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Re: [EnergyPlus_Support] Fwd: Outside air mixer is recirculating return flow: Why?



I suspect it is due to the exhaust fans. Have you tried using Cross 
Mixing objects instead?
EPlus will assume the exhaust fans exhaust the air - and will not send 
it to another zone.

Fred Buhl

anarui.oliveira wrote:
> ... Apparently, it is recirculating the exact amount of airflow that 
> I am trying to pass from some zones to adjacent zones with exhaust 
> fans (the aim was precisely to force the return path to collect its 
> air flow from those areas, which are not controlled). Is it related? 
> I can't do that?
>
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "anarui.oliveira" 
> <anarui.oliveira@...> wrote:
>
> Hello.
>
> I have set up a VAV system, with heat recovery, and manually entered 
> the exact same value for for all outside airflow variables and 
> airflow variables (the "air primary loop", the "controller:outside 
> air", the fan, the heat exchanger,... all have the same airflow 
> defined).
> I hoped, with this, to establish that the supply air should be 100% 
> OA, and no return air should be recirculated, but rather become all 
> reflief air, passing through the heat excahnger, as I had understood 
> from previous analysis...
>
> Msg 9808:
>
> Yes. this will provide 100% outside air with heat recovery and no
> recirculation. However, the outside air flow will never be more than 
> the system supply flow rate. So, when the VAV terminal units reduce 
> the total system flow rate, the outside air flow rate will be 
> reduced to match.
> Mike
>
> On 12 Jan 2008 at 1:44, anarui.oliveira wrote:
>   
>> Hello again.
>> If in the Compact HVAC:System:VAV I set:
>> - Heat recovery to sensible
>> - both the Fan Max and Min Flow rate, and both the Max and Min 
>>     
> Outside Air Flow rate to the same value,
>   
>> - and Outside Air Control Type to fixed minimum
>> do I get a system that exhausts to the outside all the return air 
>>     
> of the ATU, recirculating none to the inside and substituting it by 
> outside air, at a fixed rate, but first using the return air to do 
> sensible heat recovery?
>
> BUT, reporting the flow at the different nodes, I find that, 
> although the zone return airflows add up correctly to the "air loop 
> inlet" flow, the Outside Air Mixing Box is diverting about 37% of 
> that return flow and adding it to the outside air flow supplied by 
> the heat exchanger... which was causing the 2:1 limit error I was 
> getting at the heat exchanger, altough the defined exhaust fans are 
> not taking out nearly that much flow (in fact, I checked that the 
> return flow is as expected, until it reaches the Air Mixer)...
> The zone air distribution equipment is Direct Air in all zones 
> served by this Air Loop, so there's no change in the airflow there...
>
> And I can't figure out what is controlling this behaviour or how to 
> change it to the desired model...
>
> Can anyone help me? I'd really like to get this one working.
>
> Best regards,
> Ana Rui.
>
> --- End forwarded message ---
>
>
>
> ------------------------------------
>
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>   


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