Keywords: fresh air operation of air conditioning system in large and medium-sized shopping malls in transition season
1 Introduction
In recent years, with the development of China's national economy, the improvement of people's living standards and the enhancement of people's purchasing power, many large and medium-sized commercial buildings have been built, especially the shopping malls in prosperous areas are crowded. In order to create a comfortable shopping environment for customers, central air-conditioning facilities are widely deployed in large and medium-sized shopping malls. But many air conditioning systems can't meet the requirements, and some shopping malls need to pay a lot of energy to make the indoor environment comfortable. At present, there are more than 20 large and medium-sized shopping malls in Dalian, of which 8 adopt ceiling air conditioning systems and more than 10 adopt combined air conditioning systems. Based on the investigation and study on the all-air system of combined air conditioning unit in a shopping mall, this paper analyzes which air conditioning system form is more reasonable for large and medium-sized shopping malls.
2 Small load characteristics
Air conditioning in shopping malls belongs to comfort air conditioning. Its purpose is to create a comfortable shopping environment for customers, provide a good working environment for shop assistants and facilitate the storage of goods. The main characteristics of shopping mall load are: large internal area of large and medium-sized shopping malls, many people and complex personnel structure. Personnel load and fresh air load account for most of the cooling load, while building envelope load accounts for a small proportion. In order to ensure the lighting and advertising effect of shopping malls, shopping malls with high calorific value adopt a variety of lighting equipment (such as projection lamps, halogen lamps, etc.). ), resulting in a large lighting load. In winter, due to the load of the envelope, the heat load in the outer zone is larger, while the heat load in the inner zone is smaller due to the small influence of the envelope, while the personnel load and lighting load remain unchanged, and may even be cold load. In the transitional season, the outdoor temperature is lower than the indoor temperature, during which there is no cold load of the envelope. Sending fresh air can reduce the temperature of shopping malls.
3 the choice of air conditioning mode in shopping malls
The choice of air conditioning system in commercial buildings is related to its scale, plane structure and functional partition. Small shopping malls generally adopt split air conditioning units, while large and medium-sized shopping malls usually have three air conditioning methods: fan coil unit plus fresh air system; Ceiling air conditioning system; Total air system of combined air conditioning unit.
3. 1 fan coil plus fresh air system
Fan coil unit plus fresh air system saves available area, but the fresh air volume 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 season. The return air is filtered by the filter at the fan coil return box in the ceiling, and the filter is easily blocked, and the cleaning workload is heavy and troublesome. Especially in summer, if the filter screen is not cleaned in time, the return air volume will decrease, the condensed water will increase, the drainage will be poor, and the drip tray will overflow. This humid condition is the best environment for bacteria to breed, and it may also lead to the aggregation and growth of other bacteria and viruses, which will bring trouble and unnecessary losses to management. Due to the limitation of installation space, it is inconvenient to repair and maintain the fan coil. Not suitable for large shopping malls.
3.2 ceiling air conditioning system
Ceiling air conditioning system is a kind of air conditioning system developed in recent years, which can save the room area, reduce the building height and save air ducts. Ceiling air conditioning unit is installed in the ceiling of the use space, and the noise of the unit not only comes out through the tuyere, but also radiates directly, so the noise problem is a big problem of ceiling air conditioning unit. Secondly, there are many water supplies in return pipe, and the water pipes are installed in the ceiling, which increases the leakage. Limited fresh air volume is also a major disadvantage of ceiling air conditioning units. Because there are many air pipes and water pipes under the beam and the fresh air pipes are limited, the ceiling air conditioning system only has limited fresh air in the outer area.
3.3 Total air system of combined air conditioning unit
The total air system of combined air conditioning unit has strong ability to deal with heat and moisture load; In the transitional season, fresh air operation can be realized; Less water pipes to reduce water leakage; In winter, the supply air temperature can be adjusted by adjusting the proportion of new return air to solve the problem of excessive temperature in the inner zone in winter; Higher cleanliness can be achieved; Easy to operate, manage and maintain. These advantages make it suitable for large and medium-sized shopping malls. However, some developers are unwilling to adopt this system form because of its large room area, large cross-sectional size of air duct and large space.
