Hourly Climate Data Research Articles

Downscaling of Hourly Climate Data for the Assessment of Building Energy Performance

In Italy, the calculation of the energy needs of buildings has been mainly based on quasi-steady state calculation procedures. Nowadays, the increasing interest in more detailed energy analysis for high-efficiency buildings requires more accurate calculation methods. In this work, starting from the hourly data of UNI 10349, the downscaling of a typical meteorological year was carried out by applying different mathematical and physical models for the main climate variables considered in the energy balance of a building to be used in dynamic simulation tools. All results were validated with one-minute measurements observed at the ENEA Research Centre in Rome, Italy. The results showed an MBE% of 0.008% and RMSE% of 0.114% using the interpolation spline method for the temperature, while, for the global horizontal irradiance, applying the novel sinusoidal–physical interpolation method showed an MBE% of −0.4% and an RMSE% of 31.8% for the 1 min observation data. In this paper, an easily implemented novel model for downscaling solar irradiance for all sky conditions that takes into account the physical aspects of atmospheric phenomena is presented.

Optimum Solar Panel Orientation and Performance: A Climatic Data-Driven Metaheuristic Approach

This study presents an optimization platform based on the climatic data provided by the National Renewable Energy Laboratory (NREL) to determine the optimum solar panel orientation. Our optimization model is simpler to use than the clearness index model since there is no need to calculate the extraterrestrial insolation on a horizontal flat plate and the shape factor. This optimization approach is based on the hourly climatic data. It determines the optimum tilt angle and azimuth angle of a solar panel for the maximum power generation, considering the diurnal variation of climatic conditions. The hourly evaluation of insolation allows setting up a solar panel azimuth angle that responds to the peak power demand. The main data that impacts the solar panel performance consists of the solar direct normal incident (DNI), direct horizontal incident (DHI), global horizontal incident (GHI), ambient temperature, wind speed, and ground albedo, all of which were obtained from the NREL database for over twenty years. The accuracy of the optimization platform introduced in this study is scrutinized by investigating the three locations in the United States with different climatic conditions. The results based on the present optimization model show higher PV power than the general rule of thumb for south-facing panels with title angles the same as the latitude of the location. Moreover, the effect of deviations from optimum panel orientation is discussed to show the versatility of our technique. Our optimization model is easy-to-use, computationally efficient, and capable of being applied to other locations worldwide.

A Simplified Mechanistic-Empirical Flexible Pavement Design Method for Moderate to Hot Climate Regions

Flexible pavement structure design is a complex task because of the variability of design input parameters and complex failure mechanisms. Therefore, the aim of this study is to develop and implement a simplified Mechanistic-Empirical (M-E) pavement design method based on the 1993 American Association of State Highway and Transportation Officials (AASHTO), the National Cooperative Highway Research Program (NCHRP) 9-22, and NCHRP 1-37A and 1-40D projects. This simplified methodology is implemented into a computer code and a user-friendly software called “ME-PAVE”. In this methodology, only two equivalent temperatures, as per the NCHRP 9-22 project, are estimated to adjust the dynamic modulus of the asphalt layer(s) for Asphalt Concrete (AC) rutting and AC fatigue cracking prediction instead of using the hourly climatic data, as in the AASHTOWare Pavement ME. In ME-PAVE, the structural responses at critical locations in the pavement structure are determined by a Finite Element Module (FEM), which is verified by a Multi-layer Elastic Analysis (MLEA) program. To ensure that the simplified methodology is practical and accurate, the incorporated transfer functions in the proposed simplified methodology are calibrated based on the Long-Term Pavement Performance (LTPP) data. Based on statistical analyses, the built-in FEM results exhibit very similar trends to those yielded by MLEA, with a coefficient of determination, R2 of 1.0. For all practical purposes, the proposed methodology, despite all simplifications, yields acceptable prediction accuracy with R2 of 0.317 for the rut depth compared to the current practices, NCHRP 1-37A and 1-40D (R2 = 0.399 and 0.577, respectively); while the prediction accuracy for fatigue cracking with R2 of 0.382 is comparable to the NCHRP 1-40D with R2 of 0.275. Nonetheless, the standard error for both distresses is in good agreement based on the investigated data and the developed methodology. Finally, the conducted sensitivity analysis demonstrate that the proposed methodology produces rational pavement performance.

