Overcast Conditions Research Articles

On the Assessment of a Numerical Weather Prediction Model for Solar Photovoltaic Power Forecasts in Cities

Recent developments in the weather research and forecasting (WRF) model have made it possible to accurately estimate incident solar radiation. This study couples the WRF-solar modifications with a multilayer urban canopy and building energy model (BEM) to create a unified WRF forecasting system called urban WRF–solar (uWRF-solar). This paper tests the integrated approach in the New York City (NYC) metro region as a sample case. Hourly forecasts are validated against ground station data collected at ten different sites in and around the city. Validation is carried out independently for clear, cloudy, and overcast sky conditions. Results indicate that the uWRF-solar model can forecast solar irradiance considerably well for the global horizontal irradiance (GHI) with an R2 value of 0.93 for clear sky conditions, 0.61 for cloudy sky conditions, and finally, 0.39 for overcast conditions. Results are further used to directly forecast solar power production in the region of interest, where evaluations of generation potential are done at the city scale. Outputs show a gradient of power generation produced by the potential available solar energy on the entire uWRF-solar grid. In total, the city has a city photovoltaic (PV) potential of 118 kWh/day/m2 and 3.65 MWh/month/m2.

Balancing prediction accuracy and generalization ability: A hybrid framework for modelling the annual dynamics of satellite-derived land surface temperatures

Annual temperature cycle (ATC) models enable the multi-timescale analysis of land surface temperature (LST) dynamics and are therefore valuable for various applications. However, the currently available ATC models focus either on prediction accuracy or on generalization ability and a flexible ATC modelling framework for different numbers of thermal observations is lacking. Here, we propose a hybrid ATC model (ATCH) that considers both prediction accuracy and generalization ability; our approach combines multiple harmonics with a linear function of LST-related factors, including surface air temperature (SAT), NDVI, albedo, soil moisture, and relative humidity. Based on the proposed ATCH, various parameter-reduction approaches (PRAs) are designed to provide model derivatives which can be adapted to different scenarios. Using Terra/MODIS daily LST products as evaluation data, the ATCH is compared with the original sinusoidal ATC model (termed the ATCO) and its variants, and with two frequently-used gap-filling methods (Regression Kriging Interpolation (RKI) and the Remotely Sensed DAily land Surface Temperature reconstruction (RSDAST)), under clear-sky conditions. In addition, under overcast conditions, the LSTs generated by ATCH are directly compared with in-situ LST measurements. The comparisons demonstrate that the ATCH increases the prediction accuracy and the overall RMSE is reduced by 1.8 and 0.7 K when compared with the ATCO during daytime and nighttime, respectively. Moreover, the ATCH shows better generalization ability than the RKI and behaves better than the RSDAST when the LST gap size is spatially large and/or temporally long. By employing LST-related controls (e.g., the SAT and relative humidity) under overcast conditions, the ATCH can better predict the LSTs under clouds than approaches that only adopt clear-sky information as model inputs. Further attribution analysis implies that incorporating a sinusoidal function (ASF), the SAT, NDVI, and other LST-related factors, provides respective contributions of around 16%, 40%, 15%, and 30% to the improved accuracy. Our analysis is potentially useful for designing PRAs for various practical needs, by reducing the smallest contribution factor each time. We conclude that the ATCH is valuable for further improving the quality of LST products and can potentially enhance the time series analysis of land surfaces and other applications.

Chemical climatology of atmospheric pollutants in the eastern United States: Seasonal/diurnal cycles and contrast under clear/cloudy conditions for remote sensing

