Energy Savings from Daylighting: A Controlled Experiment

Scott Pigg and Abby Vogen, Energy Center of Wisconsin

Keywords

Abstract

Measuring energy and demand impacts from daylighting-maximizing strategies in commercial buildings can be difficult, particularly when these involve changes in fenestration and fixture specifications in addition to lighting controls. Moreover, though it is well-known that daylighting strategies affect heating and cooling loads, actual measurement of these HVAC impacts is rare.

This paper attempts to address these issues by summarizing the results of a case/control experiment conducted at the highly-instrumented Energy Resource Station near Des Moines, Iowa. For the experiment, lighting and HVAC loads were monitored for two sets of identical rooms. The rooms differed only in their electric lighting and fenestration characteristics: one set of rooms (test rooms) used reduced transmission glazing, direct/indirect fluorescent fixtures, and photosensor lighting controls; the other set of rooms (control rooms) used clear glazing, conventional overhead fixtures, and no lighting controls. This arrangement allowed for a direct comparison of energy consumption and other parameters between the two configurations over three seasons and a variety of weather conditions.

The results indicate overall operating cost savings of 22 percent for the test rooms relative to the control rooms, with 32 percent lower lighting energy use, 25 percent lower cooling energy requirements, and a 28 percent reduction in estimated demand charges. A surprising result is that the experiment showed little heating load penalty from the daylighting strategy: while heating loads were indeed higher in these rooms in very cold weather, this was offset by reduced need for terminal reheat due to room-to-room load imbalances under milder conditions.