An equation-based multiphysics modelling framework for oxidative ageing of asphalt pavements

Long-term oxidative ageing occurs in asphalt pavements when they are exposed to the ambient environment for extended periods. This ageing phenomenon is dependent on multiple physical fields, including heat transfer, oxygen diffusion from air into interconnected air voids of asphalt pavement, oxygen diffusion from air void channels to asphalt mastic inside, and growth of oxidation products in bitumen. Most existing oxidative ageing models were established via coupling of limited physical fields. However, to accurately determine the oxidative ageing effect on pavement performance, there is a need to develop a multiphysics model that integrates all ageing-related physical fields comprehensively. The challenge lies in that the ageing-related physics are circularly dependent, time-dependent and highly nonlinear. This study developed a multiphysics and time-dependent finite element model that successfully addressed the issues of high nonlinearity and circular dependency of oxidative ageing in the asphalt pavements.Specifically, a differential equation-based approach was employed to efficiently couple the multiple physical fields into one integrated model. The multiphysics framework included a pavement temperature prediction model and an integrated ageing model. The model involved a variety of inputs such as site-specific hourly climate data, parameters for oxidation kinetics of bituminous binder, volumetric properties of asphalt mixture, thermal and diffusive properties of pavement materials, and pavement structure. The pavement temperature model was validated using the pavement temperature profiles for different climate regions in the Long-Term Pavement Performance (LTPP) database. The integrated ageing model was validated using the Fourier-transform infrared spectroscopy (FTIR) data of field-aged asphalt cores in the literature. Results showed that the model can accurately predict the change in pavement temperature profile on an hourly basis and reliably predict the degree of oxidative ageing across pavement depth for different climate zones.

Spatial and temporal variability of groundwater recharge in a sandstone aquifer in a semiarid region

Abstract. With the aim to understand the spatial and temporal variability of groundwater recharge, a high-resolution, spatially distributed numerical model (MIKE SHE) representing surface water and groundwater was used to simulate responses to precipitation in a 2.16 km2 upland catchment on fractured sandstone near Los Angeles, California. Exceptionally high temporal and spatial resolution was used for this catchment modeling: hourly climate data, a 20 m×20 m grid in the horizontal plane, and 240 numerical layers distributed vertically within the thick vadose zone and in the upper part of the groundwater zone. The finest practical spatial and temporal resolutions were selected to accommodate the large degree of surface and subsurface variability of catchment features. Physical property values for the different lithologies were assigned based on previous on-site investigations, whereas the parameters controlling streamflow and evapotranspiration were derived from calibration to continuous streamflow at the outfall and to average hydraulic heads from 17 wells. Confidence in the calibrated model was enhanced by validation through (i) comparison of simulated average recharge to estimates based on the applications of the chloride mass-balance method to data from the groundwater and vadose zones within and beyond the catchment, (ii) comparison of the water isotope signature (18O and 2H) in shallow groundwater to the variability of isotope signatures for precipitation events over an annual cycle, and (iii) comparison of simulated recharge time series and observed fluctuation of water levels. The average simulated recharge across the catchment for the period 1995–2014 is 16 mm yr−1 (4 % of the average annual precipitation), which is consistent with previous estimates obtained by using the chloride mass balance method (4.2 % of the average precipitation). However, one of the most unexpected results was that local recharge was simulated to vary from 0 to >1000 mm yr−1 due to episodic precipitation and overland runoff effects. This recharge occurs episodically with the major flux events at the bottom of the evapotranspiration zone, as simulated by MIKE SHE and confirmed by the isotope signatures, occurring only at the end of the rainy season. This is the first study that combines MIKE SHE simulations with the analysis of water isotopes in groundwater and rainfall to determine the timing of recharge in a sedimentary bedrock aquifer in a semiarid region. The study advances the understanding of recharge and unsaturated flow processes and enhances our ability to predict the effects of surface and subsurface features on recharge rates. This is crucial in highly heterogeneous contaminated sites because different contaminant source areas have widely varying recharge and, hence, groundwater fluxes impacting their mobility.

