In modern society, the contradiction between rapid economic development and environmental pollution and energy shortage has become increasingly prominent. Environmental protection, greening and energy saving have become the primary issues for human beings to seek survival and long-term development. The solar centralized hot water supply system has the advantages of energy saving, convenient use, no pollution and obvious economic benefits, and has become the main application form of solar energy. The solar centralized hot water supply project is composed of heat collecting system, thermal insulation system, circulation system, circulating pump, control system, pipe fittings, etc., which can be flexibly combined according to user requirements, installation site and water consumption. Therefore, it is of positive practical significance for the optimization of the application of solar energy in the field of hot water centralized supply to discuss the design of solar energy centralized hot water supply project.
01
Scope of application of solar centralized hot water supply system
To sum up, the scope of application of solar centralized hot water supply system includes the following aspects: first, the number of sunshine hours/year in more than 1200 hours, the amount of solar radiation/year in more than 3500 joules per square meter; Second, have the installation conditions of solar centralized hot water supply system; Third, the building installation site of the solar centralized hot water supply system can be guaranteed at least 4 hours of sunshine per day; Fourth, the installation of the system will not block the sunlight of the adjacent buildings; Fifth, the working temperature of the system is in the range of 130 degrees Celsius, and the working temperature of hot water is in the range of 75 degrees Celsius.
02
Design principle of solar energy centralized hot water supply project
The following principles should be followed in the design process of the solar centralized hot water supply project:
1. Security. The project itself has a high safety, in the case of accidental damage of the vacuum tube, the overall operation of the system will not be affected, at the same time, there should be lightning protection, wind protection, anti-freezing related protective measures;
2. Stability; It should have high thermal efficiency and stable performance, and can realize constant temperature and water supply, etc.;
3. All weather. Considering the influence of complex weather factors, corresponding auxiliary energy should be provided for its heating.
4. Intelligent. It is equipped with a control system, which can automatically start or turn off heating auxiliary energy according to the temperature setting requirements while displaying the water temperature. The control system is divided into automatic operation and manual operation.
5, energy saving. Maximize the application limit of solar energy to save conventional energy as much as possible;
6. Water quality requirements; The hot water centrally supplied by solar energy should be free of odor, rust and other substances affecting human health.
Due to the low density of solar energy, its heating process is slow, and it cannot heat cold water to the hot water at the desired temperature at a time like conventional heat sources. Therefore, its heating, heat exchange, heat storage methods and equipment are different from conventional heat sources. Because of the instability of solar energy, auxiliary heat equipment should be set up in the system, and auxiliary heat equipment should be set in order to make full use of solar energy as the principle. Moreover, because the system should be set up solar energy and auxiliary heat two sets of heating system, is bound to greatly increase an investment, so the production of solar energy system should be reasonable in order to meet the average daily heat of most period of time in a year, namely the number of water, quota should be determined according to this principle, and choose the appropriate solar energy guarantee rate.
03
Analysis of design essentials of solar energy centralized hot water supply project
(1) Design of heat collection system
1. System scale design
The scale of the heat collection system should not be too large, and the distance between the total outlet of the collector array and the heat storage tank should be controlled within 300 meters. When the community is large. It can be adjacent to several buildings or a single building as a small system, and the effect of energy saving can be realized by adding station rooms.
2. Select the heating system
The heating system is divided into direct heating and indirect heating, and both have their own advantages and disadvantages. The direct heating can achieve a higher heating efficiency, while the indirect heating can effectively prevent the generation of scale, so that the service life of the collector is extended. In practical application, it is more suitable for the application of indirect heating system, and in practical application, the collector needs to carry on pressure treatment, need to add circulating pump and heat exchange equipment.
3. Select heat storage equipment
The choice of heat storage equipment is based on the premise that the indirect heating system is indeed established. The heat storage equipment includes two kinds of heat storage water tank and heat storage water tank. For large hot water supply projects, the choice of heat storage tank is more appropriate, the reason is that the water output of this heat storage method can reach hundreds of cubic meters per day, and the application of heat storage tank is suitable for projects with small hot water supply, and can be assembled on the construction site, with small investment and small occupation.
