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# does energyplus modify air density based on elevation (both indoor and outdoor air)

I am looking for a yes and no answer and if yes, then a possible reference to this in the documentation.

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Hello Rehan, I want to ask: Does energyplus change the used air density based on the changes of outdoor air temperature? for example, when outdoor air temperature is around 10 degree (C), the air density is around 1.247 kg/m3; when outdoor air temperature is around 0 degree (C), the air density is around 1.293 kg/m3. is it right?

( 2018-12-13 10:00:02 -0600 )edit

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Yes. EnergyPlus calculates the outdoor barometric pressure based on elevation. Density of air within the air systems is calculated based on outdoor barometric pressure.

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Hey Neal, I know that E+ calculates the density of air for airloops, but what about for condenser efficiency? The condenser full and part load efficiency is entered by the user in the form of a COP and the equipment curve for air-cooled chillers, DX, and VRF equipment. These curves do not take into account the de-rating of the condenser efficiency at a lower air density correct? So my understanding is the user must account for this.

( 2017-03-30 15:12:54 -0600 )edit
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Correct. The effectiveness of the outdoor coil will depend on the density of air flowing across it. This must be implicitly characterized by your EIR and capacity curves, EnergyPlus will not account for this automatically. I'm not aware of anyone quantifying this impact, but it is covered by the upcoming ASHRAE Standard 205.

( 2017-03-30 15:53:18 -0600 )edit

When is ASHRAE Standard 205 schedule to be released?

( 2017-03-30 16:11:55 -0600 )edit

When the planets align : ). The committee is working hard towards an advisory public review. Hopefully the APR will be out this summer. The real question is when will the standard be adopted.

( 2017-03-30 16:27:24 -0600 )edit