Irrigation impacts on minimum and maximum surface moist enthalpy in the Central Great Plains of the USA

Agricultural activities notably alter weather and climate including near-surface heat content. However, past research primarily focused on dry bulb temperature without considering the role of water vapor (dew point temperature) on surface air heat content. When using dry bulb temperature trends to assess these changes, for example, not including concurrent trends in absolute humidity can lead to errors in the actual rate of warming or cooling. Here we examined minimum and maximum surface moist enthalpy, which can be expressed as “equivalent temperature.” Using hourly climate data in the Central Great Plains (Nebraska and Kansas) from 1990 to 2014, the averages and trends of minimum and maximum equivalent temperature (TE_min; TE_max) were analyzed to investigate the potential impacts of irrigation. During the growing season, TE_max averages were significantly higher in irrigated cropland sites compared to grassland sites. This can be explained by increased transpiration linked to irrigation. In addition, TE_max exhibits a decreasing trend in most sites over the growing season. However, the difference of the trends under irrigated croplands and grasslands is not statistically significant. A longer time series and additional surface energy flux experiments are still needed to better understand the relationships among temperature, energy, and land cover.

Determination of Driving Rain Index by Using Hourly Weather Data for Developing a Good Design of Wooden Buildings

This research was performed to supplement the previous research about the driving rain index (DRI) for Korea determined by using daily weather data for 30 years. The average annual driving rain index (AADRI) was calculated from the hourly weather data, and the magnitude of DRI was investigated according to wind directions. The hourly climate data were obtained from the Korea Meteorological Administration (KMA) for the period 2009 to 2017. Of 82 locations investigated, seven were classified into regions where the level of exposure of walls to rain was high. The result showed quite a difference from the previous results, in which no high exposure regions were observed. Since the hourly-based and the daily-based annual driving rain index (ADRI) values showed only a slight difference, the result may be explained by the length of the periods used in both studies. The change of DRI according to wind directions showed that there was a certain range of wind directions in which driving rain easily approached building walls. It suggests that the consideration of wind directions with high DRI would be useful to develop a good design of wooden buildings from the point of wood preservation and maintenance.

Modeling the suitability of the traditional plastic greenhouse for tomato production across Colombian regions

Greenhouse tomato production in Colombia has increased at a rate of 250 t year-1 in the last decade, but yield has remained constant around 106 t ha-1 year-1. The main reasons for this trend is that greenhouses used for tomato cropping are still vulnerable to the high seasonal and intraseasonal climate variability in the Equatorial Zone. To obtain information about the relation between outdoor and indoor environments, we analyzed productive areas with a greenhouse climate model (GCM). The GCM was calibrated, validated and used to simulate the thermal behavior of traditional greenhouses under different climate conditions in Colombia. The input climate variables included global radiation, outside air and soil temperatures, relative humidity and wind velocity recorded at six locations. The locations are situated between 2000 and 3000 m a.s.l. with average temperatures between 10-20°C characterized by unimodal or bimodal rainfall regimes. Automatic weather stations recorded the hourly climate data during tropical wet and dry seasons. The modeled greenhouse was a naturally ventilated plastic one with a floor area of 5670 m2, surface of the cover including side walls of 9610 m2, and maximum roof and side ventilation area of 324 and 370 m2, respectively. The simulations were carried out with the presence of a tomato crop. The simulations showed that traditional structures keep appropriate temperatures for tomato, mainly during the dry season at the six locations. The wind profile for each season explained these results, affecting the efficiency of natural ventilation. The change in the wind profile is due to the meridional migration of the intertropical convergence zone throughout the year. Therefore this atmospheric system is a factor to take into account when designing sidewall and roof ventilation openings. For cold marginal tomato production areas, predictions showed the potential to explore passive heating systems to improve the climate during night hours.

