ABSORPTION SOLAR REFRIGERATION SISTEM FOR AIR CONDITIONING IN THE YUCATAN PENINSULA

Elizabeth Corts Rodrguez Facultad de Ingeniera Qumica,

Universidad Autnoma de Yucatn. Perifrico Norte Km. 33.5 Tablaje Catastral

13615, Col. Chuburn de Hidalgo Inn, Mrida, Yucatn C.P. 97203 Mxico

Elizabeth.cortes@uady.mx

Claudia A. Ruiz Mercado Facultad de Ingeniera Qumica,

Universidad Autnoma de Yucatn. Perifrico Norte Km. 33.5 Tablaje Catastral

13615, Col. Chuburn de Hidalgo Inn, Mrida, Yucatn C.P. 97203 Mxico

Claudia.ruiz@uady.mx

Jos Luis Castilla Carrillo

Facultad de Ingeniera Qumica, Universidad Autnoma de Yucatn.

Perifrico Norte Km. 33.5 Tablaje Catastral 13615, Col. Chuburn de Hidalgo Inn, Mrida, Yucatn C.P. 97203 Mxico

vichicastilla@hotmail.com

Wilfrido Rivera Gmez-Franco Centro de Investigacin en Energa CIE-UNAM Cerrada Xochicalco, s/n Colonia

Centro, 62580 Temixco, Morelos, Mxico. wrgf@cie.unam.mx

ABSTRACT

Nowadays there is a great worldwide concern for the increase in energy demand and the associated emission of greenhouse gases from fossil fuel combustion. In tropical regions, the use of air conditioning systems for thermal comfort using fossil fuel to obtain the electric power for the compression refrigeration systems is a common use. Alternative systems such as the absorption refrigeration systems which are effective in energy terms, since they make usable waste heat streams and the use of renewable energy sources such as solar contribute to decrease the global warming. In this research a solar absorption air conditioning prototype with a load of 5 kW and one stage was selected to be built and operate in the Yucatan Peninsula where the average annual maximum temperature is around 36 C. Savings of 15.24% of the electricity costs will be obtained.

1. INTRODUCTION

At the present times, the increase in world population requires great amounts of industrial products and higher energy requirements. Since 1900 the world population has quadrupled, and the primary energy consumption grew by a factor of 22.5. In the past 20 years the world population has increased by 1.6 million people and it is projected to will increase by 1.4 million over the next 20 years Fig. 1. Until 2008 the 78% of the global energy consumed in most industrial processes as well as power generation

used fossil fuels for its operation (1), oil industry experts estimate that the reserves today only cover the needs of the next forty years. For this reason, many countries are trying to reduce his fossil fuels consumption and increasing the use of renewable energy.

Fig. 1 Trends of population growth and primary energy needs (2). The usage and technology of renewable energy resources such as solar, geothermal, wind, and others, has showed a 6 times increase in production from 1943 to present times, according to data from the OECD (Organization for Development and Economic Cooperation), in 2006 there

was an increase of 7% and expecting a 10% of growth in 2030, as result of low cost technologies developed for non-renewable resources and high costs of fossil fuels, about that, some countries are investing considerable amounts of money in the development of technologies for energy recovery. Only from 2009 to 2010, wind power, solar and geothermal had significant technology investment growth being the solar energy the strongest with a 52% Fig 2

Fig. 2. Technological investment (billion dollars) in 2010 by energy type and percentage of growth compared to 2009 (3). Solar power, stands out from other renewable energy to be easily accessible and free, being a technology that has had more growth in the last years, because the radiant energy can transform into usable energy. Among the available technologies highlight photovoltaic cells and solar collectors. Solar collectors are devices designed to capture solar radiation, transform it into thermal energy and to raise the temperature of a fluid for later use. Solar collectors are divided into two groups: without and with concentration, the first one does not raise up than 100 C, while the last one is able to raise the temperature of fluid above 100 C using methods of optical concentration. The materials used in the collectors have lower cost than solar cells and their applications are more varied. Among the most common applications which employ solar collectors is water heating for domestic use, swimming pools thermal conditioning and electric power generation.

