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[EnergyPlus_Support] Re: Fwd: Outside air mixer is recirculating return flow: Why?
Thank you, but I checked the zones receiveing the exhaust fans flow:
the corresponding inlets are registering that incoming flow, and the
return flow from those zones is summing that airflow to the airflow
directly insufflated to that zone. The return flow after the air
mixer (after collecting all zones return flows) is correct.
Everything checks out until the return flow reaches the Air Mixing
Box; if E+ can recognize and properly account the passage of airflow
introduced by the fan, why would it create a problem further ahead?
I did what you suggest in previous versions of my model...
I'm insisting to get it working this way for two reasons:
1- My buildings' HVAC project actually works like that; it collects
all its return flow in uncontrolled zones, rather than in the zones
that are being controlled and where the flow is being insufflated,
and since I have a heat recovery unit, I thought it might
influenciate the results; I don't really have enough experience to
say if it makes that much difference, but...
2- The other reason is the 2:1 limit on the insufflated vs. return
flow in the heat exchanger, since this and other projects actually
have a higher ratio, so, in order not to overestimate the heat
recovery potential, I would want to send the extra airflow to a dummy
zone with (nearly) exterior conditions.
Thanks again,
Ana.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Fred Buhl <wfbuhl@...>
wrote:
>
> 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 ---
> >
> >
> >
> > ------------------------------------
> >
> > The primary EnergyPlus web site is found at:
> > http://www.energyplus.gov
> >
> > The group web site is:
> > http://groups.yahoo.com/group/EnergyPlus_Support/
> >
> > Attachments are not allowed -- please post any files to the
appropriate folder in the Files area of the Support Web Site.
> >
> > EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf
under the Documentation link and press the "search" button.
> > Yahoo! Groups Links
> >
> >
> >
> >
>
>
> [Non-text portions of this message have been removed]
>
------------------------------------
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