Optimum external wall insulation thickness considering the annual CO2 emissions

Increasing the insulation thickness in residential buildings leads to the reduction of operational CO2 emissions but simultaneously increases the embodied CO2 due to the insulation material. The environmentally optimum insulation thickness exists at a point where the total CO2 emissions are minimum. This work presents the optimum insulation thickness for external walls of different composition and orientation, for both the heating and the cooling period. Three different wall types and insulation materials are being presented. The dynamic thermal behavior of the external walls simulation is based on the heat conduction transfer functions method and using the hourly climatic data available for the city of Athens, Greece. The optimization methodology uses a single objective function approach, combining the simulation of the thermal behavior of external walls with an optimization algorithm. The results indicate that the optimum insulation thickness varies from 11.2 to 23.4 cm and is different for each orientation, wall type, and insulation material. In addition, the total annual CO2 emissions per unit area of the wall can be reduced by 63.2%–72.2%, depending on the insulation material and its position on the wall.

A Retrofit for Geothermal Organic Rankine Cycles based on Concentrated Solar Thermal Systems

In this study, a solar thermal retrofit unit for geothermal ORC power plants is analysed under thermodynamic and technical aspects. For the retrofit, the ORC module is extended by a solar superheater and the additional heat input is realized by parabolic trough collectors. The evaluation of the entire system is based on simulations over the period of one year. Therefore, a case study considering geothermal conditions of the Aydin-Salavatli field in the Büyük Menderes Graben in Turkey is conducted. Quasi-stationary simulations of the system are performed considering off-design behaviour of the power plant components. The calculations are based on hourly climate data. The obtained operational parameter of the ORC and solar-field emphasise the technical feasibility of the selected superheating concept in the context of thermal stability of the working fluid. For the considered solar-field sizes, the annually generated electricity is increased up to 4.5 % compared to the stand-alone geothermal power plant.

Estimating missing hourly climatic data using artificial neural network for energy balance based ET mapping applications

ABSTRACTRemote sensing based evapotranspiration (ET) mapping has become an important tool for water resources management at a regional scale. Accurate hourly climatic data and alfalfa‐reference ET (ETr) are crucial inputs for successfully implementing remote sensing based ET models such as Mapping Evapotranspiration at High Resolution with Internalized Calibration (METRIC) and Surface Energy Balance Algorithm for Land (SEBAL). In Turkey, hourly climatic data may not be available at all locations, either due to cost constraints or due to equipment malfunctioning. In this study, the artificial neural network (ANN) technique was used to estimate missing and unmeasured hourly climatic data and ETr for the agriculturally important semi‐humid Bafra plains located in northern Turkey. Modelled and actual climatic data were used to derive ET maps from two Landsat 5 Thematic Mapper images acquired on 2 September 2009 and 4 August 2010. The METRIC algorithm was used to generate ET maps. Accuracy assessment of the METRIC‐derived ET maps indicated that climatic data and ETr estimated through ANN could be used for accurately mapping ET, where hourly climatic data are missing or not measured.

Modeling and optimization of dew-point evaporative coolers based on a developed GMDH-type neural network

