AHU setup and modeling openstudio [closed]

asked 2016-03-22 10:10:28 -0600

FSilenzi gravatar image

updated 2016-03-23 06:02:47 -0600

Hi everybody, I am in need of your help again.

Basically I have a building served by an AHU. The AHU has the hot water loop connected to a district heating plant, using a fluid to fluid heat exchanger. The chilled water loop is connected to an absorption chiller that is linked to a condensing tower. I have problems setting things up, because I do not know how to select what suits better my case.

In the main VAV loop I have selected a single zone reheat set point, using the connected thermal zone as control zone. For the hot water loop, condenser water loop and the HX-district heating connecting loop, I have selected "set point manager scheduled" while for the condenser loop I have selected the "follow outside air temperature set point".

The temperature schedules are 82 °C for the HX-district heating loop, 72 °C for the hot water side, 12 °C for the chilled water loop and for the condenser water loop the reference temperature is "outdoor wetbulb air temperature". The setting for the absorption chiller and the heat exchanger are the ones preloaded in the openstudio library.

I am not sure to have done the right choices. The simulation runs but it keeps telling me that are unmet hours, even if when checking the unmet hours troubleshooting script results, the graphs does not show any missing cooling/heating. Also the zone mean temperature is more or less 22 °C, and that is correct since I selected 21 °C and 23 °C as heating and cooling thermostats for the zone. I have not selected any humidity control since the AHU installed does not include humidity control.

Is there anything crucial that I am missing? Do I need to upload the model so you can check it? This simple toy model was made to help me figure out how to model an AHU system, in order to apply this to a bigger model I am working on. I apologize if there is a similar question answered yet, but I tryed to find it via the "search" fucntion with no luck.

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Closed for the following reason question is not relevant or outdated by FSilenzi
close date 2016-03-24 02:40:01.275402


@FSilenzi there's a previous post for reducing unmet hours that might be helpful.

MatthewSteen gravatar image MatthewSteen  ( 2016-03-22 13:23:06 -0600 )edit

Hi MatthewSteen, thanks for your reply. I have checked the post already but I have still a doubt regarding the choiches I have made. Are the setpoints that I have chosen correct? Are the plant loops connected correctly?

FSilenzi gravatar image FSilenzi  ( 2016-03-23 02:42:12 -0600 )edit

Ok I have fixed the unmet hours issue. I have still trouble with HVAC load profiles: the heating one seems modeled correctly, while cooling one seems not. Infact during summer the simulation gives back a very small cooling load. If I substitute the absorption chiller whit an electric one, the model seems to work properly, so I believe the problem resides in how I have modeled the chilled water loop and the condenser loop. Thanks again for the help.

FSilenzi gravatar image FSilenzi  ( 2016-03-23 06:01:46 -0600 )edit

@FSilenzi Hello! Did you find a solution to low cooling loads when there is usage of the absorption chiller?

Psterpis gravatar image Psterpis  ( 2021-07-08 04:56:11 -0600 )edit