Considering the advantages and disadvantages of the three systems, for large and medium-sized shopping malls with large internal area, the all-air system of combined air conditioning units should be adopted. It can not only solve the problem of overheating in the inner area in winter, but also use a lot of fresh air in the transitional season, which not only improves the indoor environment, but also reduces the operating cost of air conditioning in large and medium-sized shopping malls.
4 example analysis
The May Day holiday is a period of heavy traffic in shopping malls, and it is also the spring of the transitional season. During this period, the author conducted a survey on a shopping mall in Dalian, indicating that large and medium-sized shopping malls in Dalian are suitable to adopt the all-air system of combined air conditioning units, and can realize fresh air operation in transitional seasons.
4. 1 project overview
Located in Erqi Square, a prime location in Dalian, the mall was completed in 2004 with a construction area of 50,000 square meters. * * * There are three floors underground and five floors above ground, with a height of 5.1m.. The third floor underground is a cold room; Part of the second floor underground is used as a garage, and the rest is used as a shopping mall; The first floor underground and the fifth floor above ground are shopping malls.
The total cooling load of air conditioning system is 120W/㎡, and the total heating load is 100 W/㎡. All-air system of combined air conditioning unit is adopted, and 4 air-conditioned rooms are set on each floor. Cold and heat sources of 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 people).
4.2 Test Methods
Choose May 2nd and May 3rd for the test, both days are sunny, the outdoor temperature is 19.8℃ on May 2nd and 20℃ on May 3rd, and the shopping mall passenger flow is relatively constant. On the 4th floor, all four air conditioning units will be turned on on May 2nd 1 1: 30, and turned off on May 3rd 1 1: 30. There are two air conditioners in the dining area on the fifth floor, which are turned on at 1 1: 30 on both days. All the coolers are not turned on, and all the fresh air is flowing. There are two escalators in the shopping mall. Due to the hot air rising caused by hot pressing, in order to save operating costs, only the air conditioning units on the top two floors were turned on in the mall. Due to the limitation of the operating conditions of the mall, the air conditioning unit on the 5F floor cannot be turned off, otherwise the temperature of the mall will be too high, which will lead to the normal operation of the mall. ).
The test is divided into two parts: temperature test and carbon dioxide concentration test. The 4F and 5F floors with the highest temperature in the shopping mall are selected for testing, and five relatively high temperature measuring points are selected for each floor, and the measured ground temperature is about1.5m. The intelligent temperature and humidity recorder (RHLOG-T-H) produced by Tsinghua Tongfang R&D Center Electronic Products Base is used to record the two floors from 10: 00 to/kloc-every five minutes. In addition, five testing points were selected in the inner area of each floor to test the carbon dioxide concentrations of 1 1: 00, 13: 30 and 15: 00 respectively. The instrument used is TESTO445 multifunctional measuring instrument produced by Testo Company in Germany.
The test shows that the all-air system can meet the load requirements and make the temperature in the mall meet the requirements without opening the fresh air of the chiller in the transition season. Moreover, the air quality in the mall is better when the fresh air is running than when it only meets the fresh air volume specified in the specification, which can improve the air quality in the mall very well.
4.3 Test results
Temperature test results
Take the average temperature of every half hour as the temperature of this layer during this period. The temperature from 10: 00 to 15: 30 is shown in figure 1 and figure 2.
As can be seen from the figure 1, the temperature from 10: 00 to 10: 30 is almost the same, because the air conditioner was not turned on before 10: 30. On May 2nd, the temperature of 4F layer showed an upward trend before 1 1: 30, and began to decrease at 1 1: 30, and then kept a downward trend. On May 3rd, the temperature of 4F layer decreased before 1 1: 30, and gradually increased after 1 1: 30. The temperature drop and rise after 1 1: 30 in two days are all caused by turning on and off four air conditioning units on the fourth floor at 1 1: 30 on the same day. During the period from 10: 30 to 12: 00, the temperature on May 3rd was lower than that on May 2nd, because the air conditioning unit on this floor was on from May 3rd to May 3rd, but it was not on May 2nd. After 12: 00, the temperature of 4F layer on May 2nd was lower than that on May 3rd, and the temperature difference gradually increased. When the air conditioning unit is turned on, the temperature of the mall is controlled at about 26℃. When the air conditioning unit is not turned on, the temperature of the mall reaches 28.6℃, and the maximum temperature difference is 2. 1℃.
