Modeling of a solar thermal system as a power supply alternative for a resistor water distillation system using TRNSYS

The sizing of a solar thermal system to feed the water distillers in the laboratory of the Santander Technological Units is presented, proposing a comparative study between three calculation methods (f-chart, instantaneous and ACSOL) for the estimation of the surface of solar capture, finally supported by modeling in the TRNSYS software of the final system, to evaluate its behavior dynamically during one year. Initially, a search for information is carried out to establish the models to develop each of the calculation methods, additionally technical data is collected from the laboratory equipment to determine the consumption of hot water. Subsequently, each of the calculation methods is applied in order to size the catchment surface, to finally carry out a comparative study between the results obtained, determining which is the most appropriate method for the calculation and defining the dimensions of the same, to develop a modeling of the dynamic behavior of the system through the TRNSYS Software. The final result presents a storage system with an average temperature of 62.13 ° C and solar collectors with an average temperature of 58.7 ° C for one year of operation. Finally, the operating time of the resistive stills is reduced from 11 hours a day to 6 hours with the integration of the Thermosolar system.


Introduction
The increase in energy demand in the countries grows as population increases [1] and technological developments [2], triggering high energy consumption, mostly from fossil fuels; being the biggest contributors to climate change [3].For this reason, it is currently seeking to implement non-conventional renewable energy sources for the production of electrical or thermal energy, [4] [5], as a transitional alternative for the paradigm shift in the use of fossil fuels [6].
Thus, as non-conventional renewable energies [7] [8] will play an important role for humanity [9], being an alternative solution to supply in the future, percentages of energy demand worldwide.Eventually, various developments in the use of solar radiation through small-scale [10] or large-scale thermo-solar plants; integrated with photovoltaic [11] [12] or solar concentration [13] [14], systems, they have been implemented worldwide as a source of electrical and thermal energy production [15] [16].
Within the systems with high energy consumption, the production of hot water and / or steam at residential and industrial level is immersed, applied to processes such as; residential ACS systems, laundries, poultry sector, distillation, among others [17].For their part, the distillation systems highly used in petrochemical processes, alcoholic beverages, the health sector, universities, among others, have a high energy consumption due to their generally resistive design or power using fossil fuels.Some authors [18], have developed direct solar distillation systems whose production capacity is on a small scale [19] and centralized systems applied to seawater distillation processes, for the production of fresh water, with high cost of implementation, operation and maintenance [20] [21].
Eventually, this work is aimed at the sizing of a solar exploitation system that allows the reduction of electrical energy consumption of the resistances used in the water distillation systems of the laboratories of the Santander Technology Units; that have a power of 3 kW each equipment.The design seeks to reduce the time of water treatment, which in normal working conditions oscillates in a production of 4 liters per hour, through the direct injection of the heat transfer liquid (Water) in the equipment, with an approximate inlet temperature of 60 ° C, in order to reduce the use and excessive consumption of it and taking advantage of the solar radiation of the City of Bucaramanga, Colombia.
The development of the system will be carried out through a comparative study of three different calculation methods that are: Indirect, F-chart and ASCOL 2.5, allowing a complete and detailed analysis of the system for a future implementation.Once the design of the system is in place, a modeling of its dynamic behavior will be carried out through the application of the TRNSYS software to know its operation for one year.The aim of this process is to contribute to the use of alternative and renewable generation means to reduce the high consumption of electrical energy by this equipment in percentage terms and, in turn, reduce greenhouse gas emissions, thereby reducing the environmental pollution generated in the facilities of the Santander Technology Units, through the future use of clean and inexhaustible energy from abundant solar radiation.
Finally, the document will be organized as follows.In section 2, the methodological aspects are presented, describing the analytical methods to be used to determine the size of the water heating system, as well as the TRNSYS modeling tool to evaluate the behavior for one year of operation of the system and its own characteristics.from the still.Section 3 covers the results of the system estimation and behavior modeling and finally section 4 presents the most relevant conclusions of the work.

