Mechanical Ventilation issue

Hi all!

i have some problem in setting the mechanical ventilation on my workflow.

Even if i input 3 ach (as you can see from the following screenshot)

When i check the eso file i don’t have constant value in the output “Zone mechanical ventilation air change per hour”. why? any suggestion?

PS Have you changed something on the new update version regarding the ventilation? Because before i haven’t got this issue!

Thanks a lot in advance


Hi Claudia, Chris will get back to you on this with more details. I assume you’re using the EnergyPlus component and not the OpenStudio one. Is that right?


The results that you have posted here make sense to me. The ventilation seems to be typically at 3 ACH and it is only increasing this ACH in order to recirculate air to meet the peak cooling loads in summer. In these peak cooling conditions, it likely needs to force more air past the cooling coils in order to remove the heat from the space (hence, why it jumps up to 5 ACH). Of course, this is all assuming that you are using the OpenStudio component and you are modeling a HVAC system with recirculation (like VAV).

If you are not modeling something like this, please upload the file so that I can see what is being modeled.


Thanks Chris and Mostapha for your reply.

Actually i am still using the EnergyPlus simulation component (the one updated on the 4th of september 2016) because i thought it was still working correctly and also because I always get strange errors using the open studio one.

For example, if i put in my workflow (which is working with E+) the openstudio component instead of the E+ one, once i run the simulation i receive these following errors:

- 1. The simulation has not run correctly because of this severe error:
** ** Severe ** IP: IDF line~729 Error detected for Object=DESIGNSPECIFICATION:OUTDOORAIR**

- 2. The simulation has failed because of this fatal error:
** ** Fatal ** IP: Errors occurred on processing IDF file. Preceding condition(s) cause termination.**

Do you know why?

Can I still use the EnergyPlus simulation component?

Thanks in advance



Upload you GH file and let us know what version of OpenStudio you are using. I’m afraid that I can’t know what is happening without being able to see the full script.


Hi Chris,

i have tried to upload my GH file, but nothing changed.

As regards the Openstudio version i have the 1.12.0.

Should i install the 1.13.0?

Thanks again


Ehi Chris,

I had a look with a collegue and it seems that there is a sort of “bug” on the openstudio’s idf file: as you can see from the following part of the text, after SCHAlways ON there isn’t anything but i guess there should be the semi comma (;), is it right?

** Room2_DSOA, !- Name**
** Sum, !- Outdoor Air Method**
** 0, !- Outdoor Air Flow per Person {m3/s-person}
0.00215901630740211, !- Outdoor Air Flow per Zone Floor Area {m3/s-m2}
0, !- Outdoor Air Flow per Zone {m3/s}
0, !- Outdoor Air Flow Air Changes per Hour {1/hr}**
SCHAlways ON

** Room2 Equipment List, !- Name**
** ZoneHVAC:IdealLoadsAirSystem, !- Zone Equipment Object Type 1**
** Zone HVAC Ideal Loads Air System 1, !- Zone Equipment Name 1**
** 1, !- Zone Equipment Cooling Sequence 1**
** 1; !- Zone Equipment Heating or No-Load Sequence 1**

How can i solve this problem for the following simulations?



Chris and Claudia,

Just a note- this is probably economizer behaviour. The HB default is to set an economizer, the ACH spikes will disappear if you manually set to ‘no economizer’.



The economizer makes sense since it mixes in more outdoor air when the space needs cooling and the outdoor air is cold. Please upload the GH file with the OpenStudio component so that I can see the potential bug.


Hi Chris,

Here there are the rhino and gh files.

Thanks a lot


161018.3dm (108 KB) (840 KB)