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[EnergyPlus_Support] Re: AHU & FCU



i am not sure how far along you have gotten with this issue, and i
will not be of help but i am curious from others if it is possible to
model a system similar to yours with a CV AHU serving the zone and
have a secondary FCU also in the same zone? Does energyplus allow this?

-
aj


--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "beyangj" <beyangj@...> wrote:
>
> Dear all,
> 
> I¡¯m modeling a system of FCU with fresh air handling unit. I defined
> an AIR PRIMARY LOOP which treats the fresh air and use DIRECT AIR to
> feed the zone, and the fan coil unit serve the net remaining load. In
> the ZONE EQUIPMENT LIST, I set the heating and cooling priorities to 1
> for the DIRECT AIR and 2 for the fan coils. 
> 
> There are some problems for this model,
> 
> 1. There are two inlet nodes for each zone, one inlet node is for
> outside air processed from the Primary Air Unit, and the other inlet
> node is for FCU. But I found that INLET NODE 1:System Node
> MassFlowRate and INLET NODE 2:System Node MassFlowRate are the same
> for the same zone. I set INLET NODE 1 for Direct Air and INLET NODE 2
> for FCU. The mass flow rate of these two nodes shouldn¡¯t be the same. 
> 
> 2. For my model, the AHU processes all the outside air, and no outside
> air for FCU. But I have 2 times the required fresh air for some
> working hours, half is from the AHU, half comes from the fan coil unit
> even when I set the maximum outside airflow rate of the fan coil unit
> as 0. For some hours, the flow rate of the outside air are smaller
> than the sum of the zones needed fresh air, even sometime it is less
> than that of one zone. Why they are not the same all the time? I
> wonder how I can set the flow rate of fresh air for FCU as 0, and just
> let the AHU have the desired amount of fresh air.   
> 
> 3. I found that the air flow rate of the AHU AIR LOOP INLET:System
> Node MassFlowRate is constant, much greater than the flow rate of the
> AHU outside air. I thought there must be return air recirculating. I
> also found the System Node MassFlowRate are constant for different
> nodes in a year, respectively. How can I set the flow rate of the
> return air as 0 for the AHU? The System Node MassFlowRate should be
> variable for specific node at different hour?
>  
> 4. I also found something strange. The AHU COOLING COIL CHW
> OUTLET:System Node Temp[C] is about 21[C] in the summer, but CHILLER
> CHW INLET:System Node Temp[C] is about 7.6[C], and the CHILLER CHW
> INLET:System Node Setpoint Temp[C](Hourly) is 6.67[C]. Why the AHU
> COOLING COIL CHW OUTLET temperature can be such a high temperature?
> 
> 5. There are 5 zones in this model, and there is a FCU for each zone.
> I set the 5 FCUs as the same pattern, but the air loop in the SVG file
> are different, 2 FCU air loop have return air loop, but 3 FCU loops
> seem not have return air loop. What may make the difference?
> 
> Thanks a lot in advance!
> 
> Young
>




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