Thermal

The Shanghai Tower has an envelop-typed atrium, whose inner and outer facades are all glass curtain walls. As a result, solar radiation influences the thermal environment of the atrium a lot. Non-isothermal indoor air is affected by buoyancy and large space, which makes the airflow become quite complicated. The combination of interior flow field and radiation field form a complex indoor thermal environment. The conduction, convection and radiation involved in the heat transfer process are all need to be simulated (Wang & Wu, 2009).

1 Simulation Methodology

IES <VE> and Star-CCM+ are two tools that are used to simulate the thermal environment of the atrium in summer. There are three major steps as it shows in Fig 1. The first step is to import parameters, which include annual outdoor meteorology parameter, envelop enclosure parameter, indoor load parameter, air-conditioning air inlet parameter, etc. Secondly, use IES <VE> to simulate the wall surface heat balance and room heat balance to get the inner façade temperature and air-conditioning load. The last step is using the results of step two as the boundary condition, simulating the indoor temperature and velocity field distribution in Star-CCM+.

Fig 1. United simulation structure figure (Wang & Wu, 2009)

2 Modeling

The building area of the atrium is 361 square meters. In the design phase, the heat transfer coefficient and shading coefficient of the glass are defined as 5.8W/m2·k and 0.5 respectively. Since the bottom layer of the atrium is occupied space, this area is regarded as air-conditioning control area, while the upper space is regarded as non air-conditioning control area. During modeling, every floor is set up separately to better control the indoor temperature of air-conditioning control area and non air-conditioning control area.

From Fig 2, we can find the atrium includes three parts, which have the same shape but different directions. Thus, choose the part that is at the worst condition in summer to do the numerical modeling, and the time is designed as 12:30 on 21st, July.

Fig 2. Plan of the Shanghai Tower (Wang & Wu, 2009)

Fig 3. IES <VE> model of the Shanghai Tower

(Wang & Wu, 2009)

Fig 4. Physical model in numerical modeling of the Shanghai Tower (Wang & Wu, 2009)

3 Simulation Results

There are three working conditions during simulation as Table 1 shows.

Table 1. Simulation working conditions in summer

Working Condition 1

Working Condition 2

Working Condition 3

Air-conditioning air supply is 3.5 m in height.

Lower wind returns in the same side.

There is no exhaust air on the top.

Air-conditioning air supply is 3.5 m in height.

85% lower air returns in the same side.

15% exhaust air on the top.

Air-conditioning air supply is 3.5 m in height.

Lower air returns in the same side.

There is exhaust air at the neutral plane with 26°.

There is exhaust air on the top.

3.1 Working Condition 1

Fig 5 shows that in the height of 1.5 m, the temperature is controlled at 26°. Since the time is 12:30 at noon, the solar radiation is the highest within a day; indoor air is affected by solar radiation and the greenhouse effect. The temperature goes up as the height grows. Above the fourth floor, the temperature is between 36 and 39°. At the top, the temperature gets 40°. In Shanghai, outdoor temperature that adjusted by air-conditioning in summer is designed as 34.6°. Therefore, the thermal environment of the atrium has a bad impact on the comfort level in the offices nearby, and increases air-conditioning energy consumption.

From Fig 6, it can be found that because of the direct solar radiation on the outer façade, the temperature is relatively higher; the airflow rises along the outer façade. The temperature of the inner façade is relatively lower, so when the hot air hits the inner façade, it goes down, and forms a big swirl on the top. As for the lower air, it can get to the farthest point of the outer façade. Some of it is heated before going up, some of it is discharged from the air inlet.

Fig 5. Vertical temperature distribution of the atrium under Working Condition 1 in summer (Wang & Wu, 2009)

Fig 6. Vertical velocity distribution of the atrium under Working Condition 1 in summer (Wang & Wu, 2009)

3.2 Working Condition 2

In view of the results in working condition 1, working condition 2 has done some improvement based on it, namely add exhaust air on the top, and make full use of the stack effect in the tall atrium. Compared to working condition 1, the temperature in the upper space decreases, with a highest temperature of 38°. However, this temperature is still larger than 34.6°. The effects from middle and upper space still lead to more energy consumption of office air-conditioning. If we enlarge the amount of exhaust air, more energy is needed to deal with the new air. Thus, we should consider other measures.

Fig 7. Vertical temperature distribution of the atrium under Working Condition 2 in summer (Wang & Wu, 2009)

3.3 Working Condition 3

If we want to decrease the temperature in the upper space of the atrium, we need some air with lower temperature. As the atrium is adjacent to the offices, on the basis of Working Condition 2, Working Condition 3 selects the neutral plane to exhaust 26° air to the offices. According to IES <VE>, the velocity is 22.5 kg/s.

Fig 8 presents that the temperature in lower space increases a little, part of it gets to 28°. The reason is that the exhaust air from the neutral plane is mixed with the existing air, the temperature rises, and some of the air flows to the air outlet on the bottom. By this way, the temperature under the neutral plane is well controlled, the figure is under 32° on the whole, lower than the requirement. Still, the temperature above the neutral plane goes up along with the height increase, with the highest temperature of about 38°. Later, the designers set up an air outlet on the top to let air from the air-conditioning flow to the atrium. Under this condition, the temperature of the whole atrium is controlled under 34°.

Fig 8. Vertical temperature distribution of the atrium under Working Condition 3 in summer (Wang & Wu, 2009)