One of the newest applications for collectors is in the air conditioning area, and has a great growth in response to the effects of global warming caused by greenhouse gases and decreasing the ozone layer. The high demand for thermal comfort is a great opportunity for technological development. It usually used mechanical compression cycles for thermal comfort and cooling, with the disadvantage of their high energy consumption and use of harmful refrigerants to the environment, so now is betting for the use of chemical absorption refrigeration devices, which are considered by the International Energy Agency as the technology of the future, considering as an interesting option for solving problems in industrial refrigeration and air-conditioning, for which only a few years ago was discarded. The main feature of the absorption cooling machines is that the energy consumed for its operation is mainly thermal, may come from residual heat, which facilitates their integration in cogeneration plants. Usually, the absorption units are preferable when available heat from cogeneration, residual or an inexpensive energy source. Therefore, the absorption system will have its best application with solar energy. Generally, solar air conditioning systems are composed of two subsystems: solar collection system and the refrigeration device. The first one has the function of capture energy from the sun and transmit it to the second to activate it, and then the second cool the air, it is noted that for pumping the working fluid is used conventional power. Absorption System Operation. An absorption chiller single effect within an air conditioning system comprises the same elements as one based on mechanical compression Fig. 3, except for the mechanical compressor, which is replaced by a "thermal compressor" (4). The absorption refrigeration machines utilize a mixture of two components, refrigerant and absorbent, to carry out the cooling thermodynamic cycle. These systems are based on the fact that the pressure of refrigerant vapor is altered by the presence of the absorber, which decreases with increasing amount of absorbent. So that by controlling the concentration of the mixture ensures that the refrigerant evaporates at low temperatures (below 10 C). To this must be used absorbent with a sufficiently low vapor pressure, and maintaining the solution at a temperature and concentration to which the vapor pressure is lower than

the refrigerant in the evaporator. An absorption suggests that there are aboutand 200 compounds absorbents compoundsmost common working fluids are waterand ammonia-water.

Fig. 3. Comparison between an absorption compressormachine and the mechanical compression The main types of absorption systems have one step or single effect, double effect and double absorption. The essential elements of an absorption system are: a generator, a condenser, an evaporator and an absorber. The mixture of working fluid-absorbent isthe generator which is supplied an amount of heat to separate the vapor working fluid from the absorbent at an intermediate temperature. Once it has been vaporized, the working fluid passes through the condenser where it is liquefied by heat removal at a lower temperature. Subsequently, fluid is pumped into the high pressure region where it is vaporized by supplying a quantity of heat in the evaporator at an intermediate temperature. Finally, the working fluid vapor is absorbed into the concentrated solution from the generator to the absorber, dissipating a quantity of heat, which is at higher temperature than the supply temperatures. The dilute solution passes into the generator through the expansion valve restarting the cycle again (5).

inquest of fluid that there are about 40 refrigerants

compounds. However, the water-lithium bromide

absorption compressor

mechanical compression machine.

The main types of absorption systems have one step or single effect, double effect and double absorption. The essential elements of an absorption system are: a generator, a condenser, an evaporator and an absorber.

absorbent is introduced into the generator which is supplied an amount of heat to separate the vapor working fluid from the absorbent at an intermediate temperature. Once it has been vaporized, the working fluid passes through the condenser where it is

at removal at a lower temperature. Subsequently, fluid is pumped into the high pressure region where it is vaporized by supplying a quantity of heat in the evaporator at an intermediate temperature. Finally, the working fluid vapor is absorbed into the

centrated solution from the generator to the absorber, dissipating a quantity of heat, which is at higher temperature than the supply temperatures. The dilute solution passes into the generator through the expansion

The initial cost of an absorption refrigeration plant is, in most cases higher than a mechanical compression equipment of the same capacity. The reason for this difference is the higher amount of metallic materials that is necessary for the manufacture of hfluid absorbent. However, analyzing the operating costs from the value of the energy consumed, the balance can be shifted in favor of absorption equipment, the cost of producing mechanical work necessary to obta