The specifics of using solar collectors
The main feature of solar collectors, which distinguishes them from other types of heat generators, is the cyclical nature of their operation. If there is no sun, there is no heat energy either. As a result, such attitudes are passive at night.
Average daily heat production directly depends on the length of daylight hours. The latter is determined, firstly, by the geographical latitude of the area, and secondly, by the season. During the summer period, which is the peak of insolation in the Northern Hemisphere, the collector will work with maximum efficiency. In winter, its productivity falls, reaching a minimum in December-January.
In winter, the efficiency of solar collectors decreases not only due to a decrease in the duration of daylight hours, but also due to a change in the angle of incidence of sunlight. Fluctuations in solar collector performance throughout the year should be taken into account when calculating its contribution to the heat supply system.
Another factor that can affect the productivity of the solar collector is the climatic features of the region. On the territory of our country there are many places where the sun is hidden behind a thick layer of clouds or behind a veil of fog for 200 or more days a year. In cloudy weather, the performance of the solar collector does not drop to zero, since it is able to capture scattered sunlight, but it significantly decreases.
The device and purpose of collectors
At its core, it is a flow distributor that has a main channel with inlet and outlet, as well as branches. Their number may vary. In most cases, from 4 to 6, and if more is needed, then several valves can be connected in series.
Experts, when asked what a water supply collector is, answer that it is a comb. This association is associated with external similarity, albeit schematic.
The comb for water supply can be made of metal, alloys or polymeric materials. The choice depends on the budget and purpose. The design feature is that the inlet has a smaller diameter than the outlet. This is necessary so that overpressure builds up in the distribution area.
There are models commercially available that are fitted with branch cutoff valves by default.
Collector connection assumes that each branch is extended to a separate consumer.
In this case, there are a lot of advantages:
- Each consumer receives sufficient pressure to function properly.
- It is possible to disable one of them for repair, maintenance or replacement without disconnecting the rest.
- If it is necessary to eliminate flooding, it is enough to cut off one branch and use the rest of the devices without restriction.
Another advantage of using collectors in water supply systems is that when you turn on, say, a washing machine, the water pressure in the shower does not change. This means that there are no unpleasant changes in temperature. But there are many designs, configurations and manufacturers, and in order to make the right choice, you need to know the features of these devices.
The principle of operation and types of solar collectors
It's time to say a few words about the structure and principle of operation of the solar collector. The main element of its design is an adsorber, which is a copper plate with a pipe welded to it.Absorbing the heat of the sun's rays falling on it, the plate (and with it the pipe) heats up quickly. This heat is transferred to the liquid heat carrier circulating through the pipe, which, in turn, transports it further along the system.
The ability of the physical body to absorb or reflect the sun's rays depends primarily on the nature of its surface. For example, a mirrored surface perfectly reflects light and heat, but a black one, on the contrary, absorbs. That is why a black coating is applied to the copper plate of the adsorber (the simplest option is black paint).
How the solar collector works
1. Solar collector. 2. Buffer tank. 3. Hot water.
4. Cold water. 5. Controller. 6. Heat exchanger.
7. Water pump. 8. Hot stream. 9. Cold stream.
It is also possible to increase the amount of heat received from the sun by choosing the correct glass covering the adsorber. Ordinary glass is not transparent enough. In addition, it glares, reflecting some of the incident sunlight. In solar collectors, as a rule, they try to use special glass with a low iron content, which increases its transparency. To reduce the proportion of light reflected by the surface, an anti-reflective coating is applied to the glass. And so that dust and moisture do not get inside the collector, which also reduce the throughput of the glass, the case is made sealed, and sometimes even filled with an inert gas.
Despite all these tricks, the efficiency of solar collectors is still far from 100%, which is due to the imperfection of their design. The heated adsorber plate radiates part of the received heat into the environment, heating the air in contact with it. To minimize heat loss, the adsorber must be insulated. The search for an effective way to insulate the adsorber led engineers to create several types of solar collectors, the most common of which are flat and tubular vacuum collectors.
Flat solar collectors
Flat solar collectors.
The design of a flat solar collector is extremely simple: it is a metal box covered with glass on top. As a rule, mineral wool is used for thermal insulation of the bottom and walls of the case. This option is far from ideal, since the transfer of heat from the adsorber to the glass by means of the air inside the box is not excluded. With a large temperature difference inside the collector and outside, heat losses are quite significant. As a result, a flat solar collector, which functions perfectly in spring and summer, becomes extremely ineffective in winter.
