Simulation data

The simulation data object is used to define the startup procedure and to change solver parameters for all types of simulations as well as the possibility to request parallel simulations from here (more about this below).

Field descriptions, etc:

Startup

Type {periodic, dynamic}

Days of dynamic startup The number of days that are simulated as warm-up for dynamic simulations.

The startup or warm-up phase specifies how the building should be conditioned before the actual, measured, simulation takes place. A periodic startup phase means that the first day is simulated a number of times until the system has stabilized to a steady periodic situation. A dynamic startup phase means that a selected number of days are simulated before the proper simulation starts. The latter is default from v. 4.7. For the common case when the simulation is started at the beginning of the year (and weather file), the start-up weather is taken from the end of the weather file, i.e. there will be a jump in weather conditions at new year’s eve.

How long the startup phase should be depends on how thermally heavy the building is and on its contact to the ground. The heavier the building, the longer startup phase is required. Approximately two weeks should be enough for most buildings. Large semi-heated garages, boreholes and thick concrete structures are likely to create situations where longer start-up is required.

Advanced

Integration parameters can be selected in this dialog.

Field descriptions, etc:

Tolerance This number determines how accurately equations are to be solved.

The tolerance given is the degree of accuracy reached in the calculated variables. It is absolute for small quantities (normally < 1) and relative for larger quantities (normally >1). Relaxing the tolerance should normally result in a faster simulation. However, if the tolerance is relaxed too much, the solver will have greater trouble to find a solution at all and this in turn costs execution time and causes poorer stability.

Maximal timestep The largest time step to be taken (h)

For a dynamic simulation, the solver will select the time step up to the Maximal timestep specified. Allowing very long timesteps may create stability problems for the solver that in turn cost time to resolve.

Maximum number of periods Maximum number of periods in a periodic simulation (also for periodic start-up simulation).

Tolerance for periodicity Tolerance for periodicity in a periodic simulation.

In the case of a periodic simulation, the number of periods can be limited and a tolerance chosen for the relative changes required from day to day for the simulation to be considered periodic.

Time step for output If greater than zero, recorded times in output files will have this time step (h).

If a Time step for output has been given, result files will be interpolated to have a fixed time step, enabling for example Excel comparison of results between different runs. For local variables the nearest value before the time point is used instead. Simulation time step is still variable.

If a Time step for output is zero (or left blank), the time step of output will be same as solver time steps, i.e. not equidistant in time.

Note: This result files will contain instantaneous values of measured variables, i.e. not integrated values over the given step. In order to obtain average, e.g. hourly, results use Table tab of result diagrams instead.

Time-split parallelization When checked, dynamic simulations are divided into multiple parts that are executed in parallel.

The number of separate simulation processes that are started is given in Options menu > Preferences > General > Simulation. It is often beneficial to allow a number of processes that somewhat exceeds the number of floating point processors on the computer.

This type of parallelization utilizes the fact that most buildings have a rather short "memory" or time constant. Each of the separate simulations are started with the given number of Days of dynamic startup (from the Startup tab). For buildings with long time constants, the start-up period should be selected to be long, and the benefit of this type of parallelization will diminish.