As can be seen from Figure 2, on May 2nd and 3rd, the air conditioning units on the 5th floor were all on, so the temperature trends in these two days were almost the same. However, because only two air conditioners were opened on the fifth floor, the load requirements could not be met, so the temperature tended to rise.
4.3.2 Test results of carbon dioxide concentration
Take the average value of five test points at each time point of each layer at three time points (1 1: 00, 13: 30, 15: 00) as the CO2 concentration at that time point, as shown in Figures 3 and 4.
Figure 3 Comparison of CO2 concentration in 4f layer Figure 4 Comparison of CO2 concentration in 5f layer
As can be seen from Figure 3, the concentration of carbon dioxide was very high on May 2nd, but it decreased and remained relatively constant after the air conditioning unit was turned on, and it was lower on May 3rd, and increased after the air conditioning unit was turned off. On May 1 Day, the air conditioning units on floors 4F and 5F 15: 30 will be turned on and 16: 40 will be turned off; On May 2nd, 1 1: 30, the air conditioners on floors 4F and 5F were turned on and turned off at 17: 05. Turn on the air conditioner on the 4F floor on May 3rd, and turn it off at 1 1: 30. On May 2nd, the ventilation time was longer than that in May 1, and the air conditioning unit on the 4th floor was turned on at 10:30 in the early morning of the 3rd, so the carbon dioxide concentration on the 3rd 1 1 was less than that on the 2nd.
The 5F building has been air-conditioned for two days. As can be seen from the comparison between Figure 3 and Figure 4, the change trend of carbon dioxide concentration on the 5F floor is similar to that on the 4F floor, because the 5F floor is affected by the 4F floor.
Cost of air conditioning system
During normal operation in spring (April-May), the whole shopping mall is operated by fresh air, and no water chillers are turned on. Every day, the combined air conditioning unit with power of 18 18.5kW runs for 2 hours, and six exhaust fans with power of 25kW run for 4 hours. According to the electricity price of 0.87 yuan/hour (the following expenses are calculated according to this value), the spring operation cost is 66085 yuan. Autumn (September-65438+1October) is also a brand-new wind operation. Every day, six air conditioning units with power of 15kW run for 2 hours, and six exhaust fans with power of 25kW run for 4 hours. The operating cost in autumn is 407 16 yuan. In the transitional season, the total operating cost of adopting all-air system in shopping malls is 106 and 80 1 yuan.
If it is necessary to add water chillers in spring and autumn when the wind is not fresh, according to the design requirements of the shopping mall, add 1 centrifugal water chillers, with a power of 530kW, running about 55% in spring and 70% in autumn, and running for 2 hours every day. 75kW cooling water pump has 1 set, and 75kW chilled water pump has 1 set, with 654 sets. The operating cost of shopping malls without fresh air in transition season is 2 16839 yuan.
Table 1 Operating cost comparison table Fresh air operating cost in transition season (yuan)
Operating cost without fresh air in transition season (yuan): the difference between the two operating costs (yuan)106,801216,8391kloc-0/0038.
