Configuring flow paths
Windows
Two types of windows exist: ### save for later energyplus windows
glass windows (multiplier = 0) have prefix “wind” . No wind pressure profile. 2-way flow element with one opening. No schedule.
Use spreadsheet to get:
Height (some multiplier of room height)
Width (some multiplier of room width)
Flow path is XX relative height
Right click on wall to have a window and select “flow path”
If not already done yet, double click on icon to load libraries (insert screenshot)
Select flow paths library and copy from library elements to “Load project elements”
Select window (wdop; etc.) for the Flow Element name
From previous calculation on flow path relative height, add this to the Flow Path Reletaive Elevation
Icons located in the middle of the wall, position matters for the glass window, not ‘wdop’
Operable windows (4x4), prefix “wdop”, smaller to simulate cracking the window half open (schedule = closed). This has a wind pressure profile (variable). 2-way flow element with two opening
Both (what is both?) have Discharge parameter (coefficient) = 0.78 –> not both, just need the coeff
Confirm when you need the operable window and the window flow path element
Copy and paste a window onto each outside wall that contains a window
Doors
Two types of doors elements: operable and undercut (elevation = 0)
NO EXTERNAL DOOR
Internal door = both elements
Set schedule to closed
Position does not matter
Probably the best for this is door_open3ft, not door_operable
External wall leakage
Standard practice is 3 per wall
The element (ext_wall) does not change
Right click on the wall and select Flow Path (similar to window flow path definition)
Modify the relative height and area, as per the spreadsheet
Set a wind pressure profile > Flow Path > Wind Pressure > Select “Variable” > under Name select the wind pressure profile
If necessary, select library, load, and copy wind pressure elements for the project
Standard value is 5 cm2/m2 - set by double clicking the airflow path, then selecting “edit element” for Flow Path and change to 5 cm2/m2
Copy airflow paths to all external walls
Make sure you copy all three to each external wall
Make sure wind pressure profile is selected for all airflow paths on all external walls
The wall leakage rates will update in all element assigned to the element profile
Internal wall leakage
Standard practice is 3 per wall
The element (int_wall) does not change
Modify the area, as per the wall area
Position does not matter for calculation, but should be smart so you can easily scan them
This may differ for inter-apt vs intra-apt
Standard is 2 cm2/m2 for both
Door open for an open floor-plan
You may want to simply create two-way elements the size of the openings and let mixing occur between zones based on differences in air density. Or, create one orifice high and one low => two-way flow can occur.
In the absence of having any actual leakage tests for the building (which is usually the case), I recommend taking external leakage values from Andy Persily’s article “Myths about building envelopes”. This publication summarizes the results of many known leakage tests, and breaks them down by building use and location. Notice that Florida buildings are generally leakier, so you may wish to use these values in the south. Also note that there are significant variations in leakage for similar buildings. Therefore, you may wish to check your final results with a leakier or tighter building to test its sensitivity to these variables. If the contaminant transport is primarily mechanically driven, then leakage may not be as important. However, if it is migrating through walls or into stairwells, leakage could have a large influence. Be sure to specify the same discharge coefficient and reference pressure drop as is used in the published data.
Certain elements, such as operable windows (particularly the automatic motorized ones) are very leaky. If you know these are present, it’s a good idea to specify a somewhat low leakage per area value for the leakage you don’t know and to add to this leakage for the windows in their actual location. I recommend this for any large leakage path that you have knowledge of.
I usually assume that roofs have similar leakage to exterior walls and that interior walls and floors are leakier by at least a factor of two.
Floor/Roof leakage
Goes above each ceiling
(so if you have basement and level 1, it goes on level 1)
(for roof, it goes in the blank level above the roof)
Insert a roof/basement above/below current level as needed (Inert Blank Level > Above/below current level)
Define airflow path and select roof leak (or other choice) for Flow Element Name
Go to Wind Pressure Tab to add profile and select variable
Roof wind pressure profile for roof_leakages (similar to adding wind pressure profiles for externall wall leakage rates; load library if necessary)
Elevation of roof/floor leaks is 0ft (named “relative elevation”)
Stairs have to be the zone area
You have to modify for the area below. This can be easier with ‘reveal level below’ feature under “Level” in the tool bar.
Floor = int wall value
Roof = ext wall value
If you are adding a roof that is peaked, then you should include an attic zone on level 4 and add another roof level.
Roof level would then have attic ventilation as per specs I sent previously: typically, a ridge vent and soffit or eave vents.
Currently, your “roof” leaks are attic floor leaks which is why I was making these comments.