N. Velázquez

Methodology for the energy analysis of an air cooled GAX absorption heat pump operated by natural gas and solar energy

Abstract In this work a methodological analysis and energy evaluation of an air cooled absorption system, with generator–absorber heat exchange (GAX), and operated by a hybrid natural gas–solar energy source is presented. Given the characteristic non-linearity of the resulting system of equations, the methodology proposed envisages a calculation sequence for the external currents and an iterative procedure for the internal currents. The system studied intents to be an alternative for space conditioning in the residential sector, the unit was designed with a capacity of 10.6 kW (3 Ton) of cooling and uses as working fluid ammonia–water. Giving priority to internal energy integration, an arrangement is proposed for the GAX cycle that allows 19% of solar contribution at full load, being greater at partial loads. In spite of using ambient air up to 40 °C with a relative humidity of 24% as cooling source, a COP value of 0.86 for cooling and 1.86 for heating was calculated, with an internal energy integration of 16.9 kW, 37% more than the energy that is supplied to the generator.

Aire Acondicionado Solar, para Conjunto de Viviendas en Mexicali, México

The objective of the present work is to dimension and evaluate an absorption LiBr-H2O cooling system assisted by solar energy and natural gas for air conditioning of a group of housings in Mexicali, Baja California, Mexico. The analysis of the hourly, daily and monthly operating performance in the period with more cooling demand is carried out by mean of TRNSYS 16, and it is seeking the least collection area and the highest solar fraction; that which is translated in the minimum operation cost and initial investment. It was found that the system generates conditions of the space between comfortably warm and comfortably cold, according to ISO 7730 (2005), with 287 m 2 of evacuated tubes which contribute 90% of the required energy. The system is technically feasible, since it covers the cooling demand during the summer period and it requires a similar collecting area to the available one in the housing compounds.

Achieving Resilience at Distribution Level: Learning from Isolated Community Microgrids

Increasing power system resilience at the distribution level is crucial due to the negative social impact of blackouts, as the undesired consequences get worse the longer the system restoration takes. Statistical records demonstrate that system recovery times after high-impact, low-probability events (e.g., earthquakes, tsunamis, and floods) are often faster for generation and transmission segments than for the distribution system. During the 2010 Chilean earthquake (8.8 Mw on the Richter scale), for example, the distribution system in the most affected area (almost 1.1 million customers) was not totally back in service until two weeks after the first major seismic event. In contrast, the transmission system rapidly recovered, with most of the bulk system buses re-energized by the end of the first day and the remainder during the second day. Additional installed generation capacity and repairing minor damage to most of the affected generation plants allowed for the recovery of most of the supply within a few days. Only 6.1% of the installed generation capacity required major repairs (which took up to six months to complete).

Design and Construction of an Air Cooled Ammonia Absorber

This paper presents the design criteria, methodology. and results of the basic and detailed engineering for a descending film ammonia absorber using air cooled finned tubes, which is part of an advanced absorption cooling system (solar generator absorber heat exchange cycle). The design consists in determining all the construction parameters for the air cooled ammonia absorption unit, starting with the operating conditions defined by a thermodynamical simulation of the process considering both physical and operational design restrictions. The chosen option was based on a comparison between the advantages and disadvantages of each possible array, type, and geometry. After performing the operational simulation, thermal and mechanical designs, and the consistency analysis, it was found that an absorption unit using 29 5/8 NPT 14 (BWG) steel carbon ASTM A-179 tubes, with pure SB-234 aluminum fins was the best option. The tubes are arranged in an equilateral triangle fashion, with crossed air flow cooling.

A Simulation Study on the Limitations of the Use of Evaporative Cooling for Air Conditioning in Hot Arid Climate of Mexicali, Mexico

This paper presents a study of the ambient conditions at which evaporative cooling can be used for air conditioning in the hot arid climate of Mexicali. The study is carried out using TRNSY 16 as a simulation tool, and a meteorological database generated from measured data, using the methodology suggested by the Sandia National Laboratories for constructing Typical Meteorological Years. The air conditions delivered by the evaporative cooler are evaluated by the predicted mean vote. It was found that evaporative cooling can be used at the beginning and the end of the hot season period (May to September). Only during the central months of the period not suitable conditions are present due mainly to high humidity ratios of the ambient air, under these conditions a desiccant system can be used.© 2006 ASME

Metodología para el Dimensionamiento y Optimización de un Concentrador Lineal Fresnel

