The Potential of Night Sky Radiation for Humidity Control

2015 ◽  
Author(s):  
Zachary Springer ◽  
M. Keith Sharp
Keyword(s):  
Storage Capacity ◽  
Volume Flow Rate ◽  
Ambient Air ◽  
Dew Point ◽  
Weather Data ◽  
Cooling Load ◽  
Floor Area ◽  
The Us ◽  
Night Sky ◽  
Mountain West

Ambient energy sources, including ambient air, ground and night sky, have potential for space cooling. The night sky offers the lowest temperature and, therefore, the greatest potential across most of the US. Compared to a previous analysis that considered only the sensible cooling load, the objective of this new project was to evaluate the potential of night-sky radiation (NSR) to also serve the latent cooling load. ASHRAE standard 55 was used to establish the comfort limits (22°C for room temperature and 60% relative humidity). Condensation was evaluated as the mechanism for humidity reduction, thus the dew-point temperature, 13.9°C, corresponding to the ASHRAE limits was the maximum target temperature for night-sky cooling. Typical meteorological year (TMY3) weather data was used for eleven locations representing ASHRAE climate zones. Building heat gain, infiltration/ventilation requirements and night-sky radiator size were characterized by a load-to-radiator ratio LRR defined as the infiltration/ventilation volume flow rate times the ratio of building floor area to radiator area. Three values of LRR were evaluated: 0.35, 3.5 and 35 m/hr. Three thermal storage cases were considered: 1. Annual NSR cooling potential (seasonal storage), 2. Diurnal storage, and 3. The minimum storage capacity to serve the entire annual load, as well as the effects of capacity less than the minimum. To evaluate the effect of night-sky radiator temperature on storage capacity, six NSR temperatures Trad = 13.9 to −26.1°C were tested. Results showed that even in Miami, FL (the most challenging climate evaluated), annual NSR potential exceeded the total sensible and latent cooling load, at least for the lowest LRR and highest Trad. For diurnal storage, NSR could serve 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 corresponds to the capacity required to bridge the span of time without NSR availability during which the largest cooling load occurs. This capacity decreases with decreasing LRR and decreasing Trad. For the southeast, large capacity is required, but for Louisville, for instance, sufficient capacity is provided by the equivalent of as little as 0.05 m of water over the floor area of the building for LRR = 0.35 m/hr. These results demonstrate that for much of the US, night-sky radiation has the potential to serve the entire annual sensible and latent cooling load.

The Potential of Sky Radiation for Humidity Control

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Zachary Springer ◽  
M. Keith Sharp
Keyword(s):  
Storage Capacity ◽  
Volume Flow Rate ◽  
Dew Point ◽  
Weather Data ◽  
Cooling Load ◽  
Floor Area ◽  
Space Cooling ◽  
Latent Space ◽  
Mountain West ◽  
Cooling Loads

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.

The Potential of Sky Radiation With Change in Design Parameters

2016 ◽  
Author(s):  
Adrienne M. Parsons ◽  
M. Keith Sharp
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Pipe ◽  
New Orleans ◽  
Storage Capacity ◽  
Thermal Storage ◽  
Ambient Air ◽  
Dew Point ◽  
Cooling Load ◽  
Tank Wall

This study evaluated the building cooling capacity of sky radiation, which was previously identified to have the greatest cooling potential among common ambient sources for climates across the US. [Robinson, et al. 2013b]. A heat pipe augmented sky radiator system was simulated by a thermal network with nine nodes, representing a thin polyethylene cover, white (ZnO) painted radiator plate [Duffie & Beckman 2013], condenser and evaporator ends of the heat pipe, thermal storage fluid (water), tank wall, room, sky and ambient air. Heat transfer between nodes included solar flux and sky radiation to cover and plate, wind convection and radiation from cover to ambient, radiation from plate to ambient, natural convection and radiation from plate to cover, conduction from plate to condenser or, two-phase heat transfer from evaporator to condenser, natural convection from evaporator to water and from water to tank wall, natural convection and radiation from tank wall to room, and overall heat loss from room to ambient. Nodal temperatures were simultaneously solved as functions of time using Typical Meteorological Year (TMY3) weather data. Auxiliary cooling was applied as needed to limit room temperature to a maximum of 23.9°C. For this initial investigation, a moderate climate (Louisville, KY) was used to evaluate the effects of radiator orientation, thermal storage capacity and cooling load to radiator area ratio, LRR. Louisville and two challenging climates (Miami, FL and New Orleans, LA) were then used to evaluate five cover configurations — zero, one and two covers with unconstrained temperature, and zero and one cover with temperature limited to the dew point of ambient air to simulate condensation on the cover. Results were compared to a Louisville baseline with LRR = 10 W/m2K, horizontal radiator and one cover with constrained temperature, which provided an annual sky fraction (fraction of cooling load provided by sky radiation) of 0.861. A decrease to 0.857 was found for an increase in radiator slope to 20°, and a drop to 0.833 for 53° slope (latitude + 15°, a typical slope for solar heating). These drops were associated with increases in average radiator temperature by 0.2°C for 20° and 1.5°C for 53°. A 25% decrease in storage capacity caused a decrease in sky fraction to 0.854. Sky fractions were 0.727 and 0.963 for LRR of 20 and 5, respectively. Sky fractions for the baseline system in Miami and New Orleans were 0.505 and 0.603, respectively. In all three climates, performance was little affected by constraining the cover temperature and by adding a second cover. These results confirm the potential for passive cooling of buildings by radiation to the sky. Climate, LRR and thermal storage capacity had strong effects on performance, while the cover configuration did not. Radiator slope had a surprisingly small impact, considering that the view factor to the sky at 53° tilt is less than 0.5.

