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Re: [EnergyPlus_Support] problems about vav simulation
My apologies for the slow response. I do not think you will be able to model
this as described. EnergyPlus does not have a component to control cooling
coil bypass.
Mike
On 2 Aug 2004, at 22:50, Xu H.T wrote:
> Dear
>
> I simulate a very simple case: the return air is mixed with the fresh air (the
> left part of return air is discharged into ourdoor) and then pass through the
> cooling coil and supply into the room. Using Hong Kong weather data, I find
> the humidity in the room is very high.
>
> So I change the supply strategy to the following one:
> The return air is divided into three parts. One is discharged into ourdoor
> environment like above description. The second part is mixed with the fresh
> air and then pass through the cooling coil in order to decrease temperature to
> 13â??. The third part of return air is directly mixed with the supply air
> from cooling coil (at 13â??)to get the temperature at 19â?? and then supply
> into the room. For this case, I am puzzled about how to set the primary air
> loop. Two branches are available? (the third part of return air is bypassed to
> mix with the lower temperature air from cooling coil). Also, two temperature
> are set to constant. One is 13â?? from the outlet of cooling coil. The other
> one is 19â?? for the supply temperature. The SINGLE DUCT:VAV:NOREHEAT is used.
> How to arrange the control stragegy?
>
> Thanks very much.
>
> ----- Original Message -----
> From: Michael J. Witte
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Sent: Friday, July 30, 2004 2:48 AM
> Subject: Re: [EnergyPlus_Support] problems about vav simulation
>
>
> My apologies for the delay in diagnosing the problem with this simulation.
> The short answer is that the system is undersized, this causes the supply
> air temperature to be above setpoint and the airflow to the zone increases
> to the maximum in a failed attempt to meet the zone load.
>
> Why is the system undersized?
>
> 1) The system airflow has been sized to exactly meet the design day load
> (sizing factor = 1.0), but some of the days in the weather file are more
> extreme than the design day.
>
> 2) There is a bug in the chilled water coil sizing in version 1.2.0 which is
> causing the coil water flow rate to be undersized by approximately 20%. The
> easiest solution is to raise the zone sizing factor to approximately 1.2.
> The system should then operate as expected. (This bug has been fixed for
> the next release, CR6350.)
>
> Mike
>
>
> On 22 Jul 2004, at 9:05, Xu H.T wrote:
>
> > Dear,
> >
> > I have check as the following two suggestion. However, the results seem
> still > unreasonable. For VAVsystems, it appears constant flowrate at
> fixed supply > temperature. Please help me to inspect this problem. > >
> The simulated system is very simple: mixed air flow through a cooling coil
> and > then suppied into room, using Hong Kong weather data file. I have
> uploaded the > folder: single room vav simulation > > Thanks very much.
> > > Rgs, > Xu > ----- Original Message ----- > From: Michael J.
> Witte > To: EnergyPlus_Support@xxxxxxxxxxxxxxx > Sent: Monday, June
> 28, 2004 2:17 AM > Subject: Re: [EnergyPlus_Support] one about vav
> system > > > This behavior indicates the coil is not large enough.
> Suggestions: > > 1. Make sure the OA flow rate and the supply air
> temperatures in teh ZONE > SIZING and SYSTEM SIZING objects are
> consistent with the simulation OA flow > and temperature setpoints. > >
> 2. Use COIL:Water:DetailedFlatCooling, do not use
> COIL:Water:SimpleCooling. > > If this does not fix the problem, please
> upload the input file to the files > area in the Yahoo group or e-mail
> zipped idf to energyplus-support@xxxxxxxx. > > Mike > > > On 24 Jun
> 2004, at 16:24, Xu H.T wrote: > > > Like the following email. > >
> > > I do a simulation for VAV system. The design day is used for
> sizing of > zone, > system and plant. I set the supply air temperature
> to 19C. I find > with the > design day simulation, the supply air
> temperature isn't 19 > (20.5 actually) and > the air flowrate is
> constant. However, for the run > period simulation, the > supply air
> temperature is actually 19 and the > supply air flowrate is also >
> constant. Why? Any suggestion for this > problem. Thanks. > > Xu > >
> ----- Original Message ----- > From: > zhaicq98 > To:
> EnergyPlus_Support@xxxxxxxxxxxxxxx > Sent: Thursday, > June 24, 2004
> 8:51 AM > Subject: [EnergyPlus_Support] questions about dx > vav
> system > > > I have two questions here. > > First, I am >
> simulating a VAV system with no terminal reheat. I > specify the supply
> > air temperature to be 12.8oC in cooling season and > 35oC in
> heating > season. According to results I got, it works well in >
> cooling season, > trying to keep the indoor temperature under 23oC by >
> varing the supply > air flow rate. While in winter, it keeps heating
> > the space to a high > temperature. In heating season, the supply
> air > flow rate is always at > its maximum value. I can not
> understand why > the supply air flow rate > in heating season does
> not vary. > > Second question is about the > iteration. I am using a
> multispeed DX > coil. The program terminates > when simulating the
> system in May. There > is a fatal error which says > the iteration
> limit is exceeded when > calculating the speed of the > compressor.
> I have no idea how to > resolve the problem. > > I have >
> uploaded the file named BOX4_VAV.idf to the files area. > > Thanks. > >
> ----- Original Message ----- > From: Michael J. Witte > To:
> EnergyPlus_Support@xxxxxxxxxxxxxxx > Sent: Wednesday, July 21, 2004
> 11:09 PM > Subject: Re: [EnergyPlus_Support] Glare index > > > My
> guess is that the coordinates or facing angle of the daylighting >
> reference point in these zones is incorrect. Remember that daylighting >
> reference points are always relative to the zone origin, even when World >
> Coordinates have been specified. In the dxf drawing file, the
> daylighting > reference points are drawn as a small red circle to help
> you verify the > location. You may need to comment out all of the
> daylighting objects and > then add them back one by one to make sure
> each reference point is within > the appropriate zone. If you are
> unable to resolve this, please submit your > input file. > > Mike >
> > > > > On 8 Jul 2004, at 4:26, leeslwong wrote: > > > Hi, > > >
> > I've simulated the daylight performance of a residential block which >
> > includes a kitchen, a living room, 2 bedrooms and a master bedroom. I
> > > called out the annual glare index with hourly basis of each rooms. >
> The > results show that there is no glare (means '0') in the kitchen, a
> > bedroom > and a living room. What situations would have these results?
> > But there are > glare index in other two rooms. Those five room have a
> > window facing with > the same direction (east). As I know glare index
> > never reaches '0'. > Anybody can tell me what's happening and how to >
> solve it? > > Thanks > > > lee > > > > > 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. > > Yahoo! Groups Links > > >
> > > > > > > > ======================================================== >
> Michael J. Witte, GARD Analytics, Inc. > EnergyPlus Testing and
> Support > EnergyPlus-Support@xxxxxxxx > > > > The primary
> EnergyPlus web site is found at: > http://www.energyplus.gov > > The
> group web site is: > http://groups.yahoo.com/group/EnergyPlus_Support/ >
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>
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support
> EnergyPlus-Support@xxxxxxxx
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> The primary EnergyPlus web site is found at:
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>
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========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
EnergyPlus-Support@xxxxxxxx
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