reduces the operating costs of air conditioning in large and medium-sized shopping malls.
4 Example Analysis
The May Day holiday is a period of large passenger flow in shopping malls, and it is also the transitional season of spring. During this period, the author conducted an actual survey and research on a shopping mall in Dalian City. , to illustrate that large and medium-sized shopping malls in Dalian are suitable for using a full air system with combined air conditioning units, which can achieve fresh air operation in the transition season.
4.1 Project Overview
The shopping mall is located in Erqi Square, a prime location in Dalian City. It was built in 2004 and has a construction area of ??50,000 square meters. The hotel has three floors underground and five floors above ground, with a floor height of 5.1 meters. The three underground floors are used as a refrigeration machine room; part of the second underground floor is used as a garage, and the rest is used as a shopping mall; the first underground floor and the five floors above the ground are both used as shopping malls.
The total cooling load of the air conditioning system is 120W/㎡, and the total heating load is 100 W/㎡. A full air system using combined air conditioning units, with 4 air conditioning rooms on each floor. Cold and heat sources of the air conditioning system: two 3000kW centrifugal chillers are used in summer, and two 2500kW steam-water heat exchangers are used in winter. The designed fresh air volume is 15m3/(h.person).
4.2 Test method
The test was conducted on May 2 and May 3. Both days were sunny. The outdoor temperature on May 2 was 19.8℃, and on May 3 The daily outdoor temperature is 20℃, and the shopping mall passenger flow is relatively constant. On the 4F floor, all four air-conditioning units will be turned on at 11:30 on May 2, all four air-conditioning units will be turned on at 10:30 on May 3, and will be closed at 11:30. The two air-conditioning units in the dining area on the 5F floor will be turned on at 11:30 on both days. The chillers are not turned on and fresh air is running. (There are two escalators in the mall. Due to the rise of hot air due to thermal pressure, and in order to save operating costs, the mall has only turned on the air-conditioning units on the top two floors. Due to the limitations of the mall's operating conditions, the air-conditioning units on the 5F floor cannot be turned off. Otherwise, the temperature of the mall will be too high and the mall will not be able to operate normally).
The test is divided into two parts: temperature test and carbon dioxide concentration test. The 4F floor with the highest temperature in the mall and the top 5F floor were selected for testing. Five temperature measurement points with relatively high temperatures on each floor were taken to measure the temperature about 1.5 meters from the ground. The intelligent temperature and humidity self-recording instrument model RHLOG-T-H produced by the electronic product base of Tsinghua Tongfang R&D Center is used to record the temperature of the two floors from 10:00 to 15:30 every 5 minutes. In addition, five test points in the inner area of ??each layer were taken to test the carbon dioxide concentration at 11:00, 13:30 and 15:00 respectively. The instrument used is a multifunctional measuring instrument model Testo 445 produced by the German TESTO company.
The test shows that the all-air system can meet the load requirements by running fresh air without turning on the chiller during the transition season, so that the temperature in the shopping mall can meet the requirements. Moreover, the air quality in the shopping mall when the fresh air is running is better than when the fresh air volume only meets the specifications, which can greatly improve the air quality in the shopping mall.
4.3 Test results
4.3.1 Temperature test results
An average value of the temperature every half hour is used as the temperature of the layer during that period. The temperature conditions from 10:00 to 15:30 are shown in Figure 1 and Figure 2.
It can be seen from Figure 1 that the temperatures on the two days from 10:00 to 10:30 are almost the same because the air conditioning unit was not turned on in the two days before 10:30. Before 11:30 on May 2, the temperature of the 4F layer showed an upward trend. At 11:30, the temperature began to decrease and continued to decrease thereafter. The temperature of the 4F layer showed a downward trend before 11:30 on May 3, and gradually increased after 11:30. The temperature dropped and rose after 11:30 on both days because the four air conditioning units on the 4F floor were turned on and off at 11:30 on the same day respectively. The temperature on May 3 was lower than the temperature on May 2 from 10:30 to 12:00, because the air conditioning unit on this floor was turned on from 10:30 to 11:30 on May 3, and on May 2 Not open. After 12:00, the temperature of the 4F layer on May 2 was lower than the temperature of the 4F layer on May 3, and the temperature difference gradually increased. When the air-conditioning unit is turned on, the mall temperature is controlled at around 26°C. When the air-conditioning unit is not turned on, the mall temperature reaches 28.6°C, with a maximum temperature difference of 2.1°C.
