Data from nighttime measurements of the net heat flow through several types of211u001eskylights is presented. A well-known thermal test facility was reconfigured to 211u001emeasure the net heat flow through the bottom of a skylight/light well 211u001ecombination. Use of this data to determine the U-factor of the skylight is 211u001econsiderably more complicated than the analogous problem of a vertical 211u001efenestration contained in a test mask. Correction of the data for heat flow 211u001ethrough the skylight well surfaces and evidence for the nature of the heat 211u001etransfer between the skylight and the bottom of the well is discussed. The 211u001eresulting measured U-values are presented and compared with calculations using 211u001ethe WINDOW4 and THERM programs.
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