[BLDG-SIM] Weather Normalization Question

Dave Robison drobison at teleport.com
Tue Mar 11 11:28:31 PST 2003


for the most part, I have been lurking on this group because, unlike you 
designers, our specialty is calibrated models. We've done hundreds of them, 
and there are very few doing such.

>I order up a years worth of weather
>data for the most recent year and convert it to Doe2
>format.

I don't see how one can do that. At best, you can set the actual 
temperature data into a TMY file. But you still have the old solar, 
humidity, wind speed etc. Now those data are completely incompatible with 
the hourly set of temperatures. Or do you have source for those other 
weather data? I don't believe they are being measured anymore.

>To calibrate models to reality, you must also watch out for what's
>included in the utility bills.

Yes, you have to include things like parking lot lights, if applicable.


>And, of course, there's the difference between how equipment is supposed
>to operate and how it actually operates

As-built and as-operated. That's the whole point of a calibrated model. The 
process of calibration often reveals operational opportunities for further 
savings. As such, it is a low-cost commissioning tool.

>Calibrating models entails either incredibly detailed investigation of
>the actual building,

nonsense. If you have only limited reference data (monthly bills), you 
don't need a detailed hourly model. A monthly simulation works fine and is 
a whole lot easier.

>or else application of the black art of making
>informed guesses ("engineering judgment").

Any modeling involves informed guesses -- eg) how do you model passive 
infiltration? At least with the calibrated model, you have a reality check.

>  In our experience, there's a
>significant portion of models that just won't calibrate, because the
>actual energy use is too strange and resources to investigate why are
>not infinite.

Not so. The monthly bills are a cheap resource and the simulation cost is 
minimal. The only ones we have had to reject were because the metering was 
at a different level of aggregation.


>The real objective of generating reasonable energy savings estimates,
>however, can still be met if the model is overall reasonable.

How do you define reasonable? If fact, we have found that using actual 
weather, rather than TMY, may be necessary to resolve the model sufficiently.

>  It's the
>delta in energy use attributable to the efficiency measures of interests
>that matter, not necessarily tracking down all the unusual quirks of
>utility metering and billing systems.

Yeah, but if you don't have the building defined, can you be sure of the 
calculated delta? At least if you start with a calibrated model, then move 
off it incrementally, you have some confidence that the deltas are reasonable.


>Using a whole building simulation can be a big
>improvement on that practice.

Absolutely


====================
David Robison
Stellar Processes
1033 SW Yamhill Suite 405
Portland, OR 97205
(503) 827-8336
www.ezsim.com

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