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

Numerical Analysis on Conceptual Feasibility of Hybrid Windcatcher and Turbine Roof Ventilator for Optimum IEQ and Wind Power Harvesting

This paper introduces "SmartTURVENT," a hybrid windcatcher and turbine roof ventilator system with triple benefits: enhancing indoor environmental quality (IEQ), harnessing renewable energy, and reducing carbon emissions. Utilising a transient state pressure-based solver with CFD airflow modeling, the SmartTURVENT system optimises heat exchange, achieving about 6-40% and 11-55% faster attainment of acceptable humidity levels compared to individual windcatcher and turbine roof ventilator operations, respectively. In energy harvesting, SmartTURVENT generates 0.37 W, 11.27 W, and 69.10 W at wind speeds of 2 m/s, 5 m/s, and 10 m/s, respectively. Over an 8-hour operation, SmartTURVENT reduces carbon emissions by an average of 13.0% compared to conventional systems

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

Performance investigation of a naturally driven building ventilation terminal.

Naturally driven ventilation terminals (wind vents) offer a way of improving comfort conditions while reducing building carbon emissions. The device sits on top of the building, trapping the air at higher velocity and delivering it into the interior of the building. The current cross-ventilated design combines the velocity, pressure, and density of air to produce wind driven ventilation. Currently there is scarce research investigating the performance of these devices in the United Kingdom (UK).This thesis provides a performance evaluation and optimisation of a commercially available building ventilation terminal (a benchmark) in the UK. A systematic review and optimisation of the device's geometrical components has been carried out using Computational Fluid Dynamics (CFD) and far-field experimentation.An extensive literature review was carried out to provide the framework for this investigation. Building on existing (developed) research techniques, the knowledge gaps identified in this subject area, were isolated and examined thoroughly.A new methodology for creating and dynamically modifying CFD models using complete wind vent geometry was devised. Using this technique the wind vent was subjected to systematic geometrical variation to establish the contribution of each component to the overall performance of the device.The research used full scale Far field experimentation to validate the CFD models of the wind vent. The Far field experimentation provided greater accuracy (0 - 0.08m/s) for this application, when compared to other validation techniques such as wind tunnel experimentation (0 - 0.15m/s).A new empirical methodology was devised for predicting the airflow through a wind vent. The empirical method was based on two dimensionless coefficients (0.44 and 0.3) found through the CFD experimentation research carried out.The investigation established the device is capable of meeting current British Standards Institute (BSI) guidelines, and is therefore suitable for UK applications. The BSI recommended 0.8L/sec of fresh air per m[2] floor area. The benchmark wind vent geometry delivered 1.1 L/sec per m[2] of floor area with an external wind speed of 1m/s (UK average was 4.5m/s).The key geometrical components (in isolation) were identified as the louver angle, distance between louvers and the number of louvers (now subject to patent number 0809311.4). Each of these geometrical variations provided an increase in performance over the benchmark case in the range of 27 - 45%. An optimum configuration of these parameters did not deliver the same increased performance range as the isolated case. However the optimised combination case increased the internal air movement rate using 50% less material than that of the benchmark geometry

Wind tunnel data of the analysis of heat pipe and wind catcher technology for the built environment

The data presented in this article were the basis for the study reported in the research articles entitled 'Climate responsive behaviour heat pipe technology for enhanced passive airside cooling' by Chaudhry and Hughes [10] which presents the passive airside cooling capability of heat pipes in response to gradually varying external temperatures and related to the research article "CFD and wind tunnel study of the performance of a uni-directional wind catcher with heat transfer devices" by Calautit and Hughes [1] which compares the ventilation performance of a standard roof mounted wind catcher and wind catcher incorporating the heat pipe technology. Here, we detail the wind tunnel test set-up and inflow conditions and the methodologies for the transient heat pipe experiment and analysis of the integration of heat pipes within the control domain of a wind catcher design

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