Surface-specific variable actuators - EMS

asked 2017-02-14 16:45:13 -0600

updated 2017-02-15 12:27:08 -0600

Hello, I am playing with EMS and I am trying to override variables for specific surfaces. For what I understand, the only actuators for surface-specific weather variables are:

Outdoor Air Drybulb Temperature
Outdoor Air Wetbulb Temperature
Outdoor Air Wind Speed
Convective heat transfer coefficient

Now, the questions I have are:

1) What is exactly the "Outdoor Air Drybulb Temperature"? Is it the ambient air temperature or the external wall temperature?

2) Is there a way to override surface-specific variables such as:

External wall temperature
Relative Humidity
Wind direction
Direct and diffuse radiation

Thanks

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answered 2017-02-15 07:54:34 -0600

Adam Hilton

3465 ●1 ●15

1) If you have Output:EnergyManagementSystem in your *.idf with the first field (Actuator Availability Dictionary Reporting) set to Verbose you will find a file called eplusout.edd with your output files that contains all the available actuator unique names, types, and control types. Reason I bring that up is if you look for Outdoor Dry Bulb you will see that control type a couple of times, once for the Environment unique name and then again for every surface and sub-surface in your model. So to answer your question, if you choose the Environment unique name it would be the 'ambient air temperature' as you described above and if you choose the specific surface or sub-surface unique name it would be the 'external wall temperature'. The same applies for Outdoor Air Wetbulb and Outdoor Air Wind Speed as well. Additionally, you have both Interior Surface Convection Heat Transfer Coefficient and Exterior Surface Convection Heat Transfer Coefficient.

2) You can override those values for the environment, but I'm not aware of a way to do it for a specific surface. Maybe someone has some fancy way they'd be willing to share :) In addition to the ones listed above you have Environment control types of Outdoor Relative Humidity, Diffuse Solar, and Direct Solar.

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I know it's late, but thanks for your answer. I have another question, now, regarding solar irradiation in EnergyPlus. Solar radiation impacts on the building energy consumption in terms of heat and light. I am employing a CFD software to study the temperature on each wall of the building. It takes into account incoming solar radiation as well. I can, therefore, use EnergyPlus actuators on each wall to override the surface temperature. If I impose the temperature on each surface, do I override the solar heat contribution? Does the sun impact in any other way in terms of heat gain?