4.3.5. Expression variables <br>

### 4.3.5. Expression variables

Expression variables are used for project parameterization. The parameterization consists in using of variables instead of numbers during determining of dimensions or other data in project. Possibility of parameterization is particularly useful for auditors, who perform analysis of interdependences of annual energy demand on building parameters. It enables also quick performing of many variants of object, which differ from each other by some numerical parameters described in tables and in edition fields of project data by means of these variables.

In table of „Expression variables” the User can enter unlimited number of variables determining for example heater depth, dimension of windows in light.

Each variable is identified in project by its name, which is entered in column „Name”. Name of a variable must begin with a letter or underlined characters and can consists of letters, digits and underlined characters. It can not contain spaces. Big and small letters are not discriminated.

In column „Expression” the User should enter an expression defining the variable value – directly as numerical value (in this example for instance hst = 3.0, tc = 0.5) or as an arithmetic expression, for instance 0.5*0.5.

! It is not allowed to use other declared variables in expressions describing variables.

A variable can be described by means of short description In field „Comment”, what enables quick overview, which quantity is represented by specific variable.

There are some default expression variables in the program, such as „Default storeys height”, „Default ceiling thickness”, Proportion of dimension in axes to dimension in light – for horizontal partitions” and „Proportion of outer dimension to dimension in axes – for vertical partitions”. Expressions describing proportion of dimension in axes to dimension in light and outer dimension to dimension in axes are used as multipliers by selection of program function „Recalculate partitions dimensions”. Graphical partitions have completed data concerning all dimensions of partitions, so the function „Recalculate partitions dimensions” is not useful for project loaded from Instal-therm program.

Using variables it is very easy to parameterize all calculations, replacing with them for example dimensions of designed windows, thickness and heat transfer coefficients for applied insulations. For example during edition of compartments instead of entering the numerical value of surface for windows it is possible to use names of variables. It will enable in future calculating of building for various windows dimensions. In this way it is very easy to perform analysis of heat losses or/and annual energy demand depending on individual building parameters.

Very useful can be also declaring of variables, by means of which it can be possible to declare minimal and maximal heater depth, what would enable quick selection of one-plate or two-plate radiators or only two-plate radiators.

! Variables which are defined this way concern current project and for this reason they are called local variables. They are invisible in other projects.

Expression variables can be also entered in any edition window of project data by means of key combination Ctrl+Alt+Insert. The User can find more information to this in chapter 6.