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How to use the U-value and R-value calculator?

1. Select element

Select a building element from the list to determine the external and internal surface resistances automatically. The default design values given are based on EN ISO 6946:2007. Surface resistances can also be modified manually and defined by the user. Surface resistances apply to surfaces which are contact with air and have an effect on the U-value of the building element. They depend on the direction of heat flow, surface temperature, surface emissivity and wind speed. Surface temperatures, emissivities and wind speed belonging to the default design values are given in EN ISO 6946:2007.

2. Characteristics of a layer

2.1 Select material

Select a material from the drop-down list for the first layer. The selected material will give the thermal conductivity value automatically but it can be modified freely. If you want to use a material which is not on the list, select the option user defined and type in the name of the material. In this case the thermal conductivity value needs to be added by the user.

There are three groups:

- General materials

- Thermal insulation

Basic building insulation materials. The thermal conductivity values are typical values and can be used to carry out a generic calculation. To determine the exact value of a building insulation material, seek information from the manufacturer. It is important to use the design value determined from the declared value, which is based on the characteristic 90/90 value. To get the design value, the declared value might need to be modified in accordance with EN ISO 10456 considering ageing, moisture and temperature conversion factors.

- Air layers

The thermal resistance of air layers depends on the direction of heat flow, the thickness, the emissivity of adjacent surfaces and the rate of ventilation

2.2 Thickness

Give the thickness of the layer in millimetres. When the thickness is added, the layer appears in the top corner.

2.3 Colour

The selected material gives a default colour to the layer. It can be modified using the colour palette from the drop-down next to the thermal conductivity box.

2.4 Bridged layer

Tick the box if the layer is bridged. The thermal bridge repeats throughout the whole building element with a given constant spacing. When the box is ticked, another row pops up, where the percentage and the material of the thermal bridge with its thermal conductivity can be given. The percentage (%) can be calculated as A / B (see below), where A is the width of the thermal bridge and B is the distance between the repeating thermal bridges.

Explanation of a bridged layer:

2.5 Corrections

Tick the box if correction for a layer is needed. When the box is ticked, another rows pop up, where the correction for fasteners and air voids can be given.

Correction for fasteners:

If metal fasteners penetrates the insulation, correction is necessary. The thermal conductivity and the sectional area of the fastener, the length of the fastener that penetrates the insulation, and the number of fasteners per square metre need to be given.

Correction for air voids:

Air spaces can be formed in the insulation layer and a correction might need to be done. There are three different levels which are described in EN ISO 6946 in detail. Level 0 can be chosen if there is no air voids that have significant effect on thermal transmittance.

3. Insert a new layer

Press this button to insert a new layer below an existing layer. There is no limit on the number of the layers.

4. Delete a layer

Press this button to delete a layer.

5. Restart

Press the restart button to start a new calculation.

6. Examples

From this drop-down list different examples can be selected

7. U-value

The U-value of the building element is recalculated and shown immediately and automatically when one parameter changes.

8. Print as pdf

Click this button to save the construction as PDF.

Also the construction can be saved locally as a text document with extension .ofz, which can be open again by clicking the button ‘Open file’

9. Ground floor U-value

If the options 'Slab-on-ground', 'Suspended ground floor' or 'Basement floor' are selected from the 'Select element' drop down menu, the entries for the ground floor parameters appear and the U value for the whole floor is calculated according with EN ISO 13370.

If the option 'Basement wall' is selected, the new entries appear and the U value is calculated according to EN ISO 13370. The floor slab resistance will be necessary, which can be entered directly in the corresponding entry or calculated previously by selecting the option 'Basement floor' (the data is transferred between these two options)