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CAV fan air volume overriden

asked 2017-10-12 08:45:51 -0500

Maciej Dluzen's avatar

updated 2017-10-13 03:27:26 -0500

Hi everyone,

I have set up a very simple building geometry model and HVAC as I'm trying to get to the grips with Energy Plus. Unfortunately, I have got a problem with understanding one issue, therefore I'm kindly asking for your help.

My building model is a cuboid, building envelope is adiabatic and there's not activity within the space - maximum simplification as I needed to focus on the HVAC mainly. My detailed HVAC system consists only of one constant volume fan - air flow: 12.5 m3/h, pressure rise 800 Pa, total efficiency 70%. All of the settings in the HVAC and activity tab have been set accordingly.

The problem which I encountered is that EP calculates it's own design airflow and fan power which then is taken to energy calculations, despite my user's inputs (fixed fan speed, therefore fan power should be 14.3 kW). It appears that my inputs have been overridden by EP - 1.12 kW and 0.98 m3/s

Moreover, the EP report indicates Rated Electric Power as 14.3 kW and Max Air Flow Rate 12.50 m3/s (my values - please see an attachment) and says that User-Specified values were used, although it's not truth.

Thanks for you help. Maciej

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what are you trying to model? In which objects did you set your fan power and flow rates? Are the units correct - you specify 12.5 m3/s in the last paragraph, and 12.5 m3/h earlier? Which outputs are you using to see what was sized? It's possible the sizing is as you specify, but the model is ventilating per a lower outdoor air flow rate requirement.

mdahlhausen's avatar mdahlhausen  ( 2017-10-12 13:49:47 -0500 )edit

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answered 2017-10-13 03:26:38 -0500

Maciej Dluzen's avatar

updated 2017-10-13 03:58:43 -0500

image description

I've attached screenshots of E+ report. Actually, I am trying to understand how detailed HVAC works, therefore I've started from very simple system and once I've got the hang of that, I will gradually be making the model more complicated. Sorry, for a mistake - airflow should be 12.5 m3/s everywhere. I am going to check my fresh air settings in the model.

I finally got to the bottom of this problem. The solution was to set the 'Outside air definition method' to 'By zone' and set a desired ac/h.

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Asked: 2017-10-12 08:45:51 -0500

Seen: 1,048 times

Last updated: Oct 13 '17