Climatic analysis of ventilation and thermal performance of a dome building with roof vent

This paper presents a climatic analysis of a naturally ventilated geodesic-type dome building situated in a hot climate. A comprehensive review of the literature was conducted to provide an overview of previous related research on dome-type-roof buildings. The two-floor geodesic dome building assessed in this study was based on a 3V icosahedron type and had a roof vent for natural ventilation. The airflow and temperature distributions inside the building were simulated using computational fluid dynamics modelling with the standard k-d turbulence model. The computational modelling was verified using sensitivity analysis and flux balance analysis. Validation was carried out by using a similar dome-shaped building model from the literature. The atmospheric boundary layer flow was simulated in the computational domain for a more realistic prediction of wind conditions. The thermal comfort level was assessed using the predicted mean vote method. The results showed that the integration of the roof vents was advantageous and could reduce the indoor temperature and introduce fresh air, particularly during winter. The results also revealed that natural ventilation using roof vents could not satisfy the thermal requirements during summer periods, and potential cooling solutions that could be integrated into the system are discussed

Thermal comfort and indoor air quality analysis of a low-energy cooling windcatcher

The aim of this work was to investigate the performance of a roof-mounted cooling windcatcher integrated with heat pipes using Computational Fluid Dynamics (CFD) and field test analysis. The windcatcher model was incorporated to a 5m x 5m x3 m test room model. The study employed the CFD code FLUENT 15 with the standard k-ɛ model to conduct the steady-state RANS simulation. The numerical model provided detailed analysis of the airflow and temperature distribution inside the test room. The CO2 concentration analysis showed that the system was capable of delivering fresh air inside the space and lowering the CO2 levels. The thermal comfort was calculated using the Predicted Mean Vote (PMV) method. The PMV values ranged between +0.48 to +0.99 and the average was +0.85 (slightly warm). Field test measurements were carried out in the Ras-Al-Khaimah (RAK), UAE during the month of September. Numerical model was validated using experimental data and good agreement was observed between both methods of analysis

Short- and long-term forecasting of ambient air pollution levels using wavelet-based non-linear autoregressive artificial neural networks with exogenous inputs

Roadside air pollution is a major issue due to its adverse effects on human health and the environment. This highlights the need for parsimonious and robust forecasting tools that help vulnerable members of the public reduce their exposure to harmful air pollutants. Recent results in air pollution forecasting applications include the use of hybrid models based on non-linear autoregressive artificial neural networks (ANN) with exogenous multi-variable inputs (NARX) and wavelet decomposition techniques. However, attempts employing both methods into one hybrid modelling system have not been widely made. Hence, this work further investigates the utilisation of wavelet-based NARX-ANN models in the shortand long-term prediction of hourly NO2 concentration levels. The models were trained using emissions and meteorological data collected from a busy roadside site in Central London, United Kingdom from January to December 2015. A discrete wavelet transformation technique was then implemented to address the highly variable characteristic of the collected NO2 concentration data. Overall results exhibit the superiority of the wavelet-based NARX-ANN models improving the accuracy of the benchmark NARX-ANN model results by up to 6% in terms of explained variance. The proposed models also provide fairly accurate long-term forecasts, explaining 68–76% of the variance of actual NO2 data. In conclusion, the findings of this study demonstrate the high potential of wavelet-based NARX-ANN models as alternative tools in short- and long-term forecasting of air pollutants in urban environments

A novel design of a desiccant rotary wheel for passive ventilation applications

Rotary desiccant wheels are used to regulate the relative humidity of airstreams. These are commonly integrated into Heating, Ventilation and Air-Conditioning units to reduce the relative humidity of incoming ventilation air. To maximise the surface area, desiccant materials are arranged in a honeycomb matrix structure which results in a high pressure drop across the device requiring fans and blowers to provide adequate ventilation. This restricts the use of rotary desiccant wheels to mechanical ventilation systems. Passive ventilation systems are able to deliver adequate ventilation air but cannot control the humidity of the incoming air. To overcome this, the traditional honeycomb matrix structure of rotary desiccant wheels was redesigned to maintain a pressure drop value below 2 Pa, which is required for passive ventilation purposes. In addition to this, the temperature of the regeneration air for desorption was lowered. Radial blades extending out from the centre of a wheel to the circumference were coated in silica gel particles to form a rotary desiccant wheel. Computational Fluid Dynamics (CFD) modelling of the design was validated using experimental data. Reduction in relative humidity up to 55% was seen from the system whilst maintaining a low pressure drop across the new design. As an outcome of the work presented in this paper, a UK patent GB1506768.9 has been accepted

