Solar heating systems. Reliable solar heating of a private house. Solar battery connection diagram

18.10.2019

Heating systems are divided as follows: passive (see Ch. 5); active, which mostly use liquid solar collectors and storage tanks; combined.

Abroad, air heating systems are widely used, where building structures or special stone filling under it are used as batteries. In our country, the Physicotechnical Institute of the Academy of Sciences of the Uzbek SSR and TbilZNIIEP are working in this direction, however, the results of the work are clearly insufficient and debugged solutions have not been created, although air systems are theoretically more efficient than liquid ones, in which the heating system itself is made of low-temperature panel-radiant or high-temperature with conventional heating devices. In our country, buildings with liquid systems were developed by IVTAN, FTI AN UzSSR, TashZNIIEP, TbilZNIIEP, KievZNIIEP and others and in some cases erected.

A large amount of information on active solar heating systems is given in a book published in 1980. Further, two individual residential buildings developed by KievZNIIEP, built and tested with autonomous solar heating systems are described: with a low-temperature panel-radiant heating system (a residential building in the village of Kolesnoye, Odessa region) and with a heat pump (a residential building in the village of Bucuria, Moldavian SSR ).

When developing a solar heating system for a residential building in the village. Kolesnoe, a number of changes were made to the architectural and construction part of the house (project UkrNIIPgrazhdanselskstroy), aimed at adapting it to the requirements of solar heat supply: efficient masonry with insulation for the outer walls and triple glazing of window openings were used; coils of the heating system are combined with interfloor ceilings; a basement is provided for placing equipment; additional attic insulation and exhaust air heat recovery were carried out.

In terms of architecture and layout, the house is made on two levels. On the first floor there is a front room, a common room, a bedroom, a kitchen, a bathroom and storage rooms, and on the second floor there are two bedrooms and a bathroom, an electric stove for cooking is provided. The equipment of the solar heating system (except collectors) is located in the basement; electric water heaters serve as an understudy of the system, which makes it possible to carry out a single energy input to the building and improve the comfortable qualities of housing.

Residential building solar heating system (Fig. 4.1) composed From three circuits: heat-receiving circulation and heating and hot water circuits. The first of them includes solar water heaters, a coil-heat exchanger of the storage tank, circulation pump and a tube-in-pipe heat exchanger to operate the system in summer time in natural circulation mode. The equipment is connected by a system of pipelines with fittings, instrumentation and automation devices. A two-section coil heat exchanger with a surface area of 4.6 m2 for the heat carrier of the circulation circuit and a single-section heat exchanger with a surface area of 1.2 m2 for the hot water supply system are mounted in a storage tank with a capacity of 16 m3. The heat capacity of the tank with a water temperature of +45 °C provides a three-day heat requirement for a residential building. A tube-in-pipe type heat exchanger with a surface area of 1.25 m2 is located under the ridge of the roof of the house.

The heating circuit consists of two series-connected sections: a panel-radiant section with flow heating panels that ensure the operation of the system in the basic mode with a water temperature difference of 45 ... 35 ° C, and a vertical single-pipe section with "Comfort" type convectors that provide peak system loads heating with a water temperature difference of 75 ... 70 ° C. The coils of pipes of heating panels are embedded in the plaster-finishing layer of round-hollow panels of the ceiling. Convectors are installed under the windows. The circulation in the heating system is incentive. Peak water heating is carried out by a flowing electric water heater EPV-2 with a power of 10 kW; It also serves as an understudy for the heating system.

The hot water circuit includes a heat exchanger built into the storage tank, and a second instantaneous electric water heater as a closer and backup system.

During the heating period, the heat from the collectors is transferred by the coolant (45% aqueous solution of ethylene glycol) to the water in the storage tank, which is pumped to the coils of the heating panel, and then returned back to the storage tank.

The required air temperature in the house is maintained by the automatic regulator PPT-2 by turning on and off the electric water heater in the convector section of the heating system.

In summer, the system provides for the needs of hot water supply from a "pipe in pipe" type heat exchanger with natural circulation of the coolant in the heat-receiving circuit. The transition to incentive circulation is carried out with the help of an electronic differential regulator РРТ-2.

