5. What is the application mode?

PCMs coupled with NV are an effective passive cooling strategy for office buildings. A kind of inorganic PCMs encapsulated in PVC panel developed by a Chinese manufacturer is applied in building envelope as a wall application in a naturally ventilated office building. According to differential scanning calorimeter (DSC) test [32], the latent heat of the PCM is 122.3 kJkg<sup>1</sup> in melting and 116.9 kJkg<sup>1</sup> in solidification. The phase change temperature range is 25–27°C. The thickness of PVC panel is 20 mm, and the length and width are 520 mm and 200 mm. The PCM panel is installed at the interior surface of an external wall and an internal wall of the office building through modular installation as shown in Figure 15. The PCM panel is directly connected to the wall using aluminum strips and nuts by the modular installation.

For north wall, the PCM panel is directly installed on the interior surface (see Figure 16(a)). The PCM panel exposed to indoor air is beneficial to convection heat transfer between indoor air and the PCM panel. At nighttime, the outdoor cool air is introduced into indoor space through the opened window. When the cold air flows through the PCM-based wall, the coldness is stored by PCMs. For south wall, the

Figure 15.

(a) Isometric view of the naturally ventilated office building and (b) diagram of installation position of PCM panel.

Building Envelope with Phase Change Materials DOI: http://dx.doi.org/10.5772/intechopen.85012

#### Figure 16.

influence factors on thermal performance of PCMs component are fins number and geometry. The current research works mainly focused on the effect of fins number or geometry separately. However, these two factors should be taken into consideration. To enhance heat transfer rate, the balance between fins number and geome-

In the field of PCMs heat transfer, numerical method is widely employed by architects. To obtain the appropriate geometric of fins, the building component with PCMs is optimized by COMSOL Multiphysics. The results show that PCMs complete melting time in the building component and the temperature difference of heat transfer surfaces could be used to evaluate the fins effect. The optimized building component presents the best heat transfer performance with 8 mm length, 0.2 mm width, and 5 mm spacing of fins. The temperature comparison of building component with PCMs before and after optimization is shown in Table 5. It can be seen that the heat transfer performance of the optimized component is better than non-optimized component during heat storage process. The temperature difference between top and bottom in the non-optimized component is increasing over the time. It directly gives the fact that appropriate geometry of fins makes the heat transfer much more uniform and reduce the adverse effect of natural convection in

PCMs coupled with NV are an effective passive cooling strategy for office buildings. A kind of inorganic PCMs encapsulated in PVC panel developed by a Chinese manufacturer is applied in building envelope as a wall application in a naturally ventilated office building. According to differential scanning calorimeter

116.9 kJkg<sup>1</sup> in solidification. The phase change temperature range is 25–27°C. The thickness of PVC panel is 20 mm, and the length and width are 520 mm and 200 mm. The PCM panel is installed at the interior surface of an external wall and an internal wall of the office building through modular installation as shown in Figure 15. The PCM panel is directly connected to the wall using aluminum strips

For north wall, the PCM panel is directly installed on the interior surface (see Figure 16(a)). The PCM panel exposed to indoor air is beneficial to convection heat transfer between indoor air and the PCM panel. At nighttime, the outdoor cool air is introduced into indoor space through the opened window. When the cold air flows through the PCM-based wall, the coldness is stored by PCMs. For south wall, the

(a) Isometric view of the naturally ventilated office building and (b) diagram of installation position of PCM

(DSC) test [32], the latent heat of the PCM is 122.3 kJkg<sup>1</sup> in melting and

try should be further investigated.

Zero and Net Zero Energy

heat storage process.

5. What is the application mode?

and nuts by the modular installation.

Figure 15.

panel.

26

(a) Design sketch, PCM panel exposed to indoor air; and (b) design sketch, PCM panel decorated with perforated aluminum plate.

installation of the PCM panel is the same as that of the north wall. However, considering that there is a constructional column in the middle of the south wall protruding into the interior space, the exterior of the PCM panel is decorated with perforated aluminum plate. These tiny holes in the aluminum plate can promote the convection heat transfer between indoor air and the PCM panel (see Figure 16(b)).