Analysis Methods
Currently there are various calculation methods for ACS systems, based on static, semi-static or empirical approximation procedures and dynamic simulation methods with a higher degree of complexity, which allow to determine the analysis in time intervals and controlled conditions of the system [22].Next, three sizing methods for water heating systems are described, which are:

Indirect Method
Also known as the instantaneous method, it is based on using a calculation procedure in which all operating conditions are considered to be static.Being a manual procedure, this introduces a great error in the dimensioning, but in many cases, it serves as an initial starting point.Therefore, the energy demand is compared with the possible energy production that the installation would have if the environmental and operating conditions were kept constant throughout a period of time.
In this way, the following are presented for the determination of the surface of the ASC [23]: • Determination of energy demand by applying the required% of solar coverage.
• Determination of the collector performance.
• Once the yield is known, obtain the energy production per unit area • Once the energy production per unit area is obtained, we will divide the demand by the production to obtain the necessary area to produce said demand.Finally, depending on the opening surface of each collector, determine the necessary number of solar collectors

F-Chart Analysis
The F-Chart method is an analysis that is useful for designing both forced circulation and thermosyphonic solar thermal systems, especially to select the size and type of solar collectors to supply that will meet the demands of DHW or other thermal loads.The objective of the method is to obtain the curve f and estimate the performance of a solar collector.Curve f represents the fraction of monthly heat load transformed from solar energy, being defined as a function of two parameters: absorbed energy (gain) and loss due to reflection in the solar collector [24].
The equation used in this method can be seen in the following formula [24].
The sequence that is usually followed in the calculation is as follows: • Assessment of the calorific loads for heating water destined for the production of DHW. or heating.• Assessment of incident solar radiation on the inclined surface of the collector or collectors.
• Calculation of parameter D1 • Calculation of parameter D2 • Determination of the graph f. • Assessment of monthly solar coverage.
• Assessment of the annual solar coverage and formation of tables It is important to mention that for the calculation of the parameter f, which is the monthly energy fraction provided by the solar collection system, it must be above 60% for each month (or annual average); highlighting that no month can exceed 110% taking into account the technical code HE 4 of Spain, as a guide for the application of the current method.

ACSOL 2.5
The ACSOL calculation tool is the well-known free access TRNSYS simulation software from the University of Wisconsin-Madison [28], ACSOL contains a detailed mathematical model for each principal scheme and a database of meteorological conditions, accumulators, consumption profiles, etc.Through input menus the user provides additional information about the system to be studied; collection area, type of collector, volumes, consumptions, use profiles, configuration of obstacles, control method, etc.Once the case to be simulated has been defined, the computer solves the mathematical model and generates a results report.

Modeling TRNSYS
TRNSYS is a simulation software applied to the dimensioning and evaluation of renewable energy systems, which allows to analyze the operational behavior of the systems in a given time interval, under a series of variables that simulate environmental behaviors to which the devices are subjected in real environments.
Figure 1 presents the model of the ACS system to feed the resistive water distillation system.

Figure 1. Modeling in TRNSYS
The following software types were used for the simulation process: • Weather file: Radiation (Type), allows to link data from external weather files in TM2 format.
To obtain these data, the Meteonorm software was used, geographic location, Bucaramanga, Colombia.• Collector: Solar flat plate collector (Type), is used for heating water through the capture of solar radiation.• Storage: storage and heat exchange system to finally supply the water to the resistive water distillation system.

ACS consumption equipment
The laboratories of the UTS have 3 distillers with the same technical characteristics described in Table 1, which reached a temperature of 97 ° C to carry out the distillation process.Currently, the consumption of distilled water by laboratories is approximately 15 gallons per day.

Solar Collector
A flat TS25 solar collector is selected with a yield of 63.236%, due to the support offered by the Termocol company, its efficiency, availability, cost and ease of online purchase.

