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[EnergyPlus_Support] Re: Forcing system behavior

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: Forcing system behavior
From: "sm278424" <shaunmartin@xxxxxxx>
Date: Fri, 10 Dec 2004 22:09:11 -0000
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As a user of E+, and especially in the early stage of design, you 
want to autosize most things (everything, in fact, just see what 
happens). 

The radiant panel definition requires a user-specified flow rate (you 
aren't allowed to autosize). Because of this I now seem to have to 
user-specify every parameter for the system and plant, otherwise I 
get errors.  

I'm spending time making up input values for components I don't want 
to design yet. In fact, this is why we're using E+ in the first 
place, to see how the radiant system impacts on the air handling 
system, the building envelop, and the thermal comfort of the 
occupants. 

Part of the problem is that you don't get much in the way of useful 
feedback, just wonky zone temperatures, or error messages that only 
someone debugging the program code can make immediate sense of.  If a 
coil is undersized (or oversized), it would be useful to get a 
caution message, or something.

Seems to me these are pretty major issues.

Thanks once again
Shaun Martin
 

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte" 
<mjwitte@g...> wrote:
> 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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