Flat solar collector device
1. Inlet pipe. 2. Safety glass.
3. Absorption layer. 4. Aluminum frame.
5. Copper tubes. 6. Heat insulator. 7. Outlet pipe.
Tubular vacuum solar collectors
Tubular vacuum solar collectors.
A solar vacuum collector is a panel made up of a large number of relatively thin glass tubes. An adsorber is located inside each of them. To exclude the transfer of heat by gas (air), the tubes are evacuated. It is due to the absence of gas near the adsorbers that vacuum collectors are distinguished by low heat losses even in frosty weather.
Vacuum manifold device
1. Thermal insulation. 2. Heat exchanger housing. 3. Heat exchanger (collector)
4. Sealed plug. 5. Vacuum tube. 6. Capacitor.
7. Absorbing plate. 8. Heat pipe with working fluid.
Manifold Mixing Valve Application
The manifold system consists of two types of valves: 2 - way and 3 - way. The mixing valve is used to hot water mixing, which comes from the boiler, cooled down from the heating circuit.The mixing valves can be adjusted manually or automatically using a control.
A manifold with a 3-way mixing valve is most often used for rooms with a large area of water floors (more than 200 m2).
Often these valves are equipped with weather-dependent sensors with special programs that set the optimal temperature, focusing on external factors. Such valves are used mainly for warm floors, which are the main heating element in the room.
However, such a valve has satisfied significant flaws... Firstly, by a signal from the thermostat, it can directly supply water from the boiler, the temperature of which is 80–90 degrees. This can damage the heating circuit, screed and flooring.
Secondly, such valves have a high flow capacity, as a result of which, with a slight change in the regulation in the room, it can temperature rise strongly.
A manifold with a 2-way mixing valve is used for rooms with an area of less than 200 m2. Such a valve regulates the temperature by mixing in the coolant from the return.
In this way the amount of water is controlledcoming from the boiler. Thanks to this, the warm floor will never overheat. This, in turn, extends its service life. Such a valve has a small flow capacity, smooth and stable regulation.
Where should the collector for underfloor heating water be located?
The collector must be somewhere to hide. For this it is used special manifold cabinet, which is a metal product with a door in which the fastening fittings are located.
Such cabinets are outdoor and recessed... Perforations are made in the side panels, thanks to which you can easily make holes in the required places. Many models have adjustable feet that allow you to change the height. Built-in wardrobes have a movable frame, with which they can change in depth.
To determine the required dimensions of such a product, one should know well the dimensions of all equipment that will subsequently be placed there. The collector cabinets are fixed to the floor through the legs or to the wall through the holes located on the back wall.
Applications of solar collectors
The main purpose of solar collectors, like any other heat generators, is to heat buildings and prepare water for a hot water supply system. It remains to find out which type of solar collectors is best suited to perform a particular function.
Flat solar collectors, as we found out, have good performance in the spring and summer, but are ineffective in winter. From this it follows that using them for heating, the need for which appears precisely with the onset of cold weather, is inappropriate. This, however, does not mean that there is no business at all for this equipment.
Flat collectors have one indisputable advantage - they are significantly cheaper than vacuum models, therefore, in cases where it is planned to use solar energy exclusively in the summer, it makes sense to purchase them. Flat solar collectors perfectly cope with the task of preparing water for hot water supply in the summer. Even more often they are used to warm water to a comfortable temperature in outdoor pools.
Tubular vacuum collectors are more versatile. With the arrival of winter cold, their performance does not decrease as much as in the case of flat models, which means that they can be used all year round. This makes it possible to use such solar collectors not only for hot water supply, but also in the heating system.
Comparison of flat and vacuum solar collectors.
Arrangement of solar collectors
The efficiency of a solar collector directly depends on the amount of sunlight falling on the adsorber. It follows from this that the collector should be located in an open space, where a shadow from neighboring buildings, trees located near mountains, etc. never falls (or at least for the longest time).
It is not only the location of the collector that matters, but also its orientation. The most "sunny" side in our northern hemisphere is the southern one, which means that ideally the "mirrors" of the reservoir should be turned strictly to the south. If it is technically impossible to do this, then you should choose the direction as close as possible to the south - southwest or southeast.
