Cooling of PV panels by natural convection

© Copyright SINTEF Academic Press and Norwegian University of Science and Technology 201

Operating Hardware Impact on the Heat Transfer Properties of Windows

Despite significant advancements in fenestration technology in the last two decades, the thermal transmittance of fenestration products is still significantly higher than that of walls. This corresponds to 60% of the total energy loss of a modern building envelope through the windows. Hence, further development and improvements of fenestration products are necessary. Increasingly stringent codes and standards for fenestration stimulate industry to work on improved solutions. Thus, it is crucial that assessment techniques are able to account for innovations accurately. The thermal effects of non-continuous hardware in window frames are currently ignored by international rating procedures. A preliminary investigation conducted by our team showed significant performance degradation in two of the three out-opening casement profiles caused by the presence of operating hardware. Frames with the structure made of vinyl and fiberglass consist of many air cavities that are penetrated by operating hardware made of highly conductive materials. In these frames, in order to have an accurate assessment, it may be required to employ three-dimensional modeling due to the convective nature of heat transfer within the cavities. However, in this study, we demonstrate that the three-dimensional (3D) effects of non-continuous hardware can be approximated accurately with simpler two-dimensional (2D) simulations. We then develop a simplified model based on weighted average capable of replacing the time- and computation-intensive 3D simulations with 2D simulations and validate it against market available frames and their corresponding hardware. Validation results show that our approximation technique results in discrepancies lower than 0.05 W/(m2K), or 3% of the total thermal transmittance. Thus, we conclude that simplified 2D simulation models may be used for predicting hardware impact in window frames with reasonable accuracy. As windows and glazing structures are becoming ever better thermally insulated, it is becoming even more important to be able to model the impact of the operating hardware on the total thermal performance in order to design the best windows possible and not let the operating hardware ruin an otherwise well-proven design, which is hence addressed in this study.publishedVersionThis is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cite

Impacts of Operating Hardware on Window Thermal Performance

ABSTRACT Windows are responsible for about 40 percent of the heat loss through typical building envelopes so lowering window frame and glazing unit U-factors will reduce the impact of windows on the energy use in buildings. The thermal effects of operating hardware are currently ignored in the relatively low performing double pane windows common today, but may become significant in high performance windows. This paper describes simulation studies analyzing thermal-bridging effects of non-continuous operating (and non-operating) hardware in common casement style window frame designs. We use finite volume computational fluid dynamics modeling to demonstrate the change in frame sill profile U-factor for configurations using typical hardware systems. Some conclusions can be drawn regarding the impacts of operating hardware on the thermal performance based on the individual frames profiles, although few general trends can be observed due to the large design differences between each frame section modeled in this study. Two of the three out-opening casement profiles modeled show reduced performance greater than 0.05 W/(m 2 K), which may be significant when carried to whole windows in National Fenestration Rating Council (NFRC) and International Organization for Standardization (ISO) rating systems. Fastener types, hardware location within the frame, and other factors related to the method of hardware implementation may significantly impact the effect of hardware on the frame. Neither the base performance level nor the primary frame material appears to determine the thermal effect of hardware based on those metrics alone. INTRODUCTION Minimizing thermal transmittance (U-factor) of building envelopes through the optimization of materials and components is a key energy-efficiency strategy. Windows are responsible for about 40 percent of the heat loss through typical building envelopes so lowering window frame and glazing unit U-factors will reduce the impact of windows on the energy use in buildings

Cooling of PV panels by natural convection

Building Integrated Photovoltaic (BIPV) is an important source of renewable energy production for Zero Emission Buildings, even in Norwegian climate. In the planned Powerhouse 1 building at Brattøra in Trondheim the idea to reach a zero emission building level is to use PVs as a roofing material covering the entire roof. Challenges and questions raised in the design process of this building have motivated the work reported here. Photovoltaic (PV) panels directly convert solar radiation into electricity with peak efficiency in the range of 9–12%. It means that more than 80% of the solar radiation falling on PV cells is not converted to electricity, but either reflected, transmitted or absorbed. Reflected and transmitted radiation is relatively small in comparison to absorbed radiation. Part of absorbed energy is converted into electricity and the rest is change to the heat, which increases unit temperature. Higher temperature of unit has negative influence on PV panel’s efficiency. Conducted study focuses on finding the best cooling strategy for PV panels which simultaneously perform as a roof finishing layer of large roof and test it by numerical methods. Comparison analysis of different air gap widths for natural convection cooling was done using numerical model. The results shown that 5 cm wide air gap is not sufficient to provide natural convection cooling of 70 meter-long rooftop made of PV panels. Moreover, increasing air gap width over the 25 cm seems to not giving substantial improvements of natural convection cooling. The developed model is good starting point for further study in this area. Findings and experience gained during this study hopefully can be transferred into more precise 3D modeling of this case.publishedVersio

