Simulation

Simulation settings are the key controls that define how a building model behaves during an energy simulation. In Better Building, these settings allow you to fine-tune how the simulation runs, ensuring your results are both accurate and relevant to your design.

Set EnergyPlus Version

Speckel uses EnergyPlus™ (versions 9.5.0+ and 22.2) to power all building simulations. EnergyPlus™ is a robust, open-source engine that’s been trusted since 1997 and continues to evolve with new features and improvements.

To select an Energy version, navigate to 'Modelling', select 'Simulation', and locate the 'EnergyPlus Version' dropdown. We recommend EnergyPlus™ Version 22.2 is used in all cases.

Customise Convergence Settings

Convergence settings help EnergyPlus™ decide when your model has reached a stable state before kicking off the main simulation. They’re there to make sure your results aren’t based on unrealistic or unstable conditions.

You probably won’t need to adjust these unless you’re troubleshooting a model. Custom convergence settings give access to advanced EnergyPlus™ controls that can affect both accuracy and runtime. If you’re not sure, it’s best to leave them off.

Loads Convergence Tolerance Value

Loads Convergence Tolerance Value represents the maximum allowable difference between consecutive days' maximum heating and cooling loads for individual zones during the warm-up period. This parameter is essential for determining when the simulation has achieved a steady-state condition, ensuring accuracy by indicating when load fluctuations have stabilized within acceptable limits.

Temperature Convergence Tolerance Value

Temperature Convergence Tolerance Value refers to the maximum allowable difference between consecutive days' maximum and minimum zone air temperatures during the warm-up period. This parameter helps determine when the simulation has reached a steady-state condition, ensuring accurate results by indicating when temperature fluctuations have stabilised within acceptable limits.

Maximum Warmup Days

Warm-up days ensure simulation accuracy by stabilising building thermal systems before data collection. This process addresses inaccuracies that could affect HVAC calculations. Convergence is checked by tracking parameters like zone air temperature and heating/cooling loads. Simulation begins when these parameters stay within tolerance for consecutive days, indicating steady-state conditions. Errors can arise in shorter simulations if warm-up isn't properly achieved, impacting energy and economic outcomes.

Adjust Step Size

Step Size sets how often EnergyPlus™ runs its calculations during a simulation. It’s also called the "timestep" and defines the time interval between updates in your model.

You choose the number of timesteps per hour, which determines the size of each step. For example, setting 4 timesteps per hour gives you a 15-minute interval (60 ÷ 4). That means the simulation updates every 15 minutes of simulated time. Smaller step sizes can improve accuracy but may increase simulation time.

Set a Step Size by navigating to 'Modelling' under 'Simulation' and locate the 'Step Size' slider, and set 1, 2,3 or 4 timesteps.

Adjust Solar Distribution

Solar Distribution refers to the method used to calculate the distribution of solar gains onto and inside a zone. The solar distribution method can significantly impact the results of an energy simulation.

The following Solar Distribution settings are available.

Minimal Shadowing

All beam solar that strikes a window is added to the zone as diffuse (scattered) solar, which is uniformly distributed across all surfaces in the zone. There is no attempt to model the impact of shadows on the distribution of solar gains.

Full Exterior

The model keeps track of shadowing on the exterior of the building, but once the sunlight enters a zone through a window, it is treated as diffuse solar and is uniformly distributed across all surfaces in the zone.

Full Exterior With Reflections

These options provide the most detailed modelling of solar distribution. They account for both exterior shadowing and the impact of interior furniture and partitions on the distribution of solar gains. With the "WithReflections" option, the model also accounts for reflections from interior surfaces.

To adjust Solar Distribution, navigate to 'Modelling', select 'Simulation', and locate the 'Solar Distribution' dropdown. Then select the desired Solar Distribution method.

Set Building Rotation

Building Rotation is nominated as the degrees from true North, e.g. 0° is no alteration, 90° where your building is rotated clockwise 90°.

Set Building Rotation by navigating to 'Modelling' under 'Simulation'. Then, nominate the degrees from true North and hit 'Save'.