[Bldg-sim] Simulation Calibration

[Dave Robison]

There is an easier way to get a calibrated simulation. Our firm 
provides EZSim -- a simplified simulation model developed 
specifically to calibrate to monthly utility bills. If one does not 
have interval or submetered data, why develop a model in more detail 
than you have data to support? EZSim computes one monthly result at 
the whole building level and uses actual (not TMY) weather data.  See 
http://www.ezsim.com/

Model fit can be quite good. The specification of  "5% of annual" is 
not meaningful in a statistical sense. I prefer to specify in terms 
of MSE. Note that the savings estimate is based on comparing two 
years (actual and baseline) so the standard errors add in quadrature. 
What does this mean? Monthly modeling at MSE of 5% gives an annual 
consumption estimate with MSE of 2%. Comparing two years for a 
savings estimate results in MSE of 5% of annual applied to the 
difference. A 90% Confidence Limit is .96 SE so we have a savings 
estimate of +/- 5%. Not too bad -- given that we should be looking at 
savings of, say 30%, a 5% confidence band is adequate. If you are 
looking at measures with smaller savings, there is not sufficient 
resolution. All this can be done very inexpensively using utility 
bills as the measurement in an hour or less.

The IMPVP referenced by FEMP and LEED fails to provide an adequate 
explanation or discussion if these precision issues. As far as I 
know, EZSim is the only modeling tool that reports MSE of the 
calibration fit and allows for confidence estimates. The caveat is 
that is does not explicitly provide for the myriad of design options 
available in a detailed model. However, the model can be tuned to 
match any other model. Note that it does so only at the monthly 
energy level, not at the hourly level.

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