Design of auxiliary heating equipment
1. Calculation of auxiliary heat equipment load
According to the requirements of relevant codes, the design of auxiliary heating equipment load in solar centralized hot water supply projects should not consider the solar energy utility, but take the daily heat required as the auxiliary equipment as the basis.
2, choose auxiliary heat source and auxiliary heat equipment
When choosing auxiliary heat source, it is advisable to choose heat pipe network, gas, fuel oil, heat pump, electricity, etc. Electricity should be selected as auxiliary energy for small solar centralized hot water supply system. Electric heating elements can be directly put into the heat storage water tank (box), but the application of this auxiliary heat source needs to increase the corresponding anti-scaling measures, otherwise the scale formed by its own will cause difficult to effectively heat dissipation and burn out the components. For large-scale solar hot water system, electric heating boiler should be used as auxiliary energy to achieve the purpose of durability and safety. When choosing auxiliary equipment, can undertake choosing according to conventional heat source method, and on the equipment model and the Numbers, should own unstable characteristics combined with solar energy, choose two or more sets of matching equipment, no solar energy, the equipment running at the same time, solar energy, a run, so as to achieve the aim of energy saving efficiency. The solar energy auxiliary heating air source heat pump unit is widely used. Its principle is that an auxiliary heat exchanger is added to the evaporator of the unit. Heat pump heating operation in low temperature environment, higher than the ambient temperature of solar hot water flowing through the auxiliary heat exchanger, and will enter the evaporator of the heat exchange with the outdoor air raise its temperature, thus the refrigerant in the environment of relatively high evaporation heat absorption, raise the evaporation temperature, improve the working conditions of the solar heating system.
3, layout of heat collection and auxiliary heat equipment
In the hot water storage tank, electric heating elements should be placed in the appropriate position. When there is no solar energy, electric heating and hot water storage can also be relied on to basically meet the demand for hot water. When the solar energy hot water system is larger, and heating and auxiliary heat when the water tank is used, also are independent of each other, and decorate, in tandem with the former for the hot water tank, heating effect, the latter as the auxiliary heating or hot water tank, so that when solar energy is not enough, can also play to preheat the cold water, and when, in the absence of any solar simply by auxiliary heat source to heat of hot water in the water, It can be normal heating, and it will not affect the heat collection of the hot water tank.
(3) System engineering safety design
1, anti-overheating, explosion-proof safety design
High temperature prevention and explosion-proof safety measures are very important in the design of solar centralized hot water supply project. Usually, including the following aspects of the design content: first, the pipeline of the heat collection system should be equipped with a deflator, safety valve, expansion pipe. And does not reduce the loss of the concentrated medium, can properly enhance the pressure inside the system; Second, the air radiator is set, that is, when the water temperature in the collector is too high, the air radiator is used to emit heat, so as to prevent overheating. Third, use shading equipment. The valve parts, pipe fittings and pipe materials used in the heat collecting system should be high temperature resistant materials, and the equipment, valve parts and sealing materials connected to the extreme heat pipe should also be high temperature resistant materials.
2, anti-freezing safety design
In the process of system engineering design, the problem of frost prevention should be considered for the cold area in north China and the area with possible freezing. Antifreeze measures mainly include reverse circulation, adding antifreeze, drainage, emptying, etc., and these methods have their own advantages and disadvantages, and the application process should always be based on the principle of "local conditions". Among them, this method of reverse circulation is relatively simple and more commonly used, but it has the disadvantage of power consumption. This problem can be mitigated by heat collection pipe insulation, reducing the resistance loss of the heat collection system and determining a reasonable sensor temperature.
04
conclusion
The solar centralized hot water supply system has the advantages of comfort, economy, energy saving, practicality and convenience, and the system engineering design involves many factors. The application scope of the system is defined, and the design principle of the system engineering is taken as the premise, and the above content is used for reference, so as to effectively guarantee the energy conservation and rationality of the design of the solar energy centralized hot water supply project.
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