Using free solar energy is a good way to save fuel and electricity spent on heating a private home. The massive use of solar systems is hindered by the high price of heat receivers and related equipment - a storage tank, a circulation pump, an electronic control unit and other fittings. The only way to reduce costs is to make a solar collector with your own hands from inexpensive materials and assemble a standard strapping scheme.
The principle of operation of solar heaters
Before embarking on the manufacture of a homemade solar system, it is worth exploring the device of factory-made solar collectors - air and water. The former are used for direct heating of premises, the latter are used as water heaters or non-freezing coolant - antifreeze.
Reference. Aerial installations are not very popular due to limited functionality. Solar water heaters are more in demand, because they can provide heating, hot water, and raise temperatures in outdoor pools.
The main element of the solar system is the solar collector itself, offered in 3 versions:
- Flat water heater. It is a sealed box, insulated from below. Inside is a heat sink (absorber) made of a metal sheet on which a copper coil is fixed. The top is covered with durable glass.
- The design of the air heater manifold is similar to the previous version, only the air circulated by the fan circulates through the tubes instead of the coolant.
- The device of the tubular vacuum manifold is fundamentally different from flat models. The apparatus consists of durable glass flasks where copper tubes are placed. Their ends are connected to 2 highways - supply and return, air from the flasks is pumped out.
Addition. There is another kind of vacuum water heaters, where glass flasks are tightly sealed and filled with a special substance that evaporates at a low temperature. During evaporation, the gas absorbs a large amount of heat transferred to water. In the process of heat transfer, the substance condenses again and flows to the bottom of the flask, as shown in the picture.
The listed types of collectors use the principle of direct transfer of the heat of solar radiation (otherwise - insolation) to the flowing liquid or air. Flat water heater works like this:
- Water or antifreeze moves through a copper heat exchanger at a speed of 0.3-0.8 m / s, pumped by a circulation pump (although there are gravity models for outdoor showers).
- The rays of the sun heat the absorbent sheet and the pipe of the coil tightly connected to it. The temperature of the flowing coolant rises by 15-80 degrees, depending on the season, time of day and street weather.
- To eliminate heat loss, the bottom and side surfaces of the body are insulated with polyurethane foam or extruded polystyrene foam.
- The transparent upper glass has 3 functions: it protects the selective coating of the absorber, prevents the wind from blowing the coil and creates a sealed air gap that retains heat.
- Hot heat carrier enters the heat exchanger of the storage tank — buffer tank or indirect heating boiler.
Since the water temperature in the circuit of the apparatus fluctuates with the changing seasons and days, the solar collector cannot be used for heating and hot water directly. The energy received from the sun is transferred to the main heat carrier through the coil of the tank - the battery (boiler).
An exception is solar installations for pools that heat the tank water directly or through a simple heat exchanger.
The efficiency of the tubular apparatus is enhanced by vacuum and an internal reflective wall in each flask. The rays of the sun freely pass through the airless layer and warm the copper pipe with antifreeze, but the heat can not overcome the vacuum and go outside, so the losses are minimal. Another part of the radiation enters the reflector and focuses on the water line. According to manufacturers, the efficiency of the installation reaches 80%.
We make a water collector
A vacuum type water heater can not be made at home for obvious reasons. Therefore, we take up a flat design with a heat exchanger and an absorber collecting sunlight. Ideally, you need to calculate the area of the receiver and the temperature of the outlet water, which depends on many factors:
- region of residence and level of insolation;
- ambient temperature, especially in winter;
- the area of the heat-exchange surface perceiving exposure to the sun;
- coil material and coating;
- inlet coolant temperature;
- the angle of the panel in relation to the sun;
- water flow rate through heat exchanger pipes.
On the Internet it is not difficult to find calculations of the performance of the solar collector, but we warn you - the calculations are very inaccurate.