The solar heating system of a four-room residential building in the village. Bucuria of the Moldavian SSR was designed by the Moldgiprograzhdanselstroy Institute under the scientific guidance of KievZNIIEP.

Residential building - mansard type. On the first floor there is a common room, a kitchen, a laundry room, an utility room, and on the second floor there are three bedrooms. In the basement there is a garage, a cellar is also a room for equipping the solar heating system. An outbuilding is blocked with the house, which includes a summer kitchen, a shower, a shed, an inventory and a workshop.

Autonomous solar heating system (Fig. 4.2) is a combined solar heat pump unit designed to meet the needs of heating (calculated heat loss of the house is 11 kW) and hot water supply throughout the year. The lack of solar heat and heat from the compressor of the heat pump installation is covered by electric heating. The system consists of four circuits: a heat-receiving circulation circuit, circuits of a heat pump installation, heating and hot water supply.

The equipment of the heat-receiving circuit includes solar collectors, a "pipe-in-pipe" heat exchanger and a storage tank with a capacity of 16 m3 with a heat exchanger built into it with a surface area of 6 m2. Solar collectors designed by KievZNIIEP with double-layer glazing with total area 70 m2 are placed in a frame on the southern slope of the roof of the house at an angle of 55° to the horizon. 45 was used as a coolant. % an aqueous solution of ethylene glycol. The heat exchanger is located under the roof ridge, and the rest of the equipment is located in the basement of the house.

The compressor-condensing refrigeration unit AK1-9 with a heat output of 11.5 kW and a power consumption of 4.5 kW serves as a heat pump unit. The working agent of the heat pump installation is freon-12. Compressor - piston sealless, condenser and evaporator - shell-and-tube with water cooling.

The heating circuit equipment includes a circulation pump, heating appliances type "Comfort" flowing electric water heater EPV-2 as a door closer and understudy. The equipment of the hot water supply circuit includes a capacitive (0.4 m3) STD type water heater with a heat exchanger surface of 0.47 m2 and a BAS-10/M 4-04 terminal electric heater with a power of 1 kW. Circulation pumps of all circuits are of the TsVTs type, glandless, vertical, low noise, foundationless.

The system works as follows. The coolant transfers heat from the collectors to the water in the storage tank and to the freon in the evaporator heat pump. The vaporous freon after compression in the compressor condenses in the condenser, while heating the water in the heating system and tap water in the hot water system.

In the absence of solar radiation and the heat stored in the storage tank is used up, the heat pump unit is turned off and the heat supply to the house is carried out entirely from electric water heaters (electric boilers). In winter, the heat pump unit is in operation only at a certain level of negative outdoor temperatures (not lower than -7 °C) in order to prevent water freezing in the storage tank. In summer, the hot water supply system is provided with heat mainly with the natural circulation of the coolant through a "pipe in pipe" type heat exchanger. As a result of the implementation of various modes of operation, a combined solar heat pump installation allows saving heat of about 40 GJ/year (the results of the operation of these installations are given in Chapter 8).

The combination of solar energy and heat pumps was also reflected in the engineering equipment developed by TsNIIEP

Rice. 4.3. circuit diagram heating systems in Gelendzhik

1 - solar collector; 2 - reheating heat exchanger with heat carrier from the condenser circuit of heat pumps; 3 - reheating heat exchanger with heat carrier from the heating network; 4 - condenser circuit pump; 5 - Heat pump; 6 - evaporator circuit pump; 7 - heat exchanger for heating (cooling) water in the evaporator (condenser) circuit; 8 - Heat exchanger for heating the source (raw) water; 9 - hot water pump; 10 - Battery tanks; 11 - solar circuit heat exchanger; 12 - solar circuit pump

Heat supply project for the hotel complex "Privetlivy Bereg" in Gelendzhik (Fig. 4.3).

The basis of the solar heat pump installation is: flat solar collectors with a total area of 690 m2 and three serially produced refrigeration machines MKT 220-2-0 operating in heat pump mode. Estimated annual heat generation is about 21,000 GJ, including 1,470 GJ from the solar plant.

Sea water serves as a low-grade heat source for heat pumps. To ensure a corrosion-free and scale-free operation of the heating surfaces of collectors, pipelines and condensers, they are filled with softened and deaerated water from the heating network. Compared to the traditional scheme of heat supply from a boiler house, the involvement of non-traditional heat sources is

Sun and sea water, allows you to save about 500 tons of conventional units. fuel / year.