A study of passive ventilation integrated with heat recovery

To meet the demand for energy demand reduction in heating, ventilation and air-conditioning systems, a novel design incorporating a heat recovery device into a wind tower was proposed. The integrated system uses a rotary thermal wheel for heat recovery at the base of the wind tower. A 1:10 scale prototype of the system was created and tested experimentally in a closed-loop subsonic wind tunnel to validate the Computational Fluid Dynamics (CFD) investigation. Wind towers have been shown to be capable of providing adequate ventilation in line with British Standards and the Chartered Institution of Building Services Engineers (CIBSE) guidelines. Despite the blockage of the rotary thermal wheel, ventilation rates were above recommendations. In a classroom with an occupancy density of 1.8 m2/person, the wind tower with rotary thermal wheel was experimentally shown to provide 9 L/s per person at an inlet air velocity of 3 m/s, 1 L/s per person higher than recommended ventilation rates. This is possible with a pressure drop across the heat exchanger of 4.33 Pa. In addition to sufficient ventilation, the heat in the exhaust airstreams was captured and transferred to the incoming airstream, raising the temperature 2 °C, this passive recovery has the potential to reduce demand on space heating systems

A passive cooling wind catcher with heat pipe technology: CFD, wind tunnel and field-test analysis

Wind catchers are natural ventilation systems based on the design of traditional architecture, intended to provide ventilation by manipulating pressure differentials around buildings induced by wind movement and temperature difference. Though the movement of air caused by the wind catcher will lead to a cooling sensation for occupants, the high air temperature in hot regions will result in little cooling to occupants. In order to maximise the properties of cooling by wind catchers, heat pipes were incorporated into the design. Computational Fluid Dynamics (CFD) was used to investigate the effect of the cooling devices on the performance of the wind catcher, highlighting the capabilities of the system to deliver the required fresh air rates and cool the ventilated space. Qualitative and quantitative wind tunnel measurements of the airflow through the wind catcher were compared with the CFD data and good correlation was observed. Preliminary field testing of the wind catcher was carried out to evaluate its thermal performance under real operating conditions. A cooling potential of up to 12 °C of supply air temperature was identified in this study

Evaluation of the integration of the Wind-Induced Flutter Energy Harvester (WIFEH) into the built environment: experimental and numerical analysis

With the ubiquity of low-powered technologies and devices in the urban environment operating in every area of human activity, the development and integration of a low-energy harvester suitable for smart cities applications is indispensable. The multitude of low-energy applications extend from wireless sensors, data loggers, transmitters and other small-scale electronics. These devices function in the microWatt-milliWatt power range and will play a significant role in the future of smart cities providing power for extended operation with little or no battery dependence. This study thus aims to investigate the potential built environment integration and energy harvesting capabilities of the Wind-Induced Flutter Energy Harvester (WIFEH) – a microgenerator aimed to provide energy for low-powered applications. Low-energy harvesters such as the WIFEH are suitable for integration with wireless sensors and other small-scale electronic devices; however, there is a lack in study on this type of technology’s building integration capabilities. Hence, there is a need for investigating its potential and optimal installation conditions. This work presents the experimental investigation of the WIFEH inside a wind tunnel and a case study using Computational Fluid Dynamics (CFD) modelling of a building integrated with a WIFEH system. The experiments tested the WIFEH under various wind tunnel airflow speeds ranging from 2.3 to 10 m/s to evaluate the induced electromotive force generation capability of the device. The simulation used a gable-roof type building model with a 27° pitch obtained from the literature. The atmospheric boundary layer (ABL) flow was used for the simulation of the approach wind. The work investigates the effect of various wind speeds and WIFEH locations on the performance of the device giving insight on the potential for integration of the harvester into the built environment. The WIFEH was able to generate an RMS voltage of 3 V, peak-to-peak voltage of 8.72 V and short-circuit current of 1 mA when subjected to airflow of 2.3 m/s. With an increase of wind velocity to 5 m/s and subsequent membrane retensioning, the RMS and peak-to-peak voltages and short-circuit current also increase to 4.88 V, 18.2 V, and 3.75 mA, respectively. For the CFD modelling integrating the WIFEH into a building, the apex of the roof of the building yielded the highest power output for the device due to flow speed-up maximisation in this region. This location produced the largest power output under the 45° angle of approach, generating an estimated 62.4 mW of power under accelerated wind in device position of up to 6.2 m/s. For wind velocity (UH) of 10 m/s, wind in this position accelerated up to approximately 14.4 m/s which is a 37.5% speed-up at the particular height. This occurred for an oncoming wind 30° relative to the building facade. For UH equal to 4.7 m/s under 0° wind direction, airflows in facade edges were the fastest at 5.4 m/s indicating a 15% speed-up along the edges of the building

