I have some differences in opinion from Linda in response to your questions (see below - my comments identified by YJH)
Joe
Joe Huang White Box Technologies, Inc. 346 Rheem Blvd., Suite 205A Moraga CA 94556 yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx http://weather.whiteboxtechnologies.com for simulation-ready weather data (o) (925)388-0265 (c) (510)928-2683 "building energy simulations at your fingertips"
On 6/23/2015 8:57 AM, Linda Lawrie
linda@xxxxxxxxxxxxxx [EnergyPlus_Support] wrote:
(YJH) I feel it's far better to do spatial interpolation, i.e., use the data from Cardiff IAP, rather than temporal interpolation, i.e., use the data from previous days. This is particularly true when the two stations are close together and the data gaps are long. At the least, you should plot your data against the Cardiff IAP data to get a sense of how different or similar are the two data sets. From the stuff I've done, wind speed and direction are the most sensitive, followed by daily temperature profiles, especially at night. Depending on how prominent are the differences, you can either insert the IAP data for the data gaps, or make some adjustments when doing so.At 08:59 AM 6/23/2015, lewisza1@xxxxxxxxxxxxx [EnergyPlus_Support] wrote:
I recently posted a question regarding obtaining measured weather data for the creation of EPW files, but since looking at the options, our project group would like to ask some advice on assimilating the data that we have found. To briefly describe our current situation, we have managed to obtain privately measured data from a site (apprx. 3 miles from model site) operated by colleagues at Cardiff University providing air temperature, RH, global solar irradiance (w/s), global illuminance (kLux), diffuse illuminance (kLux), wind speeds, and precipitation every five minutes (much higher granularity than necessary). We feel that this data is preferable to use over Cardiff IAP weather station due to the close proximity. We see a few problems with this data though:
1. There are data gaps (42 days unaccounted for throughout the 2014 year long period)
For this missing data, we that convert data most often just try a duplicate of a good day near the missing day.
2. We only have global irradiance, global illuminance, and diffuse illuminance as lighting data and are
afraid that this is insufficient for lighting. (We don't have diffuse or direct irradiance).
As suggested by Joe Huang in the group, I have had a look at the STRANG database, which has been able to provide me with the direct irradiance at the site coordinates through satellite data. My assumption is that it would be suitable to just subtract direct irradiance from the already measured global irradiance in our data set to obtain diffuse irradiance, and thus our lighting
If it is direct horizontal irradiance, yes. if it is direct normal, no. plus you still need direct normal. (Global - direct normal does not equal diffuse, you need a factor of solar altitude)
The EnergyPlus weather converter can split the global irradiance into direct normal and diffuse horizontal (which are needed by the EnergyPlus program).
(YJH) Wait a minute! You should definitely NOT combine your measured global horizontal irradiance (GHI) with the direct normal irradiance (DNI) from STRÅNG, because all 3 irradiances (as well as the illuminances) are highly interrelated, and mixing them from different sources can easily produce nonsensible results, such as DHI > GHI, etc.
(YJH) You should, instead, compare the GHI from the two sources, and if they're fairly close, I would use STRÅNG for both GHI and DNI.
If you really want to use the measured GHI, you must derive the DNI using an empirical model, such as the Perez Model in the WeatherConverter program. But I would have more faith in the satellite-derived solar in STRÅNG.
(YJH) see my first comment.
issue would be sorted. Is this an appropriate measure? The IDS database did not seem to have the necessary solar data recorded (but perhaps my knowledge of the database is too limited).
As for the 42 days of data gap, would it be suitable to substitute in Weather Underground (Or IDS) Data from Cardiff IAP (apprx. 30 miles away from site) combined with the STRANG data to compensate?
Yes, most probably or the technique I alluded to earlier.
(YJH) I'm not sure what you're saying here. If you mean dropping what data you have onto an existing TRY file of the Cardiff region, I would tell you a big "NO", for the same reason why I don't think you should mix GHI and DNI from 2 sources, i.e., many of the climatic elements on a weather file are interrelated and replacing just one of them and not others will give you a meaningless weather file.
And finally, since the data set we are utilizing does not provide every variable utilized by EnergyPlus in the EPW, would it be suitable to substitute this more accurate weather data into a TRY file of the Cardiff region to ensure compatibility with EnergyPlus?
(YJH) What are the missing data elements that you need for EnergyPlus? Many of the elements on an EPW are actually not used by EP. Some like dewpoint temperature can be calculated by the EP WeatherConverter (or other weather processing software). Others, like pressure, will just default to a constant value based on elevation, although I don't know what's done with wind direction. From what you've described there should be enough data to create a usable EPW.
Up to you. The weather converter for EnergyPlus can again help you with that.
You can also sum your 5 minute precipitation to an hour and use that.
Apologies for all of the questions, but this is my first time creating a weather file from multiple data sources, and I am unsure whether my outlined process has any glaring issues.
Let me know (privately) if I can help you further with any EnergyPlus Weather Converter questions.
Linda
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Posted by: Joe Huang <yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx>
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