Serdar Celik

Green Roof Storm-Water Runoff Quantity and Quality

AbstractThe design of a green roof plays a significant role in performance. In a ground-level field study, 28 built-in-place green roof models, four modular units, and four roof decks with standard black membrane were arranged in a completely randomized design. Storm-water runoff quantity and quality were monitored from September 2005 through June 2008. Results indicate that green roof systems significantly reduced storm-water runoff and that system design, growth media depth, and presence of plants impacted storm-water retention. In a second study on a building roof, two modular systems were used to evaluate water loss through evapotranspiration. Water loss of both systems was significant and influenced by system design, growth media type, and presence of plants. Finally, runoff quality analyses from the ground-level field study and from a laboratory pot experiment indicate that nitrate, total suspended solids, and turbidity are generally low in runoff after a first-flush event. Runoff water quality was ...

Energy Conservation Analysis of Various Green Roof Systems

The present paper illustrates an experimental analysis on the comparative analysis of air-conditioning energy savings of different green roof applications based on experimental measurements. Tests were carried out on nine different green roof samples, involving three types of growth media (lava, arkalyte, pumice) matched with three sedum types (kamtchaticum, spurium, sexangulare). Temperature readings at the bases of each sample were recorded for 32 months continuously at every 15 minutes. The data was processed and the heat gain of a sample building with each green roof application was calculated theoretically. The energy consumption comparisons showed that the right selection of growth media and vegetation can yield significant energy savings for air-conditioning applications.

Energetic and Exergetic Performance Evaluation of an AC and a Solar Powered DC Compressor

This study represents experimental performance analyses of an alternative current (AC) and a direct current (DC) refrigeration compressors implemented in a 79 liter refrigerator. Experiments were carried out at continuously running (ON) and periodically running (ON/OFF) operation modes. Data was analyzed and a comparison in terms of cooling capacity, power input, coefficient of performance (COP), Carnot COP, and exergy efficiency was conducted. The comparison showed that DC compressors can be much more efficient than AC compressors in refrigeration units.

Experimental and Theoretical Analysis of Evapotranspiration in Green Roof Systems

This study focuses on the water loss of green roof systems due to evapotranspiration, which is the combination of evaporation and transpiration processes. Water loss through evapotranspiration increases the capacity of a green roof to intercept additional stormwater during the following rain event and keep it out of the municipal stormwater system. Hence it is important that amount of water loss through a green roof, with known plant and growth medium properties and climate conditions, can be quantified. A theoretical model based on energy equation is used and MATLAB is employed in solving the equations due to the complexity of the problem. Relevant heat transfer equations with appropriate thermophysical properties of materials are used. Values obtained from the theoretical analysis are compared with experimental values that were gathered via a field project in which different green roof samples were tested for 2.5 years in terms of their weight under wet and dry seasonal conditions. The results from the theoretical model are found to be in close agreement with the experimental measurements, which is encouraging for predicting water loss of green roof systems in different geographic locations with known climate conditions.

Octagonal Halbach Magnet Array Design for a Magnetic Refrigerator

ABSTRACT An effective magnet array design for magnetic refrigeration systems is crucial given the space limitations and need for maintaining the required cooling capacity. Here, Halbach permanent magnet arrays (HPMA) in an octagonal orientation are studied using NdFeB permanent magnets. Gadolinium is selected as the magnetocaloric material (MCM) for the aperture inside the octagonal HPMA. The optimum outer-to-inner radii ratio for the octagonal HPMA and MCM system is found to be 2, at which the cooling energy per volume of magnet has a peak. For this ratio, the effect of using soft magnetic material, which in this study is FeVCo, inside and outside the HPMA is evaluated over a range of material thicknesses. The optimum soft magnetic material thickness outside the HPMA is obtained to be 3% of the external radius. At this thickness, soft magnetic material is also placed inside the array as a concentrator. It is found that although using soft magnetic material inside the magnet array increases the average flux, cooling energy is decreased due to using less MCM inside the aperture because of the space occupied by the soft magnetic material.