Another characteristic example of the use of new energy sources is the project of heat supply of a manor house with the help of

Solar heat pump installation. The project provides for year-round full satisfaction of the needs of heating and hot water supply of a mansard-type manor house with a living area of 55 m2. The ground serves as a low-potential source of heat for the heat pump. The estimated economic effect from the introduction of the system is at least 300 rubles. per apartment compared to the traditional option of heat supply from a solid fuel apparatus.

On the basis of the use of solar installations, the problems of heating, cooling and hot water supply of residential, administrative buildings, industrial and agricultural facilities. Solar plants are classified as follows:

by appointment: hot water supply systems; heating systems; combined installations for the purposes of heat and cold supply;
by type of coolant used: liquid; air;
by duration of work: year-round; seasonal;
according to the technical solution of the scheme: single-circuit; double-circuit; multi-loop.

The most commonly used heat transfer media in solar heating systems are liquids (water, ethylene glycol solution, organic matter) and air. Each of them has certain advantages and disadvantages. Air does not freeze, does not create big problems associated with leaks and equipment corrosion. However, due to the low density and heat capacity of air, the size of air installations, the power consumption for pumping the coolant is higher than that of liquid systems. Therefore, in most operating solar heating systems, liquids are preferred. For housing and communal needs, the main coolant is water.

When solar collectors operate during periods with negative outdoor temperatures, it is necessary either to use antifreeze as a coolant, or to avoid freezing of the coolant in some way (for example, by timely draining the water, heating it, insulating solar collector).

Solar hot water plants of year-round operation with a backup source of heat can be equipped with rural-type houses, multi-storey and apartment buildings, sanatoriums, hospitals and other facilities. Seasonal installations, such as, for example, shower installations for pioneer camps, boarding houses, mobile installations for geologists, builders, shepherds, usually operate in the summer and transitional months of the year, during periods with a positive outside temperature. They may or may not have a backup heat source, depending on the type of facility and operating conditions.

The cost of hot water solar installations can be from 5 to 15% of the cost of the object and depends on climatic conditions, the cost of equipment and the degree of its development.

In solar systems designed for heating systems, both liquids and air are used as heat carriers. In multi-circuit solar systems, different heating media can be used in different circuits (for example, water in a solar circuit, air in a distribution circuit). In our country, water solar installations for heat supply are predominantly used.

The surface area of solar collectors required for heating systems is typically 3-5 times the surface area of collectors for hot water systems, so the utilization rate of these systems is lower, especially in summer. The cost of installation for a heating system can be 15-35% of the cost of the object.

Combined systems can include year-round installations for heating and hot water supply, as well as installations operating in the mode of a heat pump and a heat pipe for heating and cooling purposes. These systems are not yet widely used in industry.

The flux density of solar radiation coming to the surface of the collector largely determines the heat engineering and technical and economic performance of solar heat supply systems.

The flux density of solar radiation varies during the day and throughout the year. This is one of characteristic features systems using solar energy, and when carrying out specific engineering calculations solar installations, the choice of the design value E is decisive.

As a design scheme for a solar heat supply system, consider the scheme shown in Fig. 3.3, which makes it possible to take into account the features of the operation of various systems. The solar collector 1 converts the energy of solar radiation into heat, which is transferred to the storage tank 2 through the heat exchanger 3. The heat exchanger can be located in the storage tank itself. The circulation of the coolant is provided by a pump. The heated coolant enters the hot water and heating systems. In the event of a lack or absence of solar radiation, a backup source of heat for hot water supply or heating is included in the work 5.

Fig.3.3. Scheme of the solar heating system: 1 - solar collectors; 2 - storage tank hot water; 3 - heat exchanger; 4 - building with floor heating; 5 - doubler (source of additional energy); 6 - passive solar system; 7 - pebble battery; 8 - shutters; 9 - fan; 10 - flow of warm air into the building; 11- supply of recirculated air from the building

The solar heating system uses solar collectors of a new generation "Rainbow" of NPP "Competitor" with improved thermal performance due to the use of a selective coating on a heat-absorbing stainless steel panel and a translucent coating of extra strong glass with high optical characteristics.

