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Wall temperature actuator overrides solar heat gain?

asked 2017-10-09 11:56:26 -0500

carlobianchi89 gravatar image

updated 2017-10-09 12:04:48 -0500

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 a building model. It takes into account incoming solar radiation as well, providing surface temperatures through a global energy balance. I can, therefore, use EnergyPlus actuators on each wall to override the surface temperature.

The question is: 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?

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answered 2017-10-10 11:19:13 -0500

You can override surface temperatures without using Energy Management System (EMS) objects. Using the SurfaceProperty:OtherSideCoefficients object, you can use a schedule to set surface temperature. However, when you use this object, "solar effects are not accounted for". This will impact the heat balance for that surface, altering the surface heat loss / gain / storage.

If you did use EMS objects, the specific object that allows users to override normal behavior is the EMS Actuator. Users must select from a list of actuators that the EnergyPlus developers included - users DO NOT have free reign to override every single feature of an EnergyPlus model.

That list of available actuators can be found in the EMS Application Guide documentation. Your question relates to the Surface Boundary Conditions actuators within the group of thermal envelope actuators. To override surface temperatures, it gets tricky because you are asked to set values for four parameters: air temperature and heat transfer coefficient for both convection and radiation heat exchange processes. This approach also requires adding a SurfaceProperty:OtherSideConditionsModel object to the input file, which is typically used to calculate boundary conditions for multi-skin facade components. When you use this approach, EnergyPlus doesn't account for solar gains on the OUTSIDE FACE of the wall surface - only convection and radiation.

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Thanks for your answer. I need some clarifications. I am currently using the EMS and I am specifying Dry Bulb Temperature, Wet Bulb Temperature and Wind Speed. I can't find any actuator for radiation heat exchange processes. Why should I set the convection coefficient actuator if I am directly setting the surface temperature?

carlobianchi89 gravatar imagecarlobianchi89 ( 2017-10-11 17:31:11 -0500 )edit

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Asked: 2017-10-09 11:56:26 -0500

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Last updated: Oct 10