A precise model of a counter-flow indirect dew-point evaporative cooler was developed using the group method of data handling-type neural network while the network was trained by extracted data from a validated numerical model. After validating the model, it was employed in a multi-objective optimization problem that implements the non-dominated sorting genetic algorithm-II method. The system was optimized in diverse climatic conditions. In this regard, Yazd, Masjed-Soleiman and Ahvaz were chosen as representatives of cities with hot, hot semi-humid and hot-humid climates in Iran. In each city, optimum values of channel length, channel gap, inlet air velocity and return to intake air ratio were found so that these decision variables maximize the average coefficient of performance and minimize the specific area of the cooler, simultaneously. The results indicated that the developed model can predict the supply air temperature accurately with less than 1°C error and due to its quick calculation process it is possible to optimize the design based on hourly climate data without any needs to very fast processors. Moreover, using the optimization, the coefficient of performance and specific area for the system designed to be used in Yazd were improved 36.3% and 30.9%, respectively. This figure at Masjed-Soleiman and Ahvaz was 16% and 7.92% improvement in the specific area at the cost of 2.63% and 2.19% reduction in the coefficient of performance, respectively. These improvements allowed the system to reach its full potential and making dew-point evaporative coolers as a suitable cooling system in diverse climatic conditions.

Updates to Hourly Climate Data for Use in AASHTOWare Pavement Mechanistic–Empirical Design

The AASHTOWare Pavement Mechanistic–Empirical Design software requires hourly temperature, wind speed, percentage sunshine, precipitation, and relative humidity to properly calculate pavement damage and distresses. Actual or measured values, which vary hourly throughout a day for a given site, are required to properly capture the damage caused by environmental loadings. Currently the mechanistic–empirical design hourly climatic data contain approximately 1,200 U.S. and 300 Canadian stations. The U.S. stations typically contain data from 1995 through 2005, and data from the Canadian stations vary in length from 10 to 50 years, with the exception of some weather stations. Some agencies expanded their historical weather data to include longer periods of time. This paper documents the process and data sources that were used to update the current set of climate stations with climate data dating back to 1979 using the North American Regional Reanalysis (NARR) database. The results of the comparison between new climate files and the existing older climate data files for use in pavement design are presented. Overall, the NARR-generated climate data showed a very good comparison. The paper details the background of the NARR and its limitations and compares the performance predictions made by using the old and new climate data. The results indicate there is no systematic bias between the two climate data sets.

Feasibility Analysis of Retrofit Strategies for the Achievement of NZEB Target on a Historic Building for Tertiary Use

Abstract According to directive 2010/31/EU, a NZEB (nearly zero energy building) is defined as a high performance building whose very low or almost zero energy needs should be mostly provided by renewable sources. The study reported in this work has the objective to establish criteria and design solutions to improve buildings energy performances in order to reach NZEB targets for those buildings characterized by historical constraints. For this purpose, a comparative numerical analysis on the space cooling and heating of a historical building sited in Agrigento (Sicily, Italy) was performed by means of two energy tools: Termo and Trnsys. The first one is a stationary energy certification software based on the algorithms and mathematical methods listed in the UNI TS 11300 standard reference. The second one is a well calibrated dynamic tool based on hourly climate data and able to take into account the thermal inertia phenomena of structures. In order to obtain reliable results, measured climate data extracted from a weather station located near the reference building were used as input for the simulations. Starting from the simulation results, several retrofit scenarios were hypothesized, in order to achieve NZEB target, and then followed by a cost analysis carried out to reach optimal economic solutions and energy savings. The study can constitute a contribution to policy formulation and adoption of measures to facilitate design choices for the energy improving of historical buildings.

An assessment of the economic and environmental feasibility of evaporative cooling unit

Performance of Indirect Evaporative Air-Conditioning (IEAC) is strongly influenced by the climate conditions and varies widely in different climate zones. This investigation conducts thermal and economic performance analysis of IEAC under climatic conditions of three cities from different zones: Amman, Aqaba, and Berlin. Based on the hourly climate data of each zone, economic assessment of IEAC is estimated using Life Cycle Cost (LCC) and Payback Period criterion according to economic figures from local markets for each location. The results revealed that IEAC is promising technology in the selected climate zones. A well-optimized IEAC can cover 99.98%, 95.26% and 84.83% from annual cooling demand in Berlin, Amman and Aqaba, respectively.