It can be seen from Figure 2 that the air conditioning units on the 5F floor were both turned on on May 2 and 3, so the temperature trends on the two days were similar. However, since only two air conditioning units on the 5F floor were turned on, it cannot be To meet the load requirements, the temperature tends to rise.
4.3.2 Carbon dioxide concentration test results
Take the average of 5 test points at each time on each floor at 11:00, 13:30 and 15:00 as The CO2 concentration of this layer at this moment is shown in Figures 3 and 4.
Figure 3 Comparison chart of CO2 concentration in the 4F layer Figure 4 Comparison chart of CO2 concentration in the 5F layer The concentration dropped and remained relatively constant, while the carbon dioxide concentration started at a lower level on May 3 and increased after the air conditioning units were shut down. The air conditioning units on the 4F and 5F floors will be turned on at 15:30 on May 1st and closed at 16:40; the air conditioners on the 4F and 5F floors will be on at 11:30 on May 2nd and closed at 17:05, and will be opened at 10:30 on May 3rd. The air conditioning unit on the 4F floor will be turned off at 11:30. The ventilation time on May 2 was longer than that on May 1, and the air conditioning unit on the 4F floor was turned on at 10:30 in the morning on the 3rd, so the carbon dioxide concentration on the 4F floor at 11:00 on the 3rd was less than the carbon dioxide concentration on the 2nd.
Two air-conditioning units were turned on on the 5F floor on both days. Comparing Figure 3 and Figure 4, it can be seen that the change trend of carbon dioxide concentration in the 5F floor is similar to that of the 4F floor. This is because the 5F floor is affected by the 4F floor. .
4.3.3 Air-conditioning system costs
During normal operation in the spring (April-May), the entire mall will operate with fresh air and no chillers. Run 18 combined air-conditioning units with a power of 18.5kW each for 2 hours a day, and 6 exhaust fans with a power of 25kW for 4 hours, calculated based on the electricity price of 0.87 yuan/hour (the following cost calculations are based on this value), running in spring The cost is 66,085 yuan. Autumn (September--October) is also a new trend. Running 6 air-conditioning units with a power of 15kW each for 2 hours a day, and 6 exhaust fans with a power of 25kW each for 4 hours, the operating cost in autumn is: 40,716 yuan. The total operating cost of the mall using an all-air system during the transition season is 106,801 yuan.
If it is not running with fresh air in the spring and autumn, a chiller must be added. According to the design of the mall, a centrifugal refrigerator with a power of 530kW needs to be added. The operation is about 55 in the spring and 70 in the autumn. It runs for about 2 hours a day. It is equipped with a cooling water pump with a power of 75kW, a chilled water pump with a power of 75kW, a system water supply pump with a power of 1.5kW, and the cooling water tower is equipped with 6 cooling water pumps with a power of 7.5kW. kW fan.
The operating cost of a shopping mall that does not use fresh air during the transition season is 216,839 yuan.
Table 1 Operating Cost Comparison Table Operating Costs of Fresh Air Operation in the Transition Season (Yuan)
Operation Costs of Not Using Fresh Wind Operation in the Transition Season (Yuan) Difference between the Two Operating Costs (Yuan) 106, 801216, 839110, 038
4.4 Result Analysis
When the outdoor temperature in Dalian is around 20°C in spring, fresh air supplied by the whole air system can reduce the indoor temperature. Customers wear thicker clothes in spring than in summer, so the temperature at this time should be lower than the design temperature in summer. The 28.6°C temperature on the 4F floor when the air conditioning unit is not turned on has exceeded the design temperature in summer and is far away from the human body's comfort zone. scope. The air-conditioning unit was turned on on the 5F floor both days. However, because only part of the air-conditioning unit was turned on, the temperature on the 5F floor still increased, and the temperature was not controlled as effectively as on the 4F floor. When the air-conditioning unit is turned on, the environment in the mall is just controlled at the edge of the comfort zone, which can not only create a better shopping environment for customers, but also achieve the purpose of energy saving.