4.4 Result analysis
When the outdoor temperature in Dalian is about 20℃ in spring, the fresh air sent by the all-air system can reduce the indoor temperature. The customer's clothing in spring is thicker than that in summer, so the temperature at this time is lower than the design temperature in summer. The temperature of 28.6℃ of 4F floor without air conditioning unit has exceeded the design temperature in summer, far beyond the range of human comfort zone. The 5F floor was air-conditioned for two days, but the temperature of the 5F floor still rose, because only part of the air conditioner was turned on, and the temperature control was not as effective as that of the 4F floor. When the air conditioning unit is turned on, the environment in the shopping 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 no air conditioning unit in the shopping mall, so the problem of insufficient fresh air is very serious. Ceiling air conditioning system and fan coil plus fresh air system have many ducts such as air pipes and water pipes under the beams, so the fresh air in the outer area is limited, and the air quality in the inner area is similar to that in the all-air system without fresh air. From the comparison chart of carbon dioxide concentration, it can be seen that the carbon dioxide concentration in the mall is obviously decreased and the air quality in the mall is obviously improved when the air conditioning unit is running in fresh air. On May 2, when the air conditioning unit was turned on, the concentration of carbon dioxide remained between 600 ppm and 700 ppm. However, the concentration of carbon dioxide is lower than 85 1ppm when it was first opened, not because of the increase of passenger flow in shopping malls for a period of time. It can be seen that it is much better to use all-air system to improve the air quality of shopping malls than ceiling air conditioning system. The mall only opened some air conditioning units on the 4th and 5th floors. If the air conditioning units on each floor of the mall are turned on, the temperature of the mall can be controlled lower and the air quality will be improved. This conclusion also applies to autumn because the climate in autumn is similar to that in spring.
All-air system operates with fresh air in the transitional season, and all fresh air sent into the mall by air conditioning units is outdoor, which effectively dilutes the dirty air in the mall. The total air supply volume is the same as that of the ceiling air conditioning system, which will not increase the operating cost of this part of the air conditioning unit.
When the air conditioning system in the shopping mall runs in the fresh air in the transitional season, it keeps the temperature and air quality in a good range, and it does not need to consume energy to achieve this comfortable environment. Through calculation, it is concluded that the operating cost of all-air system in spring and autumn is more than that of non-all-air system 1 10000 yuan. If the ceiling air conditioning system is used, its operating cost in transition season is similar to that of the all-air system without fresh air in transition season. In winter, the air supply parameters of the all-air system can be different in the inner zone and the outer zone, and the air supply parameters of each floor are also different. The air supply temperature in the inner zone can be lower than that in the outer zone, the air supply temperature at the top floor can be lower than that at the bottom floor, and the proportion of fresh air sent to the inner zone and the top floor can be increased. This not only solves the problem that the temperature in the inner area and the top floor of the shopping mall is too high in winter, but also reduces the heat load and saves the operating cost. Therefore, although the all-air system occupies the building area, its operating cost is much less than that of the ceiling air conditioning system.
5 conclusion
5. 1 fresh air can be used to control the indoor temperature and air quality in the transitional season.
5.2 The proportion of fresh air and return air in the total air system of combined air conditioning unit is flexible, and the fresh air volume can be adjusted at any time according to the requirements, so as to meet the comfort requirements of shopping malls and improve the air quality of shopping malls, which is a better method to solve the poor air quality of some large and medium-sized shopping malls with large passenger flow.
5.3 In winter, air can be supplied by layers and zones, and the temperature of the shopping mall can be adjusted by different air supply parameters to reduce the temperature difference in the shopping mall, so that customers will not feel uneven hot and cold in the shopping mall.
To sum up, it is reasonable for Dalian large and medium-sized shopping malls to adopt the all-air system of combined air conditioning units. In today's energy shortage, air conditioning system, as a large energy consumer, is very important to save energy. Under the condition of reasonable operation, the all-air system has a good shopping environment, saving operating expenses and energy. After investigation and study, the author suggests that large and medium-sized shopping malls should adopt the all-air air conditioning system of combined air conditioning units as far as possible when conditions permit, and fan coil system or ceiling air conditioning system can be considered in peripheral areas and shops.
References:
[1] Zhang Xinhua talks about air conditioning design of shopping malls and coal mine design1999 No.3.
[2] Determination of optimal operating conditions of air conditioning system in large and medium-sized shopping malls in Yaofang/Journal of Harbin Jianzhu University 1998(8)
[3] Huang Department Store Air Conditioning Design China Building Industry Press
[4] Experience in air conditioning design of large and medium-sized shopping malls in Dongguang, Hebei; Research on Applied Technology in 2003 (9)
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