Two Significant Products Available from Task 12

By the time Task 12, Building Energy Analysis and Design Tools for Solar Applications, was completed at the end of 1994, it had gained an international reputation for ground-breaking work in model development and evaluation. The participants can be proud of its many achievements, two of which are described here.

Adeline

ADELINE is an integrated lighting design computer tool that provides architects and engineers with accurate information about the behavior and performance of indoor lighting systems. Both natural and electrical lighting problems can be solved, for simple rooms or the most complex spaces.

ADELINE comprises a suite of computer programs under a use-friendly shell. Within ADELINE, SCRIBE modeler can be used to build any kind of shape that can be defined by lines, edges, and planes around solids and planes. One of the main tasks of PLINK is to associate photometric properties with each component of the model built with SCRIBE, using the material data base which has been incorporated. PLINK is used to input climatic parameters such as sunlight, clear skies, overcast skies, and average skies.

SUPERLITE then produces results such as illumination levels or daylight factors on the work plane, either with natural or electric lighting. Results can be obtained in a very short processing time (less than 5 minutes) and allow appropriate choices to be made early in the design process. SUPERLINK is a program for obtaining estimates of the interactions between daylight, artificial lighting, and the building dynamic thermal performance. RADIANCE produces realistic 3-D displays of various lighting scenarios and provides quantitative analysis such as visual comfort evaluation.

ADELINE was developed by the Task 12 Daylighting Model Development Group, led by Hans Erhorn of the Fraunhofer Institute for Building Physics (Germany).

The ADELINE software may be ordered from: (North American orders) Dr. S. Selkowitz, Building Technologies Program, Building 90-3111, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA. Phone: 1/510/486-6845, Fax: 1/510/486-4089. (All other countries) Hans Erhorn, Fraunhofer Institut für Bauphysik, Abteilung Wärmetecknik, Nobelstrasse 12, D-70569 Stuttgart, Germany. Phone: 49/711/970 3380, Fax: 49/711/970 3399. Cost: Approx. $US 500.

BESTEST

Numerous software programs are available to simulate energy performance in buildings. But these programs often produce widely divergent results--even for the identical building. Consequently, architects and engineers have not trusted the programs and have continued to design buildings without focusing on energy use.

However, a simple method is now available to systematically compare whole-building energy software programs and diagnose the sources of prediction differences, thanks to the work of researchers in the IEA Model Evaluation and Improvement Group. This method, called BESTEST (Building Energy Simulation Test), was originally developed at the National Renewable Energy Laboratory (U.S.), and then refined and field tested by members of that IEA Working Group.

BESTEST is designed to help software developers produce reliable energy software. But another important use of the method is to assure potential software users (architects and engineers) that a particular simulation program gives reasonable results or that a program is appropriate for their particular application.

The BESTEST technique applies a series of carefully specified test case buildings that progress systematically from the extremely simple to the relatively realistic. Output values for the cases--such as annual loads, temperature ranges, and peak loads--are compared and diagnostic logic used to pinpoint the algorithms responsible for prediction differences.

The more realistic cases, although geometrically simple, test the ability of the programs to model effects such as thermal mass, direct solar gain windows, window-shading devices, internally generated heat, infiltration, sunspaces, earth coupling, and deadband and setback thermostat control. The more simplified cases facilitate diagnosis by allowing excitation of certain heat transfer mechanisms.

Field trials of the method were conducted with a number of "reference" programs selected by the IEA researchers to represent the best of the state-of-the-art detailed simulation capability in the US and Europe. These included BLAST, DOE2, ESP, SERIRES, S3PAS, TASE, TRNSYS, CLIM2000, and DEROB.

In practice, the diagnostic procedures have revealed bugs, faulty algorithms, and modeling limitations in every one of the building energy computer programs studied by the researchers. For example, DOE2 is the U.S. Department of Energy's most advanced program and sets national building energy codes and standards. One series of diagnostic tests on this program detected problems with the treatment of solar absorptivity on exterior surfaces. BESTEST traced the problem to a bug in the solar absorptance algorithm associated with surfaces defined as doors. Once the algorithm was corrected, the problem disappeared.

Another diagnostic series enabled the correction of a bug in the ESP program which prevented solar energy absorbed on interior surfaces from being properly calculated. ESP is the program selected as a standard by the European Union for all EU building energy research work.

The majority of the errors found in the reference programs stemmed from incorrect code implementation. Some of the bugs may well have been present for many years. The fact that they have just now been uncovered shows the power of BESTEST and also suggests that validation is not given a high enough priority by code developers and national research programs.

Checking a building energy simulation program with BESTEST requires about 2 to 5 days. Since major programs have taken many years to produce, BESTEST represents an inexpensive and effective way to evaluate them and gain confidence in their performance predictions.

The report produced by the Model Evaluation Group is divided into three parts: The first part is a user's manual that provides instruction on how to apply the BESTEST procedure. The second part describes the development, field testing and production of data for the procedure. The third part presents the output of the reference programs in tables and graphs. A diskette is included containing weather data, some utility programs for formatting output data and all reference data in a common spreadsheet format.

The Model Evaluation Group was a cooperative effort of experts from IEA Solar Heating and Cooling Task 12 and IEA Energy Conservation in Buildings and Community Systems Annex 21. The group was chaired by Run Judkoff of NREL.

Building Energy Simulation Test (BESTEST) and Diagnostic Methods, R. Judkoff and J. Neymark, February 1995, may be ordered from: NREL, Document Distribution Service, 1617 Cole Blvd., Golden, CO 80401, USA. Fax: 1-303-275-4053. No charge.