Building Energy Simulation Program Research Articles

Modeling windows in DOE-2.1E

The most recent version of the DOE-2 building energy simulation program, DOE-2.1E, provides for more detailed modeling of the thermal and optical properties of windows. The window calculations account for the temperature effects on U-value, and update the incident angle correlations for the solar heat gain properties and visible transmittance. Initial studies show up to a 35% difference in calculating peak solar heat gain between the detailed approach and a constant shading-coefficient approach. The modeling approach is adapted from Lawrence Berkeley Laboratory's WINDOW 4 computer program, which is used in the National Fenestration Rating Council (NFRC) U-value rating procedure 100-91. This gives DOE-2.1E the capability to assess the annual and peak energy performance of windows consistent with the NFRC procedure. The program has an extensive window library and algorithms for simulating switchable glazings. The program also accounts for the influence of framing elements on the heat transfer and solar heat gain through the window.

A Procedure for Testing the Ability of Whole Building Energy Simulation Programs to Thermally Model the Building Fabric

A procedure was developed for systematically testing whole building energy simulation models and diagnosing the sources of predictive disagreement. Field trials of the method were conducted with a number of detailed state-of-the-art programs by researchers from nations participating in International Energy Agency (IEA) Task 12 and Annex 21. The technique consists of a series of carefully specified test case buildings that progress systematically from extremely simple to relatively realistic. Output values for the cases, such as annual loads, annual maximum and minimum temperatures, peak loads, and some hourly data are compared, and used in conjunction with diagnostic logic to determine the algorithms responsible for prediction differences. The more realistic cases, while geometrically simple, test the ability of the programs to model such combined effects 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 particular heat transfer mechanisms. The procedure was very effective at revealing bugs, faulty algorithms, and input errors in a group of building energy simulation programs that may be considered among the world’s best. The output data from the simulation programs can be used as reference ranges for comparing and diagnosing other detailed or simplified design tools.

Validation of building energy simulation programs: a methodology

The PASSYS project was formed in 1986 by the Commission of the European Communities with the aim of increasing confidence in passive solar heating systems. One of the ways chosen to do this was the approval/development of a European validation methodology for building energy simulation programs. The article summarizes the findings from the work of the Model Validation and Development Subgroup within PASSYS. A detailed description of the work may be found in the following two references: S.Ø. Jensen (ed.), The PASSYS project phase 1, Subgroup model validation and development, Final report, 1986–1989, EUR 13034 EN, Commission of the European Communities, Directorate General XII for Science, Research and Development, Brussels, Belgium, 1990; and S.Ø. Jensen (ed.), Validation of building energy simulation programs, Vols. 1 and 2, Research report PASSYS subgroup model validation and development, EUR 15115 EN, Commission of the European Communities, Directorate General XII for Science, Research and Development, Brussels, Belgium, 1994.

The Energy Performance Of A University Library Building

The energy performance of a four-storey library (PSZ) building of Universiti Teknologi Malaysia (UTM) has been simulated using a microcomputer-based building energy simulation program, SHEAP. The simulation results give a comparative estimate of the potential annual savings for nine parameters. Significant savings (greater than 3.7% of RM 815,680 in operating cost) can result from the use of a Variable Air Volume (VAV) system, reduced air-conditioning times and reduced electrical lighting intensity. A 25% glazed-facade can contribute about 1% in saving,while the other parameters contribute less than 0.2% in savings to be of any significance.

Daylighting design for the Pacific Museum of flight: Energy impacts

The daylighting performance of the Pacific Museum of Flight in Seathle, WA, has been analyzed using the DOE-2.1C building energy simulation program. The main exhibit areas of this museum are enclosed on three sides by glass walls and the 4500-m 2 roof is completely glazed. Because of the large glass areas, a detailed thermal simulation of the building was carried out during its design phase in order to select glazing parameters that would avoid excessive summer solar heat gain, reduce winter heat loss and, at the same time, provide enough natural light of significantly reduce electric lighting loads. Glazing choices considered included conventional glass, heat mirror, and glass with a low-emissivity coating. On/off, stepped and continuous dimming lighting control systems were analyzed. Daylighting was found to be very effective in reducing annual electric lighting load, peak electrical demand, and the overall annual energy consumption.