We statistically assessed temporal variations of observed concentrations of eight atmospheric pollutants (SO2, NO, NO2, NOy, O3, CO, NH3, and HNO3) at three urban sites and one rural site in the eastern United States for a ten-year period (4 years for NH3). Diurnal/seasonal patterns of observed mean concentrations and their decade-scale trends under different weather conditions were evaluated. Concentrations of pollutants decreased consistently during the observation period (as long as 1997–2013), although nighttime ozone during winter appears to increase because of reduced NO-O3 titration. This study shows that the decay time of major air pollutant concentrations such as SO2 and NOx can be short as a few hours to one day. We also identified substantial differences between the mean concentrations of pollutants at clear sky and overcast conditions that could introduce biases into satellite observations. Surface concentrations of SO2 and CO are distinctly higher under cloud free than under overcast conditions by ∼30% and ∼20% respectively. NO2 shows a complex pattern, but demonstrates lower daytime concentrations under cloud-free skies. All of these estimates are important for understanding the chemical climatology of these atmospheric pollutants, especially their diurnal/seasonal cycles under different weather conditions. For four-year measurements, NH3 shows a substantial difference, with clear-sky observations roughly a factor of two higher than those under overcast conditions. To track changes in the future, the full daily cycle of atmospheric pollutants monitored by geostationary satellite such as the future TEMPO mission may better capture patterns and trends.

Sunspace coupling with hyper-insulated buildings: Investigation of the benefits of heat recovery via controlled mechanical ventilation

An experimental study was conducted to examine the energetic and ergonomic impacts of an optimized mechanically controlled ventilation system, implemented on the partition wall between a hyper-insulated test building and the attached sunspace, to overcome most of the inherent limitations of a purely radiative heat transfer in presence of very low thermal transmittance envelope.The system comprised two vented holes (at floor and ceiling level), piloted by a smart controller on the basis of the temperature difference between the two air volumes. The threshold was progressively reduced from 2 °C to 0.5 °C to ameliorate the energy performance without trespassing the comfort boundaries. Calls for extra heating from the active technical system (electric radiators) were thus minimized, regardless of the climatic conditions: the energy consumption (normalized over the indoor-outdoor daily average temperature difference and over the daily mean solar irradiation) decremented by 36% and 66% respectively compared to the 1 °C and 2 °C configurations, which, in turn, exhibited similar performance. The ergonomic penalty due to thermal overshooting was statistically acceptable.The outcomes were compared to those of a previous monitoring run on the same case study, with 20% less glazed surface: the new configuration more than halved the energy expenditure.Finally, the albedo of the surrounding materials was shown to be a key-player: even under extremely cold and overcast conditions, the sunspace temperature rose up to 40 °C when fresh snow layered all around the perimeter. Further investigation could support broadening the spectrum of potentially efficient applications.

Identifying overcast, partly cloudy and clear skies by illuminance fluctuations

The overcast, partly cloudy and clear sky conditions can determine the diffuse sky radiance and luminance distributions over the sky dome, and thus are crucial for evaluating the solar energy and daylight on and through building envelopes. It is preferable to properly identify the sky condition and determining its diffuse radiance and luminance distribution patterns by the readily available data. In this work, we propose a new approach to identifying the sky conditions, especially the cloudy and clear skies mainly by the horizontal illuminance fluctuation frequency. Illuminance on ground level may fluctuate at high frequency under cloudy skies due to the broken cloud, while vary smoothly under clear skies with few cloud blockages. For input data, the proposed approach needs the horizontal global illuminance that can be readily accessible for many places instead of the “uncommon” measurements on vertical planes or in sky zenith. The fluctuation frequency factor we propose can reduce the misclassification rate for daily and half-day representative sky conditions by 5.7% and 11.5%, respectively, compared to the classifications using the clearness index only.

An Intensive Campaign-Based Intercomparison of Cloud Optical Depth from Ground and Satellite Instruments under Overcast Conditions

An Intensive Campaign-Based Intercomparison of Cloud Optical Depth from Ground and Satellite Instruments under Overcast Conditions

Broadband dependence of atmospheric transmissions in the UV and total solar radiation

