New methods for measuring spectral bi-directional transmission and reflection using digital cameras

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Architecture, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 194-201).Advanced fenestration systems are increasingly being used to distribute solar radiation purposefully in buildings. Distribution of visible light and near infrared radiation can be optimized to enhance daylighting and reduce thermal loads. Light redirecting window systems are one of many innovative fenestration systems available for improving the daylighting and thermal performance of buildings. Many emerging and existing light redirecting systems have both spectrally and angularly selective optical properties. To study these properties, a device that measures the spectral, bi-directional transmission and reflection distribution functions of complex fenestration systems is being developed at the Massachusetts Institute of Technology. This device, a goniophotometer, will measure photometric and radiometric BT(R)DFs for radiation of 380 to 1700 nanometer wavelengths, encompassing much of the solar spectrum. The device incorporates spectroradiometrically calibrated digital cameras and absorption filters to gather quasi-spectral information about reflection and transmission by complex fenestration systems. It relies on a half-mirrored, aluminum coated acrylic hemi-ellipsoid to project reflected or transmitted light towards a digital camera.(cont.) The device will be able to characterize BT(R)DFs for a variety of fenestration system materials, assemblies, and building materials. The goal of this research is to support the development of innovative, spectrally and angularly selective window systems that can improve daylighting and comfort and/or reduce cooling and heating loads in buildings. This thesis focuses on calibrating digital cameras to measure radiances with unknown spectra, developing the hemi-ellipsoid for the new goniophotometer, and developing methods for constructing quasi-spectral BT(R)DFs using this new device. The calibrated cameras also have potential for use in other applications, for example, as radiometers and photometers in rooms with light of known spectra.by Nicholas Gayeski.S.M

Predictive pre-cooling control for low lift radiant cooling using building thermal mass

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Architecture, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 143-159).Low lift cooling systems (LLCS) hold the potential for significant energy savings relative to conventional cooling systems. An LLCS is a cooling system which leverages existing HVAC technologies to provide low energy cooling by operating a chiller at low pressure ratios more of the time. An LLCS combines variable capacity chillers, hydronic distribution, radiant cooling, thermal energy storage and predictive control to achieve lower condensing temperatures, higher evaporating temperatures, and reductions in instantaneous cooling loads by spreading the daily cooling load over time. The LLCS studied in this research is composed of a variable speed chiller and a concrete-core radiant floor, which acts as thermal energy storage. The operation of the chiller is optimized to minimize daily energy consumption while meeting thermal comfort requirements. This is achieved through predictive pre-cooling of the thermally massive concrete floor. The predictive pre-cooling control optimization uses measured data from a test chamber, forecasts of controlled climate conditions and internal loads, empirical models of chiller performance, and data-driven models of the temperature response of the zone being controlled. These data and models are used to determine a near-optimal operational strategy for the chiller over a 24-hour horizon. At each hour, this optimization is updated with measured data from the previous hour and new forecasts for the next 24 hours. The novel contributions of this research include the following: experimental validation of the sensible cooling energy savings of the LLCS relative to a high efficiency split system air conditioner - savings measured in a full size test chamber were 25 percent for a typical summer week in Atlanta subject to standard efficiency internal loads; development of a methodology for incorporating real building thermal mass, chiller performance models, and room temperature response models into a predictive pre-cooling control optimization for LLCS; and detailed experimental data on the performance of a rolling-piston compressor chiller to support this and future research.by Nicholas Thomas Gayeski.Ph.D

Estimating Spectral Information of Complex Fenestration Systems in a Video-Goniophotometer

The effective use of complex fenestration systems in buildings requires knowledge of their optical spectral and directional properties. While the directional properties are commonly assessed by the measurement of bidirectional transmission or reflection distribution functions, the addition of spectral information would significantly aid in the design and analysis of such systems. This paper describes the development of a spectral estimation method that reconstructs reflectance and transmittance spectra of unknown complex fenestration samples in the Heliodome, an innovative video-goniophotometer. The estimation method relies on the digital output of a tri-chromatic charge-coupled device camera in eight filterbands to reconstruct a sample's spectrum using the truncated generalised singular value decomposition. This method is validated by comparing estimated spectra with documented reflectance and transmittance spectra of reference samples. In most spectrally selective materials, the method achieved average improvements of 50% over the Heliodome's previous quasi-spectral assessment method

Using Digital Imaging to Assess Spectral Solar-Optical Properties of Complex Fenestration Materials: A New Approach in Video-Goniophotometry

A large variety of angularly selective fenestration systems have been developed in the past two decades and show great potential in improving visual comfort while reducing energy consumption, especially when combined with spectrally selective properties. Such systems include light-redirecting glazing, shading, film coatings, reflectors and others. To assess the potential of these systems accurately and reliably, one needs to be able to predict in detail how they modify the energy, direction and spectral make-up of solar radiation. For this assessment, spectral (wavelength-dependent) Bidirectional Transmission or Reflection Distribution Functions are used, usually referred to as BTDFs or BRDFs, or more generally BSDFs for Scattering Functions

Using digital cameras as quasi-spectral radiometers to study complex fenestration systems

This work discusses the use of digital cameras fitted with absorption filters as quasi-spectral radiometers. By filtering incident light into selected wavelength intervals, accurate estimates of radiances can be made for unknown spectra. This approach is being employed as part of a new video-projection goniophotometer to study the properties of angularly and spectrally selective complex fenestration systems. Complex fenestration systems are increasingly being used to distribute solar radiation purposefully in buildings. They can be utilized to optimize energy performance and enhance daylighting. Radiance estimates from calibrated digital cameras enable the assessment of quasi-spectral, bi-directional scattering distribution functions of total radiance transmitted or reflected by a fenestration system over desired wavelength intervals. A silicon and an indium gallium arsenide digital camera are used to enable measurements across a 380 to 1700 nm wavelength interval.Massachusetts Institute of TechnologyNational Science Foundation (U.S.) (Grant No. 0533269