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Re: [EnergyPlus_Support] Re: Zone will not reach setpoint
Because the terminal units are at max capacity. Try increasing the zone
heating supply air temperature in the zone sizing object to force more
capacity in the terminal unit heating coils. I think I saw 50C supply
air temp off the terminal unit heating coils in the last run I made.
This was not enough capacity. This is getting pretty hot, but you might
try 55C. The cut-outs for resistive heating coils is somewhere between
49C (120F) and 60C (140F). If the supply air temperature is getting too
hot, you need to increase the supply air flow rate. You might have to
manually size the air flow rate if "tweaking" the autosize inputs does
not get the job done.
ZONE SIZING,
Floors 3thru5, !- Name of a zone
12.78, !- Zone cooling design supply air
temperature {C}
40.56, !- Zone heating design supply air
temperature {C} <------
JV Dirkes II wrote:
>
> Dear Richard,
>
> I ran the model with the revised "Central heating design supply air
> temperature". Lo and behold, it does a much better job of heating the
> zone. Nonetheless, it's still 2C lower than the setpoint, which is
> generally considered unacceptable for "real" buildings and won't be a
> good representation of actual energy use. Do you have any ideas why
> it won't reach the setpoint?
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>, "JV Dirkes II" <jvd2pe@...>
> wrote:
> >
> > I'll try it!
> >
> > FYI, ... back earlier in May I posted a problem (Forum message 11377)
> > noting that I had non-zero loads in the zones, but the system was
> > calculated to have zero flow / load. That file was uploaded and
> > called something like "Non-zero loads". Fred Buhl worked on it and
> > recommended that I change (guess what?) the "central heating design
> > supply temp" from 12.8C to the value it's now at. I sent him an
> > e-mail on 5/27 asking about it, but haven't heard back. Fred has the
> > "non-zero" file (so do I), but I deleted it from the Forum upload area.
> >
> > In short, your fix counters an earlier fix. There may be other factors
> > which I've inadvertantly altered since the original problem, but I
> > want you to be aware of the history....
> >
> > Also, regarding your last message about using a higher discharge
> > setting in the wimter: Good call! That will be one of the savings
> > strategies employed for the real building model. This model is a
> > "Baseline" for an ASHRAE 90.1 analysis, so I am using the
> > ASHRAE-specified HVAC and controls (which do not call for winter reset
> > of discharge temp)
> >
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>, Richard Raustad
> > <RRaustad@> wrote:
> > >
> > > You might also consider using the main air loop heating coil to
> pick up
> > > more of the load. Why did you choose to heat the air to 12.8C in the
> > > main air loop during the winter design day?
> > >
> > > Richard Raustad wrote:
> > > >
> > > > Change your "Central heating design supply air temperature (C)" to
> > match
> > > > what is entering the zone terminal unit heating coil. In this case
> > it is
> > > > 12.78 C. The zone now maintains 18-20C.
> > > >
> > > > SYSTEM SIZING,
> > > > AirLoop_AH1, !- name of an AIR PRIMARY LOOP object
> > > > sensible, !- type of load to size on
> > > > Autosize, !- Design (minimum) outside air volumetric
> > > > flow rate {m3/s}
> > > > 1, !- minimum system air flow ratio
> > > > 4.44, !- Preheat design temperature {C}
> > > > 0, !- Preheat design humidity ratio
> > > > {kg-H2O/kg-air}
> > > > 12.78, !- Precool design temperature {C}
> > > > 0.0087, !- Precool design humidity ratio
> > > > {kg-H2O/kg-air}
> > > > 12.78, !- Central cooling design supply air
> > > > temperature {C}
> > > > 12.78, !- Central heating design supply air
> > > > temperature {C} <--------
> > > > coincident, !- Sizing Option
> > > > no, !- Cooling 100% Outside Air
> > > > no, !- Heating 100% Outside Air
> > > > 0.0087, !- Central cooling design supply air
> > > > humidity ratio {kg-H2O/kg-air}
> > > > 0, !- Central heating design supply air
> > > > humidity ratio {kg-H2O/kg-air}
> > > > design day, !- cooling design air flow method
> > > > , !- cooling design air flow rate {m3/s}
> > > > design day, !- heating design air flow method
> > > > ; !- heating design air flow rate {m3/s}
> > > >
> > > > JV Dirkes II wrote:
> > > > >
> > > > > Dear E+ Forum,
> > > > >
> > > > > I've tried using V2.2.026, since that version addresses a known
> > reheat
> > > > > problem, but the model still reflects the problems noted in my
> last
> > > > post.
