Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question
4

Two different R-values for roof for a day?

asked 2016-07-24 19:55:44 -0600

siddharthpatil5's avatar

updated 2016-07-25 05:47:45 -0600

I am modelling a greenhouse and I need to give 2 different R-values for roofs. I have a roof with R2.6 during day and same with R4.6 during night. Can I do this in openstudio?

edit retag flag offensive close merge delete

1 Answer

Sort by ยป oldest newest most voted
2

answered 2016-07-25 03:55:57 -0600

If you want to be changing the properties of a construction during the simulation in EnergyPlus - the underlying engine used by OpenStudio - you need to use the Energy Management System (EMS).

This would be a pretty simple EMS program, using EnergyManagementSystem:ConstructionIndexVariable. The example 13 in the EMS Application Guide would be a very good starting point!

You need to define two constructions, "Roof-Day-R2.6" and "Roof-Night-4.6", then you define one EMS:ConstructionIndexVariable for each of these. You will need to add one EMS:Actuator for each surface where you want to change the 'Construction State' (if you have a lot of surfaces, you should leverage scripting in order to not go completely nuts).

Define an EMS:ProgramCallingManager: BeginTimestepBeforePredictor calling point would be fine for you.

Then an EMS:Program, where you would just do a simple IF based on Hour, something along the lines of:

EnergyManagementSystem:Program ,
Switch_Roof_Construction,
IF (Hour >= 8.0) && (Hour < 20.0) ,
   SET Roof_Surface1_Construct = Roof-Day-R2.6,
   SET Roof_Surface2_Construct = Roof-Day-R2.6,
ELSE,
   SET Roof_Surface1_Construct= Roof-Night-4.6,
   SET Roof_Surface2_Construct= Roof-Night-4.6,
ENDIF;

You would need to use an EnergyPlus Measure to inject (or create) the EMS code before simulation.

This might seem like a lot if you haven't touched EMS, nor EnergyPlus measures before, but it shouldn't be that hard.

edit flag offensive delete link more

Comments

Thanks Julien, I am new to this EMS but still I will try once with this.

siddharthpatil5's avatar siddharthpatil5  ( 2016-07-27 23:39:15 -0600 )edit

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Careers

Question Tools

1 follower

Stats

Asked: 2016-07-24 19:55:44 -0600

Seen: 129 times

Last updated: Jul 25 '16