Hi,
Can anyone recommended way to determine internal air velocity gradients inside a room.
This is a common requirement in building design (usually <0.3 m/sec) for occupant comfort.
I can only think of using Microflo but even this is unrealistic - what do I do if I use the System Air supply to supply the minimum 10 l/sec/person to the room .... this comes without vent openings hence I can't calculate the opening areas nor obviously the air velocity?
Is there something I'm getting wrong?
thanks
Norm
determining room air velocity gradients
-
normwheatley
- VE Student
- Posts: 27
- Joined: Thu Aug 13, 2009 11:00 pm
Re: determining room air velocity gradients
You should be using a CFD program if you are interested in resolving the temperature or velocity field within a room or zone in your thermal model. A dynamic thermal model (apacheSim) along with a bulk flow analysis program (Macroflo) will give you flow rate through holes, windows etc in the building fabric. From that you could estimate the velocity at the window/hole but it won't tell you what is going on within the room/zone. Only CFD will do that, other than experimental data of course.
Q> what do I do if I use the System Air supply to supply the minimum 10 l/sec/person to the room .... this comes without vent openings hence I can't calculate the opening areas nor obviously the air velocity?
When you import boundary conditions into Microflo the things that are set up automatically by Microflo include:
1) the inside surface temps of walls/ceiling/floor/windows and doors
2) Macroflo predicted flow rates through openings
3) internal gains
This leaves the user to set up the following manually:
4) the system involved with room conditioning
5) any air exchanges set up in the air exchange tab in the building template manager rather than calculated by Macroflo
Therefore the user has to add a boundary condtion in Microflo that represents the ventilation system that you have modelled in the thermal model. For this you need to add a "diffuser" boundary where flow enters the domain (region of interest) and an "extract" boundary where flow exits the domain. Then Microflo will calculate the flow and temperature fields that result from the boundary conditions, those imported and those added manually.
BTW Microflo can also give you thermal comfort expressed by the PMV and PPD variables.
Q> what do I do if I use the System Air supply to supply the minimum 10 l/sec/person to the room .... this comes without vent openings hence I can't calculate the opening areas nor obviously the air velocity?
When you import boundary conditions into Microflo the things that are set up automatically by Microflo include:
1) the inside surface temps of walls/ceiling/floor/windows and doors
2) Macroflo predicted flow rates through openings
3) internal gains
This leaves the user to set up the following manually:
4) the system involved with room conditioning
5) any air exchanges set up in the air exchange tab in the building template manager rather than calculated by Macroflo
Therefore the user has to add a boundary condtion in Microflo that represents the ventilation system that you have modelled in the thermal model. For this you need to add a "diffuser" boundary where flow enters the domain (region of interest) and an "extract" boundary where flow exits the domain. Then Microflo will calculate the flow and temperature fields that result from the boundary conditions, those imported and those added manually.
BTW Microflo can also give you thermal comfort expressed by the PMV and PPD variables.