Performance investigation of solid desiccant evaporative cooling system configurations in different climatic zones

Performance of desiccant evaporative cooling (DEC) system configurations is strongly influenced by the climate conditions and varies widely in different climate zones. Finding the optimal configuration of DEC systems for a specific climatic zone is tedious and time consuming. This investigation conducts performance analysis of five DEC system configurations under climatic conditions of five cities from different zones: Vienna, Karachi, Sao Paulo, Shanghai, and Adelaide. On the basis of operating cycle, three standard and two modified system configurations (ventilation, recirculation, dunkle cycles; ventilated-recirculation and ventilated-dunkle cycles) are analyzed in these five climate zones. Using an advance equation-based object-oriented (EOO) modeling and simulation approach, optimal configurations of a DEC system are determined for each climate zone. Based on the hourly climate data of each zone for its respective design cooling day, performance of each system configuration is estimated using three performance parameters: cooling capacity, COP, and cooling energy delivered. The results revealed that the continental/micro-thermal climate of Vienna, temperate/mesothermal climate of Sao Paulo, and dry-summer subtropical climate of Adelaide favor the use of ventilated-dunkle cycle configuration with average COP of 0.405, 0.89 and 1.01 respectively. While ventilation cycle based DEC configuration suits arid and semiarid climate of Karachi and another category of temperate/mesothermal climate of Shanghai with average COP of 2.43 and 3.03 respectively.

Performance Investigation of Direct Evaporative Cooling in Major Cities of Iraq

The cities of Baghdad, Basrah, and Mousl are the major cities in the middle, southern and northern parts of Iraq, respectively. In this paper, TRNSYS model is investigated to study the performance of direct evaporative cooler (DEC) in these cities. Based on the hourly climate data of each month in Typical Meteorological Year (TMY), the period of 1st of June to 31th of August is used to estimate the performance of DEC in terms of evaporative supply temperature and cooling capacity. The simulation results show that the performance of DEC is capable of providing comfort conditions in Baghdad and Mosul by lowering supply air dry bulb temperature below the design condition (24ºC) up to 2ºC in June and July and 1.5ºC in August. In addition, the maximum cooling capacity of DEC is obtained in July about (3617, 3417 and 3160) kW for Baghdad, Mosul and Basrah, respectively.

Comparison of hourly and daily reference crop evapotranspiration equations across seasons and climate zones in Australia

Estimates from the FAO Penman–Monteith (FAO-PM) and the standardized ASCE Penman–Monteith (ASCE-PM) hourly and daily reference evapotranspiration (ET0) equations were compared at daily scale, based on the hourly climate data collected from forty (40) geographically and climatologically diverse Automatic Weather Stations (AWS) across the Australian continent. These locations represent 23 agricultural irrigation areas in tropical, arid and temperate climates. The aims of this paper are to: compare the effects of different methods of estimating Clear-sky-radiation—(Rso); compare sum-of-hourly and daily ET0; compare the results of aggregation of hourly ET0 over 24h compared with daylight hours; and examine the impact of seasonality and climate type. At selected AWS locations, the hourly ET0 was calculated using the hourly FAO-PM and the ASCE-PM equations and then summed to derive daily ET0 (reported as ET0,soh). This was compared against the daily ET0 values, calculated using the corresponding daily equation (reported as ET0,daily). Using Rso calculated following the “complex” approach improves the agreement between ET0,soh and ET0,daily of both hourly equations, compared with the “simple” approach. Better agreement between ET0,soh and ET0,daily estimates for the FAO-PM and ASCE-PM were found, when the hourly values are aggregated over 24h rather than over daylight hours. The average ratio between ET0,soh and ET0,daily for the FAO-PM and ASCE-PM equations is 0.95 and 1.00, respectively. The range of the former is 0.90–0.98 and that of the latter is 0.96–1.04. There was very strong correlation between the two hourly equations at the daily time step: on average 0.997, with a range of 0.993–0.998. The results imply that the ASCE-PM hourly equation's daily ET0 values are higher than those of FAO-PM, which can be explained by the difference in the treatment of surface resistances. Better agreements between ET0,soh and ET0,daily values for winter, spring and autumn were found for the FAO-PM version, while during summer, the ASCE-PM version showed better agreement. The best agreement between the hourly and daily results for the FAO-PM version was found in temperate climates and the ASCE-PM version showed best agreement in the tropical and arid climates.

