Welcome to the TRNSYS Users Forum.
The forum is a place where people can interact and have discussions about different topics involving the use of the TRNSYS software package. Here you can post topics for discussion or questions on using TRNSYS and get advice from other users or TRNSYS experts. This forum is not intended for detailed technical support. Users should contact their distributor’s hotline for such assistance.
Some tips for success on using the forum:
- Follow the Forum Rules posted in Forum Administration.
- There are categories for different types of topics and questions. Post your topic or question into the proper category.
- Before posting a topic or question search the existing topics (and the TRNSYS Users listserv archive or Post archive) to see if a similar topic or question has already been answered.
- Use a descriptive topic name. Don’t use attention getting subjects, they don’t get attention and only annoy people.
- State the version of TRNSYS and which add-ons your are using.
- Include enough specific details for your topic of question to be answered. Just posting “Why am I getting an error?” without describing the specific error and what you are trying to do when you get the error will not receive a response that fixes your issue.
- Remember when people help you, they are doing you a favor. Be patient, help people out by posting good descriptions of what you need help with, and be polite even if a response does not solve your issue.
- Moderators may edit your post for clarity or move your topic to a more appropriate category.
Dear TRNSYS users,
I'm modelling the agricultural greenhouse with TRNSYS and TRNFlow.
The greenhouse is divided vertically into two zones (lower and upper zones) by a thermal screen that is operated according to a time schedule.
The thermal screen is physically horizontal and is located between the two zones.
In TRNFlow, I currently model this thermal screen as a large opening between the lower and upper zones.
However, since the opening is horizontal, the own height factor becomes zero, and air flow is limited to one-way flow within a time step.
My intention is to reproduce buoyancy-driven advection of warm air from the lower zone to the upper zone through the thermal screen when it is open.
Has anyone faced a similar situation, or found a practical workaround in TRNFlow to represent vertical air exchange across a horizontal opening?
Any advice or experience would be greatly appreciated.
Best regards
I have seen a few approaches to this issue.
When the screen is open and there is a large horizontal opening then in the real world situation there would be some mixing of air between the volume below the screen and the volume above it.
The first approach is to simply define a mixing flow rate between the two volumes. I don't think that this approach is possible when TRNFlow is implemented because I don't think that TRNFlow will allow to to treat the system as a hybrid between externally defined flowrates and internally calculated flow rates. It is possible if you use Type97/CONTAM for the air flow calculations. Regardless, the approach is not exactly scientific because it is really anyone's guess as to what the appropriate value of the mixing flow rate should be.
The second approach is to restrict the effective size of the opening (thus decreasing the volume of air that can transfer unidirectionally across the opening in a given time step). The idea (I think) is that temperature stratification can result in a net movement of air in one direction. The problem with this approach as with the previous one is that the size restriction of the opening is not linked to anything reals so what value to choose?
The third approach is much more defensible but is also a lot more time consuming. That is to use CFD simulations to try and characterize the net flow of air either up or down under different circumstances (i.e. different temperature differences) and to create a sort of performance map that can be used to decrease the arbitrariness of one of the two other solutions that I mentioned.
If anyone else on the forum has alternative suggestions, I would certainly welcome hearing them!
~david
