This study mainly discusses the indoor effects of natural ventilation on container houses and solar radiation on container houses to ensure the physical comfort of occupants of container houses. In terms of natural ventilation, four windows and one door are set up in eight models to study the ventilation effect, and the influence of natural ventilation flow field on solar radiation container house is analyzed. The flow field ventilation environment under the condition of natural ventilation needs to be predicted for the container house, and the natural ventilation wind speed is set to be 10 m/s. Then, indoor air flow field is analyzed, and solar radiant heat is discussed. In order to make 3D analysis as surface fitting, B-spline is used in this study as surface result analysis of fitting function.
5.1. Container House Natural Ventilation Analysis
Figure 8 shows the 3D surface analysis diagram of the flow distribution inside the container house. Under the condition of natural ventilation, air flows out from two windows, and the average velocity distribution along the XY plane is shown in
Figure 8 (Velocity, flow and 3D distribution diagram). Obviously, the velocity in the container house is under the condition of high convective ventilation. It is anticipated that in case of outlet ventilation at the stable velocity state of the container house and under natural ventilation, the outlet ventilation is slightly higher than that at the inlet of the container house, wind velocity is too concentrated at air outlets of Model-5 and 8, thus high air volume is generated. While for Model-5–8, the surrounding part at the position of 1100 cm faces the air vortex from the wall. While the windows are under natural ventilation, simultaneous natural ventilation inflow and outflow situations are allowed, therefore, due to the fact that each window is the same, in the steady state, the inflow through windows 1 and 2 and the door should be exactly the same under natural ventilation. However, the small difference in inflow is attributable to the discrete calculation, which leads to asymmetric truncation error in the computational domain. In terms of flow distribution through the interior of the central container house along the YZ plane, it is observed by observing the relatively high wind velocity zone that in the vertical surface of the upper wind, the velocity difference in the container house is very large, and the flow quantity near the wall of the container house of Model-4 (
Figure 8d) is higher than that in the center.
Figure 8a shows that when the uniform distribution of the inflow velocity is 1.92 m/s and when the maximum value of inflow average velocity is 5.12 m/s, the maximum wind velocity value of the surface velocity distribution diagram is at the place of 610 cm,
Figure 8b shows that when the uniform distribution of the inflow velocity is 2.05 m/s and when the inflow average velocity is 4.52 m/s, the maximum wind velocity value of the surface velocity distribution diagram is at the place of 610 cm,
Figure 8c shows that when the uniform distribution of the inflow velocity is 1.49 m/s and when the inflow average velocity is 4.75 m/s, the maximum wind velocity value of the surface velocity distribution diagram is at the place of 610 cm,
Figure 8d shows that when the uniform distribution of the inflow velocity is 1.51 m/s and when the inflow average velocity is 5.275 m/s, the maximum wind velocity value of the surface velocity distribution diagram is at the place of 610 cm,
Figure 8e shows that when the uniform distribution of the inflow velocity is 1.63 m/s and when the inflow average velocity is 4.46 m/s, the maximum wind velocity value of the surface velocity distribution diagram is at the place of 824 cm,
Figure 8f shows that when the uniform distribution of the inflow velocity is 1.75 m/s and when the inflow average velocity is 4.84 m/s, the maximum wind velocity value of the surface velocity distribution diagram is at the place of 392 cm,
Figure 8g shows that when the uniform distribution of the inflow velocity is 1.64 m/s and when the inflow average velocity is 4.95 m/s, the maximum wind velocity value of the surface velocity distribution diagram is at the place of 808 cm,
Figure 8h shows that when the uniform distribution of the inflow velocity is 1.58 m/s and when the inflow average velocity is 4.57 m/s, the maximum wind velocity value of the surface velocity distribution diagram is at the place of 824 cm. It can be seen from
Figure 8 that even if the inflow velocity distribution is not uniform, there will be a uniform phenomenon in the flow distribution of each chamber, and the peak value of the outlet side of the curved surface with high flow velocity will be on the high side, which is a common phenomenon. When the inflow velocity distribution is uniform, with the velocity surface distribution in
Figure 8, the flow distribution in each chamber is more uneven compared with the time when the inflow velocity distribution is uniform, this is because the uneven phenomenon directly affected by the uneven distribution of air velocity leads to the uneven changes of wind velocity backflow and pressure, that is, uneven changes of backflow pressure cause the nonuniformity of flow, and the occurrence of the phenomenon of the flow with wind velocity pressure drop indicates that the uneven distribution of the inflow velocity causes the uneven distribution of wind velocity and flow in each chamber, and this uneven wind velocity phenomenon is more serious in the different air inlet configuration, which will also cause the difference in the heat taken away at each velocity outlet, this is consistent with the conclusion of Adamu [
7].