One should not lose sight of such a parameter as the angle of inclination of the solar collector. The value of the angle depends on the deviation of the position of the Sun from the zenith, which in turn is determined by the latitude of the area in which the equipment will be operated. If the angle of inclination is not set correctly, then the optical energy loss will increase significantly, since a significant part of the sunlight will be reflected from the collector glass and, therefore, will not reach the absorber.
Collector installation
It is important to select the correct pipe cross-section. Half-inch pipe is suitable for shower and tub. At the same time, the inlet to the distributor should be wider.
Working with modern materials is quite comfortable, and any craftsman can independently assemble the collector. But before starting the workflow, you still need to draw up a diagram on paper.
The complete set of the water supply system takes place in several stages:
- A faucet or valve on a riser with any water is needed to turn off the water to fix the water system.
- Hard water filter. Such a filter cleans the water from large impurities and makes it drinkable.
- Water meters.
- Pressure reducer - may be needed in a private house. The pressure reducer reduces the pressure if it is too high for your plumbing fixtures. If it is set to the maximum allowable value, it will direct excess water into the gutter.
- Collector. It can have 2 to 6 outputs. You can install multiple collectors to get the required number of outputs.
The video provides useful tips to help you properly install the water manifold:
How to choose a solar collector of the right power
If you want the heating system of your home to cope with the task of maintaining a comfortable temperature in the premises, and hot, not lukewarm water flowed from the taps, and at the same time plan to use a solar collector as a heat generator, you need to calculate the required equipment power in advance.
At the same time, it will be necessary to take into account a fairly large number of parameters, including the purpose of the collector (hot water supply, heating or their combination), the object's heat demand (total area of heated rooms or average daily hot water consumption), climatic features of the region, features of the collector installation.
In principle, making such calculations is not so difficult. The performance of each model is known, which means that you can easily estimate the number of collectors required to provide the house with heat. Companies engaged in the production of solar collectors have information (and can provide it to the consumer) about the change in the power of the equipment depending on the geographical latitude of the area, the angle of inclination of the "mirrors", the deviation of their orientation from the south direction, etc., which makes it possible to make the necessary corrections when calculating the performance of the collector.
When selecting the required collector capacity, it is very important to achieve a balance between lack and excess of generated heat. Experts recommend focusing on the maximum possible collector capacity, that is, using the indicator for the most productive summer season in the calculations. This goes against the desire of the average user to take equipment with a margin (that is, to calculate by the power of the coldest month), so that the heat from the collector is enough even on less sunny autumn and winter days.
However, if you choose a solar collector with increased power, then at the peak of its performance, that is, in warm sunny weather, you will face a serious problem: more heat will be produced than consumed, and this threatens overheating of the circuit and other unpleasant consequences ... There are two options for solving this problem: either install a low-power solar collector and connect backup heat sources in parallel in winter, or purchase a model with a large power reserve and provide for ways to discharge excess heat in the spring-summer season.
System stagnation
Let's talk a little more about the problems associated with an excess of generated heat. So, let's say that you have installed a sufficiently powerful solar collector that can fully provide heat to the heating system of your home. But summer has come, and the need for heating has disappeared. If you can turn off the power supply for an electric boiler, or cut off the fuel supply for a gas boiler, then we have no power over the sun - we cannot “turn it off” when it gets too hot.
System stagnation is one of the major potential problems for solar collectors. If not enough heat is taken from the collector circuit, the coolant overheats. At a certain moment, the latter can boil, which will lead to the termination of its circulation along the circuit. When the coolant cools down and condenses, the system will resume operation. However, not all types of heat transfer fluids calmly transfer the transition from a liquid to a gaseous state and vice versa. Some, as a result of overheating, acquire a jelly-like consistency, which makes further operation of the circuit impossible.
Only a stable removal of the heat produced by the collector will help to avoid stagnation. If the calculation of the power of the equipment is done correctly, the likelihood of problems is practically zero.
However, even in this case, the occurrence of force majeure is not excluded, therefore, methods of protection against overheating should be foreseen in advance:
1. Installation of a reserve tank for accumulating hot water. If the water in the main tank of the hot water supply system has reached the set maximum, and the solar collector continues to supply heat, it will automatically switch over and the water will begin to heat up already in the reserve tank. The created supply of warm water can be used for domestic needs later, in cloudy weather.