A review of numerical modelling of multi-scale wind turbines and their environment

Global demand for energy continues to increase rapidly, due to economic and population growth, especially for increasing market economies. These lead to challenges and worries about energy security that can increase as more users need more energy resources. Also, higher consumption of fossil fuels leads to more greenhouse gas emissions, which contribute to global warming. Moreover, there are still more people without access to electricity. Several studies have reported that one of the rapidly developing source of power is wind energy and with declining costs due to technology and manufacturing advancements and concerns over energy security and environmental issues, the trend is predicted to continue. As a result, tools and methods to simulate and optimize wind energy technologies must also continue to advance. This paper reviews the most recently published works in Computational Fluid Dynamic (CFD) simulations of micro to small wind turbines, building integrated with wind turbines, and wind turbines installed in wind farms. In addition, the existing limitations and complications included with the wind energy system modelling were examined and issues that needs further work are highlighted. This study investigated the current development of CFD modelling of wind energy systems. Studies on aerodynamic interaction among the atmospheric boundary layer or wind farm terrain and the turbine rotor and their wakes were investigated. Furthermore, CFD combined with other tools such as blade element momentum were examined

Optimisation and analysis of a heat pipe assisted low-energy passive cooling system

Passive cooling using windcatchers have been utilised in the past by several Middle East countries to capture wind and provide indoor ventilation and comfort without using energy. Recently, researchers have attempted to improve the cooling performance of windcatchers by incorporating heat pipes. The present work encompasses existing research by optimising the arrangement of heat pipes in natural ventilation airstreams using numerical and experimental tools. The airflow and temperature profiles were numerically predicted using Computational Fluid Dynamics (CFD), the findings of which were quantitatively validated using wind tunnel experimentation. Using a source temperature of 314. K or 41. °C and an inlet velocity of 2.3. m/s, the streamwise distance-to-pipe diameter ratio was varied from 1.0 to 2.0 and the emergent cooling capacities were established to comprehend the optimum arrangement. The results of this investigation indicated that the heat pipes operate at their maximum efficiency when the streamwise distance is identical to the diameter of the pipe as this formation allows the incoming airstream to achieve the maximum contact time with the surface of the pipes. In addition, the findings showed that any increase in streamwise spacing leads to the formation of a second bell curve representing an increase in air velocity which simultaneously reduces the contact time between the airstream and the heat pipes, decreasing its effectiveness. The study quantified that the optimum streamwise distance was 20. mm at which the Sd/D (streamwise distance-to-pipe diameter) ratio was 1.0. The thermal cooling capacity was subsequently found to decrease by 10.7% from 768. W to 686. W when the streamwise distance was increased to 40. mm (Sd/D ratio of 2.0). The technology presented here is subject to an international patent application (PCT/GB2014/052263)

A review of heat recovery technology for passive ventilation applications

A review of current heat recovery devices was undertaken in an attempt to determine the major factors preventing the integration of heat recovery technology into passive ventilation systems. The increase in space heating and cooling demand in recent years combined with statutory requirements to reduce greenhouse gas emissions in the UK requires technology to be as efficient as possible, consuming the lowest amount of energy necessary. Heat recovery technology can meet this demand by lowering the energy demand necessary for heating and cooling by pre-heating or pre-cooling. Six different heat recovery devices were analysed and compared for suitability for integration into passive ventilation systems. Heat pipes and rotary thermal wheels are suggested as the technologies with the most potential for integration due to high thermal efficiency and low pressure loss across the heat recovery device in comparison to the other technologies. High efficiency is necessary to recover the maximum amount of thermal energy available. Low pressure loss across the heat exchanger is required to maintain adequate ventilation rates. The integration of heat recovery technology into passive ventilation has the potential to reduce energy demand in buildings but further research is required to optimise the recovery devices for simple installation, high efficiency and low pressure loss