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Re: [EnergyPlus_Support] Re: Oversized equipment
You mentioned "flowrate/capacity" out of range, so I presume that you are
modeling a DX cooling system. When a DX system is oversized, normally the
supply air flow rate is increased proportionally to the DX cooling capacity, so
the flowrate/capacity ratio will not be out of range. You can keep the outside
air flow rate the same by seeting the minimum outside air flow rate in the
outside air controller to the original value.
Now, if you are trying to model a system that conditions 100% outside air (with
no return air) and you want to exceed the normal range of capacity/flowrate,
there are two options. One is to simply ignore the capacity/flowrate warnings,
but there is increasing uncertainty in results as you get further away from the
limits. The other approach is to put two DX coils in series, so that th
capacity/flowrate for each individual coil is within the range acceptable to
the model, but the overall capacity of the system is now greater.
Mike
On 15 May 2006 at 8:04, eric_zhou1223 wrote:
>
> Thank you for the response,Mike. It sounds like my description of
> OAFractionSched misled you. In fact, I have to get preliminary sizes
> when I start to simulate a A/C system. The real air conditoning unit
> is however an oversized one than the E+ suggest --it can supply
> overmuch cooling amount than needs. Users have to adjuge the FA
> damper to force normal outdoor air intake. In this simulation, I
> use the real FA flow rate (about same with the autosize value) , and
> the real cooling capactiy(larger than the autosize value).
> The "flowrate/capacity" will be out of range. How can I simulate
> this case?
>
> Or I can describe it like this: I simulate an AC unit and get good
> autosize values about the unit. Then given that I want to know what
> it will look like to change to an oversized equipment, by keep
> preliminary size of OA and enlarge the nominal cooling supply two
> times --this situation I guess could happen in reality.
> I hope this time I explain the question clearer. THank you in
> advance.
>
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte"
> <mjwitte@...> wrote:
> >
> > My apologies for the delayed response.
> >
> > I am not sure I understand completely what you are trying to do.
> When
> > economizer operation is not active, the outside air flow rate is
> calculated as
> > follows. All names in quotes are field names for
> CONTROLLER:OUTSIDE AIR:
> >
> > a) If "MinimumLimit"=FIXED MINIMUM, then OAFlowRate = "minimum
> outside air flow
> > rate" * "Minimum Outside Air Schedule"
> >
> > b) If "MinimumLimit"=PROPORTIONAL MINIMUM, then OAFlowRate
> = "minimum outside
> > air flow rate" * "Minimum Outside Air Schedule" * (Current system
> flow
> > rate/Design system flow rate)
> >
> > It sound like you need to specify a value for "minimum outside air
> flow rate".
> > If you autosize this, the autosize value is the sum of the outside
> air
> > requirements in the ZONE SIZING objects for zones served by this
> air loop.
> >
> > Does this give you enough information to control the outside air
> flow as
> > desired?
> >
> > On 7 May 2006 at 4:12, eric_zhou1223 wrote:
> >
> > > Hi all,
> > >
> > > I was trying to simulate an oversized equipment in a real
> > > project. A huge amount of outside air was introduced in the
> > > simulation, because I must manually size both the capacity and
> flow
> > > rate at the same time and increase them proportionally to avoid
> the
> > > out of range error.
> > >
> > > To keep appropriate outdoor air intake, I have to remain the
> > > autosizing value of airflow rate while only to increase the
> > > autosized capacity to the real value by some way.
> > >
> > > I noticed there is a OAFractionSched in Controller:outside Air
> which
> > > now is all set to 1. Can I change it to a small number (such as
> > > 0.01) to consider a situation where an oversized equipment is
> used
> > > like in my case? Is it the key to solve an oversized unit's
> > > simulation? I found modifying OAFractionSched as 0.01 didnot
> lead
> > > to an expected result like "OA =0.01* original air flowrate" .
> > > Instead,it was a much smaller value seemingly no related to the
> > > original one.
> > >
> > > Could anybody instruct me how to simulate an oversized equipment
> > > like this? Thank you.
> > >
> > > Eric
> > >
> > >
> > >
> > >
> > >
> > >
> > > 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.idf
> and press the
> > > "search" button.
> > >
> > > Yahoo! Groups Links
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> >
> >
> > ========================================================
> > Michael J. Witte, GARD Analytics, Inc.
> > EnergyPlus Testing and Support
> > EnergyPlus-Support@...
> >
>
>
>
>
>
>
>
>
> 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.idf and press the
> "search" button.
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
>
>
========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
EnergyPlus-Support@xxxxxxxx
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