%0 Conference Paper %B 2006 ASHRAE Annual Meeting %D 2006 %T Monitored Energy Performance of Electrochromic Windows Controlled for Daylight and Visual Comfort %A Eleanor S. Lee %A Dennis L. DiBartolomeo %A Joseph H. Klems %A Mehry Yazdanian %A Stephen E. Selkowitz %K building automation and controls %K Building envelope %K commercial buildings %X

A 20-month field study was conducted to measure the energy performance of south-facing large-area tungsten-oxide absorptive electrochromic (EC) windows with a broad switching range in a private office setting. The EC windows were controlled by a variety of means to bring in daylight while minimizing window glare. For some cases, a Venetian blind was coupled with the EC window to block direct sun. Some tests also involved dividing the EC window wall into zones where the upper EC zone was controlled to admit daylight while the lower zone was controlled to prevent glare yet permit view. If visual comfort requirements are addressed by EC control and Venetian blinds, a 2-zone EC window configuration provided average daily lighting energy savings of 10-15% compared to the reference case with fully lowered Venetian blinds. Cooling load reductions were 0-3%. If the reference case assumes no daylighting controls, lighting energy savings would be 44-11%. Peak demand reductions due to window cooling load, given a critical demand-response mode, were 19-26% maximum on clear sunny days. Peak demand reductions in lighting energy use were 0% or 72-100% compared to a reference case with and without daylighting controls, respectively. Lighting energy use was found to be very sensitive to how glare and sun is controlled. Additional research should be conducted to fine-tune EC control for visual comfort based on solar conditions so as to increase lighting energy savings.

%B 2006 ASHRAE Annual Meeting %C Quebec City, Canada %V 112 Issue 2 %8 10/2006 %G eng %1

Windows and Daylighting Group

%2 LBNL-58912 %0 Journal Article %J ASHRAE Transactions %D 2002 %T Measured Winter Performance of Storm Windows %A Joseph H. Klems %X

Direct comparison measurements were made between various prime/storm window combinations and a well-weatherstripped, single-hung replacement window with a low-E selective glazing. Measurements were made using an accurate outdoor calorimetric facility with the windows facing north. The double-hung prime window was made intentionally leaky. Nevertheless, heat flows due to air infiltration were found to be small, and performance of the prime/storm combinations was approximately what would be expected from calculations that neglect air infiltration. Prime/low-E storm window combinations performed very similarly to the replacement window. Interestingly, solar heat gain was not negligible, even in north-facing orientation.

%B ASHRAE Transactions %C Kansas City, MO %V 109, Part 2 %8 07/2003 %G eng %L LBNL-51453 %1

Windows and Daylighting Group

%2 LBNL-51453 %0 Conference Paper %B Thermal Performance of the Exterior Envelopes of Buildings VI Conference %D 1995 %T Measured Performance of Selective Glazings %A Joseph H. Klems %A Mehry Yazdanian %A Guy O. Kelley %X

Measurements of the net heat flow through four selective glazings in comparison with clear double glazing under late summer outdoor conditions are presented. The solar heat gain coefficient (SHGC) for each glazing is extracted from the data and shown to be angle-dependent. Good agreement is found between measured properties and calculations with WINDOW 4.1.

%B Thermal Performance of the Exterior Envelopes of Buildings VI Conference %C Clearwater Beach, FL %8 12/1995 %G eng %L LBL-37747 %1

Windows and Daylighting Group

%2 LBL-37747 %0 Journal Article %J ASHRAE Transactions %D 1995 %T Measurement of Bidirectional Optical Properties of Complex Shading Devices %A Joseph H. Klems %A Jeffrey L. Warner %X

A new method of predicting the solar heat gain through complex fenestration systems involving nonspecular layers such as shades or blinds has been examined in a project jointly sponsored by ASHRAE and DOE. In this method, a scanning radiometer is used to measure the bidirectional radiative transmittance and reflectance of each layer of a fenestration system. The properties of systems containing these layers are then built up computationally from the measured layer properties using a transmission/multiple-reflection calculation. The calculation produces the total directional-hemispherical transmittance of the fenestration system and the layer-by-layer absorptances. These properties are in turn combined with layer-specific measurements of the inward-flowing fractions of absorbed solar energy to produce the overall solar heat gain coefficient.

This paper describes the method of measuring the spatially averaged bidirectional optical properties using an automated, large-sample gonio-radiometer/photometer, termed a Scanning Radiometer. Property measurements are presented for one of the most optically complex systems in common use, a venetian blind. These measurements will form the basis for optical system calculations used to test the method of determining performance.

%B ASHRAE Transactions %V 101, Part 1 %G eng %L LBL-36243 %1

Windows and Daylighting Group

%2 LBL-36243 %0 Journal Article %J ASHRAE Transactions %D 1993 %T Measurement of the Exterior Convective Film Coefficient for Windows in Low-Rise Buildings %A Mehry Yazdanian %A Joseph H. Klems %X

The MoWiTT field facility is used to measure the convective film coefficient over the exterior surface of a window. The MoWiTT-measured data is compared to some commonly-used experimental and theoretical models. The comparison shows that the MoWiTT data disagrees with the previously used models such as the ASHRAE/DOE-2 model. The reasons for these disagreements are discussed. An experimental model, based on the MoWiTT data, is presented to correlate the film coefficient with the difference in temperatures of the exterior glass surface and the ambient, in the natural convection region, and with the site wind speed, in the forced convection region. The wind speed is considered both in windward and leeward hemispheres. The validity of the MoWiTT model for low-rise buildings is then discussed.

%B ASHRAE Transactions %V 100, Part 1 %G eng %L LBL-34717 %1

Windows and Daylighting Group

%2 LBL-34717