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Re: [EnergyPlus_Support] Re: Forcing system behavior

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Re: Forcing system behavior
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Fri, 10 Dec 2004 10:29:04 -0600
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Perhaps a better to say it would be that mixing autosized and user-specified 
values can be done, but with great care to ensure consistency.  If you have not 
already, be sure to read the section on "Mixing User-Specified and Autosized 
Inputs" in the Input Output Reference starting on p. 328 (pdf p. 358).  
Autosizing is certainly encouraged, even preferred in many cases.

Even though the eio file reports sizes, it is sometimes difficult to know what 
they are based on when using mixed inputs.  For example, the cooling coil 
sizing uses the mixed air temperature resulting from the outside air flow rate 
collected from the Zone Sizing object(s).  But the outside air controller 
specified a higher minimum outside air flow, so the coil would be undersized.  
But as I look again at your input file, the cooling coil wasn't being autosized 
anyway.  Water and air flow rates were user-specified.

Mike


On 10 Dec 2004, at 0:16, sm278424 wrote:

> 
> 
> Mike,
> 
> Thanks for looking at that.
> 
> So, this is news. A "mixture of autosized and user-specified 
> values...generally does not work well". 
> 
> Is this even when the EIO file reports correct/acceptable values for 
> all the autosized parameters?
> 
> Just as a comment, the I/O Reference certainly does not lead one to 
> believe this is the case, the way it is written it seems to encourage 
> the use of autosizing. 
> 
> Shaun
> 
> 
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte" 
> <mjwitte@g...> wrote:
> > It is difficult to evaluate what is happening here, because the 
> file is a 
> > mixture of autosized and user-specified values.  This generally 
> does not work 
> > well in EnergyPlus.  
> > 
> > The supply air temperature not meeting setpoint appears to be a 
> problem with 
> > the cooling coil inputs.  Within COIL:WATER:COOLING, the coil 
> should be allowed 
> > to completely autosize or be completely specified.  Also, there is 
> more outside 
> > air flow specified in the outside air controller than in the ZONE 
> SIZING 
> > object.  Finally, try using COIL:Water:DetailedFlatCooling to see 
> if that will 
> > adequately control the supply air temperature.
> > 
> > Mike
> > 
> > 
> > On 8 Dec 2004, at 2:45, sm278424 wrote:
> > 
> > > 
> > > 
> > > Hi Mike,
> > > 
> > > I've uploaded a couple of files (an EPMIDF and an XLS with some 
> of 
> > > our results). Your response leaves me puzzled because the zone 
> > > setpoint is not being met, yet
> > >   -> unmet demand = 0
> > >   -> the chilled water coil deltaT at peak is only 2.4C when 5.6C 
> is 
> > > design/idf input
> > >   -> the SA volume is fixed at 73 L/s (more than the bare minimum)
> > >   -> the SA temperature is too warm because E+ says it has to be 
> > > warmer (11.67C is idf input)
> > >   -> the radiant panel flow is not at capacity
> > > 
> > > I wonder if you could see if you see any problems with our IDF 
> input.
> > > 
> > > About your earlier question, I'm using COIL:Water:Cooling.
> > > 
> > > Shaun
> > > 
> > > 
> > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte" 
> > > <mjwitte@g...> wrote:
> > > > If the unmet demand is zero, then the plant has enough capacity 
> to 
> > > meet the 
> > > > request from the chilled water coil.  If the zone setpoint is 
> still 
> > > not met, 
> > > > then the chilled water coil is not delivering enough cooling.  
> > > Either the 
> > > > airflow rate is too low, or the supply air temperature is too 
> > > warm.  This could 
> > > > be a control problem, an airflow sizing problem, or a coil 
> sizing 
> > > problem.
> > > > 
> > > > Mike
> > > > 
> > > > 
> > > > On 4 Dec 2004, at 0:40, sm278424 wrote:
> > > > 
> > > > > 
> > > > > 
> > > > > Thanks Mike,
> > > > > 
> > > > > Can I ask one further question re: zone temperatures and 
> unmet 
> > > demand.
> > > > > 
> > > > > If the unmet demand is zero, then I should have enough 
> capacity 
> > > in 
> > > > > the plant loop.  
> > > > > 
> > > > > I have a fixed zone cooling setpoint of 23C.  But in some of 
> our 
> > > > > simulations we see zone air temperatures that are several 
> degrees 
> > > > > above our setpoint.  If the capacity is there, why would my 
> zone 
> > > air 
> > > > > temp be off the setpoint?
> > > > > 
> > > > > Thanks again,
> > > > > Shaun Martin
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte" 
> > > > > <mjwitte@g...> wrote:
> > > > > > 1.  If the air loop outlet setpoint is not being met, then 
> the 
> > > coil 
> > > > > capacity or 
> > > > > > chilled water flow rate or chiller capacity is not 
> adequate.  
> > > Which 
> > > > > cooling 
> > > > > > coil model are you using?  Use COIL:Water:Cooling or 
> > > > > > COIL:Water:DetailedFlatCooling.  COIL:Water:SimpleCooling 
> does 
> > > not 
> > > > > always 
