[BLDG-SIM] hornets nest? Stay the course !!

I really must take some exception to your dismissal of using DOE2 to calculate energy savings. After all, what do you think people use DOE2, or any other energy simulation program, for?

We have done far more projects using DOE2 to estimate energy savings than I care to think about. The answers produced by the analysis must be taken with some caveats, but in general, they are the best available estimate of savings reasonably attainable. Part of what you are getting at, I believe, it the fact that people's behavior on an individual scale is unknowable and that generalized answers do not necessarily apply to specific cases.

In a commercial building this may manifest itself in the fact that part of a building is unexpectedly unoccupied, or that the facilities guy stuck a 2x4 in the outside air damper to get rid of "that stink in suite 302". If you did not anticipate these factors, then of course the energy prediction will be less accurate. On the other hand, if you could predict these factors, then DOE2 would have no problem accounting for them. If you want to conduct an energy savings analysis for a specific building, an audit is really required. If you enter an accurate description of the building and its operation, then DOE2 does an extremely good job of predicting its energy use. And that is what DOE2 is intended to do. It, of course, cannot predict deviant and unexpected behavior in the building operation on it's own ... the person modeling the building must do this.

If you apply savings analysis for a "typical" small office to a specific building operating under specific conditions, then yes, there is and should be significantly less confidence in the answer. This is an issue for the analysis itself, and is not a limitation of the analysis tool.

In residential buildings, this phenomena is even more evident. We have used DOE2.2 to predict the energy flows of residential homes throughout the U.S.. These houses were operated under test conditions, and actual energy flows were measured using co-heating and co-cooling techniques. The test protocol included adding/removing window shades, decreasing/increasing duct loss, increasing/decreasing ventilation rates, etc.. Time after time, the analysis using DOE2 was able to predict the hourly energy flows of these houses within a very small error band (on the order of 1 or 2 percent). This required a detailed model, including all the site and self shading for that individual house. But given detailed and correct inputs, DOE2 has no problem predicting accurate hourly energy use.

Now, add real people to these houses and all bets are off! It is impossible to predict the individual behavior of people. Just think, 20 years ago there were two popular singers, the wholesome Michael Jackson and the apparently perverse "Prince". Who could have predicted that Prince would turn out to be the straight family guy and the other one would become ... well, "Michael Jackson". Put both these guys in a house and try and predict the energy use ... no way! Luckily, group behavior is much easier to predict and estimates of typical energy use are possible, even for residential buildings.

We've been using DOE2.2 for a couple years now, and I encourage anyone using DOE2.1 on a regular basis to check it out. The systems/plant is much more flexible now and organized in a far more logical way. On the loads side, the use of polygons to describe spaces makes detailed models far easier (it took me awhile to realize the advantages of this approach, but once I made the switch the time savings became very evident). The addition of "expressions" to the BDL language makes for the possibility of some extremely "smart" BDL code. Okay okay, the possibility still exists of producing BDL code that thinks it's really smart, but really has a 2x4 stuck in the wrong place.

Paul Reeves

The Partnership for Resource Conservation
140 South 34th Street, Boulder, CO 80303
(303) 499-8611

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