The system uses as a heat carrier: water at positive temperatures or antifreeze during the heating period (solar circuit), water (second floor heating circuit) and air (third air solar heating circuit).

An electric boiler was used as a backup source.

Increasing the efficiency of solar supply systems can be achieved through the use of various methods of thermal energy storage, the rational combination of solar systems with thermal boilers and heat pump installations, a combination of active and passive development systems effective means and methods of automatic control.

Prepared by students of the B3TPEN31 Group

Solar heating systems are systems that use solar radiation as a source of thermal energy. Their characteristic difference from other low-temperature heating systems is the use of a special element - a solar receiver, designed to capture solar radiation and convert it into thermal energy.

According to the method of using solar radiation, solar low-temperature heating systems are divided into passive and active.

Passive

Solar heating systems are called passive, in which the building itself or its individual fences (collector building, collector wall, collector roof, etc.) serve as an element that receives solar radiation and converts it into heat.

Passive low-temperature solar heating system "collector wall": 1 - sun rays; 2 – translucent screen; 3 - air damper; 4 - heated air; 5 - cooled air from the room; 6 - own long-wave thermal radiation of the wall array; 7 - black ray-receiving surface of the wall; 8 - blinds.

Active

Solar low-temperature heating systems are called active, in which the solar receiver is an independent separate device that is not related to the building. Active solar systems can be subdivided:

by purpose (hot water supply, heating systems, combined systems for heat and cold supply);

by type of coolant used (liquid - water, antifreeze and air);

by duration of work (year-round, seasonal);

according to the technical solution of the schemes (one-, two-, multi-loop).

Classification of solar heating systems

can be classified according to various criteria:

by appointment:

1. hot water supply systems (DHW);

2. heating systems;

3. combined systems;

Type of coolant used:

1. liquid;

2. air;

By duration of work:

1. year-round;

2. seasonal;

According to the technical solution of the scheme:

1. single-circuit;

2. double-circuit;

3. multi-circuit.

Air is a widely used coolant that does not freeze over the entire range of operating parameters. When used as a heat carrier, it is possible to combine heating systems with a ventilation system. However, air is a low-heat-capacity coolant, which leads to an increase in metal consumption for the installation of systems air heating compared to water systems.

Water is a heat-intensive and widely available coolant. However, at temperatures below 0°C it is necessary to add antifreeze liquids. In addition, it must be taken into account that water saturated with oxygen causes corrosion of pipelines and apparatus. But the consumption of metal in water solar systems is much lower, which to a large extent contributes to their wider use.

Seasonal hot water solar systems are usually single-circuit and operate in the summer and transitional months, during periods with a positive outside temperature. They may have an additional source of heat or do without it, depending on the purpose of the serviced object and operating conditions.

Solar systems for heating buildings are usually double-circuit or, most often, multi-circuit, and different heat carriers can be used for different circuits (for example, aqueous solutions of antifreeze liquids in a solar circuit, water in intermediate circuits, and air in a consumer circuit).

Combined year-round solar systems for the purposes of heat and cold supply of buildings are multi-circuit and include an additional source of heat in the form of a traditional heat generator running on organic fuel or a heat transformer.

A schematic diagram of a solar heating system is shown in Figure 4.1.2. It includes three circulation circuits:

the first circuit, consisting of solar collectors 1, circulation pump 8 and liquid heat exchanger 3;

the second circuit, consisting of a storage tank 2, a circulation pump 8 and a heat exchanger 3;

the third circuit, consisting of a storage tank 2, a circulation pump 8, a water-air heat exchanger (heater) 5.

Schematic diagram of the solar heating system: 1 - solar collector; 2 - storage tank; 3 - heat exchanger; 4 - building; 5 - heater; 6 - understudy of the heating system; 7 - backup system of hot water supply; 8 - circulation pump; 9 - fan.

Functioning

The solar heating system operates as follows. The coolant (antifreeze) of the heat-receiving circuit, being heated in the solar collectors 1, enters the heat exchanger 3, where the heat of the antifreeze is transferred to the water circulating in the annular space of the heat exchanger 3 under the action of the pump 8 of the secondary circuit. The heated water enters the storage tank 2. Water is taken from the storage tank by the hot water supply pump 8, brought, if necessary, to the required temperature in the doubler 7 and enters the hot water supply system of the building. The storage tank is fed from the water supply.

