Distributed Renewable Energy Operating Impacts and Valuation Study

Section 2
• An interior diffusion lens.
• A minimum of one thermal break/dead air space in the system between the skylight dome
and the interior diffuser.
• If artificial lighting systems remain a part of the installation, the system shall include
automated lighting control(s) that are programmed to keep electric lights off during
daylight hours.
• The system must provide a minimum of 70 percent of the light output of the artificial
lighting system that would otherwise be used for all of the claimed period of energy
savings, as measured in foot-candles.
Table 2-9 compares the modeled skylight to two skylights in are use in APS’s territory that have
participated in the APS non-residential solar daylighting program. Note that the skylight used in
the eQuest model is meant to model a skylight that meets the requirements of the APS program;
the other skylights shown may exceed the requirements. Appendix H shows the APS
requirements matched to the eQuest building simulation methods for daylighting.
Table 2-9
Comparison of Modeled Skylight to Skylights Used in the APS Region
Skylight Type
U-Value
Solar Heat Gain
Coefficient (SHGC)
Visible Light
Transmittance
Natural Lighting Company: 4'x4' Passive
Daylighting System Model NL-SM 5252 from
test results
0.33–0.35
0.04–0.58
(depending on solar
altitude angle)
Not available
Ciralight: SunTracker, Active System 0.35 0.3196 0.91
Skylight for eQuest model 0.43 0.49 0.70
Data Sources for Building Simulation Models
Multiple sources were used to create the building simulation models. The sources and their use
are as follows:
• APS End-Use Data Acquisition Project (EUDAP) 15 : data for calibrating the baseline
eQuest models.
• American Society of Heating, Refrigeration, and Air Conditioning Engineers
(ASHRAE) 16 : design ventilation in the eQuest model and data for school gym calibration
on lighting energy use.
• APS Energy Efficiency Baseline Study 17 : data for calibrating the baseline eQuest models
and data on the building specifications.
15 Quantum Consulting, Inc., APS End-Use Data Acquisition Project (EUDAP), November 1997.
16 ASHRAE, “Ventilation for Acceptable Indoor Air Quality,” Standard 62-1999, Table 2 Outdoor Air
Requirements for Ventilation.
2-28 R. W. Beck, Inc. Arizona Public Service