Robin, please note that inside EnergyPlus, the calculations are based on mass flow rate. The input design volume flow rates are converted to design mass flow rates using a standard density (but with an altitude adjustment). So even though the models might be referred to as constant volume, they are really constant mass flow rate. The volume flow rates are available for reporting but are derived from mass flow rates and available with two different options for density.
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of rgen1202
Sent: Thursday, May 05, 2011 2:16 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: ZoneVentilation Volume Standard Density vary
Lixing,
I think my last problrm comes from the Actuator Node of the OutdoorAir Mixer of my loop. In fact, I have an Outdoor Air Node for Actuator Node (called Outdoor Air Inlet Node). When I look at the features of this node (current density, temperature, pressure) they are the same as the oudoor air, which is what I want. But when I look at this Node MassFlowRate, I have a constant value and the flow seams to be calculated with a constant density of 1.1704 kg/m3. I don't understand why EE+ doesn't take the current outdoor air density to calcul the MassFlow. I have uploaded my file, called venti_ailloop_1zone.idf
Thanks in advance.
Robin
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "rgen1202" <robin.genoud@...> wrote:
>
> Lixing,
>
> I am aware of this density calculation. But I am still surprized of the way EnergyPlus model the ventilation(and the infiltration too) because if I model the mechanical ventilation with an Air Loop containing one exhaust fan constant volume and a 100% OA mixer, I get a constant Mechanical Ventilation Volume Standard Density. Therefore, the MassFlowRate in this case isn't calculated with the outdoor air density but with the standard density and I don't understant why.
>
> In fact, I am interested in the building energy consumption, and I don't know which model is the more accurate, since I have a significative difference in the cooling load due to outdoor a
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