Se presenta una metodologia de dimensionamiento para concentradores lineales Fresnel de espejos curvos y cavidad invertida tipo concentrador parabolico compuesto. El objetivo es determinar los parametros geometricos del concentrador que permitan obtener la maxima eficiencia de captacion de energia solar. La metodologia propuesta utiliza un procedimiento analitico y la tecnica de trazado de rayos, por medio de la cual se llevo a cabo un estudio parametrico evaluando las horas de operacion correspondientes a un dia representativo del mes critico de la ciudad de Mexicali Baja California, Mexico. Para un concentrador de siete espejos curvos de 34.3 cm de ancho y absorbedor tubular de 4.2 cm de diametro, las dimensiones resultantes fueron: espaciamiento de 10 cm, distancia focal de 1.8 m y cavidad de 19.7 cm de ancho. Con estas dimensiones se obtiene una concentracion geometrica de 11.9 y una eficiencia de captacion solar de 82.4%.

Thermal Analysis of a Conical Receiver in a Parabolloid Dish to be Used as Generator in an Advanced Solar Thermal Cooling System

In this paper an experimental thermal analysis made to a conical receiver attached to a solar parabolloid dish concentrator is presented, the purpose of this study is to know if it fulfills the requirements as far as quality and amount of energy demanded by a generator of a solar thermal cooling system (Solar-Branched-GAX Cycle). The analyzed system consists of a conical receiver of 19 cm of diameter by 20 cm of height, which was mounted to a focal length of 80 cm in a communications conventional antenna of 190 cm diameter, prepared with a reflecting coat. The concentrator was mounted in a multipurpose proving stand of solar collectors, with a solar tracking system in two axes. The analysis was carried out by evaluating experimentally three cases, which consisted of: A) receiver smooth, B) Receiver smooth with glass cover and C) Receiver with fins in the inner tail cone. According to the obtained results it can be concluded that the system of parabolloid disc concentrator using a conical receiver with fins is a very interesting option to be used as a generator of a solar thermal refrigeration system, since steam for a volumetric flow of 0.480 l/min can be generated.Copyright

A Solar Position Sensor Based on Image Vision

Solar collector technologies operate with better performance when the Sun beam direction is normal to the capturing surface, and for that to happen despite the relative movement of the Sun, solar tracking systems are used, therefore, there are rules and standards that need minimum accuracy for these tracking systems to be used in solar collectors’ evaluation. Obtaining accuracy is not an easy job, hence in this document the design, construction and characterization of a sensor based on a visual system that finds the relative azimuth error and height of the solar surface of interest, is presented. With these characteristics, the sensor can be used as a reference in control systems and their evaluation. The proposed sensor is based on a microcontroller with a real-time clock, inertial measurement sensors, geolocation and a vision sensor, that obtains the angle of incidence from the sunrays’ direction as well as the tilt and sensor position. The sensor’s characterization proved how a measurement of a focus error or a Sun position can be made, with an accuracy of 0.0426° and an uncertainty of 0.986%, which can be modified to reach an accuracy under 0.01°. The validation of this sensor was determined showing the focus error on one of the best commercial solar tracking systems, a Kipp & Zonen SOLYS 2. To conclude, the solar tracking sensor based on a vision system meets the Sun detection requirements and components that meet the accuracy conditions to be used in solar tracking systems and their evaluation or, as a tracking and orientation tool, on photovoltaic installations and solar collectors.

Simulación Dinámica y Estudio Comparativo de diferentes Configuraciones de Sistemas de Enfriamiento Evaporativo para Mexicali, México

The design and evaluation of several configurations of evaporative cooling systems for air conditioning of a dwelling for low-income sectors in Mexicali, Mexico using simulation with TRNSYS 16.A is presented in this paper. The configurations studied include direct as well as indirect evaporative cooling with heat exchange and also systems with solid desiccant. The main rating parameters to classify the different configurations are the internal comfort conditions, the efficiency and the number of required equipments. The results show that the best configuration is one that includes a heat exchanger that pre-cools the air inlet stream with a cooling stream delivered by air coming from the dwell, but there is a small fraction of the time during the day that comfort is not met. If thermal comfort is to be met during the whole day, solid desiccant systems are the best choice.

Development of a Cheap and Simple Sensor-Based Polar Tracking System

The present work describes the design and construction of a Sensor-Based Polar Tracking System. It was implemented to drive a Photovoltaic module with four panels parallel connected, but it can be used to work with any concentrator with this type of tracking. This system looks for the most incidence radiation region, increasing the amount of collected energy, and therefore increasing the amount of electric energy produced. To control the motion of the electromechanical mounting, a very simple and economic circuit has been developed. Whole system has been tested in different applications like: solar radiation measurement, supplying the energy to a water pump for a Solar Thermal cooling and also to an evaporative cooling system. Experimental results show an increase of the collected energy up to 29% compared with a fixed PV module.Copyright