Glazing g-value

Hi Steve,

The most important point to be aware of is that different parts of the Glazing data menu are used depending on what calculations/simulations you are looking to run.

While a G value is displayed, it cannot actually be changed manually as it is calculated according to the layers of glazing that have been set up, as below.  Please note that the layer data is used by Simulations only.

On the other hand if you are looking to run Design Database calculations then the information in the top right corner of the Glazing data menu is used. Your glazing manufacturer will be able to provide you with this data.

A more thorough explanation of the above can be found here.

Hi Steve,

The most important point to be aware of is that different parts of the Glazing data menu are used depending on what calculations/simulations you are looking to run.

While a G value is displayed, it cannot actually be changed manually as it is calculated according to the layers of glazing that have been set up, as below.  Please note that the layer data is used by Simulations only.

On the other hand if you are looking to run Design Database calculations then the information in the top right corner of the Glazing data menu is used. Your glazing manufacturer will be able to provide you with this data.

A more thorough explanation of the above can be found here.

Thanks Shane - I have looked at the more thorough explanation via the link. However, as I understand from this, changing the g value using the layer data will not have any effect on a Part L analysis. I tried altering the layer data here and this seems to be true.

My question is – How can I change the g value for a Part L calc when it seems that the only inputs available are in the red and green sections?

The reason I’m asking this question is that when trying to reduce the solar gain shown in Criterion 3 of a Part L BRUKL report one way of doing this (apart from reducing the area of glazing or specifying exterior solar shading) would be through low g values. When producing a SBEM design stage report, specific glazing details are often not known, but if I can recommend to a client that they use glazing with a u value of X and g value of Y to reduce solar gains, therefore reducing air con usage and in turn reducing CO2 emissions, this would help my clients.

Is there a way of entering the g value using the boxes available to me under a Part L analysis?

Hi Steve,

Yes that is correct, the Part L calculation will not use the Layer Data. There is no way of entering such a G-value I'm afraid - the data fields that are used by the Part L calculation in Hevacomp are solely determined by the inputs required by SBEM, and this is not one of them.

I would recommend having a look at the Limiting Solar Gains section of the NCM Modelling Guide as offers advice such as how to achieve certain G-Values, example below. Your glazing manufacturer should also be able to provide such information.