Integration and application of passive cooling within a wind tower for hot climates (original) (raw)

Integration and Application of Passive Cooling Within a Wind Tower

ASHRAE, 2014

Increasing emphasis on reducing power consumption has raised public awareness of natural and renewable energy resources, particularly the integration of passive cooling systems in buildings such as wind towers. Wind towers have been in existence in various forms for centuries as a non-mechanical means of providing indoor ventilation. In hot conditions where there is a relatively low difference between internal and external temperatures, the cooling capabilities of wind towers which depend mainly on the structure design itself are inadequate. Therefore it is essential to cool the air in order to reduce the building heat load and improve the thermal comfort of its occupants during the summer months. The aim of this work was to incorporate heat transfer devices in a wind tower to meet the internal comfort criteria in extreme external conditions. Heat transfer devices were installed inside the passive terminal of the wind tower unit, highlighting the potential to achieve minimal restriction in the external air flow stream while ensuring maximum contact time, thus optimising the cooling duty of the device. Computational Fluid Dynamics (CFD) modelling and experimental wind tunnel testing were conducted to investigate the performance of a wind tower system incorporating the heat transfer device arrangement. Results have indicated that the achieved indoor air speed was reduced by 28 – 52 % following the integration of the heat transfer device configurations. Furthermore, the study concluded that the proposed cooling system was capable of reducing the air temperatures by up to 12 K, depending on the configuration and operating conditions. Good agreement was observed between the CFD simulation and the experimental results.

Numerical Investigation of the Integration of Heat Transfer Devices into Wind Towers

2013

The purpose of this study is to incorporate heat transfer devices inside the passive terminal of a wind tower unit, highlighting the potential to achieve minimal restriction in the external air flow stream while ensuring maximum contact time, thus optimising the cooling duty of the device. Computational Fluid Dynamics (CFD) was used to develop a numerical model of a wind tower system and simulate the air flow pattern around and through the device to the test room. Results have indicated that the average internal airflow rate was reduced following the integration of the vertical and horizontal heat transfer device configuration, reductions of 4.11 % and 8.21 % was obtained respectively. Furthermore, the proposed cooling system was capable of reducing the air temperatures by up to 15 K. The technology presented here is subject to IP protection under the QNRF funding guidelines.

CFD analysis of a heat transfer device integrated wind tower system for hot and dry climate

Applied Energy , 2013

Increasing emphasis on reducing power consumption has raised public awareness of natural and renewable energy resources, particularly the integration of natural ventilation systems in buildings such as wind towers. The aim of this work is to incorporate heat transfer devices in a wind tower to meet the internal comfort criteria in extreme external conditions. Heat transfer devices were installed inside the passive terminal of the wind tower unit, highlighting the potential to achieve minimal restriction in the external air flow stream while ensuring maximum contact time, thus optimizing the cooling duty of the device. Computational Fluid Dynamics (CFD) was used to develop a numerical model of a new wind tower design and simulate the air flow pattern and pressure coefficients around and through the wind tower to a test room. Results have indicated that the average internal airflow rate was reduced following the integration of the vertical and horizontal heat transfer device configuration, reductions of 7% and 10% was obtained from the achieved numerical models. The work compared the effect of evaporative cooling and heat transfer devices on the thermal performance of the passive ventilation device. The proposed cooling system was capable of reducing the air temperatures up to 15 K, depending on the configuration and operating conditions. Furthermore, the study also highlighted that the proposed system was able to provide the recommended rates of fresh supply even at relatively low external wind speeds. The technology presented here is subject to IP protection under the QNRF funding guidelines

Computational analysis of a wind tower assisted passive cooling technology for the built environment

This work investigates a novel closed-loop thermal cycle containing cylindrical heat pipes integrated within a roof-mounted circular wind tower to achieve internal comfort. The water-filled copper heat pipes having an outer diameter of 20 mm were systematically arranged in a horizontal orientation. Water was used as the working fluid instead of synthetic refrigerants in order to make the system carbon-neutral alongside maintaining the indoor air quality of the built environment. The three-dimensional Reynolds-Averaged Navier–Stokes (RANS) equations along with the momentum, continuity and energy equations were solved using the commercial FLUENT code for velocity and pressure field simulations. Using the inlet wind speeds varying from 1 m/s to 5 m/s, the results of the study showed that the proposed cooling system was capable of meeting the regulatory fresh air intake requirements per occupant of 10 L/s. In addition, the results showed that a passive cooling capacity ranging between 6 K and 15 K depending on the operating configuration. The findings of the study were validated by comparing the results with similarly analysed wind tower structures found in previous literature. The present work successfully classified the sustainable operation of natural ventilation systems in delivering energy-free cooling in regions encompassing hot and moderately humid or humid climatic conditions. The technology presented here is subject to an international patent application (PCT/GB2014/052263).

