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Re: [EnergyPlus_Support] Re: high surface temperature

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Re: high surface temperature
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Tue, 29 Jul 2003 14:24:51 -0500
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Hannah:

Differences in solar gains are causing the differences between your 
design days and your "real" day from the weather file.  The design 
days are set to a clearness of 1.0 on July 21, and these values are 
used to generate sun angles and solar intensities for the design 
days.  For the weather file day, you are using September 2, so the 
sun angles are very different and the solar intensities will be 
whatever was measured on that day of the weather file.  You would 
have to inspect the weather file data to see if September 2 is a 
cloudy or clear day.  

The initialization algorithm repeats the first day of each 
environment until the results from two successive days agree within 
the convergence tolerances (set in the BUILDING object).  So, the 
effect on the building is as if the design day, or the first day of a 
weather file run, occured for several days in a row.  This is why you 
see a different result when you start the weather file simulation on 
7/1 vs. 9/2.  When you start the simulation on 7/1, the first day 
(7/1) is repeated to initialize, then the remaining days are 
simulated sequentially.  So, 9/2 is affected by the thermal history 
from the few days preceding it (9/1, 8/31, etc.).  When you start the 
simulation on 9/2, the thermal history is a string of 9/2 days 
repeated.  So, if 8/30-9/1 in the weather file have significantly 
different temperatures and solar than 9/2, this will cause a 
different result.

The basic MRT question is driven by the roof.  The roof surface 
temperatures are driving the MRT due to solar load on the roof.  The 
roof construction has thermal mass with light insulation and the 
adiabatic floor is very massive (8 inches of concrete) so it stores a 
significant amount of heat radiated from the hot roof.

Mike




On 17 Jul 2003, at 23:28, hannahyan wrote:

> I am trying to answer my own question here: why the surface 
> temperature or MRT seems too high when I simulated natural 
> ventilation using design day data. 
> 
> Actually what I want to see is not design day, but a hottest day in
> Seattle. I selected Sep. 2nd to test. I uploaded a Excel file to
> "FILES", the name is :
> 
> XLS_WestZone_SmallOpening_0902_SimulationCompare.xls
> 
> The chart shows four simulations for this day. 
> 
> A.	No wind, maximum outside temp 36 C, 10 C daily temperature 
> range (from ASHRAE Seattle design day data),  
> B.	No wind, maximum outside temp 36 C, 20.7 C daily temperature 
> range,
> C.	5 m/s south wind, maximum outside temp 36 C, 20.7 C daily 
> temperature range,
> D.	Real weather data, simulated from 7/1~9/10, so there would no
> initialization issue. On Sep. 2nd, maximum outside temp 36.7 C,
> minimum 16 C, 3~5m/s wind (S/N) E.	Similar to (D), but simulation
> starts from 9/2. 
> 
> The results show big difference between real weather data and design
> day (same maximum temp, but small daily temperature range and no
> wind). So the question changed to what data to use for system sizing,
> especially for natural ventilation.  
> 
> In addition, the initialization's influence seems not negletable.
> Could any inside people give some explanation from the warm-up
> algorithms?
> 
> 
> Hannah
> 
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Hannah Yan 
> <hannahyan@y...> wrote:
> > Rick,
> > 
> > Thank you for the offer. See the attached file.
> > 
> > Let me explain the situation a little bit. For the
> > west and east exterior walls, I used 4 inch brick
> > outside and 3 inch insulation inside. South, north
> > walls and floors are interior walls. Ceiling is
> > exposed to outside weather. 4 cooling design days are
> > simulated. For the hottest day (1st day), at the cool
> > night(25C outside), MRT in the room arrives 35C. At
> > the hottest time, the south wall and west wall are
> > about 2 C higher than the inside air temperature. 
> > 
> > It is true that there is not much ventilation. But I
> > still suspected about the initialization, and I want
> > to know how to eliminate the initialization effect for
> > design days. 
> > 
> > 
> > 
> > --- Rick Strand <rkstrand@u...> wrote:
> > > Hannah:
> > > 
> > > It is difficult to give you any advice about the
> > > validity of the surface 
> > > temperatures you are seeing because the text of your
> > > message is relatively 
> > > vague.  How much higher are the temperatures than
> > > you are 
> > > expecting?  EnergyPlus does have an initialization
> > > process that it goes 
> > > through, but it should iterate enough days during
> > > the warmup process to 
> > > eliminate the initial conditions.  If you like, you
> > > can send me your input 
> > > file and I will see if the temperatures seem
> > > unreasonable.  That would 
> > > allow me to look at your other concern as well.
> > > 
> > > Rick Strand
> > > 
> > > At 09:25 AM 7/17/2003 -0700, you wrote:
> > > >Hi,
> > > >
> > > >I am simulating a natural ventilation environment
> > > for
> > > >several cooling design days without wind. There are
> > > >some thermal mass on the floor but not too much for
> > > >walls. I think the air temperature looks good, but
> > > >surface temperature and MRT seem a little bit high
> > > >than I expected. I suspect this is because E+ has
> > > some
> > > >special initialization that may influence. What do
> > > you
> > > >think?
> > > >
> > > >Beside, I found air change rate in .csv output
> > > column
> > > >BM seems too high and not corresponds to the
> > > >infiltration volume in column BL. Is this a bug or
> > > >something else?
> > > >
> > > >Thanks,
> > > >
> > > >
> > > >
> > > >
> > > >__________________________________
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References:
- Re: [EnergyPlus_Support] high surface temperature
  - From: Hannah Yan
- [EnergyPlus_Support] Re: high surface temperature
  - From: hannahyan

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