Investigation of fuel cell technology for long-haul trucks

Verkefnið er unnið í tengslum við Háskóla Íslands og Háskólann á AkureyriAlmost 95% of transportation sector uses liquid hydrocarbons made from fossils as primary fuel. That sector is responsible for 21% of CO2 in European Union (Eurostat 2004) and 21% of Australian’s greenhouse gas emissions (Tasman 2004). Many improvements to conventional truck technology proofed that it possible to reduce emissions of SOx, NOx and particles by special systems assembled in vehicles but it is impossible to implicate sophisticated systems which can reduce to zero CO2 emissions because of huge dimensions and complexity. Usage of hydrogen as energy carrier is considered as one of the most feasible and suitable for transportation. Instead of using hydrogen as a fuel for internal combustion engines where efficiency is constrained by the Carnot law, this energy carrier can be converted to electricity directly by electrochemical reaction in the device called fuel cell with high efficiency while not generating tailpipe CO2 emissions or other pollutants. In this mater thesis study of feasibility of fully operational heavy duty truck powered by hydrogen is done. The most suitable technologies of powertrain components are investigated in order to create preliminary design of full-scale hydrogen fuel cell truck. Conducted research pointed that the most suitable technology for electrochemical conversion of hydrogen is high temperature PEM fuel cell. The most energy and cost effective technology for hydrogen storage seems to be compressed hydrogen at pressure of 35 MPa. Further investigation indicated supercapacitors as probably the most suitable technology for energy buffer. It seems to be effective to use hub motors instead of conventional driveline mechanism. Calculation and comparison of gravimetric power and energy density for drivelines of hydrogen fuel cell and conventional diesel trucks is the next focus of this paper. Investigation showed that the hydrogen fuel cell powertrain can be comparable with conventional diesel powertrain in terms of gravimetric energy density. Advantages and disadvantages of innovative hydrogen drivetrain are presented. Additionally, the investigation of the best technology for refrigeration unit for semi-trailer which can cooperate with fuel cell is conducted. This master thesis also includes comprehensive design of small-scale model of fuel cell hydrogen truck. Small-scale model was designed and partially constructed in order to demonstrate feasibility of hydrogen fuel cell innovative application and to deliver important information about performance and behavior of particular system elements of the hydrogen fuel cell powertrain. The final section focuses on refueling infrastructure and possibility of direct introduction of hydrogen fuel cell truck technology in Poland. Modified powertrains which includes on-board reformer are analyzed

Thermal Modeling and Investigation of the Most Energy-Efficient Window Position

The energy consumption in buildings contributes substantially to the worldwide energy use and greenhouse gas emissions. One of the crucial elements defining energy consumption is the building envelope, which in modern designs includes growing share of fenestration. Due to recent improvements of windows and walls, the thermal bridging effects occurring on their connections, become more significant. Window-to-wall connections appear to be especially important and can contribute up to 40% of the total heat loss caused by thermal bridges in building envelope. Thus, this study is investigating thermal properties of window-to-wall connections. The main scope of the work is to determine the most efficient window position in the window opening regarding minimizing thermal bridging effects. Five different wall constructions are investigated along with two windows with different U-values. The thermal simulation results show that the window position has a crucial impact on the amount of energy loss through the thermal bridges. For each wall type, the most energy-efficient position is found, resulting from detailed analysis of sill, head, and jambs construction details. For some cases placing the window in the most energy-efficient position reduces linear thermal transmittance (LTT) over 50%. Among considered positions, the temperatures on the internal surface of the assemblies are weakly influenced by the window position. Example calculations show that significant share of energy losses from the fenestration presence is caused by thermal bridge occurring on window-to-wall.Acknowledgements. This work has partly been funded by the Research Council of Norway, Lian Trevarefabrikk and Lawrence Berkeley National Lab- oratory (LBNL) through the NTNU and SINTEF research project “Improved Window Technologies for Energy Efficient Buildings” (EffWin), and the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Building Technology, Building Technologies Program of the U.S. Department of Energy under Contract no. DE-AC02-05CH11231.acceptedVersio

Cooling of PV panels by natural convection

Building Integrated Photovoltaic (BIPV) is an important source of renewable energy production for Zero Emission Buildings, even in Norwegian climate. In the planned Powerhouse 1 building at Brattøra in Trondheim the idea to reach a zero emission building level is to use PVs as a roofing material covering the entire roof. Challenges and questions raised in the design process of this building have motivated the work reported here. Photovoltaic (PV) panels directly convert solar radiation into electricity with peak efficiency in the range of 9–12%. It means that more than 80% of the solar radiation falling on PV cells is not converted to electricity, but either reflected, transmitted or absorbed. Reflected and transmitted radiation is relatively small in comparison to absorbed radiation. Part of absorbed energy is converted into electricity and the rest is change to the heat, which increases unit temperature. Higher temperature of unit has negative influence on PV panel’s efficiency. Conducted study focuses on finding the best cooling strategy for PV panels which simultaneously perform as a roof finishing layer of large roof and test it by numerical methods. Comparison analysis of different air gap widths for natural convection cooling was done using numerical model. The results shown that 5 cm wide air gap is not sufficient to provide natural convection cooling of 70 meter-long rooftop made of PV panels. Moreover, increasing air gap width over the 25 cm seems to not giving substantial improvements of natural convection cooling. The developed model is good starting point for further study in this area. Findings and experience gained during this study hopefully can be transferred into more precise 3D modeling of this case

