Paul Berdahl

The thermal radiance of clear skies

Measurements of the longwave radiance of the sky were made during the summer of 1979 at Tucson, Arizona; Gaithersburg, Maryland; and St. Louis, Missouri. The global longwave radiation (wavelengths greater than 3 μm) was monitored with a pyrgeometer and the distribution of this radiation in several spectral bands at five different zenith angles was monitored with a spectral radiometer. This paper presents results for the global sky radiation during clear sky conditions. The spectral radiometer was used to calibrate the pyrgeometer and to detect the presence of clouds. The results can most appropriately be summarized in terms of the correlation between the global sky emissivity ϵsky and surface dewpoint temperature Tdp(°C). The global sky emissivity is defined as the ratio of sky radiance to σTa4, where Ta is the absolute air temperature near the ground, and σ is the Stefan-Boltzmann constant. Based on 2945 night-time measurements in all three cities we find ϵsky=0.741 +0.0062Tdp with a standard error of estimate of 0.031. A similar relationship with almost identical coefficients holds during daylight hours.

Characteristics of infrared sky radiation in the United States

Abstract A new algorithm has been developed for calculating the thermal radiant temperature of the sky. It is based on a simple empirical and theoretical model of clouds, together with a correlation between clear sky emissivity and the surface dewpoint temperature. Hourly sky temperatures have been calculated based on typical meteorological year (TMY) weather data sets. A summary of the results is presented for calculations made at 193 TMY sites within the continental United States. The results are displayed in the form of monthly contour maps, histograms, and graphs for the purpose of determining regions of the country in which the radiative cooling of buildings appears to be a promising heat rejection strategy.

Radiant refrigeration by semiconductor diodes

Dousmanis et al. [Phys. Rev. 133, A316 (1964)] demonstrated that GaAs light‐emitting diodes could produce a cooling effect if the quantum efficiency (ratio of photon flux to junction current) is very close to unity (e.g., >0.97). Here, it is pointed out that for narrow‐bandgap semiconductors, the quantum efficiency need not be so high to produce cooling. Also, for narrow‐bandgap semiconductors there is an additional cooling mode in which the reverse‐biased diode cools its radiant environment by absorbing infrared radiation. Maximum cooling rates per unit of junction area are on the order of n2σT4, where n is the index of refraction, σ is the Stefan–Boltzmann constant, and T is the temperature. For small cooling rates the efficiency for cooling can approach the limit imposed by the second law of thermodynamics.

Summary of results from the spectral and angular sky radiation measurement program

Abstract Extensive measurements of the thermal IR radiance of the sky were obtained at 6 U.S. locations: Tucson, AZ; San Antonio, TX; Gaithersburg, MD; St. Louis, MO; West Palm Beach, FL; and Boulder City, NV. Fifty thousand observations were obtained at half hour intervals during 1979 and 1980. Each observation consists of measurements in 7 spectral bands, wavelengths (in microns) of 8.1–13.7, 8.3–9.1, 9.4–9.9, 10.0–11.4, 14.0–15.8, 16.6–21.6 and 6–17 at zenith angles of 0, 20, 40, 60 and 80°. The data have been expressed and presented as apparent sky emissivities. It is shown that the measured spectral and angular sky emissivities can be reliably estimated from a knowledge of the total (global) sky emissivity, using an empirical “sky emissivity” equation. The results are of particular relevance to the performance of radiative cooling systems designed to make use of spectral and/or angular selectivity.

Galvanomagnetic luminescence of indium antimonide

We report measurements of the absolute spectral intensity due to galvanomagnetic luminescence of intrinsic InSb at room temperature. Together with a calculation of carrier and photon transport, these measurements form the basis for a new technique for the determination of carrier lifetimes and diffusion lengths. The excess carrier lifetime for InSb is found to be 6 ns, and the ambipolar diffusion length at 1.9 T is 3 μm. The spectrally integrated luminescence has a bilinear form in terms of the exciting current density  j and magnetic field B: ΔF=GB j, where ΔF is the change in the total emitted radiant energy flux from the thermal equilibrium value ( j=0). In particular ΔF can be negative. The new thermodynamic transport coefficient G has the value 1.8 μW A−1 T−1 at 33 °C and decreases with increasing temperature.

A copper/silica catalyst prepared from a monolayer film of copper 2,2′-bipyridine dimer on CabOSil☆

Abstract A dinuclear copper complex was supported as a monolayer film on Cab-O-Sil (2.27 wt% Cu) as a model for Cu/silica. The supported and unsupported metal complexes were characterized by elemental analyses, EPR, SQUID, DRIFTS, and mass spectrometry (EI and FAB) techniques. The magnetic properties and infrared vibrational spectra were altered when the complex interacted strongly with the support by an ion exchange mechanism. The samples were subsequently decomposed by heating in oxygen to produce a highly dispersed supported CuO/silica. This sample was reduced in H2 and the catalyst was exposed to NO and N2O under controlled conditions in separate experiments. The results of these characterizations are discussed in the framework of the theories of catalytic ensembles.

Radiative heat pumps using narrow-bandgap semiconductors☆

Abstract The solid state radiative heat pump (SSRHP) concept is introduced. It offers the potential to pump infrared radiation - for heating and cooling - with high second law efficiency. In particular, some of the limitations of Peltier-effect heat pumps can be circumvented. Two approaches for constructing SSRHP devices will be described. In one approach the device is a large-area p-n junction, similar to an IR (light) emitting diode. In the second approach one uses orthogonal electric and magnetic fields to alter equilibrium carrier concentrations of electrons and holes near the crystal surface, altering the IR emission due to electron-hole recombination radiation. This phenomenon is usually termed galvanomagnetic luminescence (GML). Either approach can be used to make radiative heat pumps. Materials suitable for SSRHP devices are narrow-bandgap semiconductors with direct bandgaps in the range of 0.03–0.3 eV for room temperature operation. Obvious candidates are InSb, Hg 1−x Cd x Te and Pb 1−x Sn x Te . As a first step in the evaluation of InSb, our laboratory has made absolute spectral measurements of its galvanomagnetic luminescence. These and related measurements in Russia, Japan and Germany are discussed.

Radiative Heat Pumps Using Narrow-Bandgap Semiconductors

The Solid State Radiative Heat Pump (SSRHP) concept is introduced. It offers the potential to pump infrared radiation--for heating and cooling--with high second law efficiency. In particular, some of the limitations of Peltier-effect heat pumps can be circumvented. Two approaches for constructing SSRHP devices are described. In one approach the device is a large-area p-n junction, similar to an IR (light) emitting diode. In the second approach one uses orthogonal electric and magnetic fields to alter equilibrium carrier concentrations of electrons and holes near the crystal surface, altering the IR emission due to electron-hole recombination radiation. This phenomenon is usually termed galvanomagnetic luminescence (GML). Either approach can be used to make radiative heat pumps. Materials suitable for SSRHP devices are narrow-bandgap semiconduc-tors with direct bandgaps in the range of 0.03-0.3 eV for room temperature operation.