RE: [EnergyPlus_Support] Re: cooled beam with VAV

Dear all,

Once the DOAS will be established based on occupancy it means that you will have an airflow pattern on your ACB based on occupancy schedule, but you need to have it based on a zone required cooling or heating capacity (because something should induce this secondary air in ACB. This means DOAS should be driven by two parameters: fresh air for people and required cooling capacity. Once required cooling capacity is not zero, but occupancy is zero, then Energyplus should send such amount of fresh air which will satisfy demand of ACB. For VAV ACB there is a graphs which shows dependency between ratio of cooling capacity/ max cooling capacity @ max primary airflow and the ratio of primary airflow/max primary airflow. So a schedule of minimum amount of fresh air should respect that.

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: 08 September 2015 16:06
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Re: cooled beam with VAV

Francesco,

I think you are suggesting:

Model a VAV DOAS
Supplement that with 4 pipe fan coils in each zone

I'm not sure what you mean by "calculate the fan power/flow ratio of the fan coils in order to consider that in the real design the recirculated air goes through the AHU"

Assuming that the fan coil fan energy is ~0 (because a chilled beam has no fan), and the pump energy for the fan coils is about the same as for chilled beams ... that sounds like a nice solution.

Part of your challenge will be to establish zones and zone scheduling in such a way as to represent the occupant diversity properly. You want the VAV box to actually turn OFF (zero flow) when no one is in the room, so you can't just use a fractional diversity schedule (values 0 - 1.0). I think it must be either 0 or 1, no in-between values.

I did something similar a while ago for a hotel which had room HVAC interlocked with whether the room was rented or not. I made some assumptions about the occupancy rates and made sure some of the rooms were completely off / unoccupied, while others were on a regular schedule.

On Tue, Sep 8, 2015 at 9:32 AM, fpasserini.tn@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

Do you have any idea of a possible workaround, please?
I would model a VAV system without cooled beams and I would balance the cooling loads with fan coils (I would calculate the fan power/flow ratio of the fan coils in order to consider that in the real design the recirculated air goes through the AHU).
Do you think that the calculated energy consumption would be an acceptable approximation?
Best Regards
Francesco

James V Dirkes II, PE, BEMP, LEED AP
CEO/President
The Building Performance Team Inc.
1631 Acacia Dr, GR, Mi 49504

Direct: 616.450.8653
jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx

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