For heating, water from the storage tank 2 is supplied by the pump of the third circuit 8 to the heater 5, through which air is passed through with the help of a fan 9 and, having heated up, enters the building 4. In the absence of solar radiation or a lack of thermal energy generated by solar collectors, the work turn on backup 6.

The choice and layout of the elements of the solar heating system in each case is determined by climatic factors, the purpose of the object, the mode of heat consumption, and economic indicators.

Schematic diagram of a single-loop thermosyphon solar hot water system

A feature of the systems is that in the case of a thermosiphon system, the lower point of the storage tank should be located above the upper point of the collector and no further than 3-4 m from the collectors, and with pump circulation of the coolant, the location of the storage tank can be arbitrary.

The use of "green" energy supplied by natural elements can significantly reduce utility costs. For example, by arranging solar heating of a private house, you will supply virtually free heat carrier low temperature radiators and underfloor heating systems. Agree, this is already saving.

You will learn everything about “green technologies” from our article. With our help, you can easily understand the types of solar installations, how they are constructed and the specifics of operation. Surely you will be interested in one of the popular options that are intensively working in the world, but not yet very popular with us.

In the review presented to your attention, design features systems, connection schemes are described in detail. An example of the calculation of a solar heating circuit to assess the realities of its construction is given. Photo collections and videos are attached to help independent masters.

On average, 1 m 2 of the earth's surface receives 161 watts of solar energy per hour. Of course, at the equator this figure will be many times higher than in the Arctic. In addition, the density of solar radiation depends on the time of year.

In the Moscow region, the intensity of solar radiation in December-January differs from May-July by more than five times. However modern systems so efficient that they can work almost anywhere on earth.

Almost half of all energy produced is used to heat the air. The sun also shines in winter, but its radiation is usually underestimated.

On a December afternoon, not far from Zurich, physicist A. Fischer was generating steam; this was when the sun was at its lowest point and the air temperature was 3°C. A day later, a solar collector with an area of 0.7 m2 heated 30 liters cold water from garden water supply up to +60°С.

Solar energy in winter can easily be used to heat indoor air. In spring and autumn, when it is often sunny but cold, solar space heating will allow you not to turn on the main heating. This makes it possible to save some energy, and therefore money. For houses that are rarely used, or for seasonal housing (dachas, bungalows), solar heating is especially useful in winter, because. eliminates excessive cooling of the walls, preventing destruction from moisture condensation and mold. Thus, the annual operating costs are basically reduced.

When heating houses with solar heat it is necessary to solve the problem of thermal insulation of premises on the basis of architectural and structural elements, i.e. When creating an efficient solar heating system, houses should be built that have good thermal insulation properties.

Heat cost
Auxiliary heating

Solar contribution to home heating
Unfortunately, the period of heat input from the Sun does not always coincide in phase with the period of appearance of thermal loads.

Most of the energy we have at our disposal during summer period, is lost due to the lack of a constant demand for it (in fact, the collector system is to some extent a self-regulating system: when the carrier temperature reaches an equilibrium value, heat absorption stops, since heat loss from the solar collector become equal to the perceived heat).

The amount of useful heat absorbed by the solar collector depends on 7 parameters:

1. the amount of incoming solar energy;
2. optical losses in transparent insulation;
3. absorbing properties of the heat-receiving surface of the solar collector;
4. efficiency of heat transfer from the heat sink (from the heat-receiving surface of the solar collector to the liquid, i.e. from the value of the efficiency of the heat sink);
5. transmittance of transparent thermal insulation, which determines the level of heat loss;
6. the temperature of the heat-receiving surface of the solar collector, which in turn depends on the speed of the coolant and the temperature of the coolant at the inlet to the solar collector;
7. outdoor temperature.

Solar collector efficiency, i.e. the ratio of the energy used and the incident energy will be determined by all these parameters. Under favorable conditions, it can reach 70%, and under unfavorable conditions, it can decrease to 30%. The exact value of efficiency can be obtained from a preliminary calculation only by fully modeling the behavior of the system, taking into account all the factors listed above. It is obvious that such a problem can be solved only with the use of a computer.

