Abstract: This paper discusses the performance of CO₂ adsorption device and its utilization to save energy in buildings. This new device adsorbs CO₂ and a small amount of moisture in the CO₂ capture process, and it evaporates pure CO₂ by thermal energy in the desorption process. This study shows the possibility of implementing a CO₂ capture device in the operation of an air ventilation system for high performance air cooling and heating of buildings. This innovative strategy provides a means to recirculate indoor air to save energy for a certain period of time and the potential for an energy-efficient operation of buildings. This study presents the analysis of CO₂ adsorption performance measurements and evaluates the application of the device by numerical calculations. The results of simulations for the tropical summer and Central European winter season show that 30–60% of air ventilation energy for cooling and heating can be saved competed to conventional systems. Based on these results, this study describes the possibility of using this system to recirculate indoor air using the CO₂ capture device to save energy and minimize air cooling and heating loads. This novel strategy introduces a new paradigm of air ventilation and can replace conventional air ventilation systems for certain period of time.
Permalink: https://doi.org/10.1016/j.enbuild.2014.11.017

Abstract: This paper proposes a novel ventilation strategy for capturing CO₂ with scheduled occupancy diversity, and changes in recirculating ratio and infiltration rate. While many publications have described filters and a lamp that can efficiently capture and remove most pollutants (such as VOCs, dust, odors and viruses) to levels equivalent to those of conventional air dilution systems, no such system exists for CO₂. This paper evaluates a strategy to recirculate air in the breathing zone through simulations with occupancy diversity factors from ASHRAE 90.1 2004 and Duarte et al.’s results for weekdays from 6 AM to 9 PM to evaluate a possibility of implementing a CO₂ capture device. Using a lower indoor air recirculation ratio in spaces with high CO₂ concentration is more effective at reducing CO₂ concentration in the breathing zone. The results indicate that maximizing the air recirculation ratio by using the CO₂ capturing unit could replace conventional air ventilation systems by sufficiently reducing the concentration of CO₂ and supplying enough oxygen for occupational safety and health. Such a system could save air cooling or heating energy in buildings in hot or cold days or seasons, or when there are high outdoor pollution levels for a limited period of time.
Permalink: https://doi.org/10.1016/j.buildenv.2015.02.012

Abstract: The present work is dedicated to the numerical study of statistical characteristics of spatially-evolving supersonic turbulent boundary layers (STBL) with cooled walls. Large-Eddy Simulations (LESs) are performed to gain further insight into the role of wall temperature on the mean and fluctuating-flow properties of STBL. The velocity fluctuations, which are scaled according to the Morkovin’s hypothesis, have shown acceptable agreement with available experimental and DNS results of literature. However, the van Driest transformed skin friction C_f,inc lies below the incompressible theoretical curves as a function of Re_θinc for cold STBL, whereas compressible skin friction is found to be relatively higher for cold wall boundary layers than adiabatic boundary layers. The variation of total shear stress remains unaffected throughout the boundary layer for 0.5 ≤ T_w/T_r ≤ 1. The total temperature fluctuations are non-negligible for cold cases and surface cooling changes the near-wall turbulent structures. Additionally, the streamwise velocity and temperature fluctuations for the coldest isothermal STBL case are strongly correlated compared to the anti-correlation behavior of the adiabatic STBL in the near-wall region (y⁺ ≈ 9). Furthermore, the pressure fluctuations are found to be non-negligible for cooled boundary layers and a positive correlation between pressure and density fluctuations are observed in the log-layer. These tendencies have also been verified through a detailed statistical analysis of the unsteady flow-field.
Permalink: https://doi.org/10.1016/j.ijheatmasstransfer.2014.10.025

