Location = Libraries/Location Specific/Weather
The Type and Sub Type options that can be selected from the drop down lists in that area of the workspace, which filter the Source Library to display the variables the user can select to include, along with a value, in a Library Entry.
Note: The links within the table are to the EnergyPlus Input Output Reference and the explanations of the objects.
| Type Options | Sub Type Options | EnergyPlus Objects (IO Reference links) |
Sizing Period |
Design Day | SizingPeriod:DesignDay |
Sizing Period |
Weather File Condition Type | |
Sizing Period |
Weather File Days | |
WeatherProperty |
SkyTemperature | WeatherProperty:SkyTemperature |
WeatherFile |
WeatherStation |
Site:WeatherStation |
The design day input describes the parameters to effect a “design day” simulation, often used for load calculations or sizing equipment. Using the values in these fields, EnergyPlus “creates” a complete days’ worth of weather data (air temperatures, solar radiation, etc.) Normal operation uses the default range multipliers as shown in Figure 6 though users may choose to input their own multiplier schedule. Likewise, normal operation specifies one “humidity indicating condition” which is used to calculate the humidity ratio at maximum temperature – this is used as the constant humidity ratio for the entire day. Again, this can be overridden by specifying a relative humidity schedule or requesting generation of an hourly wet-bulb temperature profile. Multiple design days may be specified.
This numeric field specifies the month. That, in conjunction with the day of the month and location information, determines the current solar position and solar radiation values for each hour of the day.
This numeric field specifies the day of the month. That, in conjunction with the month and location information, determines the current solar position and solar radiation values for each hour of the day.
This alpha field specifies the day type for the design day. This value indicates which day profile to use in schedules. For further information, see the Schedule discussion later in this document {Group -- Schedules}. Note that two of the possible day types are SummerDesignDay and WinterDesignDay – allowing the user to customize schedules for the design conditions.
This numeric field should contain the day’s maximum dry-bulb temperature in degrees Celsius. (Reference Appendix A of this document for EnergyPlus standard units and abbreviations). The MacroDataSets design day files show extreme temperature for locations as indicated in the ASHRAE HOF design condition tables.
If you are happy with lows at 5am and highs at 3pm, you can ignore this field. If you want to specify your own temperature range multipliers (see earlier discussion at the Temperature Range field description), you can specify a type here and create a day schedule which you reference in the next field.
If you specify MultiplierSchedule in this field, then you need to create a day schedule that specifies a multiplier applied to the temperature range field (above) to create the proper dry-bulb temperature range profile for your design day.
If you specify DifferenceSchedule in this field, then you need to create a day schedule that specifies a number to be subtracted from dry-bulb maximum temperature for each timestep in the day. Note that numbers in the delta schedules cannot be negative as that would result in a higher maximum than the maximum previously specified.
If you leave this field blank or enter DefaultMultipliers, then the default multipliers will be used as shown in the “temperature range” field above.
This numeric field is the constant barometric pressure (Pascals) for the entire day.
This numeric field is the wind speed in meters/second (constant throughout the day) for the day. The MacroDataSets design day files includes wind speed values (99.6% - heating, 1% cooling) as indicated in ASHRAE HOF design condition tables. But, you should be aware that traditional values for these are 6.7056 m/s (15 mph) for heating and 3.3528 m/s (7 mph) for cooling. A reminder is shown in the comments for the wind speed values. The comments also note the extreme wind speeds from the ASHRAE tables.
This numeric field is the source wind direction in degrees. By convention, winds from the North would have a value of 0., from the East a value of 90.
This numeric field indicates whether or not the building surfaces are wet. If the value is 1, then it is assumed that the building surfaces are wet. Wet surfaces may change the conduction of heat through the surface.
This numeric field indicates whether or not there is snow on the ground. If the value is 1, then it is assumed there is snow on the ground. Snow on the ground changes the ground reflectance properties.
This field allows the user to select ASHRAEClearSky, ASHRAETau, ZhangHuang, or Schedule for solar modeling in the calculation of the solar radiation in the design day. ASHRAEClearSky and ZhangHuang use the Clearness value as part of their calculations. ASHRAETau invokes the revised model specified in Chapter 14 of the ASHRAE 2009 HOF and uses Taub and Taud values (below). Technical details of the models are described in the Engineering Reference. The Schedule choice allows you to enter schedule values for the day’s profile (use the next two fields for the names).