Figure 8e, H shows the highest outlet velocity peak value, while the inflow air velocity surface peak value is in low distribution, it will change the average velocity of air inflow, and there will be a change in the reduction of heat exchange amount. When the average velocity is less than 1.6 m/s in the figure, the decrease of heat exchange amount increases with the increase of the average velocity, and the magnitude of increase is very big, this is because of the average velocity distribution, and when the average value of the inflow velocity distributed is bigger and bigger, the slope of the velocity surface distribution expression is bigger, namely, the bigger the average velocity is, the more uneven the head-on wind velocity distribution is, and the amplitude of attenuation is more and more gentle, this is because with the increase of the average velocity, the air wind resistance becomes smaller and smaller.
5.2. Analysis of Natural Ventilation Contour Plot of the Container House
Figure 9 shows the air velocity as the profile of the result. Eddy behavior can be seen by operating the part of the inlet wind velocity distribution and from around the contour plot of the model of the indoor air velocity distribution with the reference wind velocity of 10 m/s, because the air layer is under natural ventilation, air viscosity and molecular attraction transfer to the air, the dense area in
Figure 9c Model 3 is at the place of the contour plot with the maximum velocity. But this velocity increases the airflow in the direction of the air belt.
Figure 9d as the opening and outlet of the container house, the distance configuration between the two is increased, but the opening of one more door is added between them, which significantly increases the wind velocity. Therefore, the potential wind velocity realized by the entrance of the more concentrated container house as shown in
Figure 9 is air ventilation, and the indoor air velocity decreases with the increase of the window distance.
Figure 9a shows the possibility of maximum natural ventilation in the middle of the air velocity distribution along the
X-axis of the container house. To study the impact on the air, the indoor partition is here, with only the simulation results of the container house, as shown in
Figure 9. The more uniform requirement for flow distribution of indoor air in both cases seems to be satisfied in part of most container houses. The establishment of the air velocity distribution along the
Z-axis in the middle is compared in
Figure 9.
Figure 9 shows the case of the symmetrical parts of the eight models of the airflow pattern. The airflow patterns of all models have different velocity directions, and there is the shape of a large vortex at the place of 400 cm of the contour plot in Model-1 (
Figure 9a), its position is in the center of the house, although not always the same. Similar phenomenon is found in Model-12 and Model-3, but the flow patterns between completely different cases are obtained.
The result of the high air exchange rate between the container house and the supplied air, and the mixed convection formed by the asymmetric open window from the configuration position of the windows and door in
Figure 9c Mode 3 affect the accelerated air supply, which extends all over the entire indoor ventilation ultimately because of the action of inlet air pressure, therefore, the positions of opening air supply and exhaust outlet are relatively important. In addition, the effect of recirculating flow occurs due to the deceleration development on the right side near the door.
Figure 9e,f,h show that the natural wind on the left has a relatively low flow rate on the area on the right side of the air supply and on the right side of the exhaust outlet. Therefore, because of the influence of the flow rate of the air supply, the contour plot shows that the rest are almost the same.
