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RE: [EnergyPlus_Support] Fwd: Outside air mixer is recirculating return flow: Why?
Cross Mixing would induce air exchange( in both directions) . I would
suggest a Mixing Obj to result in a one way air transfer from one zone
to another.
Minu Agarwal
CoSA, Buro Happold Consulting Engineers PC
100 Broadway
New York, NY 10005
USA
Telephone: +1 212 334 2025
Fax: +1 212 334 5528
________________________________
From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Fred Buhl
Sent: Monday, March 31, 2008 2:56 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: 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
<mailto:EnergyPlus_Support%40yahoogroups.com> , "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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