> > > > > > deliver adequate capacity under certain conditions (this 
> model 
> > > will 
> > > > > not be 
> > > > > > available in the next release).
> > > > > > 
> > > > > > 2.  It is very difficult to get a hybrid forced air/radiant 
> > > system 
> > > > > to behave as 
> > > > > > desired with current EnergyPlus control options.  In your 
> case, 
> > > if 
> > > > > you want the 
> > > > > > radiant system to modulate, then why use a VAV air system?  
> > > Perhaps 
> > > > > a constant 
> > > > > > volume system would be better.  Also, you should set the 
> air 
> > > system 
> > > > > to run as 
> > > > > > the first cooling priority, so the radiant system can pick 
> up 
> > > the 
> > > > > remaining 
> > > > > > load.  Alternatively, perhaps the VAV system is oversized?  
> If 
> > > it 
> > > > > is sized 
> > > > > > smaller so that it cannot meet the entire cooling load, 
> then it 
> > > > > will open to 
> > > > > > full flow, thus supplying a constant volume of air.
> > > > > > 
> > > > > > 3.  With cool surfaces for radiant slabs, it would be 
> expected 
> > > that 
> > > > > comfort is 
> > > > > > maintained at higher dry bulb temperatures.  Check all of 
> the 
> > > > > comfort inputs to 
> > > > > > make sure thay are appropriate (clothing, activity level, 
> air 
> > > > > velocity).
> > > > > > 
> > > > > > 4.  These unmet demands are why #1 is happening.  The 
> chiller 
> > > plant 
> > > > > is not able 
> > > > > > to meet the load, so the chilled water supply temperature 
> > > rises, 
> > > > > and then the 
> > > > > > coil cannot meet the supply air setpoint.  Everything is 
> > > > > simultaneous in 
> > > > > > EnergyPlus, so unmet demands result in unmet setpoints.
> > > > > > 
> > > > > > 5.  Zone/Sys Sensible Heating (and Cooling) do not include 
> > > radiant 
> > > > > slab system 
> > > > > > loads.  (I see we need to clarify the definition of this, 
> or 
> > > change 
> > > > > the way it 
> > > > > > is reported.)  Also, if there is outside air, that will 
> place a 
> > > > > load on the 
> > > > > > cooling coil which is not included in the load delivered to 
> the 
> > > > > zone.
> > > > > > 
> > > > > > Mike
> > > > > > 
> > > > > > 
> > > > > > On 1 Dec 2004, at 20:48, sm278424 wrote:
> > > > > > 
> > > > > > > 
> > > > > > > 
> > > > > > > Hi, again,
> > > > > > > 
> > > > > > > I'm modeling a single zone with a VAV system and a 
> radiant 
> > > panel. 
> > > > > I 
> > > > > > > control the mixed air temp, HC water inlet and CC water 
> inlet 
> > > > > with 
> > > > > > > the AIR LOOP OUTLET node, which is controlled by a 
> SETPOINT 
> > > > > MANAGER 
> > > > > > > to a setpoint of 12.2C.
> > > > > > > 
> > > > > > > What happens at peak cooling load is both the radiant 
> panel 
> > > and 
> > > > > the 
> > > > > > > VAV box go to full flow, and E+ allows the AIR LOOP 
> OUTLET 
> > > > > > > temperature to modulate.
> > > > > > > 
> > > > > > > 
> > > > > > > My questions:
> > > > > > > 
> > > > > > > 1. Is there any way to lock in the AIR LOOP OUTLET temp 
> in 
> > > order 
> > > > > to 
> > > > > > > allow the supply volume to vary? 
> > > > > > > 
> > > > > > > 2. Can the supply temp and volume both be locked at 
> specific 
> > > > > values, 
> > > > > > > so that the radiant panel modulates more fully?  Can you 
> > > suggest 
> > > > > > > appropriate radiant panel schedules for this? 
> > > > > > > 
> > > > > > > 3. In our models we've seen the FANGER PMV produce PPD 
> values 
> > > of 
> > > > > > > between 6-10% when zone mean air temperatures are 
> relatively 
> > > high 
> > > > > eg 
> > > > > > > 77-79F (the PPD formula is from the Engineering doc).  
> Does 
> > > this 
> > > > > make 
> > > > > > > sense to you?  The comfort band seems too wide, in most 
> > > buildings 
> > > > > > > complaints start flowing whenever zone DB temperatures 
> exceed 
> > > 75F.
> > > > > > > 
> > > > > > > 4. When we get UNMET DEMAND on our plant loops in these 
> > > > > simulations, 
> > > > > > > the values are very high, much more than the total zone 
> loads 
> > > > > would 
> > > > > > > ever be. We can't explain the values.
> > > > > > > 
> > > > > > > 5. With this model the total zone load is the rad panel 
> > > cooling 
> > > > > rate 
> > > > > > > + the CC rate, but the Zone/Sys Cooling Rate values are 
> all 
> > > over 
> > > > > the 
> > > > > > > place (but usually quite low). Why should this be?  
> > > > > > > 
> > > > > > > 
> > > > > > > 
> > > > > > > Thanks
> > > > > > > Shaun Martin
> > > > > > > 
> > > > > > > 
> > > > > > > 
> > > > > > > 
> > > > > > > 
> > > > > > > 
> > > > > > > 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@g...
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > 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
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > >
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 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@g...
> 
> 
> 
> 
> 
> 
> 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
> 
> 
> 
> 
> 
> 
> 
> 
> 






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