Vacuum solar collector for home heating

Recommendation points

• What collectors to use
• Payback period
• Examples of typical assemblies
• Connection to the DHW and heating system
• Increase in operating temperature

Sources of solar energy have received little attention. Obviously, the main benefit of such installations is their autonomy, but there are exceptions. In this article, we will talk about solar collectors as a fairly efficient, and most importantly, a rational source of energy for the home..

What collectors to use

With the exception of special varieties, collectors are of two types: flat and vacuum. The principle of operation of both is reduced to heating from solar radiation (in which 40-50% of the waves are thermal) of a certain system of tanks, the outer side of which has a coating with a high coefficient of infrared absorption, and a coolant circulates inside. The only difference is that in vacuum collectors, the tubes are heated directly at the focus of sunlight and practically do not give off heat due to the airless environment. At the same time, in flat collectors, heat is transmitted through the absorber plate, to the back side of which channels are soldered (can be laid inside the absorber plate).

Actually, it is about vacuum collectors that should be discussed in the realities of Russian nature. They are much more expensive than flat collectors, but their efficiency is also higher. In addition, flat collectors are practically ineffective in winter: the cold wind cools them faster than the sun heats up. The field of application of such devices is southern latitudes with a warm climate, country and summer houses, as well as all kinds of tourist facilities.

Regardless of the type of heating, the principle of the collector itself is unchanged. Often it connects heat pipes into a common tank, where condensation of the liquid evaporated during the heating process occurs. Heat transfer in this way is much faster, but there are also more efficient solutions..

Payback period

The cost of an average vacuum manifold ranges from 600 to 1500 USD. This cost includes not only the collector, but also the storage tank of the recommended volume and materials for connecting to the domestic hot water supply system. But the cost of installation services in the total amount is not taken into account: too large a run in prices by region and conditions at the facility.

Nevertheless, it is easy to check the payback of a particular instance. Take, for example, the collector SVK-A-30 of the ATMOSFERA trademark, which costs 1100–1200 USD. There are 30 vacuum tubes in it, their total maximum power is 2.5 kW / h, the collector receives up to 7.6 kW of thermal energy per daylight. There is no storage tank in the collector, but we have the right to conventionally assume that the cost of it and the plumbing is equivalent to the price of an electric boiler of comparable power.

The average daily capacity of the collector is 5.5 kW, which is enough to heat 120-140 liters of water from 10 to 50 ° C. Having spent the same amount of electricity at the rate of 4.68 rubles / kWh, we will receive an average of 25 rubles per day, or about 10 thousand rubles per year. Accordingly, the collector’s payback period will be about eight years, which is not bad at all with a guaranteed service life of 25 years. Plus, there are some ways to increase your ROI. In general, the more powerful the installation, the sooner it will fully justify itself..

Examples of typical assemblies

There are not very many options for integrating the collector into home plumbing. Here are some typical solutions as their complexity increases:

1. Just a collector. It is connected to the domestic hot water system like a conventional water heater. Works only during daytime with natural flow. By adjusting the pressure, you can change the outlet water temperature.

2. Collector + storage tank. There are a lot of such solutions and they are popular, but an additional load of 100-200 kg per one point of the roof sets some restrictions. The tank has good thermal insulation and, as a rule, does not cool down overnight.

3. Collector + indirect heating boiler (BKN). It is used when it is impossible to install a heavy tank on the roof, but has other advantages. First of all, the use of not water in the first heat exchange circuit, but a more energy-intensive emulsion.

4. Collector + circulation system. Allows you to receive hot water as soon as the tap is open. Water circulates in the system under pressure and has approximately the same temperature at any point in the circuit. Sometimes the capacity of the water supply system is large enough and the entire filling of the system consists of shut-off valves, a circulation pump and a pressure regulator. In some cases, it may be recommended (or required) to install an expansion tank or internal accumulator. Typically, collectors without heat exchanger are used.

5. Collector + heat pump. A very serious and technological solution for supplying the whole house with heat and hot water. Due to the increased heat exchange at low temperatures, the system squeezes the maximum out of the energy received, heating the outlet water to 80–95 ° C in a large enough volume to heat the entire building. It is clear that several collectors will be required for such a system, but the result will be inexpensive heating of housing in the next 40-50 years, plus hot water supply.

As you can see, the difference between collectors in any of these systems is the presence / absence of a built-in tank. Otherwise, they are all the same: water supply and drainage pipes, typical connections of heat pipes with a collector, one of the special fastening systems. Thanks to this, the collectors easily and harmoniously fit into already functioning heating systems, increasing savings even without a complete transition to green energy..

Connection to the DHW and heating system

The connection to the heating circuit is carried out in parallel: water from the collector enters the supply pipe, the intake is from the return, if necessary, the collector circuit is supplied with its own circulation pump. It is very important to install valves at the tapping points in order to regulate the flow to obtain the desired temperature..

They cut into the hot water supply system in two ways. The first uses a BKN or other intermediate heat exchanger. In this case, it is not difficult to link two contours. But if the collector is used in parallel with other water heaters, it is placed in a series circuit as close as possible to the cold water intake point and used as a preheating circuit.

Connecting the solar collector to the heating and hot water system: 1 – solar collector; 2 – pumping station; 3 – expansion tank; 4 – heat accumulator; 5 – heating system; 6 – cold water supply; 7 – hot water intake; 8 – boiler (used if necessary)

Increase in operating temperature

The obvious way to increase the leaving water temperature is to reduce heat loss during transfer from the collector. For this, the pipes are wrapped in protective covers made of foamed rubber or polypropylene, they protect the joints, the laying is carried out only inside the building.

Since the collector tube is heated in a concentrated beam of light, the temperature of the liquid inside can be very high (over 200 ° C). Accordingly, if you reduce the flow of heated water, the temperature will increase over time. Unfortunately, today there are very few automated systems that maintain the temperature at the desired level. As an option, devices with a compressor and an evaporator are used – small heat pumps. In this case, at the outlet to hot water or heating, the water temperature will adhere to the set values ​​by changing the power of the unit.