CFD and Wind Tunnel Study of the Performance of a Multi-Directional Wind Tower with Heat Transfer Devices

The aim of this work was to investigate the performance of a multi-directional wind tower integrated with heat transfer devices (HTD) using Computational Fluid Dynamics (CFD) and wind tunnel analysis. An experimental scale model was created using 3D printing. The scale model was tested in a closed-loop wind tunnel to validate the CFD data. Numerical results of the supply airflow were compared with experimental data. Good agreement was observed between both methods of analysis. Smoke visualisation test was conducted to analyse the air flow pattern in the test room attached underneath it. Results have indicated that the achieved indoor air speed was reduced by up to 17% following the integration of the cylindrical HTD. The effect of varying the number of HTD on the system's thermal performance were investigated. The work highlighted the potential of integrating HTD into wind towers in reducing the air temperature.

CFD and Wind Tunnel Study of the Performance of a Uni-Directional Wind Tower with Heat Transfer Devices

Computational Fluid Dynamics (CFD) and wind tunnel analysis were conducted to investigate the performance of a uni-directional wind catcher. A detailed experimental benchmark model was created using rapid prototyping and tested in a closed-loop subsonic wind tunnel. An accurate geometrical representation of the wind tunnel test setup was recreated in the numerical modeling. Experimental results for the indoor and external airflow, supply rate, and pressure coefficients were compared with the numerical results. Smoke visualisation experiment was also conducted to further analyse the detailed airflow structure within the wind catcher and also inside the test room. Following the successful validation of the benchmark CFD model, cylindrical Heat Transfer Devices (HTD) were integrated into the uni-directional wind catcher model to reduce the temperature of air induced into the ventilated space. The findings of the CFD study displayed that the proposed wind catcher was capable of reducing the supply temperature by up to 12 K within the micro-climate depending on the outdoor air speed. However, the addition of the cylindrical HTD also reduced the air supply rates by up to 20 – 35 %.

Climatic analysis of a passive cooling technology for the built environment in hot countries

The aim of this work was to determine the ventilation and cooling potential of a passive cooling windcatcher operating under hot climatic conditions by replicating the monthly wind velocity, wind direction, temperature and relative humidity (RH) observed in a hot-desert city. The city of Ras-Al-Khaimah (RAK), UAE was used as the location of the case-study and available climatic data was used as inlet boundary conditions for the numerical analysis. The study employed the CFD code FLUENT 14.5 with the standard k-í µí¼€ model to conduct the steady-state RANS simulation. The windcatcher model was incorporated to a 3 x 3 x 3 m 3 test room model, which was identical to the one used in the field test. Unlike most numerical simulation of windcatchers, the work will simulate wind flows found in suburban environment. The numerical model provided detailed analysis of the pressure, airflow and temperature distributions inside the windcatcher and test room model. Temperature and velocity profiles indicated an induced, cooler airflow inside the room; outside air was cooled from 38˚C to 26-28˚C, while the average induced airflow speed was 0.59 m/s (15% lower compared to a windcatcher w/out heat pipes). Field testing measurements were carried out in the Jazira Hamra area of RAK during the month of September. The test demonstrated the positive effect of the integration of heat pipes on the cooling performance but also highlighted several issues. The comparison between the measured and predicted supply temperatures were in good agreement, with an average error of 3.15%.

Comparison between evaporative cooling and a heat pipe assisted thermal loop for a commercial wind tower in hot and dry climatic conditions

Elsevier, 2013

Increasing focus on reducing energy consumption has raised public awareness of renewable energy resources, particularly the integration of natural ventilation devices in buildings such as wind towers. The purpose of this paper was to compare the traditional evaporative wind tower technique with a proposed wind tower system consisting of heat pipes. Computational Fluid Dynamics (CFD) was used to develop a numerical model of a wind tower system and simulate the air flow pattern around and through the device. A baseline heat exchanger section containing cylindrical heat pipes was constructed to simulate the multiphase flow behaviour of two-phase heat pipe working fluids including water and ethanol. Heat transfer rate was obtained at 113 and 106 W for water and 72 and 116 W for ethanol respectively. The second part of the study incorporated the cylindrical heat pipes within the control domain of a roof-mounted wind tower, highlighting the potential to achieve minimal restriction in the external air flow stream while ensuring maximum contact time, thus optimizing the cooling duty of the device. A comparison was established with the conventional evaporative cooling methodology. The proposed cooling system consisting of heat pipes was capable of reducing the air temperatures by 12–15 K, depending on the configuration and operating conditions. The technology presented here is subject to IP protection under the QNRF funding guidelines.

Investigating the Potentials of Wind Towers for Passive Cooling In Hot Dry Climates / Passive Design Paper work

Due to the Global Warming and the huge changes in the climate, massive demands for mechanical cooling system raised in hot climate regions. These demands resulted as a high increase in Carbon emissions proportions, which affects our life's and our environment negatively. Consequently, in the last two decades, Scientists began to develop traditional methods and elements in architecture, which was positively adapted with its climate and last for many centuries before the leap of technology in the 20th century. Wind catchers are one of these vital features, which provides cooling and natural ventilation system, in traditional architecture, in hot climates. This paper is going to investigate the potentials of these towers as a passive cooling system, and what are the new technologies that can be integrated in it, like evaporative cooling, ground cooling and solar chimneys, to make it a contemporary solution in hot dry climates. The study will be a literature review on different techniques of these towers and what are the latest knowledge for each technique through presenting some modern examples.

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.