Calendar

Calendar Settings allow you to control when and how your building simulation runs, helping you model realistic seasonal conditions and peak loads.

Starting Day

Set the specific day your simulation begins. This can affect how building performance is calculated throughout the year, particularly for heating, cooling and lighting demands. It’s especially relevant for simulations that don’t span a full 12 months, where seasonal variations can skew results depending on the start date.

Daylight Savings

Enable or disable Daylight Savings to better align simulation time with real-world schedules. This setting affects internal building operations like lighting, occupancy and HVAC, as well as the accuracy of daylight simulation outputs when using Radiance.

Summer Design Days

Add specific Summer Design Days to represent peak summer conditions for HVAC sizing. These days help simulate the worst-case cooling load scenarios. If no custom days are added, the model defaults to the standard summer design day in the site’s EnergyPlus Weather File (EPW).

You can also fully customise Summer and Winter Design Days to match your local climate conditions or specific design targets.

Month and Day

Select the specific calendar date that represents the peak summer or winter condition. This helps simulate the most extreme thermal loads your building might face. The chosen date should align with typical design conditions in your region, such as the hottest day in January or the coldest in July.

Max. Drybulb Temperature

This is the highest outdoor air temperature expected on the selected design day. It represents the worst-case thermal condition for cooling (summer) or heating (winter) system sizing. Accurate inputs here are essential for ensuring that your HVAC systems can handle peak loads.

Daily Temperature Range

Enter the difference between the highest and lowest temperatures for the design day. A larger range often indicates clear skies and strong solar gain, while a smaller range may suggest cloudy conditions or high humidity. This input helps model how indoor temperatures may fluctuate in response to outdoor swings.

Humidity Condition Type

Choose how humidity is defined for your design day. This setting affects how EnergyPlus calculates the moisture content of the air and its impact on cooling loads. You can select from the following options:

Dewpoint

The temperature at which air becomes fully saturated and condensation begins. Useful for evaluating comfort and condensation risk, particularly in humid climates.

Enthalpy

Represents the total heat content of the air, including both sensible and latent heat. This method is useful for more advanced simulations where both heat and moisture are key concerns.

Humidity Ratio

Expresses the mass of water vapour per unit mass of dry air. It's a direct measure of air moisture and is commonly used in psychrometric calculations.

Wetbulb

Indicates the lowest temperature air can reach through evaporation. This is helpful for estimating cooling loads in systems that rely on evaporative cooling.

Wetbulb / Dewpoint at Max. Drybulb °C

Enter the humidity value that corresponds to the maximum drybulb temperature on your selected design day. This field reflects the air’s moisture content during peak conditions and is essential for calculating total cooling loads, especially where humidity is a major factor. The input should align with the Humidity Condition Type selected above.

Solar Model Indicator

This setting defines how solar radiation is modelled for the design day. Each option calculates solar heat gain differently based on atmospheric clarity and solar geometry. Selecting the right model can improve the accuracy of simulations involving solar exposure and daylighting.

ASHRAE Clear Sky

A simplified model representing ideal, cloud-free conditions. It assumes a theoretical clear-sky scenario and is commonly used for standardised performance testing or sizing calculations.

ASHRAE Tau

Uses empirical Tau values (atmospheric transmissivity) to calculate direct and diffuse solar radiation. It's more representative of real-world conditions than the Clear Sky model, making it suitable for design-day simulations.

ASHRAE Tau 2017

An updated version of the ASHRAE Tau model, using improved datasets and revised algorithms introduced in the 2017 ASHRAE Handbook. Offers better alignment with more recent climate norms and measurement techniques.

Zhang Huang

A more detailed and data-driven model that uses additional atmospheric parameters. This option is useful in climates with complex sky conditions or when a more nuanced solar profile is required for daylight or heat gain studies.

Optical Depth for Beam and Diffuse Irradiance

These values describe how solar radiation is filtered by the atmosphere:

Beam Irradiance

Relates to direct sunlight.

Diffuse Irradiance

Accounts for scattered sunlight reaching the building indirectly. Higher values mean more solar is absorbed or scattered, reducing solar gains. Adjust these based on local atmospheric conditions like pollution, humidity or altitude.

Daylight Savings

Toggle this option if your selected design day occurs during daylight savings time. This setting shifts the simulation clock accordingly and can affect lighting schedules, solar angles and HVAC operation. It's particularly important when working with time-sensitive schedules or daylighting performance.

Winter Design Days

Add Winter Design Days to simulate peak winter conditions for heating system sizing. These represent the coldest days the building may need to withstand. If left empty, the simulation uses the default winter design day from the project’s EPW file.