Effect of Thermal Storage on the Cooling Capacity of Ambient Sources

2014 ◽  
Author(s):  
Brian S. Robinson ◽  
M. Keith Sharp
Keyword(s):  
Storage Capacity ◽  
Thermal Storage ◽  
Ambient Air ◽  
Cooling Capacity ◽  
Ground Temperature ◽  
Cooling Load ◽  
Space Cooling ◽  
Wide Range ◽  
Sky Temperature ◽  
Night Sky

Ambient sources, including ambient air at dry-bulb and wet-bulb temperature, ground temperature and night sky temperature, were evaluated for their potential to provide space cooling in locations across the U.S. While ground temperature is constant beyond a certain depth, the other sources have fluctuating temperatures, which present intermittent potentials for cooling. Simultaneously, cooling demands also fluctuate with outdoor temperature. Thermal storage can bridge intervals of time during which cooling is needed in the building, but ambient source temperature is too high to provide cooling. The duration of these intervals and the thermal storage capacity required to meet cooling needs based on ambient source potential prior to the interval were quantified for all eleven climate zones across the continental U.S using TMY3 weather data. The thermal storage capacity required to meet the entire annual cooling load is dictated by the span of time without ambient source cooling potential that has the greatest ratio of cooling load to ambient source cooling potential prior to the interval. This maximum thermal storage capacity, normalized by building overall loss coefficient, (this ratio has units of time) was one day or less for night sky temperature for all but the three warmest climates. This ratio was one day or less for wet-bulb temperature for four locations, and for dry-bulb temperature for only two locations. Ground temperature provided continuous cooling potential in all but the three warmest climates, where ground temperature was warmer than the indoor comfort temperature. Because the maximum thermal storage capacity was determined in most climates by uncommon and infrequent coincidence of high cooling demand and low ambient source cooling potential, smaller thermal storage provided substantial cooling capacity in most cases. For instance, ten percent of the maximum supplied 99% of the cooling load for the dry-bulb ambient air source in Albuquerque, and 0.1% of the maximum served over 90% of the cooling load with night sky radiation in New Orleans and Phoenix. While considerable development of hardware and control algorithms to utilize ambient sources for space cooling has occurred, this study shows the potential of these sources to further reduce demands for conventional energy for space cooling across a wide range of climates.

The Cooling Potential of Sky Radiation With Variations in System Parameters

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
M. Adrienne Parsons ◽  
M. Keith Sharp
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Pipe ◽  
Storage Capacity ◽  
Thermal Storage ◽  
Ambient Air ◽  
View Factor ◽  
Water Tank ◽  
Cooling Load ◽  
Tank Wall

