Research Papers

The Potential of Sky Radiation for Humidity Control

[+] Author and Article Information
Zachary Springer

Department of Mechanical Engineering,
University of Louisville,
Louisville, KY 40292

M. Keith Sharp

Department of Mechanical Engineering,
University of Louisville,
Louisville, KY 40292
e-mail: keith.sharp@louisville.edu

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received September 11, 2017; final manuscript received December 19, 2018; published online February 19, 2019. Assoc. Editor: Jorge Gonzalez.

J. Sol. Energy Eng 141(4), 041006 (Feb 19, 2019) (10 pages) Paper No: SOL-17-1378; doi: 10.1115/1.4042452 History: Received September 11, 2017; Revised December 19, 2018

The potential of sky radiation (SR) to serve the latent space cooling loads was evaluated. Using ASHRAE standard 55 comfort limits (room temperature 22 °C, relative humidity 60%, and dew-point temperature 13.9 °C), condensation was the chosen mechanism for humidity reduction. Typical meteorological year (TMY3) weather data were used for eleven ASHRAE climate zones. Three values of load-to-radiator ratio (LRR) (infiltration/ventilation volume flow rate times the ratio of building floor area to radiator area) were evaluated: 0.35, 3.5, and 35 m/h. Three thermal storage cases were considered: 1. Annual cooling potential, 2. Diurnal storage, and 3. Minimum storage capacity to serve the entire annual load. Six SR temperatures Trad = 13.9 to −26.1 °C were tested. Even in the most challenging climates, annual SR potential exceeded the total sensible and latent cooling load, at least for the lowest LRR and the highest Trad. For diurnal storage, SR served less than 20% of the load in the hot and humid southeast, but the entire load in the mountain west. The minimum storage capacity to meet the entire annual load decreased with decreasing LRR and decreasing Trad. For the southeast, large capacity was required, but for Louisville, for instance, sufficient capacity was provided by 0.05 m3 of water per m2 of floor area for LRR = 0.35 m/h. These results demonstrate that for much of the U.S., sky radiation has the potential to serve the entire annual sensible and latent cooling load.

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Fig. 1

Enthalpy change from outdoor (TMY3 data) to indoor air (22 C, 60% relative humidity) in Miami, FL. Left–August 1, right–January 1.

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Fig. 2

Sky radiator system schematic

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Fig. 3

Left–Hourly dry-bulb and sky temperatures for August 1. Right—Monthly high and low sky temperatures. Dark bars indicate the monthly high and light bars show the monthly low.

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Fig. 4

Annual dehumidification load and SR capacity at each site with varying radiator temperature for LRR = 03.5 m/h

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Fig. 5

SR fraction when energy storage is unlimited

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Fig. 6

SR fraction with a diurnal energy storage cycle

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Fig. 7

Volume of water required to achieve the highest possible SR fraction

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Fig. 8

Required storage material volume for Miami (LRR = 3.5 m/h)

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Fig. 9

Required storage material volume for Louisville (LRR = 3.5 m/h)

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Fig. 10

Required storage material volume for Rock Springs (LRR = 3.5 m/h)

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Fig. 11

Storage-to-load ratio (SLR)

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Fig. 12

Storage-to-radiation ratio (SRR)

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Fig. 13

SR fraction versus fraction of maximum storage capacity for Miami, Louisville, and Rock Springs, radiator temperature is 13.9 °C (the results for Rock Springs do not vary with LRR)

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Fig. 14

Normalized energy in thermal storage throughout the year in Louisville when radiator temperature is 13.9 °C



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