Abstract
Abstract:
The need for air conditioning in rural areas in which there is no source of traditional electrical power leads to look for an alternative solution by thermal solar energy. Usually the population of these areas uses typical movable house (TMH) for living. Solar thermal system drive vapor jet refrigeration cycle (VJRC) is an alternative solution replaces the vapor compression refrigeration cycle.
Mathematical model will be carried out for (VJRC) using Engineering equation solver (EES) software program at various design conditions (generator, evaporator and condenser temperature). Especially attention on the performance of the cycle. Cooling load for one TMH using TRNBuild software program will be estimated under standard design conditions for Hebron and Jericho cities.
Hourly simulations for cooling load and solar thermal cooling system will be carried out over six months period (hottest months) considering climatic data for the two cities using TRANSYS software program coupling with EES. The performance of the overall system will be calculated. Energy consumption will evaluate. Effect of climate, evacuated tube solar collector tilt angle and area, hot storage tanks will study to meet the required human comfort, optimum operation conditions and parameters will be decided for the two climate regions.
Introduction:
The increasing demand for thermal comfort has led to a rapid increase in cooling system use and, consequently, electricity demand due to air-conditioning in buildings. The global contribution from buildings towards energy consumption, both residential and commercial, has steadily increased reaching figures between 20% and 40% in developed countries 1. Deployment of thermal energy refrigeration, using low-grade heat or solar energy, would provide a significant reduction of energy consumption. Among the various technologies for thermal refrigeration, heat-driven ejector seems the most promising alternative to the traditional vapor compression refrigeration cycle. 2.vapor jet refrigeration cycle (VJRC) is simple to construct, rugged, low maintenance and has few or no moving parts making it a highly reliable system with an ability to run from low temperature solar heat or other waste heat, which can result in much cheaper operation of the cooling system.
Ejectors are classified into two types depending on the position of the nozzle; constant-pressure mixing ejector and constant-area mixing ejector, in the constant-pressure mixing ejector the exit plane of the nozzle is located within the suction zone upstream of the constant area section, and the static pressure throughout the mixing zone is assumed constant. In the constant-area mixing ejector, the primary nozzle exit is located in the constant area section, where the mixing of the primary and secondary flows occurs and the pressures of the two streams are not equal. The constant-pressure mixing ejector is used more than constant-area mixing ejector because it has higher entrainment ratio and COP at the same conditions.
In (VJRC), water can be used as the refrigerant. Like air, it is perfectly safe. These systems were applied successfully to refrigeration in the early years of this century. At low temperatures the saturation pressures are low (0.008129 bar at 4 °C) and the specific volumes are high (157.3 m3/kg at 4 °C). The temperatures that can be attained using water as a refrigerant are not low enough for most refrigeration applications but are in the range which may satisfy air-conditioning, cooling, or chilling requirements 3.Using the water in VJRC Compared with other commonly used refrigerants (Halocarbons, hydrocarbon and mixtures refrigerants), water is inexpensive, has a high latent heat, and has minimal environment impact (ODP and GWP).
VJRC can operate at low generator temperature around 100 °C. It can easily be powered by high efficiency flat plate or evacuated tube solar water collectors. Since the cooling load is commonly synchronized with the availability of solar energy, this becomes an attractive application of solar energy. Palestine is located within the solar countries and considered as one of the highest solar potential energy in the world, this makes it one of the best countries to use the solar thermal energy in the solar thermal air conditioning systems, especially in rural areas where there is no or insufficient electricity and there is a sufficient lands for solar collectors.
Transient system simulation program (TRNSYS) and Engineering Equation Solver (EES) coupling are used to model and analyze the solar thermal refrigeration systems. EES software program is used to build a mathematical model of the refrigeration cycle and simulate the effect of operation conditions, and TRNSYS software program is used to simulate and analysis the system using solar thermal power system under different operation conditions and parameters at various regions and climate, and find the optimum design parameters for the system.
This simulation study based on constant-pressure mixing ejector with variable geometry using water as working fluid, the source of heat in the generator is the solar energy collected by solar collectors in two different cities in West Bank in Palestine, the cooling load of the cycle is used to cover the cooling demand for a TMH that commonly used in the rural areas in this cities.
Problem:
The global contribution from buildings towards energy consumption due air conditioning has steadily increased reaching about 30% in summer seasons in Palestine. In addition many rural areas in Palestine suffer from insufficient electricity that used in traditional air conditioning system to achieve the human comfort. This forced the population to used diesel generator to generate electricity demand that is high cost and non-sustainable.
Palestine is located within the solar countries and considered as one of the highest solar potential energy in the world, this makes it one of the best countries to use the solar thermal energy in the solar thermal refrigeration systems.
Using the solar thermal energy to operate solar cooling systems is the best solution to reduce the fuel consumption, cost, harmful emissions and handle the peak time. VJRC is one of the most solar cooling systems that can operate at low generator temperature (around 100 °C) using evacuated solar collectors.
Objective:
• Investigate the performance of the VJRC: Computer modeling will carried out on single VJRC. The system will demonstrated on EES software program under various operation conditions, the generator temperatures of 80-120°C, evaporator temperature of 5-15°C and condenser temperature of 25-40°C.
• Weather data collection and simulation: Weather data collection and filtration for Hebron city in the south of west bank and Jericho city in the east of west bank. Hourly simulation for weather data includes ambient temperature and solar radiation of the two cities mentioned.
• Cooling load simulation: Hourly simulation for cooling load demand for a typical movable house used in rural areas at the two cities mentioned. This house built at standard constructions in Palestine.
• VJRC driven by solar energy simulation: Hourly simulation for VJRC driven by solar energy to supply the cooling load demand at different climate of the two cities mentioned above, and studies the effect of the different parameters on the performance of the system and human comfort and finds the optimum design parameters for the system, the simulation attention on the following:
1- Investigate the effect of tilt angle of the solar collector in summer season.
2- Investigate the effect of solar collector area.
3- Investigate the effect of thermal storage tank.