Thermal and exergetic analysis of a rotary-type magnetic cooling system

Despite the high theoretical performance limits of magnetic refrigeration systems, coefficient of performance (COP) of these systems can be lower due to abortive magnet and magnetocaloric material (MCM) assembly orientation and space limitation. To address both of these problems, a rotary-type magnetic cooling system with varied geometric properties was modelled and simulated. Heat transfer from the MCM, which was selected to be gadolinium (Gd), to the working fluid, was considered as volumetric energy generation. Three different geometries of disc-MCM assembly were studied where the inner and outer radii were selected as 5, 10, 15 mm, and 10, 15, 20 mm, respectively. It was observed that the gradient between steady-state temperature and the room temperature decreases with decreasing gadolinium-to-disc area ratio. Conductive heat transfer through the thickness of the disc was found to be inconsiderable compared with the convective heat transfer through the top surface.

Thermal Evaluation of Green Roof Systems Containing Bottom Ash Growth Media

This paper presents a study on the use of furnace bottom ash (FBA) as a growth medium in green roof applications. Experimental tests were performed on three different green roof samples, involving FBA as the growth media and three sedum types (kamtchaticum, spurium, sexangulare) matched with it. Theoretical analysis was conducted for modeling the heat transfer through the green roof samples. Temperature readings at the surface center, bottom center, and bottom edge of each sample were recorded for 12 weeks with a data sampling frequency of 15 minutes. The results were compared with roofs without vegetation. These reference roofs are covered with black (EPDM), and white (TPO) roofing membranes. The study showed that green roof samples with FBA yielded better thermal performance compared to conventional roof membranes. However plant survival and coverage could be an issue in green roof systems using FBA if necessary amount of plant maintenance is not performed.

Thermal Comparison of Reflective and Non-Reflective Roofs with Thin-Film Solar Panels

The present paper illustrates an experimental and comparative thermal analysis of reflective (white) and non-reflective (black) roofing membranes paired with thin-film solar photovoltaic panels. Tests were carried out on two different membranes, thermoplastic olefin (TPO), and ethylene propylene diene monomer (EPDM). Solar irradiance along with temperature readings on the surface, between the panel and membrane, and below the membrane were recorded for 16 months at 15 minute intervals. The data was processed and the temperature effect was observed. The interface temperatures for TPO/PV and EPDM/PV assemblies were found to be different, which could affect the performance of solar panels at various levels depending on the material type used in fabricating the photovoltaic panels.

Thermal Analysis of a Grooved Refrigerating System Evaporator

[Abstract] A heat exchanger with a suction line of copper ribbed-tube was developed and applied as an evaporator of a refrigeration circuit. The evaporator tubes have grooves on the inner surface in order to provide a more mixing flow and a large effective wetted area. Thermal and flow analyses were performed on a prototype refrigerating system with the ribbed-tube evaporator. The same analysis was performed on the refrigerating system but with a smooth-tube (non-grooved) evaporator. Temperature and pressure measurements were made for each of the two refrigerating systems. The turbulence model applied in the study is the standard k-epsilon accounting for the turbulent kinetic energy and dissipation rate. The two systems were compared in terms of heat exchanger effectiveness, overall coefficient of performance (COP), run-time ratio and pressure drop. The heat exchanger effectiveness of the ribbed-tube evaporator was found to be 7% higher compared to the smooth-tube evaporator. The COP value of the system employing the ribbed-tube evaporator was also found to be higher. Also the results obtained from the study of the runtime ratios showed that the system using the ribbed-tube evaporator will save significant energy for the same cooling effect. Although the pressure drop for the ribbed-tube evaporator was found to be slightly higher than that for the smooth-tube evaporator, the same compressor used in the two systems was able to overcome this pressure drop increase.

Forced Convection Heat Transfer at the Heat Exchanger of the Thermoacoustic Refrigerating System

Experimental investigations on the oscillatory flow, heat transfer at the heat exchanger of the thermoacoustic refrigeration system were performed. Significant factors that influence the heat transfer and construction of this system were identified. Results were correlated in terms of Nusselt number, Prandtl number and Reynolds number to obtain a useful new correlation which was compared to the closest related existing correlations in the literature. Results show that using straight flow heat transfer correlations as done presently in a number of analyses and design of this system could result in significant errors.