Abstract: In this paper, the characteristics of train-tunnel interaction at a tunnel entrance has been investigated numerically. A three-dimensional numerical model using the remeshing method for the moving boundary of a passenger train in Iran railway was applied. The turbulent flows generated by the moving train in a tunnel were simulated by the RNG κ−ε turbulence model. The simulations have been carried out to understand the effect of the train speed as well as the influences of the hoods and air vents on the pressure waves, drag, and side force coefficients. The results show that the maximum drag coefficient occurs when the train enters the tunnel and is equal to 2.2. The air vents and enlarged hood at the portal are demonstrated to attenuate the pressure gradient and drag coefficient about 28% and 36%, respectively. Furthermore when train is entering the tunnel asymmetrically, a side force is created that pushes the train toward the tunnel wall, which the maximum side force is 900 N.
Permalink: https://doi.org/10.1016/j.tust.2014.10.005

Abstract: Currently, the application of solar Photovoltaic (PV) systems on energy efficient buildings such as passive house, zero energy building (ZEB) and net-positive energy building (NPEB) is becoming increasingly attractive, particularly in Europe and North America. The rooftops of residential and commercial buildings are ideal places for the installation of PV systems. The work presented in this article aims at parametric analysis of PV systems applied to a 100 m2 flat rooftop of a Norwegian residential building in Oslo. The study shows the effect of PV module types, the modules’ row spacing, and installation tilt angle on the electrical energy yield. The study also includes the economic and environmental aspects of a selected PV system.
Permalink: https://doi.org/10.1016/j.egypro.2015.12.167

Abstract: Modern highly glazed buildings require solar shading in order to obtain visual and thermal comfort for the occupants in addition to obtain a low energy use of the building. For the system to respond to the external conditions in an intelligent manner, automated operation is needed. When utilising an automatic solar shading system, it is important to use a control strategy that is accepted and preferred by the occupants. Consequently, the objective of this study is to investigate occupant satisfaction with respect to visual comfort under two blind strategies: one simple control strategy with closed slats when the solar shading is activated and one more detailed control strategy that utilises the cut-off angle of the slats or a minimum slat angle of 15° when solar shading is activated. Results from the study are helpful in the development of control strategies for blinds and are indications of how blinds should be treated in building design. Responses from 40 participants in a repeated measure design survey revealed that the detailed control strategy was significantly more popular among the test subjects than the simple control strategy. Comments by the participants gave strong indications that view to the outside influenced the choice of preferred control strategy. Even if the detailed control strategy was found to be the most preferred, the results indicate that it was not sufficient to avoid glare. Based on the results, both glare and view aspects should be incorporated in the building design to a greater extent than what is common practice today. It can further be recommended that more effort is put into finding optimal set points for activation of the solar shading and for controlling the tilt angle of the blind in order to obtain a more robust control strategy with limited overrule actions.
Permalink: https://doi.org/10.1016/j.solener.2015.02.031

Abstract: Modern office buildings are often designed with highly glazed facades, with an intention of being sufficiently day lit. However, extensive daylight supply has its backside, as glare might be a considerable concern. From a building design perspective it is important to be able to make reasonable predictions of discomfort glare from windows already in the early design stage when decisions regarding the façade are taken. This study focus on verifying if simple illuminance based measures like vertical illuminance at eye level or horizontal illuminance at the desk are correlated with the perceived glare reported by 44 test subjects in a repeated measure design occupant survey and if the reported glare corresponds with the predictions from the simple Daylight Glare Probability (DGPs) model. Large individual variations were seen in the occupants’ assessment of glare in the present study. Yet, the results confirm that there is a statistically significant correlation between both vertical eye illuminance and horizontal illuminance at the desk and the occupants’ perception of glare in a perimeter zone office environment, which is promising evidence towards utilizing such simple measures for indication of discomfort glare in early building design. Further, the observed response indicate that the participants in the present study were more tolerant to low illuminance levels and more sensitive to high illuminance levels than the DGPs model would predict. More and larger studies are needed to confirm or enfeeble this latter finding.
Permalink: https://doi.org/10.1016/j.buildenv.2015.05.040