Atmospheric broadband transmissions of clouds, aerosols, and ozone in the erythemally weighted ultraviolet (EUV, 290–320 nm), total (spectrally integrated) ultraviolet (TUV, 290–363 nm), and total global solar (GS, 305–2800 nm) spectral regions were analysed with ground-based measurements in Seoul, Korea (37.57°N, 128.98°E) from March 2004 to February 2013. The annual average total transmission expressed as a fraction of the clear-sky irradiance was 77.6% in the EUV, 73.6% in the TUV, and 72.0% in the GS spectral regions. The corresponding values for cloud transmission were 78.4%, 73.9%, and 71.7%. In overcast cloudy conditions, atmospheric transmission was reduced by 45.9%, 50.2%, and 56.6% in the three spectral regions, respectively, indicating the dominant effect of clouds. Aerosol and ozone transmissions had almost the same annual average. Annual average atmospheric transmission effectively decreases with increasing wavelength from EUV to GS regions. However, we found that there was a difference in wavelength dependence of atmospheric transmission for monthly averages, which seems related to the monthly variation of total column ozone (TCO), aerosol, and cloud amount. It is also found that there is a critical value of TCO (TCO =370 DU) for the wavelength dependence of transmission. Higher ozone amount than this turnaround value can cause an increase in transmission from the EUV to GS regions. The monthly wavelength-dependent effects may be attributable more to the different climatological characteristics of the TCO rather than aerosols and clouds.

Frost rings in 1627 BC and AD 536 in subfossil pinewood from Finnish Lapland

Frost rings can provide direct evidence of anomalously cold summertime conditions on hemispheric scales. Here we report frost rings in subfossil pinewood from Finnish Lapland dated dendrochronologically to AD 536 and 1627 BC. These exact calendar dates have been vividly discussed in the literature in the respective contexts of a cold climate anomaly/dust veil/crop failure/famine/Justinianic Plague and the Minoan eruption of Thera (Santorini). Coinciding anomalies in growth and carbon isotope ratios (δ13C) indicate cold and overcast conditions in these years in Finnish Lapland, typical to conditions induced by volcanic dust veils. This evidence reinforces the view of multiple climatic drivers strongly effecting contemporary societies around AD 536 and provides important new evidence regarding the 1627 BC event. We report a frost ring for this year, and also consider evidence from Lapland for other Thera candidate eruptions in the 16th century BC. The marker years 1560 BC and 1546 BC in bristlecone pine tree rings in North America are positioned within negative departures in our δ13C data. Most likely, the frosts occurred somewhere in July and were driven by dust veils from Northern Hemisphere. Although not indicative of volcanic provenance, frost rings and other dendroclimatic proxies dated to exact calendar years offer important time markers for chronological frameworks which can synchronize archaeological, historical and environmental data to further our understanding of environmental changes at scales that matter to human societies.

Design and validation of a compact embedded photometric device for real-time daylighting computing in office buildings

Studies have shown that the exposure to daylight can have substantial visual/non-visual benefits for building occupants. To optimise daylighting provision while maintaining a comfortable visual environment, daylighting control systems have been investigated by architectural design and academic research for a number of years. However, real-time regulation of daylighting in buildings requires transient daylighting simulation with high accuracy and, daylighting simulation, as performed to date, is significantly impacted by the employed sky luminance distribution models which only crudely reproduce the real sky characteristics due to oversimplification and limited luminance sampling inputs.In this paper, an embedded photometric device is proposed to combine high dynamic range (HDR) imaging based high-resolution sky luminance monitoring with quasi real-time on-board daylighting computing, composed of a low-cost image sensor and a field programmable gate array (FPGA) micro-processor. A deliberate calibration procedure of the whole imaging system, regarding its spectral response (spectral correction error f’1 = 8.89%), vignetting effect and signal response, was formulated and validated experimentally. The device was made to measure a wide luminance range (150 dB) including that of the direct solar disk, sky vault, and landscape simultaneously. Finally, experiments during predominant clear and overcast sky conditions were conducted respectively to assess its performance in daylighting simulation, both qualitatively and quantitatively. The experimental results demonstrated its quality in solar tracking as well as its capability to reduce daylighting simulation error to 17∼13 of that of a common practice using the conventional Perez all-weather sky model for workplane illuminance calculation in office buildings.

