In this tutorial we're going to look at how we define glazing in the zebra model. Glazing can be a bit more complicated than other aspects because we have a source of heat loss through the glazing and the framing material, and also because we have solar gains through the windows and we need to capture inputs that reflect all these aspects.

The first inputs you can see on the Glazing sheet are to set the U-Value and the G-Value of the glass. The U-value which reflects the thermal losses we'll have through the glass and the G value which reflects the amount of sunlight that will get through the glass. We've given some default values beside the inputs, so for you can use typical values for double-glazing, for example

After you've entered those two you need to define your glazing sets. A glazing set can either be a single window or it can be a set of window with similar properties. Generally if a group of windows is the same in terms of their orientation, framing and their shading level you might group them into one set to save time with inputs. For each glazing set we start by giving it a name, then we indicate which wall door or roof element the glazing is inside. This list will be populated from the values we've input already into the walls and doors sheet and also into the roof sheet. We can assign a glazing element either to a roof element or to a wall/door element.

The next four entries are the entries which reflect the geometry of the window. We start with the glazing area which is the area of the glass itself, then we have the frame area (the area of the frame material), the perimeter length which is the area of the boundary around the window frame, and then the length of the glass frame-divider and this is the total length of the interface between the frame and the glass. The reason we need these values is because the glazing area is where we will use the U value for glazing thermal losses and it will also be used to calculate how much sunlight will come through the frame. The frame area is where we will use a typical U-value for framing material for thermal losses, and the perimeter and the length of the glass-frame divider are needed because we have thermal bridges both around the perimeter of the window, and at the interface between the glass and the framing material. With these four values the model has what it needs to calculate total U-value for the window as a whole including all aspects.

After these four inputs we have the permanent shading which is shading from hills or surrounding buildings, and then temporary shading for heating and cooling. This second pair of inputs is things like roller blinds we might have to offer shading in the summer but roll them up in the winter.

Lastly, we have the number of the window sets.

Most of these inputs are fairly simple. These four geometric properties are the most complicated ones, but we have two tools here which help us to determine these values. You can access these by clicking on the star icons, which will take you to the calculators sheet. In this sheet you will have additional tools to calculate these four geometric properties, which you must then copy and paste (remember to use paste->special->values) back into the row in the glazing sheet.

The first general tool allows you to define the geometry of a rectangular window, by specifying the width, height, and thickness of the frame and any dividers. The four geometric properties will then be calculated from this. This is useful if you have some basic information about the design of your window. The second simplified tool, is useful if you only have an idea of how the windows might be. This gives you a list of images, and you can choose the one which looks the most similar in terms of glazing/frame ratio. You then enter the total hole area of your window set, and the four geometric properties will be generated based on your selection.

If we increase the complexity level we will find a number of additional inputs to the glazing tab. These are values that would have been assumed at lower complexity levels. These inputs include the assumed U value for the frame, the assumed losses around the thermal bridge at the perimeter of the window, the assumed losses at the thermal bridges at the interfaces between the glass and the framing, a maintenance factor which basically reflects how clean the window is, and a factor which accounts for the sun rays not being perpendicular for the glass. You can if you wish amend some of these values but often these defaults are fine.

As well as those additional inputs you'll see a lot more detail on the calculations that have been performed at higher complexity levels.