Thermal improvements of box-window using shading attachments. Hot-box measurements

This research explores shading potential for improving the thermal properties of a box-window. Two different types of shades along with three placements were considered. Ten configurations were tested in a hot-box apparatus and compared to base window performance. Condensation issues that may arise after shading installation were also studied.Measurements showed that shading installed along with the original box-window has a positive impact on the window thermal performance. The highest U-value reduction by 35% (from 1.9 to 1.0 W/m2K) was achieved by a roller-shade with low-emissivity layer and constrained airflow on shade perimeter, installed inside the window recess. Temperature analysis showed a higher risk of condensation on the indoor window surface due to shade introduction on the indoor side of the window.Shading placement within the box-window gave improvements of 34% (reduced U-value from 2.0 to 1.3 W/m2K) for reflective roller-shades placed between the window frames. Shades in this position do not increase the risk of condensation on the indoor surface of the window. The probability of condensation inside the box-window may be lowered by draught-proofing indoor frames and maintaining ventilation through the outdoor frame.Shades proved to be effective at improving the thermal properties of box-windows

Cooling of PV panels by natural convection

Building Integrated Photovoltaic (BIPV) is an important source of renewable energy production for Zero Emission Buildings, even in Norwegian climate. In the planned Powerhouse 1 building at Brattøra in Trondheim the idea to reach a zero emission building level is to use PVs as a roofing material covering the entire roof. Challenges and questions raised in the design process of this building have motivated the work reported here. Photovoltaic (PV) panels directly convert solar radiation into electricity with peak efficiency in the range of 9–12%. It means that more than 80% of the solar radiation falling on PV cells is not converted to electricity, but either reflected, transmitted or absorbed. Reflected and transmitted radiation is relatively small in comparison to absorbed radiation. Part of absorbed energy is converted into electricity and the rest is change to the heat, which increases unit temperature. Higher temperature of unit has negative influence on PV panel’s efficiency. Conducted study focuses on finding the best cooling strategy for PV panels which simultaneously perform as a roof finishing layer of large roof and test it by numerical methods. Comparison analysis of different air gap widths for natural convection cooling was done using numerical model. The results shown that 5 cm wide air gap is not sufficient to provide natural convection cooling of 70 meter-long rooftop made of PV panels. Moreover, increasing air gap width over the 25 cm seems to not giving substantial improvements of natural convection cooling. The developed model is good starting point for further study in this area. Findings and experience gained during this study hopefully can be transferred into more precise 3D modeling of this case

Operating Hardware Impact on the Heat Transfer Properties of Windows

Despite significant advancements in fenestration technology in the last two decades, the thermal transmittance of fenestration products is still significantly higher than that of walls. This corresponds to 60% of the total energy loss of a modern building envelope through the windows. Hence, further development and improvements of fenestration products are necessary. Increasingly stringent codes and standards for fenestration stimulate industry to work on improved solutions. Thus, it is crucial that assessment techniques are able to account for innovations accurately. The thermal effects of non-continuous hardware in window frames are currently ignored by international rating procedures. A preliminary investigation conducted by our team showed significant performance degradation in two of the three out-opening casement profiles caused by the presence of operating hardware. Frames with the structure made of vinyl and fiberglass consist of many air cavities that are penetrated by operating hardware made of highly conductive materials. In these frames, in order to have an accurate assessment, it may be required to employ three-dimensional modeling due to the convective nature of heat transfer within the cavities. However, in this study, we demonstrate that the three-dimensional (3D) effects of non-continuous hardware can be approximated accurately with simpler two-dimensional (2D) simulations. We then develop a simplified model based on weighted average capable of replacing the time- and computation-intensive 3D simulations with 2D simulations and validate it against market available frames and their corresponding hardware. Validation results show that our approximation technique results in discrepancies lower than 0.05 W/(m2K), or 3% of the total thermal transmittance. Thus, we conclude that simplified 2D simulation models may be used for predicting hardware impact in window frames with reasonable accuracy. As windows and glazing structures are becoming ever better thermally insulated, it is becoming even more important to be able to model the impact of the operating hardware on the total thermal performance in order to design the best windows possible and not let the operating hardware ruin an otherwise well-proven design, which is hence addressed in this study.</jats:p