Lighting and Solar exposure analysis

There are very interesting things to be analysed, when a classroom is the subject.

First of all, the important thing is having enough natural light reaching everywhere.


In Bulgaria (my country) the  regulations require to have at least 300 lux measured in the dark corners of the room, at 70cm distance from the floor (the regular school desk high is 60-70cm depending on the age of the students).

So, in Ecotect, I made a model of a classroom (7,5 x 11meters) facing east with 3 regular windows with 4,4m2 each (or 13,2m2)  and a desk at the darker corner of the room which is 70cm from the floor.

the model

I measured the light at 10am in the morning, on 21st of december (when the light conditions are worst). From the analysis I can see that the light at the corners is not enough for the requirements. And as a result, I need bigger windows

The windows here have a surface of 5,5m2  (or 16,5m2 for all of them). As a result, the lux measured at the darker corner of the desk is close to 370lux, so now I can say that the result is good and it can meet the regulations in Bulgaria.


Lets start again with a geometry made in Ecotect. I will use the same classroom, for which I already know how big windows should be. But to make it more real, I will have to use a corridor zone behind the classroom, and 2 more classrooms surrounding my zone which I will explore. The idea is having more options and things to change.

Firstly, lets see how the room is performing if there are 30 kids (65W each-typing) inside all of the classrooms, but the materials are standart (single brick walls etc.). The operation hours are set to weekdays only between 7:00 and 18:00. The air change rate for the classrooms are 0,5 and for the corridor is set to 2. Natural ventilation system.

winter period

summer period

We can see, that during the time of occupancy the temperatures inside the classroom are almost equal and are close to the lower normal conditions (18-25 degrees) even though the temperature outside is very different. That is because of the high U-value of the standard materials of Ecotect, which allows the temperature losses during the time when there is nobody in the classrooms. However, 30 kids typing (65W) are enough to heat up the room close to 18 degrees. However, this is not enough for a classroom and other problem is that the first 1 hour is very cold through the year and it takes time for having close to normal conditions inside.

In Bulgaria, the National standard requires different (far lower) U values for the materials used in constructions. The requirements are: walls inside-not more than 0,5; doors/windows-not more than 2; walls (exterior) – not more than 0,35; roofs, slabs etc (exterior) – not more than 0, 25; etc.

winter period-BG National standard materials

summer period-BG National standard materials

We can see, that now, using the Bulgarian National standard materials for all seasons we have comfortable temperature inside the classroom that does not depend on the occupancy so much. Also, there is no more 1 hour uncomfortable temperature period before having normal temperatures inside like in the previous graph. On top of that, we can see that during the summer period, there is no need for occupancy, the temperatures are constantly between 22-24 degrees, doesn`t matter of how many people are there.

But can we spend less money from somewhere? What about having cheap windows with higher U-value (single glazed)

winter period-BG materials-cheap windows

summer period-BG materials-cheap windows

During the summer period, we can see that with cheaper windows there is almost no difference, but during the winter period, the classroom is almost cold, even when there is occupancy inside. And 18 degrees are not enough for sitting kids. So, good windows are must.

It is interesting to see how things are different during the winter (the worst case), if there are no kids in the other classrooms but only in the classroom where we are making the thermal analysis.

winter period-no kids in the other classrooms


Low U-value walls, roofs, windows, etc worth investing in climate conditions like in Bulgaria.

The occupancy does not make a big difference when a good materials were used.

The cheap windows are not good enough because of the cold winter. During the summer, there is no difference. So maybe for hot climates, expensive windows are not the key, but a good isolation on the roof, walls, etc.

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