{"id":1215,"date":"2016-09-21T17:17:59","date_gmt":"2016-09-21T15:17:59","guid":{"rendered":"http:\/\/www.htflux.com\/en\/?page_id=1215"},"modified":"2016-10-12T17:20:07","modified_gmt":"2016-10-12T15:20:07","slug":"psi-g-slab-on-grade","status":"publish","type":"page","link":"https:\/\/www.htflux.com\/en\/documentation\/psi-g-ground-contact-calculations\/psi-g-slab-on-grade\/","title":{"rendered":"\u03a8g – slab on grade (ISO)"},"content":{"rendered":"

\u03a8g-calculation with slab on or near the grade level according to ISO 10211 and ISO 13370<\/h1>\n

This method is used for slabs that are located on or near the surface level of the ground. Generally this method should be used when the energy loss of the detail is described by using a single U-value for the wall and the Ug<\/sub> value for the floor. With this version HTflux will do the calculation of Ug<\/sub> according to the method described in ISO 13370. This value should match with the one you are using for your building energy performance. If for some reason you want to preset a given Ug<\/sub> value, instead you can use the manual input method.
\nThe \u03a8g value calculated with this method will compensate for the wall’s contact to the ground, the actual slab edge heat flux and the heat flux through the floor slab itself.<\/p>\n

The \u03a8g value will be calculated by measuring the heat-flux of the model and subtracting the heat-fluxes described by U-values afterwards:\"psig-formula-slab-on-grade\"
\nThe calculation is therefore very similar to other \u03a8 value calculations. The important difference is that you will have to use the Ug<\/sub> value for the floor slab heat flux and not the U-value of the floor slab itself. This adapted value is based on the U-value of the slab, but also contains the thermal resistance of the ground itself. Based on the slab dimension and U value of the floor an effective thickness for the ground will be calculated. Since the Ug<\/sub> value of is also considering the insulating effect of the ground below, it will always be lower than the U value of the floor slab itself. (more information on this can be found in the\u00a0 standard ISO 13370.)
\nSince the \u03a8g calculation will also consider the difference between the actual floor slab heat flux and the heat flux as described by Ug<\/sub>, it is important to perform the simulation using the correct width of the model (B’\/2).\u00a0 It will only be valid for this width. However for larger floor slabs the ISO standard defines a limit: if you perform the calculation for a model with a characteristic floor slab dimension<\/a> of 8m (=4m model width), the resulting \u03a8g can be used for any slabs larger than this also.<\/p>\n

Detailed work-flow<\/h2>\n

1) calculate the characteristic floor slab dimension.<\/h3>\n

see characteristic floor slab dimension<\/a> for reference.<\/p>\n

2) draw the model of the slab edge<\/h3>\n

Draw a model of your slab edge width that equals B’\/2. Make sure to use the appropriate dimensional reference<\/a>.
\nIf B’ exceeds 8m you should always use a width of 4m for the model. To the top side you should draw at least 1m of the wall measured from the top of the floor or ground-level (whatever is higher) to comply with the rules in ISO 10211. You might have additional elements in your wall in this area, in this case you should draw up to 1m of the homogeneous wall above this region.<\/p>\n

3) add soil block<\/h3>\n

Add a block of soil with a width and height of 2,5 x B’ to your model. If this value exceeds 20m use 20m instead.
\nUse the correct material for the soil block. The standard ISO 13370 recommends to use<\/p>\n