Settings for the Ambient Properties
To add an Ambient Properties node to any Component, on the Physics toolbar click Ambient Properties or right-click the Definitions node under the Component and choose Ambient Properties.
In the Ambient Properties node (), you can define ambient variables to be available as inputs from several features: the temperature Tamb, the absolute pressure pamb, the relative humidity , the wind velocity vamb, and the direct and diffuse solar irradiances Isn,amb and Ish,amb.
See Heat Flux, Diffuse Surface (Surface-to-Surface Radiation Interface), Temperature, Initial Values, or External Radiation Source for examples of features of the Heat Transfer interface that have ambient variables available as inputs.
See Initial Values, Moisture Content, or Moisture Flux for examples of features of the Moisture Transport interface that have ambient variables available as inputs.
Three options are available for the definition of the Ambient data:
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When User defined (the default) is selected, the Temperature Tamb, the Absolute pressure pamb, the Relative humidity , the Wind velocity vamb, the Precipitation rate P0,amb, the Clear sky noon beam normal irradiance Isn,amb, and the Clear sky noon diffuse horizontal irradiance Ish,amb should be specified directly.
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When either Meteorological data (ASHRAE 2013) or Meteorological data (ASHRAE 2017) or Meteorological data (ASHRAE 2021) is selected, the ambient variables are computed from monthly and hourly averaged measurements, made over several years at weather stations worldwide. See Processing of ASHRAE Data for more information. Further settings for the choice of the location, time, and ambient conditions are needed; and additional input fields are displayed underneath.
Location
In this section you can set the location by choosing among more than 8000 weather stations worldwide. Two options are available for the selection of the Weather station:
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When From list is selected, click on the Set Weather Station button to open the Weather Station browser that allows you to select a Region, a Country, and a Station. The station details (World Meteorological Organization reference, location, and geographical coordinates) are displayed underneath.
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It is also possible to select a station From reference by entering the corresponding World Meteorological Organization reference, which is a 6-digit number.
A single country may be available for more than one region selection if it has stations spread over different regions. For example, United States of America is available in the Country list when either North America, Eurasia, or Oceania is selected in the Region list.
When a station is selected From list, its World Meteorological Organization (WMO) reference is displayed in the user interface. The WMO references can also be retrieved from maps offered by third parties like the one available as of this product release on http://ashrae-meteo.info/.
Time
The Date and Local time should be set by entering values or expressions in the Day, Month, Hour, Minute, and Second fields of the two tables.
If On is selected in the Specify year list, a value or expression for the Year should also be set. As the data are given as averages over several past years, this input is only used for the detection of leap years, in order to interpolate the data over the months.
For temporal studies, these inputs define the start time of the simulation. By default, the Update time from solver check box is selected, and the time is then automatically updated with the time from the solver to evaluate the variables by interpolation of the measured data. Clear this check box to manually set the time update.
See Ambient Data Interpolation for more information about the interpolation of data over months and hours.
See Processing of ASHRAE Data for more information about the data.
A time unit suitable for simulations over a day or a year may be set in the Study Settings section of the Time Dependent node, by using for example h for hour, d for day, or a for a year. See Using Units in the COMSOL Multiphysics Reference Manual for more details.
Ambient Conditions
Based on the measured data, several conditions are available for the Temperature, the Dew-point temperature, the Wind speed, and the Precipitation rate. The formula for each condition is recalled in Table 3-11, Table 3-12, and Table 3-13. The Average conditions correspond to weighted means of the measured data, whereas the other conditions are obtained by applying standard or modified deviations (Low, High, and User defined coefficient for deviation conditions), user defined corrections, or wind correlations to the average conditions; or by taking the minimum or maximum of the measured data (Lowest and Highest conditions). More information about these definitions can be found in Ambient Variables and Conditions.
Table 3-11: Temperature Conditions
Condition
Definition
Average
Low
High
Lowest
Highest
User defined coefficient for deviation
User defined correction
Heating wind correlation(1)
Cooling wind correlation(1)
 (1)These correlations are not related to the wind speed conditions described in Table 3-13.
Table 3-12: Dew-point temperature Conditions
Condition
Definition
Average
Low
High
Lowest
Highest
Table 3-13: Wind Speed Conditions
Condition
Definition
Average
Low
High
Lowest
Highest
Table 3-14: Pressure Conditions
Condition
Definition
Average
Low
High
Lowest
Highest
The conditions set for Temperature and Dew-point temperature should be consistent in order to keep the temperature larger than the dew-point temperature. However, all settings combinations are available, and the relative humidity is majored by 1 when necessary.
The sum of the Clear sky noon beam normal irradiance and the Clear sky noon diffuse horizontal irradiance is available through the postprocessing variable ht.Is_amb, defined as the Ambient solar irradiance.