Displacement (stratified) Ventilation

[David]

Hi there,

Just a quick entry to give you a start...

To model a displacement system in an auditorium you will need to zone the space vertically to account for the stratification of the air and use MacroFlo combined with ApacheHVAC to model the displacement system.

I'd recommend that displacement systems are simulated by dividing the room into two levels:
1. An occupied level up to 1.8m and
2. An upper level representing the remainder.

The system air is supplied at low level and passed on to the upper level.

As a rule of thumb, convective gains occurring in the lower level from people, equipment or lights should be apportioned between the levels in the ratio 1/3 to the lower level and 2/3 to the upper level. This ratio reflects the tendency of the warm air to rise in plumes.

The 2/3 ratio must be added as a watts figure as opposed to W/m2, as holes and windows in a floor reduce the calculated watts. Therefore a floor with a 100% hole (or window) will result in no watts from a W/m2 entry.
If you have a Plenum:

You can set up a proportional control on your HVAC network to sense the return air temperature. This will allow you to vary the supply air temperature into the plenum. Make sure you check the admittance values for the construction assigned to the plenum and also check the internal surface resistance values to ensure that they are suitable for your calculation.

You can calculate the peak and cooling loads using CIBSE loads calculation. Make sure you have the correct ventilation rates, constructions and internal gains assigned.

Hope that helps,
David.

[thumelen]

Hey there David,

I guess your post is long time ago. But I was wondering how to assign my floors as holes ?
I would really appreciate if you could help me

[Complex Potential]

Thumelen

All that means is that you connect your vertical zones with holes by replacing floors and/or ceilings with holes at surface level.

CP

[thumelen]

Thumelen

All that means is that you connect your vertical zones with holes by replacing floors and/or ceilings with holes at surface level.

CP

So, under which module should I be able to do this ? ModelIT or Apache ? or I should have done it in Google SketchUp first before even importing the file into IESVE ?

[Complex Potential]

You add the holes to the basic geometry through ModelIT and then ensure that the macroflo check box is ticked when you run the apache simulation.

[thumelen]

Took me some time but I figured it out. Apparently its possible to import a building with the holes pre attached.

Identification of walls, roofs, floors, holes, windows, doors
Walls, roofs, floors:
Faces with opacity of 100 are treated as walls/roofs/floors.
Holes:
In SketchUp, faces between zones drawn with opacity of zero are treated as holes between zones. If
a face is “cut out” or deleted from another surface, this is treated as a hole.
NOTE: Exterior holes in external surfaces are treated as windows by the <Virtual Environment> suite
of tools, because in the <VE>, holes in external surfaces are not allowed.
Windows:
Faces with opacity between 1 and 99 are treated as windows.
Doors:
A face drawn on another surface with opacity of 100.

Source : http://www.iesve.com/website/var/assets ... s_rev2.pdf

[Complex Potential]

Thanks for reporting back. This will come in handy if I ever start importing models but, for now, I think I'll stick with building them myself. Then I know for sure it's been done right.

[NebK22]

The 2/3 ratio must be added as a watts figure as opposed to W/m2, as holes and windows in a floor reduce the calculated watts. Therefore a floor with a 100% hole (or window) will result in no watts from a W/m2 entry.

Is there a way to get around this? I'm trying to model displacement ventilation for two stories with 50+ rooms. This method sounds really tedious as I'd have to calculate the total heat gain and assign them to each individual stratified space. I'm still in the early stages of design considerations, is there a way to simpler way to model the stratified space?

Thanks!

[NebK22]

Got the answer from an IES staffer, thought I'd share:

I’m afraid not. A displacement ventilation system has some very specific modelling requirements in order for proper accounting of the system operation to take place. Other system types generally don’t require this level of attention early on.

I would suggest you use the Tabular Room Data Edit tool to perform some fast excel operations on the data. This may save some time.

Hope this helps.

- Ben K