Conditions for analytical methods
In order to apply the three methods following the same parameters, it was necessary to identify those variables that directly intervene in the efficiency of the design.Consequently, the table presents the conditions used in each of the three analytical methods, in order to size the initial ACS system and compare the results of the three estimates and finally determine the appropriate size.

Results
Table 3 presents the main characteristics of the estimates of the ACS systems feeding the resistive distillation system of the laboratories of the Santander technological units, applying the analytical methods and the conditions described in section 2.5, highlighting: • The instantaneous method projects a system composed of 19 solar collectors with an annual yield of 51.95% for a time of 6.67 hours of operation during the day.The amount of energy produced is 3,372 kWh / m ^ 2. • The f-chart curves method was initially applied with the 19 collectors, based on the results obtained in the instantaneous method.The result was that no month of the year fulfilled the 60% coverage required by the application of the method to cover the demand for water from the distillation system.The result of the system performance was 19%.• Subsequently, the method of f-chart curves based on an experimental test method was applied again in order to identify the number of collectors necessary to cover the minimum demand of HE 4, determining 81 collectors to cover with 61% of the annual yield. .
• Finally, the ACSOL 2.5 software was used where the conditions presented in Table 3 and the catchment surface determined by the instant no method were simulated.As a result, the system with 19 collectors presents a performance of 97.55% and Figure 2 presents the relevant data of the energy balance of the system.For its part, Figure 3 presents the schematization of the system to be implemented for the supply of hot water to the resistive distillation system.Based on the results obtained by the three analytical methods (See Table 3), the system will be made up of 19 sensors and the connection circuit presented below.Once the size of the system was determined, the modeling was carried out in TRNSYS in order to look at the behavior of the system.Figure 4 presents the radiation data used in the simulation process and highlights: • The average daily radiation of the city of Bucaramanga, Colombia is in a range of 4-8 ℎ/ 2 , allowing the collectors to reach temperatures of up to180°C.Finally, Figure 6 presents the behavior of the storage system that would be connected to the resistive distiller of the Laboratories of the Technological Units of Santander, highlighting: • The tank will store a mixture of water vapor in some moments with temperatures up to 120°C.
• The average annual temperature of the liquid that enters the tank and leaves the resistive still is 62.13 °C.

Conclusions
Resistive distillation systems have high electrical energy consumption, which is why non-conventional renewable energies would be an alternative to supply the electrical and / or thermal needs of the devices.Currently, the drawback lies in the cost of implementing systems for high flow production of distilled water through technologies that take advantage of non-conventional renewable sources.This analysis seeks to provide an alternative to the high dependence on electricity supply for the production of distilled water and the most relevant conclusions are presented below: IOP Publishing doi:10.1088/1757-899X/1299/1/0120119 -The analytical methods for the sizing of the ACS system allowed estimating the area of collectors required to supply the demand of the distillation system.The instantaneous method allowed to have an initial estimate with a coverage percentage of 51.95%.The method of the fchar curves was uncertain and its estimation differs from the other methods used.For its part, ACSOL 2.5 allowed to analyse the results obtained by the instantaneous method, resulting in a coverage of 97.55% and the final schematization of the system to be implemented.
-The modeling in TRNSYS allowed to dynamically evaluate the behavior of the dimensioned system through the analysis methods in the city of Bucaramanga, Colombia.The collection surface was 45.6 m ^ 2, equivalent to 19 collectors with an average annual temperature of 58.7 ° C at the outlet of the solar collectors and an average annual temperature in the storage tanks of 62.13 ° C. Finally, the system dimensioned and subsequently modelled in TRNSYS is an alternative to be integrated into the resistive distillation system of the laboratories of the Santander Technological Units, satisfying the operating needs of the system and reducing the daily use of the still 11 hours.to 6 hours.

Table 3 .
Anaitic Way Analysis methods Catchment Area 2