Performance of global luminous efficacy models and proposal of a new model for daylighting in Burgos, Spain

Abstract Daylighting is recognized as an important and useful strategy in the design of energy efficient buildings. Daylight is still the best source of light for good colour rendering and visual comfort. In this study, a new model of global luminous efficacy over a horizontal surface is proposed. A comparative study of eighteen classic models is presented, to obtain global horizontal illuminance, using both, the original formulation and new formulae with local adaptations, in order to determine the most suitable models for the conditions in Burgos (Spain). With this aim in mind, the selected models consisted of six models developed for all sky conditions, five models for clear sky conditions, three for partly cloudy sky and four for modelling overcast sky conditions. These eighteen models were also compared with the proposed model using experimental global illuminance measurements for different sky conditions. It was shown that the proposed model behaved in a better way than most of the classic models selected from the literature; both for all sky conditions and for particular sky conditions (clear, partly cloudy and overcast). The proposed model was therefore generally applicable, with no need to employ a different model for each particular sky condition.

Declining diurnal temperature range in the North China Plain related to environmental changes

The decreases in diurnal temperature range (DTR) observed in most regions are generally linked to the increase in cloud cover. However, declining clouds and rising aerosols observed over the North China Plain (NCP) of China make it elusive to elucidate the underlying mechanisms behind the declining DTR observed in this region. Here, we analyze the changes in DTR characteristics in the NCP based on 54-year surface temperature observations, in combination with collocated environmental variable measurements. Overall, there is a significant declining trend of DTR from 1960 to 2014 at a rate of − 0.12 °C/decade, largely due to a larger increase in minimum temperature during the night. The cloud effect on DTR is further explored by comparing DTR under clear-sky and overcast conditions, which exhibits a distinct annual cycle with a minimum in summer and a maximum in winter. The decreasing rate of DTR under overcast condition is − 0.30 °C/decade, much faster than the rate of − 0.17 °C/decade under clear-sky condition, indicating steady increases in the nighttime warming effect of middle- or high-clouds. Also, the elevated aerosol concentration could contribute to the declining DTR, due to the cooling effect of aerosols. Moreover, the effect induced by sunshine duration and water vapor on DTR cannot be ignored either. All of the aforementioned environmental variables combine to affect the long-term trend of DTR, despite their different roles in modulating DTR. Our findings call for better understanding of the influence of environmental factors on regional climate system at the diurnal timescale.

Effects of sky conditions on net ecosystem productivity of a subtropical coniferous plantation vary from half-hourly to daily timescales

The dynamic changes of solar radiation have received wide attention in global change studies, but there are controversies about the influence of diffuse radiation on ecosystem carbon sequestration. Using eddy covariance measurements from 2010 to 2012, the effects of sky conditions extracted from adjacent sunny, cloudy, and overcast days on net ecosystem productivity (NEP) of a subtropical coniferous plantation were examined from half-hourly to daily scales. Half-hourly NEP responded to the changing radiation more efficiently on overcast days compared to sunny days, but such response did not differ obviously between cloudy and sunny days. Compared with sunny conditions, apparent quantum yield (α) under overcast (cloudy) conditions changed 282.4% (41.7%) in spring, 140.3% (−4.2%) in summer, 218.5% (38.9%) in autumn, and 146.2% (0.5%) in winter, respectively; annually, α under overcast (cloudy) conditions increased by 225.9% (19.8%) in 2010, 189.8% (6.0%) in 2011, and 159.5% (21.4%) in 2012, respectively. Moreover, the potential NEP at the light intensity of 150 and 750 W m−2 was improved due to increased diffuse fraction. However, both daytime NEP and daily NEP were significantly lower under overcast skies than under sunny and cloudy skies. Compared with sunny days, daily NEP on overcast days decreased by 127.7% in spring, 126.4% in summer, 121.8% in autumn, and 100.6% in winter, respectively; annually, daily NEP decreased by 122.5% in 2010, 141.7% in 2011, and 109.9% in 2012, respectively. Diurnal patterns of daily NEP were quite similar between sunny and cloudy days. Both path analysis and multiple regression showed that solar radiation, especially diffuse radiation, was responsible for the variations of NEP under different skies across seasons, but this effect may be weakened by seasonal droughts. This study implies that the effects of sky conditions on NEP are timescale dependent and should be paid more attention in ecosystem carbon cycle study.

