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  • Publication
    Experimental analysis of thermal storage tank configurationin a solar cooling installation with an absorption chiller
    (2006-09-14) Rodríguez Aumente, Pedro Acisclo; Izquierdo Millán, Marcelo; Lecuona Neumann, Antonio; Salgado Mangual, Rafael A.
    The use of air conditioning systems in Spanish dwellings is gaining popularity, as the installed units grows by 0,8 million per year. The most popular air conditioning system today is the vapor-compression cycle. This kind of system consumes a considerable amount of electric energy as it incorporates a mechanical compressor in its cycle and utilizes refrigerants that can be dangerous to the environment. A solution to this kind of equipment can be found in Solar Facilities configured to produce cold water for air conditioning purposes by means of an absorption chiller. This kind of equipment can be driven by a heat input produced by the solar facility. This machine consumes a very low amount of electric energy and presents great advantages for the environment. Nevertheless, the need of a heat reservoir to operate in the afternoon hours, where solar radiation is not enough to drive the chiller, is indispensable in a solar facility. To serve this purpose, the introduction of a thermal storage tank has to be made. There are two basic internal configurations of a thermal storage tank in a solar cooling facility. These are Stratification and Well-mixed configuration. Experimental results show that for solar cooling applications, having a homogeneous mixture temperature in the thermal storage tank produce more daily cooling energy than in an stratified one, although the solar field efficiency is lower. This gives the facility more autonomy of operation in the afternoon, when the sun goes down and radiation is not enough for the application. Effects on the facility produced by Well-mixed configuration are: efficiency reduction on the solar collector’s field , 0,27, higher daily COP’s, 0,33, and extended solar cooling time of about two hours.
  • Publication
    Simulation of an absorption based solar cooling facility using a geothermal sink for heat rejection
    (International Solar Energy Society (ISES), 2008-10) Burguete Arguedas, Ana; Rodríguez, María del Carmen; Rodríguez Aumente, Pedro Acisclo; Salgado Mangual, Rafael A.
    An important issue of solar cooling facilities based on absorption cycles and sometimes not given the necessary attention is the recooling process of the absorber and condenser. This is critical in the overall behaviour of the facility because the condensation and absorption temperatures will affect the COP and cooling capacity of the chiller. Most of the time the recooling process is made by using a wet cooling tower in a closed loop through the absorber and condenser. The use of a wet cooling tower gives good results in terms of cooling capacity and COP, but presents some health risk, like legionella, and its use is restricted to the industrial sector and places where water scarcity is not present. This paper presents the modification of the already validated TRNSYS simulation of a solar cooling facility, implementing a geothermal heat sink instead of the wet cooling tower in order to dissipate the heat generated internally in the absorption chiller. Simulation results shows that a geothermal heat sink composed of 6 boreholes of 100 meters of depth should be sufficient in order to substitute the wet cooling tower, for a typical Spanish single family dwelling.
  • Publication
    Optimized Design of Hot Water Storage in Solar Thermal Cooling Facilities
    (2008-05) Rodríguez Aumente, Pedro Acisclo; Venegas Bernal, María Carmen; Lecuona Neumann, Antonio; Rodríguez, María del Carmen; Salgado Mangual, Rafael A.
    Solar thermal installations can provide a significant contribution to the energy needs of cooling demand of single family buildings. Unfortunately oversizing facility elements is not uncommon. Most of the design flaws concern collector field or auxiliary elements, such as backup boilers or electric resistances inside storage devices. This leads to lower than expected facility COP and SCOP, but also higher cost. Customer dissatisfaction is the result. This paper presents a numerical model of the multiple purpose solar thermal facility installed at Universidad Carlos III de Madrid (UC3M) using the TRNSYS® tool. The solar cooling facility (http://termica.uc3m.es/solar.htm) is completely monitored for its performance characterization in the production of AC, DHW and heating. Operational data for various summer seasons have been recorded, simultaneously with 7 meteorological variables. The experimental facility includes a single effect BrLi absorption chiller working at part load under summer season. TRNSYS is a completely feasible platform for simulating solar facilities and is commonly used by researchers and planners, for its simplicity and ease manipulation. This simulation tool contains general solar cooling elements found in most experimental facilities and has been kept as simple as possible. The model developed aims at analyzing facility elements in order to resize collector field and storage volumes. Furthermore it allows studying different configurations of the facility and the control schemes. These configurations include different hot water storage capacities within the facility allowing comparing with the facility without any kind of storage excepting its own thermal inertia. The simulation has been validated with instantaneous and seasonal experimental data for different summer seasons including 2003, 2004 and 2005. Simulation results show that there is a hot storage tank capacity that optimizes the facility in terms of COP, SCOP and total cold produced. Even with no storage at all, the facility still improves its behavior from current operating conditions. Simulation and experimental results are compared and an optimum configuration of the facility is proposed.