5.3. Analysis of Solar Radiation Thermal Field in the Container House
Four different temperature fields are mainly analyzed, namely 25°, 30°, 35° and 40°, as mentioned earlier, for the purposes of CFD simulating and predicting the air flow patterns in the container house. The main concern is the air flow in the container house to explore the dynamic state of wind flow under natural ventilation in order to obtain more information for the analysis of wind velocity affecting the thermal field. Because of the complexity of the flow field of the container house, the position of the entrance seems to affect the appropriate approach. Fresh air is provided to the container house, and is located in the front through three openings. The radiant heat is received from the surface of the container house, CFD boundary conditions are especially sensitive wind velocity flow, when the air flow and unreasonable pressure distribution combination model are found, zero pressure boundary conditions are defined as the computational domain of the side boundary and the upper boundary.
The optimal convective heat flux is the maximum value that the temperature difference between the air supplied and the air change rate reaches in the middle position 600 cm, and the air supply and discharge position is very important, meanwhile it affects the determination of radiation heat distribution. In this case, at the center line air supply position, the optimal placement position for exhaust is in Model 3 and Model 4. The reduction of convective heat flux makes the discharge be close to 0–200 cm. Air temperature reduces, it may changes in a curved-surface manner as the surrounding air temperature may increase, the surrounding surface temperature change is not conducive to natural ventilation, so as to reduce the temperature of the indoor air, which will be a negative impact on the temperature of the indoor air in ventilation. The following is a comparative difference diagram between eight models at different temperatures.
The container house Model-1
Figure 10 shows that the maximum indoor temperature is 50.7 °C due to the effect of solar radiation and ambient temperature 25 °C, while the temperature at the middle position 600 cm is 36 °C. The effect of natural ventilation can be clearly seen, the convection phenomenon in the container house can reduce the maximum temperature of the container house under the solar radiation effect by about 15 °C, while the lowest indoor temperature can be maintained at about 27 °C. The indoor ambient temperature rising to 30 °C will keep heat the surface of the container house due to solar radiation, plus the surrounding ambient temperature factor, so that the indoor temperature maintains at a stable state
Figure 10b. However, when the ambient temperature reaches 35 °C, the temperature field change will increase and be more intense in the central part, therefore, the mass flow rate of the air outlet is more closely related, the temperature gradient change is smaller, thus forming a three-dimensional curved surface distribution diagram of uneven temperature field distribution direction (
Figure 10c,d). Because the air outlet is located in the middle of the space and the inlet is at the asymmetric position, it increases the chance that the cold air in this area will take away the hot air from the inlet velocity. However, because of the configuration of the air inlet, the cold air at the air outlet in the central area can have full cyclic action in the space, therefore, when the effect of thermal energy (1000 w/m
2) emitted by the solar radiation of the container house exerts an influence, it is located in the central area, therefore, the mass flow rate of the air outlet is more closely related, the temperature gradient change is smaller, thus forming an uneven temperature field distribution.
Figure 11a of the container house Model-2 shows that the maximum indoor temperature is 44.9 °C due to the effect of solar radiation and ambient temperature of 25 °C. The temperature at the low temperature position of 613cm is 27 °C, so that the maximum temperature of the container house under the solar radiation effect can be reduced by about 18 °C. When the indoor ambient temperature rises to 30 °C, the solar radiation continues to heat the surface of the container house, plus the ambient temperature factor, the maximum indoor temperature can reach 51 °C
Figure 11b. However, when the ambient temperature reaches 35 °C and 40 °C, the change of the temperature field is relatively stable, while from 100 cm to the part located in the central area, there is a small temperature gradient change, 800–1000 cm forms an uneven temperature field distribution as shown in
Figure 11c,d. Since the air inlet and outlet configurations are both located in the middle of the space, the cold air in this area is too concentrated so as to affect the flow rate to take away the hot air on both sides of the space, so the mass flow rate at the air outlet is more related, and there is a relatively small temperature gradient change, which forms the condition to influence two lateral uneven temperature field distribution. When the ambient temperature reaches 40 °C, the indoor ambient temperature rises to 63 °C.