Clinical observation of Wumeiwan combined with triple therapy for treatment of chronic atrophic gastritis

Objective To explore clinical efficacy and safety of Wumeiwan combined with triple therapy for treatment of chronic atrophic gastritis (CAG). Methods According to the random indicator method, 113 patients with CAG were divided into control group (n=56) and treatment group (n=57). Patients of control group were treated with triple therapy, while treatment groupwere treated Wumeiwan combined with triple therapy. The two groups were treated for 3 months. Clinical effect was evaluated after treatment. The helicobacter pylori (Hp) conversion to negative of the two groups was compared and recorded. The Hp overcast conditions of the two groups were compared. The serum TNF-α, IL-6, IL-8 and peripheral blood CD3+, CD4+, CD8+, CD4+/CD8+ of the two groups before and after treatment were compared. The adverse reactions of the two groups during the treatment were compared. Results Total effective rate of treatment group was 94.7% (54/57), which was significantly higher than the control group 82.14% (46/56), and the difference was statistically significant (χ2=4.401, P=0.036). Hp overcast rate of treatment group was 88.2% (45/51), which was significantly higher than the control group 48.0%(24/50), and the difference was statistically significant (χ2=18.883, P=0.000). After treatment, the serum TNF-α (1.43 ± 0.17 mg/L vs. 1.97 ± 0.22 mg/L, t=14.615), IL-6 (30.79 ± 3.65 ng/L vs. 41.13 ± 4.10 ng/L, t=14.166), IL-8 (7.52 ± 1.32 ng/L vs. 9.60 ± 1.77 ng/L, t=7.090) in the treatment group were lower than those in the control group (P<0.05). After treatment, the peripheral blood CD3+ (75.12% ± 16.44% vs. 67.33% ± 14.37%, t=2.680), CD4+ (39.02% ± 11.41% vs. 33.49% ± 10.61%, t=2.667), CD4+/CD8+ (1.58 ± 0.35 vs. 1.19 ± 0.32, t=6.179) in the treatment group were higher than those in the control group (P<0.05), the peripheral blood CD8+ (24.75% ± 9.69% vs. 28.12% ± 11.29%, t=1.704) in the treatment group were higher than those in the control group (P<0.05). There was no significantly difference of the adverse reaction rates of the two groups during treatment (χ2=0.134, P=0.714). Conclusions The Wumeiwan combined with triple therapy for treatment of CAG has a good efficacy and low adverse reactions, has serious anti-inflammatory effects, can improve the body immunity, and it was worthy clinical application. Key words: Gastritis, atrophic; Wu Mei Wan; Triple therapy; Efficacy; Safety

Electricity self-sufficiency of single-family houses in Germany and the Czech Republic

Motivated by a research project that studies the future of the energy system in rural areas at the border between Germany and the Czech Republic, and by the publication of the COSMO-REA high-resolution regional reanalysis data sets for Europe in 2017, this study presents a methodology for generating maps indicating minimum battery and photovoltaics sizes for self-sufficient single-family houses. The methodology consists of three subsequent parts: First, spatiotemporal data sets of electricity demand for single-family houses in rural and low-density urban areas are generated. Second, spatiotemporal data sets of photovoltaics potential are computed based on (a) a technical photovoltaics model, (b) two decades of hourly solar irradiance and temperature data, and (c) snow cover data from the Land Surface Analysis Satellite Applications Facility. Third, a linear optimization model serves to define photovoltaics and battery systems sizes and to generate the corresponding maps. The resulting maps cover Germany and the Czech Republic and are generated for 18 technical and weather-dependent scenarios. The results show how challenging it could be to achieve complete independence from the grid in certain locations. Especially relevant for the sizing of the systems are long periods (several days in a row) of low photovoltaic energy generation due to overcast sky conditions or snow cover of the panels. Furthermore, the results offer a scientifically based source of information for sizing photovoltaics and battery systems in the two countries.

