With the increasing of people's living standard, large and medium-sized city residents growing demand for domestic sanitary hot water, especially the purchase of residential domestic hot water equipment, almost without exception, to be installed. Real estate developers in order to enhance the quality and grades of green eco-housing, but also trying to make their own residential product comes with hot water equipment. The salient features of the energy-saving and environmentally friendly, solar hot water systems more and more popular, small split-type solar water heating systems have mushroomed in places such as villas, high-rise residential balcony. In this paper, solar and electric auxiliary heating system, for example, talk about design ideas and experience of split-type solar water heating systems.

Common design in the form of a split domestic solar water heating systems

Villas, high-rise residential use of solar power air conditioner systems, split solar water heating systems for domestic heating methods are used to split under pressure in the secondary circuit. This heating method has a stable, reliable, and easy. Split pressure secondary loop system there are very many types, each with advantages and disadvantages are therefore required to the scientific selection of villas, high-rise residential hot water supply characteristics. Now cited several solar and electric heating, a combination of split bearing secondary circuit of solar energy systems, and analyzed separately.

1.1 solar and electric heating combined form - tank the upper single electric heating coil heat exchanger, water tank built-in

Figure 1, the solar collector - the lower part of the water tank heat exchanger coil - circulation line - circulating pumps, etc. constitute a circulation loop. When the solar collectors absorb sunlight, the heat transfer medium inside the solar collector is heated warming; heat transfer medium flows through the role of the circulating pump to tank the lower heat exchanger coil, the lower part of the tank water heating; tank lower water temperature, automatically rise to the tank upper part of the upper water tank cold water automatically sink to the tank lower part. So on, so after nearly a day's work, solar energy gradually to the water tank all heating. When when solar insufficient water tank the upper water temperature below the set temperature, the electric heating device is located in the upper start automatically, and the upper water of the tank is heated to the desired temperature. In order to achieve the 24-hour hot water tank the upper electric heating devices are usually in a duty status. When the tank upper part of the water temperature below the set temperature, the electrical heating device automatically starts automatically stop until the tank upper part of the water temperature reaches the set temperature after.

Through the above analysis we can see that the system is relatively simple, relatively low cost, but there are two drawbacks:

Consecutive rainy days, solar heating, only water tank upper hot water, while the lower part of cold water. In the evening or morning concentrated using hot water, there is the problem of inadequate water supply. When no hot water, must wait a very long time to heat the water (assuming that the electric heating power is 2kW, 80kg of water heated from 15 ℃ to 45 ℃ heating about 1.5 hours). This is obviously inconvenient for users.

Second, in order to improve the heat transfer capacity, the heat exchanger coil to use more brass. However, the liner material of the tank more steel plate coated with high temperature enamel, the enamel surface local presence of a microporous copper - iron - water is likely the formation of electrochemical corrosion. Iron as the anode, copper cathode. Since copper (Yin) very local small iron (Yang) pole, so may cause the tank partial perforation leaks.

1.2 solar and electric heating combined with the form of two - tank top and bottom pairs of electric heating, built-in coil heat exchanger tank

Figure 2 and Figure 1 the difference is that the tank top and bottom of Figure 2, each with an electric heating device. tube solar water heater system intelligent controller based on the tank lower part of the temperature and time of day, automatically determines whether to activate the lower part of the electric heating device so as to ensure the time the tank lower part of the temperature to reach the standards set in the afternoon, to avoid the lack of rainy days hot water problem, but there are still hidden electrochemical corrosion resulting in perforation. Compared with Figure 1, Figure 2 increase in the tank an electric heating device, and need intelligent control, Figure 2 is higher than the cost of the system in Figure 1.

1.3 solar and electric heating combined with the form of three - tank top and bottom pairs of electric heating water tank external heat exchanger in Figure 3 and Figure 2 is the difference between the heat exchanger coil in the tank system, and additional water tank external a heat exchanger. Figure 3 system, the advantage of avoiding the shortcomings of Figure 1 and Figure 2 system, there is no hot water, inadequate and electrochemical corrosion perforation specially made solar energy and does not require a dedicated water tank, pressure tank selected to bring the ordinary electric water heater electric heating can. The lack of system in Figure 3 is: to be equipped with an external heat exchanger, circulating pump and Figure 1, Figure 2 System, the system cost, and external heat exchangers need to occupy a certain space, but also increase the system power consumption, system efficiency is greatly reduced.