[BLDG-SIM] Weather Normalization Question

[Dave Robison <drobison@xxxxxxxxxxxx>]

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