This study evaluated the building cooling capacity of sky radiation, which was previously identified to have the greatest cooling potential among common ambient sources for climates across the U.S. A heat pipe augmented sky radiator system was simulated by a thermal network with nine nodes, including a thin polyethylene cover with and without condensation, white (zinc oxide) painted radiator plate, condenser and evaporator ends of the heat pipe, thermal storage fluid (water), tank wall, room, sky and ambient air. Heat transfer between nodes included solar flux and sky radiation to cover and plate, wind convection and radiation from cover to ambient, radiation from plate to ambient, natural convection and radiation from plate to cover, conduction from plate to condenser, two-phase heat transfer from evaporator to condenser, natural convection from evaporator to water and from water to tank wall, natural convection and radiation from tank wall to room, and overall heat loss from room to ambient. A thin layer of water was applied to simulate condensation on the cover. Nodal temperatures were simultaneously solved as functions of time using typical meteorological year (TMY3) weather data. Auxiliary cooling was added as needed to limit room temperature to a maximum of 23.9 °C. For this initial investigation, a moderate climate (Louisville, KY) was used to evaluate the effects of radiator orientation, thermal storage capacity, and cooling load to radiator area ratio (LRR). Results were compared to a Louisville baseline with LRR = 10 W/m2 K, horizontal radiator and one cover, which provided an annual sky fraction (fraction of cooling load provided by sky radiation) of 0.855. A decrease to 0.852 was found for an increase in radiator slope to 20 deg, and a drop to 0.832 for 53 deg slope (latitude + 15 deg, a typical slope for solar heating). These drops were associated with increases in average radiator temperature by 0.73 °C for 20 deg and 1.99 °C for 53 deg. A 30% decrease in storage capacity caused a decrease in sky fraction to 0.843. Sky fractions were 0.720 and 0.959 for LRR of 20 and 5, respectively. LRR and thermal storage capacity had strong effects on performance. Radiator slope had a surprisingly small impact, considering that the view factor to the sky at 53 deg tilt is less than 0.5.

Space Cooling Potentials for Ambient Energy Sources Across the US

2011 ◽  
Author(s):  
Brian S. Robinson ◽  
M. Keith Sharp
Keyword(s):  
Los Angeles ◽  
New Orleans ◽  
Thermal Storage ◽  
Ambient Air ◽  
Ground Temperature ◽  
Cooling Load ◽  
Space Cooling ◽  
The Us ◽  
Sky Temperature ◽  
Indoor Comfort

While solar energy provides a source for passive space heating across a variety of climates, other ambient energy sources may be more appropriate for passive space cooling. These ambient resources include ambient air at dry-bulb and wet-bulb temperatures, ground temperature at locations where the soil is cooler than the indoor comfort temperature, and night-sky radiant temperature, which is substantially lower than ambient air in most climates. The focus of this study was on comparing these sources to cooling loads across climates in the US. Using a degree-day approach, annual cooling potentials were calculated for over 800 TMY3 locations. Color-themed maps for each ambient source at several indoor comfort temperature ranges were constructed as visual references for design purposes. In addition, eight US cities (Denver, CO, Los Angeles, CA, Louisville, KY, Madison, WI, Miami, FL, New Orleans, LA, Phoenix, AZ and Washington DC) were selected to represent a range of climate characteristics, including seasonal ambient temperature, diurnal temperature swings, humidity and sky clearness. For each city, an ambient potential to cooling load ratio (ALR) was calculated, with the potential based on an indoor comfort temperature range of 68°F – 72°F and the load calculated with a base temperature of 65°F. ALR, which neglects phase lags between source and load and the associated need for thermal storage, exceeded one for dry-bulb air and for ground temperature for all locations except Miami, New Orleans and Phoenix. Wet-bulb ALR exceeded one for all locations except Miami, and sky ALR exceeded one for all locations. Finally, the effect of limited thermal storage was estimated by calculating daily ambient source fraction, fas, which is the daily ambient cooling potential divided by the daily cooling load. fas thus approximates the cooling potential of systems with one day’s worth of thermal storage, and has an upper limit of one. Fas, the annual sum of fas, equaled one for ground temperature for Los Angeles and Madison and for sky temperature for Denver and Los Angeles. Fas for ground temperature was above 0.9 for all locations except Miami, New Orleans and Phoenix. Fas for sky temperature exceeded 0.6 for all locations. By utilizing all possible combinations of ambient sources, half of the selected locations attained Fas equal to one and the minimum for all locations still exceeded 0.65.

scholarly journals A Typical Meteorological Year Generation Based on NASA Satellite Imagery (GEOS-I) for Sokoto, Nigeria

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Olayinka S. Ohunakin ◽  
Muyiwa S. Adaramola ◽  
Olanrewaju M. Oyewola ◽  
Richard L. Fagbenle ◽  
Fidelis I. Abam
Keyword(s):  
Energy Systems ◽  
Building Energy ◽  
Global Solar Radiation ◽  
Dew Point ◽  
Weather Data ◽  
Maximum Temperature ◽  
Building Energy Simulation ◽  
Dew Point Temperature ◽  
Northwest Region