개방형 사무실 주변부 공간의 조광제어에 대한 담천공 조건의 영향

개방형 사무실 주변부 공간의 조광제어에 대한 담천공 조건의 영향

Experimental studies of a variable capacity direct-expansion solar-assisted heat pump water heater in autumn and winter conditions

A variable capacity direct-expansion solar-assisted heat pump (DX-SAHP) system was studied experimentally under the meteorological condition of Qingdao located in the East China area. It was mainly made up of a solar collector/evaporator, a variable-frequency rotary-type hermetic compressor, a micro-channel condenser, and an electronic expansion valve. A series of experiments were carried out, in order to evaluate the performance of the DX-SAHP system during the autumn and winter period, including the system coefficient of performance (COP), the electric power to the compressor, the evaporating and condensing pressures, and the discharge temperature of the compressor. Experimental results showed that for the base case considered in this study, under the sunny and overcast day conditions in the autumn, the average COP was higher than 4.0 and 3.0, respectively. Even in the extreme weather of the winter conditions, the average COP was also higher than 2.5. In general, with the increase of water temperature, the compressor speed increased gradually, and the corresponding electric power of the compressor increased sharply. The condensing pressure also increases, as does the discharge temperature of the compressor, while the evaporating pressure remains a relatively low level with smaller variations.

Power performance analysis of a transparent DSSC BIPV window based on 2 year measurement data in a full-scale mock-up

Among transparent solar cells or modules, the DSSC (Dye-sensitized solar cell) has a relatively low production cost compared to silicon-based solar cells and provides a range of colors for building design. On the other hand, its commercialization has been limited by the low power generation efficiency and durability. Few studies have examined the power generation performance of a full scale DSSC module applied to actual buildings. In this study, a long-term performance test was conducted on vertical and inclined DSSC BIPV (Building Integrated Photovoltaic) windows applied to a full-scale mock-up facility to verify the power performance and power characteristics of transparent DSSC BIPV glazing under actual conditions over a 2 year period.The DSSC module was fabricated by the serial connection of nine 2.26Wp transparent DSSC sub-modules. The multi-layered DSSC BIPV glazing, which was composed of a “DSSC module (9mm)” + “air space (12 mm)” + “clear glass (5mm)” was joined to the curtain wall frame of the test cell facility.The unit size of the DSSC BIPV glazing was 0.975 m (W) × 0.965 m (H) and its maximum capacity was 20.34Wp. The size of the test cell facility was 3 m (W) × 3 m (H) × 9 m (D). The building is a container type insulated with 100 mm urethane foam. Four and two DSSC BIPV windows were installed on the vertical south wall and on the 30° sloped roof, respectively. Through the monitoring system, the power performance data of each DSSC BIPV windows and meteorological data were analyzed over a two year period (from 1st Jan. 2015 to 31st Dec. 2016).The 2 year data showed that the average daily power yield for each month of the vertical DSSC BIPV window ranged from 1.75 to 3.93 kWh/kWp·day (average 2.53 kWh/kWp·day), whereas that of the 30° sloped DSSC BIPV window ranged from 2.16 to 5.34 kWh/kWp·day (average 3.60 kWh/kWp·day).The operating power efficiency of the vertical DSSC BIPV window ranged from 2.65 to 4.14% with an average of 3.40%, whereas that of the sloped DSSC BIPV window was in the range of 2.64–3.63% with a mean of 3.01%. The power generation efficiency of the vertical plane BIPV window was higher than the sloped BIPV window. In contrast to the average daily power yield, the power efficiency of the vertical window was higher than that of the sloped window, which may be due to the higher efficiency of the DSSCs under overcast conditions. This is consistent with the power performance of the DSSC BIPV windows according to the sky conditions, which showed an increase in power efficiency with increasing cloud cover or decreasing solar intensity.

