Re: [EnergyPlus_Support] Zone Ventilation : Design Flow Rate

On Tue, Sep 25, 2012 at 10:33 AM, Richard Raustad <RRaustad@xxxxxxxxxxxx> wrote:

Test it, test it, test it.

Run a simulation with and without the ZoneVentilation:DesignFlowRate object.
You should find that the PTHP flow rate is the same for both simulations, but the loads will change.

Don't forget to report variables needed to verify operation. PTHP OA flow rate, PTHP SA flow rate, PTHP PLR, zone sensible load predicted, etc.

On 9/25/2012 10:10 AM, Vinay Devanathan wrote:

Thanks for your replies.

I would like to know how this situation would be handled by E+ -

I have a PTHP object for space conditioning with 0 cfm OA at all times. I also have a ZoneVentilation:DesignFlowRate object exhausting 55 cfm mimicking bathroom exhaust from the space. In this situation how would the PTHP operate (0 OA cfm by definition)? Would the continuous Zone Ventilation object exhaust make the PTHP operate with a 55 cfm OA to make up for the difference?

Thank you.

On Sep 24, 2012 2:36 PM, "Jim Dirkes" <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

Dear Vinay,

Linda, as usual, is correct. (When she says ?I believe?.?, that normally means ?without a doubt?, since she has forgotten more than what the rest of us know J)

The DesignFlowRate object, in my understanding, establishes minimum outdoor airflow rates for the Air Loop, but as Linda says, has no interaction with any Zone Exhaust fans. Below are my notes from past projects and correspondence with the Help Desk; they may be helpful.

Zone Air Balance

The zone return air is calculated as:

CFM supply - CFMexhaust = CFMreturn.

If the CFMexhaust > CFMsupply , CFMreturn will be 0. If the return flow rate is 0, the OA controller must provide the air needed for the supply air duct, so OA flow will be 100%.

b.      E+ sums up all the zone exhaust air flow rates for a system, denotes this as the system exhaust air. The flow rate at the mixed air node (the supply air flow rate) is the sum of the system level exhaust flow and the return air flow. The outside air flow is whatever is set by the outside air controller, but it is constrained to be >= the system exhaust flow. All of this is based on the assumption that zone exhaust exits the system. Zone exhaust should not be used to send air from one zone to another.

c.       System air balance is affected by cycling fans or those with differing schedules. A cycling AHU fan, if OFF while an exhaust fan is ON, will generate an ?imbalanced airflow? warning. The same is true if one schedule has the AHU fan off while the exhaust fan is ON.

d.      Logic for the ?imbalanced airflow? warning is: ???????????

James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.com
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Linda Lawrie
Sent: Monday, September 24, 2012 2:09 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Zone Ventilation : Design Flow Rate

I believe the answer is NO.

At 12:05 PM 9/24/2012, Vinay Devanathan wrote:

Hello All,

I remember I have had this question arise sometime previously too.

Could anyone tell me how the EXHAUST type ventilation works in ZONEVENTILATION:DESIGNFLOWRATE object. Does E+ automatically make up an equal CFM into the zone as that specified to be EXHAUSTED in order to maintain ZONE AIR BALANCE?

Hope to hear from someone soon.

Thank you.

Vinay
-- 
Richard A. Raustad
Senior Research Engineer
Florida Solar Energy Center
University of Central Florida
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