Computer simulation of buildings and solar energy systems are being used increasingly in energy assessments and design. This paper evaluates the typical meteorological year (TMY) for Sokoto, northwest region, Nigeria, using 23-year hourly weather data including global solar radiation, dew point temperature, mean temperature, maximum temperature, minimum temperature, relative humidity, and wind speed. Filkenstein-Schafer statistical method was utilized for the creation of a TMY for the site. The persistence of mean dry bulb temperature and daily global horizontal radiation on the five candidate months were evaluated. TMY predictions were compared with the 23-year long-term average values and are found to have close agreement and can be used in building energy simulation for comparative energy efficiency study.

scholarly journals Ozone and NO<sub>x</sub> chemistry in the eastern US: evaluation of CMAQ/CB05 with satellite (OMI) data

2015 ◽  
Vol 15 (4) ◽  
pp. 4427-4461 ◽  
Author(s):  
T. P. Canty ◽  
L. Hembeck ◽  
T. P. Vinciguerra ◽  
D. C. Anderson ◽  
D. L. Goldberg ◽  
...  
Keyword(s):  
Air Quality ◽  
Surface Ozone ◽  
Quality Standards ◽  
Ambient Air ◽  
Daily Maximum ◽  
Air Quality Model ◽  
Ozone Monitoring Instrument ◽  
Air Quality Standards ◽  
The Us ◽  
Us Northeast

Abstract. Regulatory air quality models, such as the Community Multiscale Air Quality model (CMAQ), are used by federal and state agencies to guide policy decisions that determine how to best achieve adherence with National Ambient Air Quality Standards for surface ozone. We use observations of ozone and its important precursor NO2 to test the representation of the photochemistry and emission of ozone precursors within CMAQ. Observations of tropospheric column NO2 from the Ozone Monitoring Instrument (OMI), retrieved by two independent groups, show that the model overestimates urban NO2 and underestimates rural NO2 under all conditions examined for July and August 2011 in the US Northeast. The overestimate of the urban to rural ratio of tropospheric column NO2 for this baseline run of CMAQ (CB05 mechanism, mobile NOx emissions from the National Emissions Inventory; isoprene emissions from MEGAN v2.04) suggests this model may under estimate the importance of interstate transport of NOx. This CMAQ simulation leads to a considerable overestimate of the 2 month average of 8 h daily maximum surface ozone in the US Northeast, as well as an overestimate of 8 h ozone at AQS sites during days when the state of Maryland experienced NAAQS exceedances. We have implemented three changes within CMAQ motivated by OMI NO2 as well as aircraft observations obtained in July 2011 during the NASA DISCOVER-AQ campaign: (a) the modeled lifetime of organic nitrates within CB05 has been reduced by a factor of 10, (b) emissions of NOx from mobile sources has been reduced by a factor of 2, and (c) isoprene emissions have been reduced by using MEGAN v2.10 rather than v2.04. Compared to the baseline simulation, the CMAQ run using all three of these changes leads to a considerably better simulation of the ratio of urban to rural column NO2, better agreement with the 2 month average of daily 8 h maximum ozone in the US Northeast, fewer number of false positives of an ozone exceedance throughout the domain, as well as an unbiased simulation of surface ozone at ground based AQS sites in Maryland that experienced an ozone exceedance during July and August 2007. These modifications to CMAQ may provide a framework for use in studies focused on achieving future adherence to specific air quality standards for surface ozone by reducing emission of NOx from various anthropogenic sectors.

scholarly journals EVAPORATIVE WATER AND AIR COOLERS FOR SOLAR COOLING SYSTEMS. ANALYSIS AND PERSPECTIVES

2017 ◽  
Vol 52 (5) ◽  
Author(s):  
A. Doroshenko ◽  
K. Shestopalov ◽  
I. Mladionov
Keyword(s):  
Systems Analysis ◽  
Ambient Air ◽  
Dew Point ◽  
Cooling Process ◽  
Evaporative Water ◽  
Cooling Systems ◽  
Solar Cooling ◽  
Multistage System ◽  
Process Implementation ◽  
Polymeric Structures

The concept of evaporative coolers of gases and fluids on the basis of monoblock multichannel polymeric structures is presented. Different schemes of indirect evaporative coolers, in which the natural cooling limit is the dew point of the ambient air  are discussed. In such systems the cooling temperature is lower than the wet bulb temperature of the ambient air. Special attention is paid to the recondensation of water vapor for deep evaporative cooling. It is shown that for the solution of the recondensation problem it is necessary to vary the ratio of the contacting air and water flows, particularly in each stage of the multistage system. Recommendations for the deep cooling process implementation in the evaporative coolers of gases and liquids are given.

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