Assignment 2 - MODELLING IN ECOTECT

The model is made of three zones of 50 m², which all have windows on the south facing façade. The used weather data is those of Trondheim, which position is 61,7° latitude, and 10,2° longitude. First, we will analyse the solar radiation which is soaked up by the 4 facades and by the floor. Then, we will analyse the average hourly and daily solar exposure of a shaded South facing window. Finally, we will talk about the daylight factor distribution in the room adjacent to the window with a shading device, and compare it to the daylight factor distribution in the room adjacent to a window without any shading device.

Analysis of solar radiation

The total incident solar radiation includes the direct and diffuse solar radiation falling on objects (facades or floors).

Incident solar radiation on the outdoor facades

Daily diffuse radiation{*}: East, South and West facing facades always absorb the same amount of daily diffuse radiation, while a North facing façade absorbs about 5 times less diffuse radiation. Summer is the period where the diffuse radiation is the highest: on average, 1179 Wh/m²* *_are soaked up by a South, East or West façade per day. The diffuse radiation is a bit lower in spring, with on average 831 Wh/m² absorbed by a S/E/W facing façade per day. It reduces even more in autumn, with average daily values of 303 Wh/m², and reaches the lowest point during the winter days, with only 91 Wh/m²._*

Daily direct radiation: East and South facing facades soak up the same amount of daily direct radiation. West facing facades absorb about 1,5 times less direct radiation than those two other oriented facades. Of course, there isn't any direct radiation going to the North facing facade. Here again, summer is the period where the direct radiation is the highest: on average 1640 Wh/m² are soaked up by a South or an East facing façade. This value reduces a bit during spring, where only 1355 Wh/m² are absorbed. Then, it reduces until 482 Wh/m² on average per day during the autumn, and reaches the lowest point during the winter days, with only 184 Wh/m².
We can notice that a façade absorbs more direct radiation than diffuse radiation, but the diffuse radiation isn't negligible at all, as it represents about 38% of the daily solar radiation.

Incident solar radiation on the floor

During the summer, the incident solar radiation entering the room is very high: it can reach 1920 Wh. But the area on the floor which soaks up that energy is very small: only 6 m² near to each window. The reason of that is that the sun follows a very high path at that time of the year. During the spring, the incident solar radiation can go until 1360 Wh, so it is a bit lower than in summer. At that time, the sun follows a lower path, so the area of the floor receiving solar radiation is larger than those in summer: it is about 8 m² per window.
This is very positive: During the summer, we want to protect the buildings from the warm solar radiations, to prevent overheating. So it is a good point that not many incident solar radiations can enter the room. As the lighting of summer days is very high, avoiding the solar radiation to enter a room won't make a dark atmosphere. On the contrary, it will give the room a more constant light and protects the inhabitants from the dazzling sun.
During the autumn, the sun path is a little bit lower than during the spring, even it remains quite similar. Though, we can see that difference in the area of incident solar radiation entering the room: 12 m² per window. We can also clearly see that difference in the energy of the solar radiations. It can only go up until 420 Wh during autumn days, as it could grow until 1360 during the spring days. In the winter, this energy is even lower. It can go to maximum 120Wh at some points. But in compensation, the area soaking incident solar radiation through a window is the largest: it is of about 20 m².
These sun radiations go also more deeply in the room, and offer then a better lighting during the darker winter days. Indeed, in winter, we want to catch as much as light and heat as possible. As the energy of the winter solar radiations isn't very high, it isn't disturbing to have a lot of solar radiations entering the room.

Analysis of solar exposure of a shaded window

Average hourly solar exposure

We have designed a shading device which blocks direct sun penetration between the 1^st of May and the 30^th of September.