Intercomparison Between VIIRS and CrIS by Taking Into Account the CrIS Subpixel Cloudiness and Viewing Geometry

AbstractThe Cross‐track Infrared Sounder (CrIS) onboard the Suomi National Polar‐orbiting Partnership (SNPP) has high radiometric accuracy, which can be used to intercompare and understand the radiometric performance of the thermal emissive bands of the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the same platform. Previous studies usually selected uniform scenes to avoid potential uncertainties due to geolocation errors. This study focuses on all scenes (including nonuniform scenes), as well as CrIS subpixel cloudiness, local zenith angle and surface type, and their impacts on VIIRS/CrIS intercomparisons. A geolocation error correction scheme is applied to mitigate the geolocation mismatch between CrIS and VIIRS. Intercomparison results of three days from 19 to 21 September 2016, a quarterly warm up/cool down calibration period, show overall good agreement in terms of radiance biases (less than 0.2 K in terms of brightness temperature) between VIIRS and CrIS, for scene temperatures between 220 and 300 K; however, larger biases are evident outside of this range. The three factors—CrIS subpixel cloudiness, local zenith angle, and surface type—show weak impacts on VIIRS radiance biases. Both clear‐sky and overcast conditions have slightly different radiance biases from other partially cloudy conditions because of more contributions from colder or warmer scenes. The time series show the impact of warm up/cool down and the effectiveness of the correction algorithm for reprocessing VIIRS M15 and M16 data sets. The methods and tools can be applied to monitor and validate other infrared imager/sounder duos onboard the same platform.

Thermal infrared imaging for the detection of relatively warm lacustrine groundwater discharge at the surface of freshwater bodies

Thermal infrared (TIR) imaging has been previously applied to survey relatively large thermal footprints in coastal zones, lakes, reservoirs and rivers. In freshwater systems, the buoyancy of relatively warm groundwater during the winter months allows for the surface identification of groundwater discharge or thermal pollution using TIR imaging. However, information regarding the performance of TIR for resolving this warm groundwater upwelling is limited, particularly at fine spatial scales and variable discharge rates. In order to evaluate the suitability of TIR to trace warm groundwater upwelling at the water surface of lakes, ponds and reservoirs (e.g. lacustrine groundwater discharge (LGD) in shallow near-shore zones) we conducted a mesocosm experiment with a TIR camera situated 4 m above the water surface to capture thermal patterns in response to different groundwater discharge rates, weather conditions and the diurnal cycle. A fiber optic distributed temperature sensing system (FO-DTS) installed at 2 cm below the water surface was used to ground-truth spatial patterns observed in TIR images. Results show the impacts of both the diurnal cycle of net radiation and prevailing weather conditions on the accuracy of TIR imaging for resolving warm groundwater discharge. Most reliable results were obtained under overcast weather conditions and during the night. The results of our study provide guidance for those looking to use TIR for conducting thermal tracing of LGD at the surface of freshwater bodies during winter.

Reducing Heat Gains and Cooling Loads Through Roof Structure Configurations of A House in Medan

Heat gains and heat losses through building surfaces are the main factors that determine the building’s cooling and heating loads. Roof as a building surface that has the most exposed area to the sun, contribute most of heat gains in the building. Therefore, the amount of solar heat gains on the roofs need to be minimized by roof structure configurations. This research aims to discover the optimization of roof structure configurations (coating material, structure material, inclination, overhang, and insulation) as one of passive design strategies that reduce heat gains and cooling loads of a house in Medan. The result showed that case four, white-painted metal roof combined with 45° roof pitched, 1.5m overhang, and addition of insulation, indicates the minimum heat gains production and the less cooling loads during clear sky day but not in the overcast sky condition. In conclusion, heat gains and cooling loads of a house in Medan could be diminished during clear sky day by the addition of roof coating with high reflectance low solar absorbtance, the slope roof, the extension of wider veranda, and the addition of insulation in the roof structure.