Example. The fact is taken as the basis: on a clear day, 500-800 W of solar energy gets onto 1 m² of surface. Further, using the school formula m = Q / 1.163 x Δt, we determine the mass of water heated at 40 ° C by a 1 m² heat exchanger: 500 / 1,163 x 40 = 10.7 liters per hour. With an insolation of 800 W / m², 17.2 l / h can be heated. But the devil is in the details: the initial figure of 0.5-0.8 kW per square meter is a very approximate figure.
We offer a simplified approach to the issue described in the step-by-step instructions:
- Determine the place and area that you are ready to give to the collector.
- Based on material prices, select the appropriate option for assembling the coil and housing.
- Make a prototype, connect to heating or water supply according to the correct scheme. We will show the binding methods in the following sections of this article.
- Test the heating circuit at home and make further conclusions about increasing / decreasing the power, changing the design and so on.
Now we will go through each stage separately, focusing on the pitfalls.
Placement of a thermal installation
Actually, there are only two options for the location of the home-made collector: on the roof of the building or in the open area of the house area. When choosing a place, follow simple rules:
- The site should be lit as much as possible during the day, not obscured by trees and other outbuildings.
- When installed on the roof, a more gentle slope is selected, where solar radiation always gets. It is clear that the steep part of the broken mansard roof will not work.
- Do not take a hot water installation intended for heating or hot water supply far from your home. The length of the supply piping, heat loss and installation cost will increase.
- Orient the ground collector so that the sun, visually moving from east to west, constantly illuminates the heat sink. The installation angle of the panel is 60 ± 15 °.
Note. The efficiency of the heating element can be increased with the help of a parabolic solar concentrator collecting rays in a single beam, which is sent to the absorber. The construction and assembly methods of the concave mirror are shown in the video.
Solar plants, designed to heat water in a summer shower, are located on the roof of this building and are connected by gravity. Devices for heating pools are located next to the bowl of the tank.
Material selection
We made a selection of accessories for the manufacture of solar water heaters on the basis of reviews and topics discussed at the popular Forumhouse forum. So, the rectangular box of the receiver is usually made of a wooden beam or ready-made frames of old windows. The back wall of the housing is insulated with basalt wool, polystyrene foam or extruded polystyrene foam.
Tip. The bottom of the box can be made of foil polymer insulation. The metal layer will serve as an absorber - you do not have to put an additional sheet.
Home craftsmen make heat exchangers from a variety of pipes:
- black polyethylene (HDPE);
- corrugated stainless steel;
- copper and aluminum;
- polypropylene and metal plastic;
- crosslinked polyethylene;
- panel steel radiators.
From the point of view of efficiency and durability, it is better to use tubes made of aluminum, copper and stainless steel with the best thermal conductivity. The lack of material is the high price.
Plastic pipes are much cheaper than metal pipes and easier to install. But when using polymers, a number of nuances must be taken into account:
- any plastics gradually deteriorate under the influence of ultraviolet radiation;
- the walls of the PPR pipes are too thick, conduct heat poorly;
- high-quality plastic is too expensive for our purposes, and cheap often stratifies on bends and quickly collapses in the sun;
- cross-linked polyethylene “remembers” the initial bend in the bay, it is convenient to make an annular coil out of it, and straightening is not easy;
- HDPE pipes you need to buy a food series (with a blue stripe), it is better protected from ultraviolet radiation.
Reference. The simplest version of a pool heat exchanger is a black garden hose laid with a “snail”. The minus of the material is cracking of rubber from prolonged exposure to the sun.
HDPE thin-walled pipes are an excellent choice in terms of price / quality ratio. The black surface absorbs solar heat well, connecting fittings are inexpensive. The pipeline is attached to the absorber with plastic clamps or a tin strip on the screws.
As the absorbent sheet, ordinary or stainless steel painted black can be used. The ideal option is sheet aluminum or copper.
The top of the box is closed with the following transparent materials to choose from:
- ordinary or reinforced glass;
- transparent plastic wrap;
- thin cellular polycarbonate.
Tip. Do not use ready-made double-glazed windows from plastic windows as a translucent element. In winter, with a large temperature difference between the street air and the closed collector chamber, the two-layer package does not withstand and cracks.