There is a serious problem of insufficient fresh air in shopping malls without air-conditioning units. Ceiling air conditioner systems and fan coil plus fresh air systems have limited fresh air ducts due to the large number of air ducts, water pipes and other pipes under the beams. Therefore, there is only limited fresh air in the outer area, and the air quality in the inner area is different from that of the full air system. The situation is similar when sending fresh air. From the carbon dioxide concentration comparison chart, it can be seen that when the air conditioning unit is running with fresh air, the carbon dioxide concentration in the mall drops significantly, and the air quality in the mall improves significantly. On May 2, when the new air was running, the carbon dioxide concentration remained between 600ppm and 700ppm after turning on the air-conditioning unit. The carbon dioxide concentration did not increase due to the increase in passenger flow in the mall after it was opened for a period of time. Instead, it was 851ppm higher than the 851ppm when it just opened. Low. It can be seen that it is much better to use an all-air system than a ceiling-mounted air conditioner system to improve the air quality in shopping malls. The mall only has some air conditioning units on the 4F and 5F floors. If the air conditioning units on every floor of the mall are on, the temperature in the mall can be controlled lower and the air quality will be improved. This conclusion is also applicable to autumn, which has a similar climate to spring
The whole air system operates with fresh air in the transition season. All the fresh air sent into the mall by the air conditioning unit is outdoor fresh air, which efficiently dilutes the air in the mall. Dirty air. The total air supply volume is the same as that of the ceiling-mounted air conditioner system, so the operating costs of this part of the air conditioner unit will not be increased.
When the shopping mall air-conditioning system is running with fresh air during the transition season, the temperature and air quality of the shopping mall are controlled within a good range, but in order to achieve this comfortable environment, there is no cost of energy waste. Through calculation, it can be concluded that the fresh air operation of the all-air system in spring and autumn saves more than 110,000 yuan in operating expenses per year compared with the non-fresh air operation. If a ceiling-mounted air conditioner system is used, the operating costs in the transition season are similar to those of an all-air system without fresh air in the transition season. In winter, the fully air-conditioned system can have different air supply parameters for the inner and outer zones, and different air supply parameters for each floor. The air supply temperature in the inner zone can be lower than the air supply temperature in the outer zone, and the top air supply temperature can be lower than the bottom air supply temperature. The proportion of fresh air in the inner area and the top floor can be increased, which not only solves the problem of excessive winter temperatures in the inner area and the top floor of the shopping mall, but also reduces the heat load and saves operating costs. Therefore, although the all-air system occupies a building area, its operating costs are much less than that of a ceiling-mounted air conditioner system.
5 Conclusion
5.1 In the transition season, fresh air operation can be realized to control indoor temperature and air quality.
5.2 The proportion of fresh air and return air in the combined air system of the combined air conditioning unit is relatively flexible. The fresh air volume can be adjusted at any time according to requirements to meet the comfort requirements of the mall and improve the air quality of the mall. It is an important solution to the current problem. A better solution is to solve the problem of poor air quality in some large and medium-sized shopping malls with large passenger flow.
5.3 In winter, the air supply can be layered and divided into zones. The temperature of the mall can be adjusted through different air supply parameters to reduce the temperature difference in the mall so that customers will not feel uneven hot and cold in the mall. .
To sum up, it is more reasonable for large and medium-sized shopping malls in Dalian to adopt a full air system with combined air conditioning units. At present, there is a shortage of energy, and it is crucial to save energy in the air-conditioning system, which is a large energy consumer. Under reasonable operation conditions, the all-air system can provide a good shopping mall environment, save operating costs, and also save energy. After investigation and research, the author recommends that large and medium-sized shopping malls should try to adopt a full air conditioning system with combined air conditioning units when conditions permit. Fan coil systems or ceiling-mounted air conditioning systems can be considered in outer areas and store rooms.
References:
[1] Zhang Xinhua briefly talks about the air-conditioning design of shopping malls, Coal Mine Design, Issue 3, 1999
[2] Yao Yang, Wang Fang, large and medium-sized shopping malls Determination of the optimal operating conditions of the air conditioning system Journal of Harbin University of Architecture and Architecture 1998 (8)
[3] Huang Xuging Department Store Air Conditioning Design China Architecture Industry Press
[4] Jidong Guangda Research on Experience and Application Technology of Air Conditioning Design in Medium-sized Shopping Malls 2003 (9)
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