The depletion of natural resources leads to an increase in gas and electricity prices. Therefore, in the near future, the transition to the use of alternative energy, such as solar energy, is relevant.
I offer a description of the solar heater option and the use of solar energy to heat water, for example, in a country house or in a private house.
solar water heater
Many summer residents or residents of a private house use a shower, in which the water is heated by solar energy in a metal container on the shower. The disadvantages of this simplest design are obvious. The temperature of water from such a container is completely dependent on the weather and changes significantly during the day. In addition, you need to monitor the water level in the tank.
In the proposed solar heating installation, these disadvantages are manifested to a lesser extent, and therefore it is more convenient and useable.
To increase the speed of heating the water and its temperature, an additional heating manifold is used. And to preserve the accumulated heat, the thermal insulation of the storage tank and the heating manifold is used. This allows you to have warm water in fairly cool weather, even if the sun did not shine for long. Water enters the tank through the constantly open taps 10, 3, and therefore there is no need to monitor the water filling. The outlet of heated water through taps 4 and 7, and for the shower and 9. (see fig.)
The heated water as lighter from the heating collector rises to the top of the storage tank. Its place is taken by the colder one from the bottom of the tank. The heating manifold should be located slightly below the tank, then colder water enters the heater.
The design of the storage tank is a metal container of arbitrary, but better rectangular shape. This inner container is inserted into the outer case and placed on bricks or wooden blocks. The outer casing is metal or wooden. After installing the pipes, the gap between the bodies is filled with a heat insulator. It can be polyurethane foam, polystyrene, glass wool or other material.
A good version of the heating manifold body can be made using the technology of modern glass units for window frames with additional thermal insulation. Or the body can be made using the technology of manufacturing the tank, but the top must be glazed. Pipes of preferably rectangular cross-section are attached to the inner metal body of the heating manifold on clamps, through which water circulates when heated. The inner metal casing and pipes are painted black for better solar heating. Therefore, the sun’s rays heat up the entire metallic interior of the heating manifold. Pipes of rectangular cross-section have a large area of contact with the black metal sheet at the bottom, therefore they heat up faster and give off heat to water. Thanks to the glazing, heat is not dissipated, the heating capacity of the device is increased and a high water heating temperature can be reached. You can get heated water in cool weather even in early spring and until late autumn. The collector should be sloped towards the south.
The withdrawal of heated water from the top of the tank has a significant advantage over the withdrawal from the bottom. With a short-term appearance of the sun in cloudy weather, the water has time to heat up only in the upper part of the tank, and in the lower part it remains cold. Therefore, much more heated water can be obtained from this design.
In summer, the temperature of heated water can be quite high, so for a shower it is better to use it through a faucet tap, mixing it to the desired temperature with cold tap water.
The dimensions of the tank and manifold are not critical. The larger the tank, the more water can be stored, and the larger the collector, the higher the heating rate and the temperature of the water in the tank. The power of solar radiation in the summer noon reaches 1000 watts for each square meter of the area of the heating collector, and in winter it is ten times less. The black inner surface of the collector has little reflectivity and 80% to 90% of the thermal energy is transferred to the collector. A small part of the solar energy is reflected by the glass and absorbed by it when it gets dirty.
Roughly for a tank with a capacity of 0.5m3, a collector with an area of 2-3m2 and a total length of pipes in the collector of 15-20m with a rectangular section of 40mm * 60mm is sufficient. The diameter of the pipes connecting the manifold to the tank is at least one inch.
With good thermal insulation, the water will heat up in sunny weather and at subzero ambient temperatures, but during severe long frosts and cloudy weather, the water in the collector can freeze and an accident may occur. It is possible to use systems of automatic control and electric heating of the collector, but it is better to drain the water from the collector and the tank for the winter period. Then you can use a conventional gas water heater in addition to the tank through the tap 5. How to fill the system and drain water from the manifold is easy to understand from the figure.
