I did not use your DesignDay data, because I did not agree with the content. When I overwritten them with the correct one, the warning were different. I should have said that you IDF did not use the DesignDay sizing simulation. I showed you in the DOS listing, that your design day warming up was not performed. It is not a red herring as you have described. If you do not use the DesignDay object correctly, please do not claim that the EPlus choke the autosizing. You do have DesignDay object specified, but they were not correct. If you do not accept, it is fine with me and you need not read on. "To me, the biggest limitation of the "design day" concept is that it assumes all buildings will experience their peaks under the same conditions, which we all know is not true." This statement is false. Are all the DesignDay data for the same building at different loacation the same? Never. Your reference building has a different epw for each climatic zone, and therefore have different DesignDay data for every zone.
This is true, because the user does not know why sizing is required and cannot find or do not know how to generate a DesignDay object correctly. By naming it the coldest day does not mean that it is the correct coldest day data.
When EPlus use the Coldest day data for sizing in the other Sizing object format, it knows what field to use and what to ignore. It is smarter than the way you transferred the numbers into the three fields, without knowing other requirements.
You are doing the annual simulation without the proper sizing (I am not saying DesignDay sizing because there are other option mentioned by Linda.) and experienced your fatal crash.
That is why there are two simulation control in EPlus. I do the LOAD first and then do the others and not necessary HVAC. There are many other things you can do in EPlus.
Once the maximum values are entered in the IDF, the LOAD run is not needed any more. If you do not run the LOAD first, you do not know the system capacity you need.
If you do not manually enter the maximum condition, the EPlus will find these again by doing a LOAD, and then proceed with the zone, system, and plant sizing. LOAD is not done at avery time step as you may have assumed. Autosizing is not done at every time step either.
This is already done for you in the .stat file. DesignDay data are compiled from these data. There are so many of them, because it simplify your choice for down sizing. 0.4% means, that there are so many days that the conditions will exceed these data. But it is only a statistical calculation.
The weather man can tell you that he cannot predict more than a few days. TMY is not real and is only for those who wanted to compare the findings in the report. Your building cannot change the weather.
Eplus can do this, if you use the correct object. (See the manual or Linda's reply on the similar topic.) No need to have more format as yours
This is not true. If you are in California simulating buildings in California, you only need to compile the DesignDan object once for your lifetime (may be, if that is you do not relocate.)
If you know the location, you can run a DesignDay sizing without the weather file. That was what I did. How do I come up with the LA International DesignDay? I look for a location on the same Latitude. It is the earth tilt angle with the sun that change the OD temperature in the annual cycle.
As I said in my previous mail, that the dry bult temperature is at 2 pm, range is the temperature between 2 pm and 5 am. The wetbulb is the RH at the MDB.(Max. dry buld) This is for Summer, and the sky clearance is 1.
For Winter, the DryBulb and the Wetbulb should be the same, and the range is zero, because the skyclearance is 0. (Cloudy the whole day) You did not know and did not follow this rule for the DesignDay data construction.
Where or how do you choose the data by the software? .epw annual TMY data? I already said this data is not local and current.
I use the everage for the previous 24 hour as the day everagy, then customize the DesignDay data. You can then verify your building material entries, etc.
This means that you are over confident. I have already explained why your Winter designDay object data was not correct, and it triggered the extreme conditions.
I mentioned that California is a long state, because that make the choice of weather station easier. At that latitude there were only one weather station. You preferr the zone weather file. I would never have the need to use it.
On the other hand, if one forced the cloud to be opaque, why should the ODT change. When the ground is covered with snow, it is always 0°C, why does not it flow the wind chill.
Wetbulb equals the drybulb simply means thet the RH is 100% at MDB. Nothing special.
200°C was by the RH out of range. The EPlus continued and gave you a warning. The fatal crash is from another number you have entered or changed. It has gone.
I think it is time for me to leave too. Bye.
Dr. Li To: EnergyPlus_Support@xxxxxxxxxxxxxxx CC: jeremiah@xxxxxxxxxxxxxxxxxxxxxx From: YJHuang@xxxxxxxxxxxxxxxxxxxxxxxx Date: Sat, 17 Mar 2012 13:57:37 -0700 Subject: Re: [EnergyPlus_Support] Fatal error with sizing of AC coil, what could be the problem?
Jeremiah,
It turns out that I did have two DesignDay definition in the file, so that was a "red herring". The conversation has now shifted to my Design Day being faulty, even though it was labeled as a HeatingDesignDay. My contention, though, is that no matter what are the design day conditions, unless they're outside of physical reality, EnergyPlus should not choke in its autosizing calculation (please see my previous post for details). I think that design day calculations have been overstressed and mystified to some degree. They're largely a carry-over from the old days before simulations were available and engineers picked a "design temperature" to manually calculate the size of equipment to put in (I always liked the joke I heard from a former DOE staff, who opined that most contractors use the "door method" , i.e., "whatever equipment fits through the door"). "Design temperatures" has since morphed into "design days" , "monthly design days", "5-day design sequences", etc., so maybe eventually we will just do an annual simulation (or multiple year simulations). To me, the biggest limitation of the "design day" concept is that it assumes all buildings will experience their peaks under the same conditions, which we all know is not true. Your suggestion of having the simulation program automatically choose the peak days presents some difficulties for EnergyPlus. DOE-2 can do this because it simulates LOADS and HVAC in sequence, so by the time it gets to the system simulation, it knows which days have the highest heating and cooling loads and sizes the HVAC accordingly. EnergyPlus, however, does LOADS and HVAC in the same time step (but still in sequence within the time step), so it would not know the peak days unless it were to repeat LOADS twice. The other way, of course, is to preprocess the weather file but then you'll have the worst of both - no coupling with the building, and no knowledge of weather outside of what's in the weather file. Joe Joe Huang White Box Technologies, Inc. 346 Rheem Blvd., Suite 108D Moraga CA 94556 yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx www.whiteboxtechnologies.com (o) (925)388-0265 (c) (510)928-2683 "building energy simulations at your fingertips" On 3/17/2012 11:59 AM, CleanTech Analytics wrote:
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