Theoretical Evaluation of Night Sky Cooling in the Czech Republic

Energy necessary for cooling of building in summer season makes a big part of energy required for building operation. Redundant heat removal in summer can be realized in various ways. One of possible methods, mainly in desert areas, is using thermal radiation against night sky. The paper deals with theoretical efficiency evaluation of night sky cooling in climatic condition of Czech Republic. The numerical simulations of non-steady heat transfer and internal thermal comfort evaluation in an office room has been performed. We have considered a cooling system consists of radiating panels placed on the roof, connected by pipes with the cooling ceiling in an office room. The radiating panel is used to cool down the cooling water by convection and heat radiation against the night sky.At first we processed the real hourly climatic data for city Brno and by using the extra-terrestrial solar irradiation we calculated night sky temperature during cloudy conditions and other necessary climate parameters for the long-term simulations. From this file of data, we selected seven typical combinations of equivalent sky temperatures, external air temperatures and wind velocities in order to cover the external conditions during the summer nights. Next we assumed a variable mean temperature of water flowing through the radiating panel in order to be able of computing its thermal performance. Then we carried out seven simulations of chosen radiating panel with these boundary conditions by means of computational fluid dynamics method (CFD) in the software Fluent. The data obtained were processed in the own software so we set the appropriate regression functions describing the thermal behaviour of radiating panel, which was then used for long-term thermal performance simulations in software TRNSYS. The multi zone model in TRNSYS links the building and its equipment with thermal the cooling ceiling model as well as with the water loop containing the radiating panels. This computer model is capable of simulating the night sky cooling impact on the building and its internal environment. Since the investigation we carried out at the chosen office building, we used the typical office operation inclusive the schedules of occupancy, natural ventilation, heat gains from lightning, equipment etc. Then have performed two long-term simulations with and without night sky cooling.The simulations have shown the outlet temperature of the radiant panel below the external air temperature in a few cases. This finding confirms the positive effect of radiation transfer against the night sky in the climate of Czech Republic. The thermal comfort was evaluated according the standard ISO 7730 and has been found the significant improvement of internal thermal comfort by using the night sky cooling in the testing office building.

The effect of quantum efficiencies on the optimum orientation of photovoltaic modules – A comparison between crystalline and thin film modules

Global irradiance spectra vary with location, different viewing angles and times of day, depending on the fraction of direct and diffuse irradiance. Owing to big differences in spectral responses, PV module technologies might therefore show a differing behaviour with varying orientation and tilt angles. The purpose of this work is to verify the thesis, that thin film modules are – due to their spectral response – more suitable for horizontal orientation than crystalline. Diffuse irradiation (except from circumsolar radiation) can be captured best by a horizontal surface and consists to a greater fraction of short wavelengths than direct irradiation. At the same time thin film modules primarily absorb photons of short wavelengths and could therefore be better suited for horizontal application.Based on the semi-empirical spectral model Sedes2 and quantum efficiency data, a model has been developed to analyse differences in optimum orientation of several PV module technologies. In a first step, hourly global irradiance spectra are generated from a 1year dataset of hourly climate data derived from long-term averages by the Meteonorm database for two sites in different climes. Based on this, average photocurrent densities are computed for each technology and for a matrix of different orientation and tilt angles using quantum efficiency data. Normalised to their maximum, the photocurrent densities are compared between the technologies. The results we obtained show, that for each site the maximum relative photocurrent densities are located at about the same orientation for all technologies, i.e. the optimum orientation is the same. At horizontal orientation, thin film modules show a slightly higher value of normalised average photocurrent densities than monocrystalline modules. Yet, for a whole year this advantage lies below 1% for both sites.