In order not to worry about the timely draining of water from the heater in case of unexpected frosts and to receive some amount of warm water even in winter, the solar heating installation can be slightly improved. Since the amount of solar thermal energy and daylight hours in winter is less, and heat losses are greater, it is necessary to increase the area of the heating collector, apply good thermal insulation and double glazing. In the storage tank, connect the collector inlet and outlet with a heat exchanger in the form of a spiral of pipes. The heating manifold and the heat exchanger are filled with antifreeze, antifreeze, or other liquid that does not freeze in the area. If there is a heat exchanger in the tank, it is imperative to install an expansion tank for antifreeze liquid. When using a solar heater in cold weather, in order to cool the water in the tank less, it is necessary to increase the difference in height between the heating collector and the tank.
The heating unit is pressurized by the water in the system, but with quality manufacturing it can serve for many years. To protect against unexpected leaks, a metal sheet with curved edges and water drainage can be provided under the unit. In the event of short-term water interruptions, a non-return check valve in the water supply pipe can partially help. But many of the latest improvements are optional.
The heated water is collected, first of all, in the upper part of the tank, therefore, water is drawn from the upper part of the tank, which makes it possible to use even short clearings in cloudy weather. For uninterrupted supply of heated water at any time and in any quantity, it is possible to work together a solar water heater and a gas water heater or an electric water heater, for example, in a storage tank.
It is especially convenient to use a gas water heater or an electric water heater after the storage tank with automatic temperature control. Then even a small heating of water in the solar collector, for example, in the off-season or in winter, will reduce the consumption of the main energy carrier in the form of electricity or gas. With the regular use of heated water, solar energy as an alternative energy can be profitable even now.
The amount of energy of the Sun falling within 1 sec. on a site of 1 m² placed on the border of the atmosphere perpendicular to the sun’s rays, the solar constant is called equal to approximately 1400 W / m² or 2.0 cal / cm² * min. On the surface of the Earth, after passing through the atmosphere, the energy decreases and for calculations it is usually taken 1000 W / m².
Calculation of the economic efficiency of a solar heating installation.
The amount of heat received by the solar water heater is calculated by the expression:
Qt.w.r = Fpan Dav Here, W
where Fpan is the surface of the collector’s heat-absorbing panel, m2;
Dav – total specific flux to the surface, W / m2;
Here is the reflective value of the heat reflecting panel
The specific heat flux of solar radiation Dav depends on the geographical location of the object of application of the solar heat receiver.
The table shows the data of the daily change in the specific heat flux of solar radiation at an inclination at an angle of 460 to the horizon of the heat receiver surface at a latitude of 560 N. when the heat receiver is tilted to the horizon at an angle of 460 with a southern orientation (Moscow – Kazan – Kurgan – Krasnoyarsk – Bratsk)
Measurement date by month
Total daytime radiation
With a vertical arrangement of window glazing, the specific heat flux will be approximately 25% less than the data in the table.
EXAMPLE of calculation for practical use of an alternative water heater:
A cottage near Moscow has a hot water supply system from the heat of solar radiation. The solar collectors used have a surface area of 1 m2 and a reflectance of Vot = 0.68.
Required: determine the amount of heated water in three collectors installed on the roof of the cottage with a southern orientation at an angle of 460 to the horizon.
Solution: Using the formula, we calculate the amount of heat of solar radiation in the daytime, supplied to three collectors.
In April, the amount of solar radiation heat entering during the daytime:
Qt.w.p.4 = 3 * 7185 * 0.68 = 14657.4 W * h / day.
Tap water temperature in April tх.water. = 120С, we determine the amount of water heated per day for the DHW system:
Qg.v.4 = Qt.w.r.4 * 3.6 / Сw (tg.v.4 – th.w.4) = 14657.4 * 3.6 / 4.2 * (50 – 12) = 261.7 kg / day.
In May, at a tap water temperature of 160C, the amount of heated water will be 297 kg / day.
Accordingly, in June, at a tap water temperature of 180C, the amount of heated water will be 313 kg / day. published by econet.ru
Author: Sergey Youzhny
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