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[EnergyPlus_Support] Re: different results with different run periods?
Hi,
Thanks a lot Dr. Li for giving some information about warmup problem. After reading your comments I did a test.
In 1st case, the run period starts from a cloudy day and EnergyPlus performs 22 warmup days.
In 2nd case, the run period starts one day later, which is a sunny day and and EnergyPlus performs 17 warmup days.
The bad thing is that the difference between results of these 2 cases in the first 2 months of the run period is too much to neglect. Yes! Just one day and a noticeable change in the next 2 months.
To be precise:
In the 1st month, the 1st case reports a 16% lower average zone temperature. In the 2nd month, the 1st case reports a 3% lower average zone temperature.
Do you have any idea, which kind of day (sunny or cloudy) is better for starting a weather data-based simulation? I have a feeling that when EnergyPlus needs high number of warmup days, the results in the first months are not acceptable.
Do you know any reference to address this problem, rather than the documents in the EnergyPlus package?
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@...> wrote:
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> Hi, Amy EPlus Engineering Manual has some details on the use of different temperature references for comfort study and some new charts for natural vented cases. The old comfort guide lines did not take into account of the adaptability of human behaviour to outdoor temperature. People living in the warmer country do not need the same degree of cooling as those in the colder region. The PMV values in the simulation may need to be modified. As this is a post processing value, it may be done on a spread sheet, if you know the desired HR, RH% at the new guide line temperature. I have not done this myself. One of my former student reading for PhD is working on this topic. Because it also involves the air current moving across the skin and clothing, the heat balance simulation without some air flow control is not sufficient.
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> Dr. Li
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: amyquartette@...
> Date: Wed, 8 Feb 2012 22:03:58 +0000
> Subject: [EnergyPlus_Support] Re: different results with different run periods?
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> Hi Dr.Li,
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> I'm researching on the comfort of my models within the uncontrolled
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> seasons. Maybe I should just run the annual simulation to get some results. Thank you for your help!
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> best wishes,
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> Amy
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> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@> wrote:
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> > Unless you are working with a comfort model, the operative temperature has no special meaning.
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> > For a zone, it is the average of the Mean AIr Temperature and the Mean Radiant Temperature.
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> > I usually only look at the Zone MAT, because it is the result of the heat balance and is the value to compare with the zone set point temperature.
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> > ==============Because the MRT is related to radiation, therefore, the operative temperature would vary with shading. MRT is also activited by internal lighting and people.=================
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> > I do not know why you wanted to look at one day simulation of a weather file. You make one annual weather file simulation and get the data for the whole year. You can view the data down to timesteps, or view any section of an annual graph and any cobination of the variables using the ResultViewer. You can extract one day data from the single annual spread sheet for comparison as well. The initialization error in digital calculaton is always there, and is minimized by the warming up process. ================Warming up process for DesignDay is different from that for the weather file. I do not know the exact process. The 23°C was for the general temperature value initialization, and might have been changed in the current version.=======================When I said, "I usually run six or more days and compare the last three days.", I acatually run the same three days with the multiple simulation option, so that the similation is repeated three times with the same data. If the second set and the third set of result are nearly equal, the warming up is complete. This was just to test the warming process and have no real application. If you believe this test, then the simulation from sixth day onwards would have negligible initialization error.
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> > Dr. Li
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> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
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> > From: amyquartette@
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> > Date: Tue, 7 Feb 2012 11:24:28 +0000
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> > Subject: [EnergyPlus_Support] Re: different results with different run periods?
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> > Thanks, Linda and Dr. Li!
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> > The zones are not being controlled and the difference of the operative temperatures are about 2°C. Both have no shadow calculation,which I may turn it on next time with 1 day frequence. I didn't change the warmup days and convergence, since I've no idea about them.
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> > I think I should run a 7 days periode to get a relative accurate value for the last day.
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> > However I would like to know, what is the initial operative temperature of a weather file simulation of a giving run periode. Could someone tell?
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> > Thanks in advance!
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> > Amy
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> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@> wrote:
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> > > This is a very frequent question on Zone mean temperature. The anual simulation starts from 23°C, i brief, as any digital calculation requires some initial values. Therefore the first three days are the same, if they are all from Jan 1. If the three days are from the middle of an anual simulation, the short three day one would not be the same. I usually run six or more days and compare the last three days. The DesignDay simulation repeats a few times (second groups of warm up times) until the begining midnight and ending midnight value are the same. This implies that the previouday condition is the same as the current one. Therefore, if the building does not cool down at night, the temperature of the building would be higher in the morning. A weather file simulation would look quite different, when the day is preceded by a cloudy raining day.=====================When using operative temperature, the additional check on "shadowCalculation" would be required. In the WinterDesignDay object, the skyclearance is normally set to zero.
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> > > Dr. Li
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> > > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
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> > > From: linda@
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> > > Date: Mon, 6 Feb 2012 08:09:12 -0700
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> > > Subject: Re: [EnergyPlus_Support] different results with different run periods?
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> > > Make sure that you have the "ShadowCalculation" in
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> > > How far off are they? Are your zones being controlled? There
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> > > is some influence of warmup days -- are they the same for both and
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> > > At 08:03 AM 2/6/2012, amyquartette wrote:
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> > > dear all,
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> > > I have run an annual simulation of my e+ file for the operative
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> > > temperatur of a zone. Then I ran with the same file with a run period
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> > > which has only 3 days. The results of the operative temperaturs for the 3
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> > > days of the 2 simulations are not the same.
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> > > Could someone explain the reason and tell what I should be aware
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> > > of?
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> > > Thank you very much!
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> > > Regard,
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> > > Amy
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