TRNSYS Modeling of a Hybrid Lighting System: Energy Savings and Colorimetry Analysis

Abstract

The TRNSYS (TRaNsient SYstems Simulations) Hybrid Lighting Model was revised so that two colorimetric indices pertinent to indoor illumination, the correlated color temperature (CCT) and color rendering index (CRI), could be predicted by the model. For calculation of the CCT and CRI relevant to the hybrid lighting system, the spectral power density (SPD) of beam normal radiation was needed. Though TRNSYS provides algorithms to calculate the magnitude of beam normal radiation on any surface, no methods were provided in TRNSYS to determine the SPD of solar radiation. This thesis describes the inclusion of a spectral model in TRNSYS: Gueymard's SMARTS2 (Simple Model of the Atmospheric Radiative Transfer of Sunshine) algorithm. This algorithm was used to calculate the SPD of beam normal radiation as a function of solar position, atmospheric turbidity, moisture content, and other atmospheric parameters. The TRNSYS hybrid lighting model, augmented by SMARTS2, was used to analyze building illumination and energy loads for a 2500 m2 office building equipped with a hybrid lighting system (HLS). The HLS uses two-axis tracking collectors to collect beam normal radiation that is later divided into visible and infrared components. The visible radiation is piped to luminaires inside the building using optical fibers, while the infrared radiation is focused on thermal photovoltaic arrays and used to generate electricity. The TRNSYS model calculated annual building energy loads (lighting, cooling, and heating) and energy savings in office buildings located in six U.S. cities: Honolulu, HI; Tucson, AZ; Reno, NV; Atlanta, GA; Seattle, WA; and Madison, WI; that were equipped with hybrid lighting systems. Using local utility rates and assuming 52 lm/W lamps efficacies (the commercial average in the U.S.), the annual energy savings per m2 collector area in these cities were: $240-Tucson, $140-Reno, $320-Honolulu, $40- Atlanta, $50-Madison, and $60-Seattle. For the colorimetry analysis, four representative lamp SPDs - warm white fluorescent, full spectrum fluorescent, tungsten incandescent, and halogen incandescent - were defined as standard indoor light source spectrums. Two cities were chosen to perform the analyses in: Tucson, which represented a clear climate with consistent beam normal radiation values, and Seattle, a cloudier climate. The CCT and CRI were calculated each hour during office working hours. When cloudy, the CCT and CRI of the illumination inside took on the values of the lamp providing it, but when beam normal radiation was available these values were influenced by the 5000-5500 K CCT and 80 CRI of the beam normal radiation transmitted though the HLS. Histograms showing the number of hours at varying CCT and CRI ranges for different locations and with different lamps are presented in Chapter 7.