Figure 12 of the container house Model-3 shows that the maximum indoor temperature is 43.9 °C due to the effect of solar radiation and ambient temperature of 25 °C; the low temperature is 26 °C at the window position of 584 cm, the temperature difference is about 18 °C, when the indoor ambient temperature rises to 30 °C, the solar radiation continues to heat the surface of the container house, plus the ambient temperature factor, the maximum indoor temperature can reach 48.9 °C as shown in
Figure 12b. When the ambient temperature reaches 35 °C, the change of temperature field is similar to that at 30 °C, but the maximum indoor temperature reaches 52.8 °C, the highest temperature is located in the area of 900 cm, but when the environment temperature reaches 40 °C, uniform temperature field distribution is as shown in
Figure 12d, and indoor temperature falls below 60 °C, the temperature is lower than other temperature field. The model is located in the middle of the space due to the air inlet configuration, the asymmetric fluid flows on both sides of the container house at the outlet, so the cold air can effectively take away the radiant heat in the space. The mass flow rate of some air inlet in the central area has bigger high pressure wind velocity relationship, which results in a relatively uniform temperature field distribution.
In
Figure 13d of the container house Model-4, the model is located in the position between the two sides of the space due to the air inlet configuration. The inlet and outlet run from opposite directions, which leads to the wind velocity moving directly from the inlet to the outlet, so the cold air is unable to effectively take away excess radiant heat, forming an uneven temperature field distribution in the middle of the container house. The maximum indoor temperature is 58.6 °C due to the effect of solar radiation and ambient temperature of 40 °C, the indoor temperature is lower than other models, but the intermediate temperature is in the high environment, which affect the area where people often carry out activities.
Figure 14 of the container house Model-5 shows that the change in the air inlet position of the door results in that the maximum indoor temperature has reached 52 °C as shown in
Figure 14a due to the effect of solar radiation and ambient temperature of 25 °C, when compared with the positions of the aforementioned four doors in the middle. However, when the ambient temperature reaches 40 °C, the temperature of the temperature field changes to 67.47 °C, the temperature reaches the highest in the area of 900 cm, and there is also a larger temperature gradient change, forming an uneven temperature field distribution as shown in
Figure 14d. Since the position of the most important door inlet configuration changes to the right side of the space, the cold air on the left side of the area can not effectively take away solar radiation heat in the space. Therefore, when the ambient temperature reaches 40 °C, the indoor ambient temperature will rise to 67.7 °C.
Figure 15 of the container house Model-6 shows that the change in the air inlet position of window 4 affects the change of the whole temperature field, which results in that the maximum indoor temperature has reached 51.25 °C as shown in
Figure 15a due to the effect of solar radiation and ambient temperature of 25 °C. When the ambient temperature reaches 35 °C and the temperature field changes, the temperature field discharges air by shifting from the left side to the right side along window 4.
Figure 15c clearly shows that the temperature gradient belt shifts from the position of 270 cm with temperature of 36 °C to the position of 870 cm with temperature of 37 °C.
Figure 16 of the container house Model-7 shows that the maximum indoor temperature is 53.4 °C due to the effect of solar radiation and ambient temperature of 25 °C. With the change in the air inlet position of window 2, asymmetry of the window and and effect of the wind on the cross-flow velocity, the effect of natural ventilation can be clearly seen. The convective phenomenon in the container house makes the maximum temperature reduce by 4 °C when the container house under the effect of solar radiation and the ambient temperature of 40 °C in
Figure 14d of Model-6 are compared. However, the effect of the window opening size and Models 1–4 can not effectively take away radiant heat from the indoor air flow in the central area, so the air outlet and mass flow rate are more related, and there is a smaller temperature gradient change, forming more uniform temperature field distribution in the middle.
Figure 17 of the container house Model-8 shows that as the air outlet configuration is located on the right side of the space, resulting in the problem of excessive concentration of cold air in the entry area. When the ambient temperature is 40 °C, the highest indoor temperature in the eight models reaches as high as 78.04 °C, so the air inlet configuration influence factor is very high, the cold air can fully circulate in the space, the air inlet and outlet of natural ventilation are very important influence factors, and the asymmetric opening produces cross air flow, which can form a uniform distribution of temperature field. And the eddy current also has considerable effect on the entire indoor air flow of the container house, so the effect of natural ventilation is obvious.