> > > > >
> > > > > Can anyone help?
> > > > >
> > > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > <mailto:EnergyPlus_Support%40yahoogroups.com>, "JV Dirkes II"
> > > > <jvd2pe@>
> > > > > wrote:
> > > > > >
> > > > > > Dear E+ Forum,
> > > > > >
> > > > > > I am still hoping for some help with this problem. I've added
> > report
> > > > > > variables, tried different settings, double and triple checked
> > all th
> > > > > > input, and still cannot get the zone to warm up.
> > > > > >
> > > > > > Thanks in advance.
> > > > > >
> > > > > > p.s., The uploaded file is called "ZoneTooCold.zip"
> > > > > >
> > > > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > <mailto:EnergyPlus_Support%40yahoogroups.com>, "JV Dirkes II"
> > <jvd2pe@>
> > > > > > wrote:
> > > > > > >
> > > > > > > Dear E+ Forum,
> > > > > > >
> > > > > > > My current model includes a variable volume air handler
> and VAV
> > > > boxes
> > > > > > > with reheat coils. The zone which represent 90% of the
> building
> > > > never
> > > > > > > reaches its setpoint on the Winter Design Day.
> > > > > > >
> > > > > > > Per report variables, the air handler has proper temperature
> > heating
> > > > > > > hot water (82C) and the discharge temperature is at the
> expected
> > > > > > > setpoint (12.9C). Air flow is autosized.
> > > > > > >
> > > > > > > The zone reheat coil is also autosized and has the same
> > heating hot
> > > > > > > water temperature as the air handler. Per report
> variables, the
> > > > > > > reheat coil has water flow and is using energy, but only
> > heats the
> > > > > > > zone to 5C instead of the setpoint (21.1C).
> > > > > > >
> > > > > > > I've tried manually sizing the reheat coils much larger than
> > the
> > > > load,
> > > > > > > but they continue to use only a small fraction of their
> > capacity and
> > > > > > > the zone stays too cold. Please let me know what might
> > prevent the
> > > > > > > reheat coils from warming the zone properly. Thanks!
> > > > > > >
> > > > > > > p.s., I've uploaded the file in case it will be helpful.
> > > > > > >
> > > > > >
> > > > >
> > > > >
> > > >
> > > > --
> > > > Richard A. Raustad
> > > > Senior Research Engineer
> > > > Florida Solar Energy Center
> > > > University of Central Florida
> > > > 1679 Clearlake Road
> > > > Cocoa, FL 32922-5703
> > > > Phone: (321) 638-1454
> > > > Fax: (321) 638-1439 or 1010
> > > > Visit our web site at: http://www.fsec.ucf.edu
> <http://www.fsec.ucf.edu>
> > <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu>>
> > > >
> > > > UCF - From Promise to Prominence: Celebrating 40 Years
> > > >
> > > >
> > >
> > > --
> > > Richard A. Raustad
> > > Senior Research Engineer
> > > Florida Solar Energy Center
> > > University of Central Florida
> > > 1679 Clearlake Road
> > > Cocoa, FL 32922-5703
> > > Phone: (321) 638-1454
> > > Fax: (321) 638-1439 or 1010
> > > Visit our web site at: http://www.fsec.ucf.edu
> <http://www.fsec.ucf.edu>
> > >
> > > UCF - From Promise to Prominence: Celebrating 40 Years
> > >
> >
>
>
--
Richard A. Raustad
Senior Research Engineer
Florida Solar Energy Center
University of Central Florida
1679 Clearlake Road
Cocoa, FL 32922-5703
Phone: (321) 638-1454
Fax: (321) 638-1439 or 1010
Visit our web site at: http://www.fsec.ucf.edu
UCF - From Promise to Prominence: Celebrating 40 Years
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