Warm up and thermal storage are the issues
here. A repeated run period will have a different thermal history at the
beginning compared to a single run period.
When EnergyPlus starts an environment
period, it repeats the first day over and over to “warm up” the thermal storage
and history conditions. The second pass for a repeated run period will
have the thermal history from the end of the previous run period rather than from
day 1 as for the first pass thru the run period.
I would expect the second run and the
first run to differ slightly during the first days but not well into the run
period. The number of days would be about the same number of days as it
takes for warm up to complete.
Brent Griffith
EnergyPlus Development Team
From:
Sent: Tuesday, December 23, 2008
11:02 AM
To: Linda
Subject: RE: [EnergyPlus_Support]
Re:which one is right?
I
wonder what will happen, if you run your simulation three times.
Will the third run be the same as or nearer to the second run?
I
am thinking of the effect of the initial warming up period.
You are starting on a Winter day, and the simulation starts with a neutral
temperature of 23°C,
I beleive.
Dr. Li
To:
From: liuyun22@yahoo.
Date: Tue, 23 Dec 2008 02:08:22 -0800
Subject: Re: [EnergyPlus_
ooi:
Thank you for the answer!
I did two simulations using the same weather file. The only difference in the
two
idf files used in the simulations is the
settings in object RunPeriod. In the
first run, the field "Number of
times runperiod to be done" was set to 1 and in
the second run this value is changed to
2.
I got different results on heating load / cooling load and the results for the
first run is:
heating:
2.18412E+12GJ
second run:
heating: 2.15145E+12GJ
the run period is from fifth November to fifth March of the next year.
The difference may be small for the total value, but it is large for houly
value
of some days. The houly result is still
different，and this trend will be obvious
for the intermittent cooling or heating.
One day's result is in the attachment.
I am using E+ ver 2.2.
Thanks a lot!
Yunjie
From: ooi
<ooi_kb3@hotmail.
To:
Sent: Tuesday, December 23, 2008
8:44:00 AM
Subject: [EnergyPlus_
Yun Jie,
Cooling load depends on Heat transfer through the walls,
windows, floors, ceilings and roof. Air movement through door, window openings
also contribute
Basically, heat transfer can be by conduction, convection
and radiation and this depends on outside environment. Generally, the data on
outside environment is given by the weather file. If the year’s hourly data on
temperature, radiation, wind speed and direction does not change and the
setpoint for the indoor temperature does not change, then the two years’ energy
consumption should not change.
ooi
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