Since the flux density of solar radiation is constantly changing, it is possible to use the total sums of radiation per day or even per month for calculation estimates.

In table. 1 as an example are given:

average monthly amounts of solar radiation received, measured on a horizontal surface;

amounts calculated for vertical walls facing south;

sums for surfaces with an optimal slope angle of 34° (for Kew, near London).

Table 1. Monthly amounts of solar radiation for Kew (near London)

The table shows that a surface with an optimal angle of inclination receives (on average during 8 winter months) about 1.5 times more energy than a horizontal surface. If the sums of solar radiation arrival on a horizontal surface are known, then in order to convert to an inclined surface, they can be multiplied by the product of this coefficient (1.5) and the accepted value of the solar collector efficiency, equal to 40%, i.e.

1,5*0,4=0,6

This will give the amount of useful energy absorbed by the inclined heat-receiving surface during a given period.

In order to determine the effective contribution of solar energy to the heat supply of a building, even by manual calculation, it is necessary to draw up at least monthly balances of demand and useful heat received from the Sun. For clarity, consider an example.

Using the data above and considering a house with a heat loss rate of 250 W/°C, the location has an annual degree-day of 2800 (67200°C*h). and the area of solar collectors is, for example, 40 m2, then the following distribution by months is obtained (see Table 2).

Table 2. Calculation of the effective contribution of solar energy

Month	°C*h/month	The amount of radiation on a horizontal surface, kW*h/m2	Useful heat per unit collector area (D0.6), kWh/m2	Total useful heat (E*40 m2), kWh	Solar contribution, kW*h/m2
A	B	C	D	E	F	G
January	10560	2640	18,3	11	440	440
February	9600	2400	30,9	18,5	740	740
March	9120	2280	60,6	36,4	1456	1456
April	6840	1710	111	67,2	2688	1710
May	4728	1182	123,2	73,9	2956	1182
June	-	-	150,4	90,2	3608	-
July	-	-	140,4	84,2	3368	-
August	-	-	125,7	75,4	3016	-
September	3096	774	85,9	51,6	2064	774
October	5352	1388	47,6	28,6	1144	1144
November	8064	2016	23,7	14,2	568	568
December	9840	2410	14,4	8,6	344	344
Sum	67200	16800	933	559,8	22392	8358

Heat cost
Having calculated the amount of heat provided by the Sun, it is necessary to present it in monetary terms.

The cost of generated heat depends on:

fuel cost;

calorific value of fuel;

overall system efficiency.

The operating costs thus obtained can then be compared with the capital costs of a solar heating system.

In accordance with this, if we assume that in the above example, the solar heating system is used instead of a traditional heating system that consumes, for example, gas fuel and generates heat at a cost of 1.67 rubles / kWh, then in order to determine the resulting annual savings, it is necessary 8358 kWh provided by solar energy (according to the calculations in Table 2 for a collector area of 40 m2), multiplied by 1.67 rubles / kWh, which gives

8358 * 1.67 \u003d 13957.86 rubles.

Auxiliary heating
One of the questions most frequently asked by people who want to understand the use of solar energy for heating (or any other purpose) is the question, "What do you do when the sun doesn't shine?" Having understood the concept of energy storage, they ask the following question: “What to do when there is no more thermal energy left in the battery?” The question is legitimate, and the need for a redundant, often traditional system is a major stumbling block to the widespread adoption of solar energy as an alternative to existing energy sources.

If the capacity of a solar heating system is not sufficient to sustain a building through a period of cold, cloudy weather, then the consequences, even once per winter, can be severe enough to require a conventional full-scale heating system to be considered as a backup. Most buildings heated by solar energy need a full backup system. At present, in most areas, solar energy should be considered as a means to reduce the consumption of traditional forms of energy, and not as a complete substitute for them.

Conventional heaters are suitable substitutes, but there are many other alternatives, for example:

Fireplaces;
- wood stoves;
- wood heaters.

Suppose, however, that we wanted to make a solar heating system large enough to provide heat to a room in the most adverse conditions. Since the combination of very cold days and long periods of cloudy weather is rare, the additional solar power plant size (collector and battery) that would be required for these occasions would be too expensive for relatively little fuel savings. In addition, most of the time the system will operate at less than nominal power.