Sky Temperature, or radiative sky temperature, is internally calculated by EnergyPlus using an algorithm using horizontal infrared radiation from sky, cloudiness factors and current temperature. The algorithm is fully described in the Engineering Reference document. For flexibility, the following object can be entered to override the internal calculations. Much of the literature describes the sky temperature as relative to either dry bulb or dewpoint temperature.
Allowable entries here are: ScheduleValue, DifferenceScheduleDryBulbValue, or DifferenceScheduleDewPointValue. In each case the following field must specify a valid schedule name. ScheduleValue – the values in the schedule are used as the sky temperature. DifferenceScheduleDryBulbValue – the values in the schedule are used as a difference to the dry bulb temperature value (+values would then be greater than the dry bulb temperature, -values would then be less than the dry bulb temperature) for the resulting sky temperature value. DifferenceScheduleDewPointValue – the values in the schedule are used as a difference to the dewpoint temperature value (+values would then be greater than the dewpoint temperature, -values would then be less than the dewpoint temperature) for the resulting sky temperature value.
This field specifies a schedule name to accomplish the sky temperature calculation from the previous field. A Schedule:Day:* (i.e., Schedule:Day:Hourly, Schedule:Day:Interval, Schedule:Day:List) should be specified if the name in the name field matches a SizingPeriod:DesignDay object. If the name is one of the weather file period specifications (i.e. matches a SizingPeriod:WeatherFileDays, SizingPeriod:WeatherFileConditionType or RunPeriod), then the schedule name must match a full year schedule (i.e. Schedule:Year, Schedule:Compact, Schedule:File, or Schedule:Constant).
The Site:WeatherStation object is used to specify the measurement conditions for the climatic data listed in the weather file. These conditions indicate the height above ground of the air temperature sensor, the height above ground of the wind speed sensor, as well as coefficients that describe the wind speed profile due to the terrain surrounding the weather station. There are necessary correlations between the entries for this object and some entries in the Building object, specifically the Terrain field.
Weather stations throughout the world (ref: WMO – World Meteorological Organization) take their measurements at standard conditions:
§ Air temperature is measured at approximately 1.5 m above ground
§ Wind speed is measured at 10 m above ground
§ Weather station is in a flat, open field with little protection from the wind.
When using weather data from standard sources (e.g., TMY2, IWEC, TMY, or ASHRAE design day data), it is not necessary to use the Site:WeatherStation object. However, if you are using custom weather data or real-time weather data, you may need to read and understand the concepts in the Site:WeatherStation object.
The measurement conditions at the weather station (i.e., the weather file) are used by EnergyPlus in conjunction with the Terrain field of the Building object, or optionally with the Site:HeightVariation object (see below), to calculate the local variation in atmospheric properties as a function of height above ground. Outdoor air temperature decreases with height, while wind speed increases with height. The algorithms for this calculation are in the Engineering Reference.
The Site:WeatherStation object is useful when working with a custom weather file that includes data that were not measured at the WMO standard conditions. For example, the weather data could be measured on site, or on the roof top of a nearby building. The wind speed profile coefficients can be estimated from the table below or calculated beforehand using more sophisticated techniques such as CFD modeling of the weather station terrain.
If the Site:WeatherStation object is omitted from the input file, the WMO standard measurement conditions are assumed.
The height [m] above ground for the wind speed sensor.
The wind speed profile exponent for the terrain surrounding the weather station. The exponent can be estimated from the table above or calculated beforehand using more sophisticated techniques, such as CFD modeling of the weather station terrain.
The wind speed profile boundary layer thickness [m] for the terrain surrounding the weather station. The boundary layer can be estimated from the table above or calculated beforehand using more sophisticated techniques, such as CFD modeling of the weather station terrain.
The height [m] above ground for the air temperature sensor.
For example, if you are using weather data measured on the top of your building, you should set the Wind Sensor Height Above Ground and the Air Temperature Sensor Height Above Ground to equal the height of your building (say 30 m). The Wind Speed Profile Exponent and Wind Speed Profile Boundary Layer Thickness should be set to match the values associated with the Terrain field of the Building object, or the equivalent fields of the Site:HeightVariation object.
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