Assembly recommendations
The process of manufacturing a solar collector is so obvious that it does not make sense to paint step-by-step instructions. The task is to make the most airtight chamber by installing a heat exchanger on a metal absorber inside. We will just give some advice in order to protect you from mistakes:
- Heat exchanger tubes can be laid longitudinally or with a spiral (snail). Make the distance between adjacent lines (turns) small - from 1 to 4 cm.
- The air tightness of the case is achieved by lubricating the joints with silicone sealant or by laying rubber seals.
- The tubes are attached to the base in any convenient way - with plastic clamps, a metal strip or simply fixed on the sides with self-tapping screws.
- The entire internal cavity is painted with heat-resistant black enamel (sold in aerosol cans).
- The thickness of the insulating layer on the back of the water heater is at least 50 mm.
- It’s easiest to pull a transparent film on top - this is the best option for a prototype. Subsequently, it is not difficult to replace glass.
Another recommendation. Wooden parts should be treated with an antiseptic.Cover the frame welded from steel profiles with a primer and 2 layers of light paint.
After assembling the heat sink panel, fill the coil with water and check for leaks. Then test the solar collector - connect the output to the tank, install the panel in the sun and periodically measure the temperature of the water, taking into account the heating time. Based on real indicators, it is easy to determine the performance of a water heater.
Wiring diagram
A collector designed for heating water in the shower is connected to a storage tank by gravity flow. An important condition: the solar installation should be located below the main tank, so that hot water of lower density rises through the pipe and displaces the cold one. The design of such a system is shown in the drawing.
When connected to a boiler or heat accumulator, the solar collector acts as a full-fledged heat source. Solar system manufacturers suggest the use of a two-pipe pressure scheme, which includes the required binding elements:
- circulation pump developing a pressure of 0.4 bar;
- expansion tank membrane type;
- automatic air vent;
- safety valve, designed to operate at a pressure of 2 bar;
- pressure gauge;
- thermometer;
- shutoff valves, make-up valve;
- controller with two temperature sensors;
- thermal insulation for supply pipelines.
An important point. If a battery of several collectors is connected to the buffer tank, the pump capacity and the volume of the expansion tank must be increased. The minimum capacity of the membrane tank is 10% of the total amount of coolant in the circuit.
The scheme works like this:
- The heat sink attaches to the lower coil of the buffer tank, where the water is colder.
- The controller by means of sensors compares the temperature of the water (antifreeze) in the supply pipe and the heat accumulator.
- The electronic unit stops the pump when the temperature of the water in the tank is equal to or higher than the flow temperature.
- Air entering the circuit is discharged through an automatic valve installed at the top of the system.
- In case of overheating of the coolant due to the pump stopping (it is impossible to turn off the sun), the safety valve will operate and relieve excess pressure.
The most expensive circuit element is an electronic control unit. How can I do without a controller:
- buy on Aliexpress a cheaper thermostat, triggered by a temperature difference;
- set a day-night timer and a mechanical thermostat to turn off the pump when the buffer tank is at maximum heat.
How the cheap Chinese control unit works (price - $ 15), see the video review:
Solar heating
Installation of air heating is done in a similar way, only the heat exchanger is made of pipes of a larger diameter, and the blower is provided by the fan. The radiation receiver is made by craftsmen from the following materials:
- aluminum corrugation for ventilation;
- plastic bottles inserted one into the other;
- carved beer cans.
In the box, 2 holes are made for air pipes, a fine mesh is laid inside, eliminating the ingress of insects. The fan - a cooler from the computer - is installed on one of the openings, the heat exchange part is painted black. The supply pipes are insulated and laid in a heated room. The air manifold assembly algorithm is shown in the video:
Conclusion
The attractiveness of solar collectors is due to rising energy prices. Although the performance of water heaters decreases in winter, solar heat provides significant savings in fuel consumption by the main source - the boiler. If you want to heat your country house as much as possible with free solar energy, we advise you to pay attention to installations with mirror concentrators.These extremely effective devices are widely used in Europe and America.