An intermediate-level model of external convection for building energy simulation

An ‘intermediate-level’ computer code for simulating convective heat exchange at the external facades of a building is described. The code is intermediate in complexity between the traditional data correlations found in guidebooks, and high-level air flow models based on techniques developed in the field of computational thermo-fluid dynamics. It takes into account most of the key dependent variables, including wind speed and direction, the change in shape and height of the atmospheric boundary layer over different terrains, and relative dimensions of the building. The computer is used to generalize available data correlations for the individual flow regimes that prevail around buildings, such as stagnation, boundary layer, and separated flows. Although external convection is normally wind-induced, the code also takes account of the influence of buoyancy-driven motion at low wind speeds. The computations of this improved model compare favorably with the albeit limited experimental data available for real buildings. The improved external convection model has been incorporated as a subroutine in a building energy simulation code: the NBSLD (U.S. National Bureau of Standards Load Determination) program. Simulations were performed for two ‘test houses’ subject to U.K. and U.S. weather conditions respectively. The variation in the computed heating/cooling loads due to the replacement of the original external convection algorithm by the intermediate-level one is reported. These results form the basis for a discussion of the likely sensitivity of dynamic building thermal models to the treatment of external convection with regard to the simulation of both energy consumption and internal environmental conditions. Intermediate-level convection models are advocated as offering the best prospect for meeting the needs of building energy simulation programs in terms of accuracy, economy, and user-friendliness.

Simplified daylighting energy savings for non-daylighting building energy simulation programs

The California Legislature mandated the California Energy Commission (CEC) to establish and periodically update energy efficiency standards for new buildings. To this end, a sensitivity analysis was conducted by the Standards Development Office of the California Energy Commission for nonresidential buildings. The purpose of this parametric analysis was to determine which variations in building parameters actually have significant energy impacts. A “generic” building model was developed and implemented in conducting this sensitivity analysis. The generic model was used as an analytical tool in modeling the energy impact of building parameter variations, as well as architectural and mechanical energy-saving measures on the energy use of each module. It is recognized that the level of significant energy impact is equivalent to, or bounded by the accuracy of the energy analysis tools in predicting energy usage in actual buildings. For the computer program used, DOE 2.1A this accuracy is within ±5%. Since DOE 2.1A and most of the other building energy simulation programs do not have daylighting algorithms, another calculation tool was used to determine daylight availability and lighting power reduction on an hour-by-hour basis for each orientation. This is accomplished with a daylight reduction factor (DRF). Quicklite, a simplified daylighting program, calculated footcandle (lux) levels based on outdoor ambient light levels, physical room dimensions and properties. To assess the impact of the Quicklite calculated footcandle (lux) levels on artificial lighting use, a control scheme was assumed, and a DRF was calculated based on annual sky conditions by climate zone. Once the DRF values are known for each orientation, the electric lighting schedule can be modified. A new profile number, representing the proportion of installed lighting switched on at that hour, replaced the daily lighting schedules when daylighting was utilized (09:00 – 17:00). To test this methodology, a sensitivity analysis was conducted between DOE 2.1A with Quicklite modifications and DOE 2.1B which has a daylighting preprocessor. The results displayed a 3.6% variation in total energy use. We conclude that daylighting calculations for design days using simplified programs can be used to approximate daylighting energy savings in building energy simulation programs that allow zoned lighting schedules but do not calculate daylight contributions.

Glazing energy performance and design optimization with daylighting

This study systematically explores the influence of glazing systems on component loads and annual energy use in prototypical office buildings. The DOE-2.1B building energy simulation program, which contains an integrated daylighting model, is used to determine fenestration energy performance in diverse climates. The sensitivity of total energy use to orientation, window area, glazing properties (U-value, shading coefficient, visible transmittance), window management strategy, installed lighting power, and lighting control strategy are all described. We examine the conditions under which daylighting reduces net anual energy use as well as those conditions under which energy use may increase. Combinations of wall and fenestration properties that minimize net energy requirements as a function of climate and orientation are described.

A Daylighting Computation Procedure for use in DOE-2 and other Dynamic Building Energy Analysis Programs

A computer model is discussed for estimating the annual energy performance of a daylighted building. The model is designed for inclusion into larger building energy simulation programs such as DOE-2, BLAST, and NBSLD, where it will provide means of evaluating the impact of daylighting as it relates to the building's total energy requirements. Algorithms have been developed for determining hourly sky conditions, hourly interior daylight, and hourly adjusted electric lighting load. Comparisons with field measurements show a correlation in most cases within 30 percent of real conditions.

On the Maintenance of saturated standard cells at 3 deg C through the use of thermoelectric cooling : Karoli, Alton R., The Eppley Lab., Inc., and Robert E. Nelson, Energy Conversion, Inc., Preprint, Instrument Society of America, Oct., 1964, 7 pgs, illus.

Experiments performed at the Swiss Federal Laboratories for Materials Testing and Research (EMPA) test cell located in Duebendorf, Switzerland were used for empirical validations of building energy simulation programs. Four solar gain experiments were run with either an exterior Venetian blind or an interior mini-blind mounted over a glazing unit with the blind slats in the horizontal position and with the outer slat edge toward the ground tilted downward 45°. Models of the test cell setup were constructed in two distinctive building energy simulation programs, EnergyPlus and HELIOS, and the measured cooling power in the test cell was compared with the simulated cooling powers. For these experiments, the mean percentage of the absolute mean differences for EnergyPlus and HELIOS were all within 6.1 and 7.1%, respectively.