2. Heated pool water. Owners of houses with a swimming pool (whether indoor or outdoor) have an excellent opportunity to remove excess heat energy. The volume of the pool is incomparably greater than the volume of any household storage device, which means that the water in it will not heat up so much that it will no longer be able to absorb heat.
3. Draining hot water. In the absence of the opportunity to spend excess heat usefully, you can simply drain the heated water in small portions from the storage tank for hot water supply into the sewer. The cold water entering the container will lower the temperature of the entire volume, which will continue to remove heat from the circuit.
4. External heat exchanger with fan. If the solar collector has a large capacity, the excess heat can also be very large. In this case, the system is equipped with an additional circuit filled with refrigerant. This additional circuit is connected to the system by means of a heat exchanger equipped with a fan and mounted outside the building. If there is a risk of overheating, excess heat enters the additional circuit and is "thrown" into the air through the heat exchanger.
5. Discharge of heat into the ground. If, in addition to the solar collector, the house has a ground source heat pump, the excess heat can be directed into the well. At the same time, you solve two problems at once: on the one hand, you protect the collector circuit from overheating, on the other hand, you restore the heat reserve in the soil depleted during the winter.
6. Isolation of the solar collector from direct sunlight. From a technical point of view, this method is one of the simplest. Of course, you shouldn't climb onto the roof and hang the manifold manually - it's hard and unsafe. It is much more rational to install a remotely controlled shutter, like a roller shutter. You can even connect the damper control unit to the controller - in case of a dangerous increase in temperature in the circuit, the manifold will close automatically.
7. Draining the coolant. This method can be considered cardinal, but at the same time it is quite simple. If there is a risk of overheating, the coolant is drained by means of a pump into a special tank integrated into the system circuit. When conditions become favorable again, the pump will return the coolant to the circuit, and the collector will be restored.
Other system components
It is not enough to simply collect the heat radiated from the sun. It still needs to be transported, accumulated, transferred to consumers, all these processes need to be monitored, etc. This means that in addition to the collectors located on the roof, the system contains many other components, which may be less noticeable, but no less important. Let's focus on just a few of them.
Heat carrier
The function of the coolant in the collector circuit can be performed either by water or by an anti-freeze liquid.
Water has a number of disadvantages that impose certain restrictions on its use as a heat carrier in solar collectors:
- First, at negative temperatures, it solidifies. To prevent the frozen coolant from bursting the pipes of the circuit, with the approach of cold weather it will have to be drained, which means that in winter you will not receive even small amounts of thermal energy from the collector.
- Secondly, a not too high boiling point of water can cause frequent stagnation in the summer.
Non-freezing liquid, unlike water, has a significantly lower freezing point and incomparably higher boiling point, which increases the convenience of using it as a heat carrier. However, at high temperatures, "non-freezing" can undergo irreversible changes, so it should be protected from excessive overheating.
Pump adapted for solar systems
To ensure the forced circulation of the coolant along the collector circuit, a pump adapted for solar systems is required.
DHW heat exchanger
Heat transfer from the solar collector circuit to the hot water supply or to the heating medium of the heating system is carried out by means of a heat exchanger. As a rule, a large-volume tank with a built-in heat exchanger is used to accumulate hot water. It is rational to use tanks with two or more heat exchangers: this will allow taking heat not only from the solar collector, but also from other sources (gas or electric boiler, heat pump, etc.).
Reservoir classification
Switchgears differ in the material of the housing and parts and the methods of fastening
This is important to consider when selecting, becausenot all products will fit plastic pipes
There are the following types of collectors:
- Steel (made of stainless steel). Resistant to fire and high temperatures. The products are distinguished by their neat appearance and light weight, the collector is easily mounted on the wall.
- Brass (sometimes nickel plated). They have a high cost, but they are durable. They do not rust or deteriorate from high temperatures.
- Polypropylene. They are lightweight and resistant to corrosion.
By the method of fixation, devices are classified as follows:
- with eurocone;
- threaded;
- with compression fittings that allow you to firmly connect plastic or metal-plastic pipes;
- with fittings for pipes made of plastic for soldering;
- combined.
Also, the collectors are available in 2 colors for installation in hot and cold water. Devices are divided according to the number of outlets.
