Jim,
Actual weather data should be more important for calibrating a model to utility bills than for predicting ECM savings. Calibration usually corresponds to one year of utility data, and as you show below, weather
can be highly variable year-to-year. (You could calibrate to an average of multiple years of data, and the variability would be reduced, making actual weather data less important.) For predicting savings however, you are concerned with performance over a period
of five to twenty years (or whatever the expected lifetime of the measure is), so weather variability should have minimal influence.
It is an easy exercise to test the sensitivity of a particular model to weather by doing parametric runs using weather files from cities that are somewhat hotter or colder, say a few hundred miles north or south.
This older study found 5% or less difference in general between using actual and TMY data (p. 58 of 128):
Of course, YMMV.
Best of luck with your presentation,
Bill
From: bldg-sim-bounces@xxxxxxxxxxxxxxxxxxxxx [mailto:bldg-sim-bounces@xxxxxxxxxxxxxxxxxxxxx]
On Behalf Of Jim Dirkes
Sent: Thursday, June 28, 2012 11:49 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx; bldg-sim@xxxxxxxxxxxxxxxxxxxxx
Subject: [Bldg-sim] Food for thought....
Dear Forums,
I am busy preparing a short talk for the Fall ASHRAE Energy Modeling Conference. The topic is “An Approach for Calibrating Existing Building Energy Models to their Utility Consumption”.
As part of the preparation, I will address the issue of how much difference might result in energy conservation measure savings predictions if you use
actual weather data for the billing period versus TMY data.
To get a rough idea how much variation there might be, I looked at Degree Days for a span of years. What a variation! (for the city I’m studying at least)
I am not yet sure how that affects total energy consumption – you’ll have to attend my presentation in Atlanta to find out
J.
In the meantime, I am starting to think that existing building energy models should use
actual weather, not TMY data. Have any of you run similar comparisons for existing building models?