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RE: [EnergyPlus_Support] Re:which one is right?



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: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Yuen Liu
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: EnergyPlus_Support@yahoogroups.com
From: liuyun22@yahoo.com
Date: Tue, 23 Dec 2008 02:08:22 -0800
Subject: Re: [EnergyPlus_Support] Re:which one is right?

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 differentand 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.com>
To: EnergyPlus_Support@yahoogroups.com
Sent: Tuesday, December 23, 2008 8:44:00 AM
Subject: [EnergyPlus_Support] Re:which one is right?

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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