Regardless of simulation engine, what assumptions can you make for operable windows and how do you model them? Does any simulation tool have an explicit algorithm or component for operable windows?
In EnergyPlus, there are several ways to model operable windows:
The AirflowNetwork:MultiZone:Component:SimpleOpening and AirflowNetwork:MultiZone:Component:DetailedOpening objects can be added to the model in an AirFlowNetwork to represent operable windows. This paper provides a good overview of how the AirFlowNetwork operates.
The ZoneVentilation:WindandStackOpenArea object allows users to define basic parameters like the size and orientation of the opening, as well as the limits on the outdoor conditions (temperature, wind speed) that determine whether the window is open or closed. The flow through the opening is based on the both the wind speed and the stack effect in the zone at each timestep the window is open. This object can be used without setting up an AirFlowNetwork in the model.
To piggy back and Andrew's option 2, OpenStudio has a separate surface type for operable vs. fixed windows. This was done primarily so each window type can take unique default construction, but doesn't otherwise change what happens in EnergyPlus. Both fixed and operable windows are translated as sub-surfaces. I have often thought that an OpenStudo E+ measure that would use the operable tag to create the WindandStackOpenArea objects for you at runtime. This way there is a dynamic link between your geometry and the inputs to the WindandStackOpenArea object.
@David Goldwasser - did you ever put that measure together to tag different window types to be used with "WindandStackOpenArea" object?
I didn't make that exact measure, but I did make a fan assist night ventilation measure that looks at operable vs. fixed windows to see which zones to add zone ventilation to. The measure then adds a series of zone mixing objects where there are air walls or interior operable windows. Here is a link to the measure and here is a link to a post with more details.. The measure includes a PDF guide since it was made with very specific use case in mind.
Thank you David.
The Add Wind and Stack Open Area measure adds ZoneVentilation:WindandStackOpenArea objects to zones with windows of a specified construction.
While OpenStudio tags windows as fixed or operable, EnergyPlus does not have this distinction. So you need to specify a window construction.
In DOE-2, operable windows are modeled as natural ventilation in SYSTEM using the Sherman-Grimsrud Infiltration Model (when I asked the author Max Sherman whether this was an acceptable use of his model, Max said it was actually better suited for large bulk flows than through small cracks and leaks!). S-G is a single-zone model, so there's no capability to model air flow from zone to zone, as is possible with network models. However, at the single-zone level it uses similar physics with a wind-driven and a temperature driven component. For many years, natural ventilation was allowed only with the RESYS (residential) system, but starting with 2.1E it was also made available to other air systems. The amount of window openings is entered as a FRAC-VENT-AREA, and controlled using either the temperature or enthalpy difference between indoors and out. One thing I've like about the control is that it first tests if natural ventilation can hold the setpoint, and if not, it then models the windows as closed and simulates the A/C.
In IESVE there is a module called "MacroFlo" which allows the user to define specific external openings as operable windows, or even holes (useful for louvered openings). You can further specify openable area, a profile allowing the degree of opening to be specified as a function of time, threshold temperature which allows the window opening to be controlled on the basis of room temperature, as well as other features. This data is then used in the annual energy simulation module, and can easily be turned on or off as necessary.
One way to model operable windows is to use Energy Management System. You can set-up several constructions for windows and then vary between them according to certain physical values. You can find manual in EnergyPlus installation folder under Documents/EMSApplicationGuide.pdf
Comments
There are a lot of good answers here for specific tools. Maybe my question was too broad to ask for "any simulation tool". It makes it hard to choose a correct/best answer.
To recast the question a little bit, given that many tools have some way to model operable windows--explicit capability or workaround--what assumptions do you use for the inputs and controls? I have not looked at all of the tools and capabilities mentioned so far, but I'm guessing they all take vaguely similar inputs for setting threshold temperatures (when its open/closed), maybe flow rates or ACH in some cases, etc.
@Peter Ellis I have noticed that may questions ask "How do I model XYZ." I recommend editing these questions to either one of "What feature do I use to model XYZ" and/or "What modeling assumptions should be made when modeling XYZ" Does this make sense? I don't know how to suggest changes to a question yet. Some people (like you) put this into the detailed description, but I think it should go into the question title itself for clarity on the main list of questions.