A solar heating system designed to supply 50% of the heating load can only provide enough heat for 1 day of very cold weather. Doubling the size solar system the house will be provided with heat during 2 cold cloudy days. For periods longer than 2 days, a subsequent increase in size will be just as unjustified as the previous one. In addition, there will be periods of mild weather when a second increase is not required.

Now, if we increase the collector area heating system by another 1.5 times to last 3 cold and cloudy days, then theoretically it will be enough to provide 1/2 of the entire needs of the house during the winter. But, of course, this may not be the case in practice, since sometimes 4 (or more) consecutive days of cold cloudy weather happen. To account for this 4th day, we need a solar heating system that can theoretically collect 2 times more heat than the building needs during the heating season. It is clear that cold and cloudy periods may be longer than foreseen in the design of the solar heating system. The larger the collector, the less intensively each additional increment of its size is used, the less energy is saved per unit area of the collector, and the less the return on investment for each additional unit area.

However, bold attempts have been made to store enough thermal energy from solar radiation to cover the entire heating demand and to abandon the auxiliary heating system. With the rare exception of systems such as sunny house G. Hay, long-term heat storage is perhaps the only alternative to an auxiliary system. Mr. Thomason came close to 100% solar heating in his first home in Washington; only 5% of the heating load was covered by a standard oil-fired heater.

If the auxiliary system covers only a small percentage of the total load, then it makes sense to use electric heating, despite the fact that it requires the production of a significant amount of energy in the power plant, which is then converted into heat for heating (10500 ... 13700 kJ are consumed in the power plant to produce 1 kWh of thermal energy in the building). In most cases, an electric heater will be cheaper than an oil or gas oven, and the relatively small amount of electricity needed to heat a building may justify its use. In addition, the electric heater is a less material-intensive device due to the relatively a small amount material (compared to the heater) used for the manufacture of electric coils.

Since the efficiency of a solar collector increases significantly if it is operated at low temperatures, then the heating system must be designed to use as low temperatures as possible - even at the level of 24...27°C. One of the advantages of the Thomason warm air system is that it continues to extract useful heat from the battery at temperatures close to room temperature.

In new construction, heating systems can be counted on to use lower temperatures, for example by extending tubular-finned radiators with hot water, increasing the size of the radiant panels or increasing the volume of air at a lower temperature. Designers most often opt for space heating using warm air or the use of enlarged radiant panels. An air heating system makes the best use of low-temperature stored heat. Radiant heating panels have a long delay (between turning on the system and heating the air space) and usually require higher operating temperatures than hot air systems. Therefore, the heat from the storage device is not fully utilized at lower temperatures, which are acceptable for systems with warm air, and the overall efficiency of such a system is lower. Oversizing a radiant panel system to achieve results similar to those obtained with air can incur significant additional costs.

To increase the overall efficiency of the system (solar heating and auxiliary backup system) and at the same time reduce the overall cost by eliminating downtime constituent parts, many designers have chosen the path of integrating the solar collector and battery with an auxiliary system. The common elements are:

Fans;
- pumps;
- heat exchangers;
- governing bodies;
- pipes;
- air ducts.

The figures in the article Systems Engineering show various schemes of such systems.

A pitfall in designing interfaces between systems is the increase in controls and moving parts, which increases the likelihood of mechanical failure. The temptation to increase efficiency by 1-2% by adding another device at the junction of systems is almost irresistible and may be the most common reason for the failure of a solar heating system. Normally, the booster heater should not heat the solar heat accumulator compartment. If this happens, then the solar heat harvesting phase will be less efficient, since this process will almost always take place at more high temperatures Oh. In other systems, lowering the temperature of the battery due to the use of heat by the building improves the overall efficiency of the system.

The reasons for other disadvantages of this circuit are due to the large heat loss from the battery due to its constantly high temperatures. In systems where the auxiliary equipment does not heat the battery, the latter will lose significantly less heat if there is no sun for several days. Even in systems designed in this way, the heat loss from the container is 5...20% of the total heat absorbed by the solar heating system. With an auxiliary heated battery, the heat loss will be much higher and can only be justified if the battery container is inside the heated room of the building