Figure 11: the model with a shading device over a window of a south facing facade

Single day solar exposure

Figure 12: Solar exposure for the brightest sunny day (9^th of July)
The shaded window is mainly shaded at 100% during the brightest sunny day, on the 9th of July. Only between 10 am and 1 pm, the shading is of 90%.
The incident radiation is composed of direct and diffuse radiations. While hitting a window, a part of the incident radiation will be transmitted, another part will be reflected, and the last part will be absorbed.
During the brightest sunny day, the hourly solar exposure of direct rays is particularly high: it rises from 0 to 840 W/m² between 2 am and 7.30. Then, between 7.30 and 5 pm, the solar exposure of direct rays remains quite stable and very high (between 840 and 934 W/m², with a maximum reached at 1 pm.), before getting down again between 5 pm and 10 pm. The hourly exposure of diffuse radiation is much lower than those of direct radiation: it rises from 0 to 80 W/m² between 2 am and 12, before getting down again between 12 and 10 pm. But still, there are some diffuse rays during the whole day. This is not the case of the incident radiation: the transmitted and absorbed rays are only significant between 9 am and 3 pm. And there is no significant reflected radiation at all. By adding up those three types of radiation, we find that the incident rays can send a maximum of 91 W/m² at 12 o'clock.

Figure 13: Solar exposure for the most overcast day (15^th of January)

During the most overcast day, on the 15th of January, the window with a shading device is not shaded at each moment of the day. The reason is that we designed a shading device which would totally block the direct sun penetration between the 1^st of May and the 30^th of September. So, on the 15th of January, nearly the whole area of the window soaks up sun radiation between 10 am and 2 pm. Then the shading of the window is only of about 30%, with non shading peaks at 10 am and 2 pm, where the shading goes down to 10%. Otherwise, from 3 pm to 9 am, the window is totally shaded.
During that same overcasted day, the amount of direct solar rays is equal to zero, and there are very little diffuse solar rays: around 24 W/m² between 11 am and 1 pm. The amount of incident radiation is insignificant.

Average daily solar exposure

Figure 14: average daily solar exposure of the shaded window

w By calculating the average daily incident solar radiation, we can see that February and March are the months with the highest solar radiation passing through the window. Indeed, between 1 pm and 2 pm, the solar radiations can reach 270 W/m². From February to April, and from September to October, the incident solar radiation is higher than 180 W/m² between 11 am and 3 pm. Globally, the period of the day where the incident solar radiations are the highest (more than 120 W/m²) is between 10 am and 4 pm during spring and autumn. During the winter, it is only between 12 and 2 pm, and during the summer, there is no solar radiation with a higher energy than 120 W/m².
Indeed, the shading device which prevents the insight of direct sun radiations during that period is responsible of a maximum power of only 120 W/m2 between 12 and 2 pm. The solar radiations are the highest in spring and autumn because the shading devise hasn't been calculated to block the direct solar rays during those periods. It lets the solar rays entering the room. Moreover, during those months, the sun path is lowering, so there is more incident solar insight passing through the window.

Analysis of the daylight factor distribution in the room adjacent to the window with shading device

The daylight analysis has been calculated with the following conditions:

• sky luminance: 2000 lux (peculiar to Trondheim weather)
• sky luminance distribution model : overcast sky conditions
• average window cleanliness

We can see that, in the case of a window protected by a shading device, the daylight factor in the room is very low: it is mainly of 0,6 to 1,6%, and only 2 m² have a daylight factor of 2,6%.
If the window is not protected by a shadow device, the daylight factor will increase: Indeed, 7 m² have now a daylight factor of more than 2,8%, of which 4 m² have a daylight factor which is higher than 4,8%, and 1 m² has a daylight factor which is higher than 8,8%.
So, by putting a shading device, it reduces overheating and dazzle, but this is offset by a reduction of the day light factor inside the room.



As we have seen, there is a high solar radiation on South and East facing facades during the summer and spring. So we can understand the need of designing a shading device which would block direct sun radiations during that period of the year. This will prevent the building from overheating and will protect its users of the dazzling sun. By thinking about adapted solar protections, we can reduce our need in cooling the building during the summer. But it's important that those protections do not prevent the building from reaching its first aim during the winter: absorbing as much solar heat and sunlight as possible. This is why the shading panel is very efficient: It protects the building from high solar radiations during the summer, and it lets the solar radiations entering the building during the winter, when the sun path is lower.