Actual installation effect of the PCM panel is shown in Figure 17. To examine the application effect of PCMs coupled with NV strategy in hot season, full-scale field thermal environment test is conducted in a typical week of hot season. Indoor air temperature, surface temperature, and heat flux of the wall with the PCM panel are carefully investigated. To obtain the cooling potential of PCMs coupled with NV, the scenario of the wall without the PCM panel is modeled using EnergyPlus with the actual weather data during the test period. The accuracy and reliability of the method is validated by comparing the simulated and experimental results with maximum relative error of 2.95% and average relative error of 0.96%.

The indoor thermal environment before and after the application of PCMs coupled with NV is compared with experiment and simulation results. It can be observed from Figure 18(a) that the interior surface heat flux of the wall with the PCM panel is significantly greater than that without the PCM panel. It demonstrates that PCMs absorb and release a lot of heat from indoor air during the melting or solidification process. Therefore, the interior surface peak temperature of the wall with the PCM panel is greatly reduced with respect to wall without the PCM panel as shown in Figure 18(b). Accordingly, the indoor air peak temperature is greatly reduced using the PCM panel. The maximum reduction of indoor air temperature is up to 1.1°C (see Figure 18(c)).

Figure 17. Actual installation effect of the PCM panel: (a) exposed to indoor air and (b) decorated with perforated aluminum plate.

6. Conclusions

Building Envelope with Phase Change Materials DOI: http://dx.doi.org/10.5772/intechopen.85012

1. Comparative experimental investigations of thermal performance of PCMbased lightweight wallboards are conducted in the artificial controlled condition with harmonic temperature changing. The thermal performance of PCM-based lightweight wallboards is carefully analyzed. Two kinds of controlled conditions

are compared: different PCM layout areas and different PCM layer arrangements are adopted. Moreover, a simple thermal design method is proposed and verified with the artificial controlled experimental results.

2. A typical naturally ventilated office building has been modeled with EnergyPlus, and several simulations have been carried out based on 10

representative cities of Western China. The climatic and seasonal suitability for application of PCMs coupled with NV strategy is investigated from three aspects: suitability of PCT, comparisons of three different cooling strategies, and application advantage. Moreover, a performance-based inverse design method is proposed to determine the typical climate characteristics.

3. Based on two methods of thermal transfer enhancement of PCMs applied in building envelope, PCMs and building component with PCMs are optimized in material and component level, respectively. The optimum proportion of CNTs in the composite PCM is obtained through experiment. Appropriate geometry

optimization methods can promote the heat transfer performance of PCMs and

4.A kind of PCM panel is applied as wall application in a naturally ventilated office building. Full-scale field indoor thermal environment test is conducted in a typical week of hot season. The thermal performance of the wall with PCM panel is superior to the wall without the PCM panel. The heat storage capacity of the wall can be improved by 40%, and the indoor air peak temperature can

This work was supported by "the 13th Five-Year" National Science and Technology Major Project of China (No. 2018YFC0704500), Natural Science Foundation of China (No. 51838011 and No. 51808429), Shaanxi Province Key Research and Development Plan (No. 2017ZDXM-SF-076), China Postdoctoral Science Foundation (No. 2018 T111026), and Natural Science Foundation of Shaanxi Province (No.

We declare that there is no conflict of interest exits in the chapter, as well as the

of fins is optimized by numerical simulation. Results show that two

be reduced by 1.1°C in the test period of hot season.

chapter is approved by all authors for publication.

AALL Area of the wallboard, m<sup>2</sup>

APCM Area of PCM, m<sup>2</sup>

improve the utilization of PCMs.

Acknowledgements

Conflict of interest

Nomenclature

29

2017JQ5005).

Figure 18.

(a) Interior surface heat flux of north wall, (b) interior surface temperature of north wall, and (c) indoor air temperature.
