MINISTRY ENERGY AND ELECTRIFICATION USSR

MAIN SCIENTIFIC AND TECHNICAL DEPARTMENT
ENERGY AND ELECTRIFICATION

METHODOLOGICAL INSTRUCTIONS
FOR CALCULATION AND DESIGN
SOLAR HEATING SYSTEMS

RD 34.20.115-89

SERVICE OF EXCELLENCE FOR SOYUZTEKHENERGO

Moscow 1990

DEVELOPED State Order of the Red Banner of Labor Scientific Research Energy Institute named after. G.M. Krzhizhanovsky

PERFORMERS M.N. EGAI, O.M. KORSHUNOV, A.S. LEONOVICH, V.V. NUSHTAYKIN, V.K. RYBALKO, B.V. TARNIZHEVSKY, V.G. BULYCHEV

APPROVED Main Scientific and Technical Directorate of Energy and Electrification 12/07/89

Head V.I. GORY

Validity period is set

from 01.01.90

until 01.01.92

These Guidelines establish the procedure for performing calculations and contain recommendations for the design of solar heating systems for residential, public and industrial buildings and structures.

The guidelines are intended for designers and engineers involved in the development of solar heating and hot water supply systems.

. GENERAL PROVISIONS

where f - share of the total average annual heat load provided by solar energy;

where F - surface area of ​​the SC, m2.

where H is the average annual total solar radiation on a horizontal surface, kW h/m2 ; located from the application;

a, b - parameters determined from equation () and ()

where r - characteristics of the thermal insulation properties of the building envelope at a fixed value of the DHW load, is the ratio of the daily heating load at an outside air temperature of 0 °C to the daily DHW load. The more r , the greater the share of the heating load compared to the share of the DHW load and the less perfect the building design is in terms of heat losses; r = 0 is taken into account only DHW systems. The characteristic is determined by the formula

where λ is the specific heat loss of the building, W/(m 3 °C);

m - number of hours in a day;

k - ventilation air exchange rate, 1/day;

ρ in - air density at 0 °C, kg/m3;

f - replacement rate, approximately taken from 0.2 to 0.4.

Values ​​of λ, k, V, t in, s laid down when designing the SST.

Values ​​of coefficient α for solar collectors Types II and III

	Coefficient values
	α 1	α 2	α 3	α 4	α 5	α 6	α 7	α 8	α 9
	607,0	80,0		1340,0	437,5	22,5	1900,0	1125,0	25,0
	298,0	148,5	61,5	150,0	1112,0	337,5	700,0	1725,0	775,0

β coefficient values ​​for solar collectors Types II and III

	Coefficient values
	β 1	β 2	β 3	β 4	β 5	β 6	β 7	β 8	β 9
	1,177	0,496	0,140			0,995	3,350	5,05	1,400
	1,062	0,434	0,158	2,465	2,958	1,088	3,550	4,475	1,775

Values ​​of coefficients a and bare from the table. .

The values ​​of the coefficients a and b depending on the type of solar collector

	Coefficient values
		0,75
		0,80

where qi - specific annual heating capacity of SGVS at values f different from 0.5;

Δq - change in the annual specific heat output of the SGVS, %.

Change in annual specific heat outputΔq from the annual intake of solar radiation on a horizontal surface H and coefficient f

. RECOMMENDATIONS FOR DESIGNING SOLAR HEATING SYSTEMS where З с - specific reduced costs per unit of generated thermal energy SST, rub./GJ; Zb - specific reduced costs per unit of thermal energy generated by the basic installation, rub./GJ. where C c - reduced costs for SST and backup, rub./year; where k c - capital costs for SST, rub.; k in - capital costs for the backup, rub.; E n - standard coefficient of comparative efficiency of capital investments (0.1); E s is the share of operating costs from capital costs for the SST; E in - the share of operating costs from the capital costs of the backup; C is the cost of a unit of thermal energy generated by the backup, rub./GJ; N d - the amount of thermal energy generated by the backup during the year, GJ; k e - effect from reducing environmental pollution, rub.; k n - social effect from saving the salaries of personnel servicing the backup, rub. Specific reduced costs are determined by the formula where C b - reduced costs for a basic installation, rub./year;	Definition of the term
	solar collector	A device for capturing solar radiation and converting it into thermal and other types of energy
Hourly (daily, monthly, etc.) heating output	The amount of thermal energy removed from the collector per hour (day, month, etc.) of operation
Flat solar collector	Non-focusing solar collector with an absorbing element of a flat configuration (such as “pipe in sheet”, only from pipes, etc.) and flat transparent insulation
Heat-receiving surface area	Surface area of ​​the absorbing element illuminated by the sun under conditions of normal incidence of rays
Heat loss coefficient through transparent insulation (bottom, side walls of the collector)	Heat flow into the environment through transparent insulation (bottom, side walls of the collector), per unit area of ​​the heat-receiving surface, with a difference in the average temperatures of the absorbing element and the outside air of 1 ° C
Specific coolant flow in a flat solar collector	Coolant flow in the collector per unit area of ​​the heat-receiving surface
Efficiency factor	A value characterizing the efficiency of heat transfer from the surface of the absorbing element to the coolant and equal to the ratio of the actual heat output to the heat output, provided that all thermal resistances of heat transfer from the surface of the absorbing element to the coolant are zero
Surface blackness degree	Ratio of surface radiation intensity to black body radiation intensity at the same temperature
Glazing transmittance	The fraction of solar (infrared, visible) radiation incident on the surface of the transparent insulation transmitted by transparent insulation
Understudy	A traditional source of thermal energy that provides partial or complete coverage of the thermal load and works in combination with a solar heating system
Solar Thermal System	A system that covers heating and hot water loads using solar energy

Appendix 2

Warm specifications solar collectors

	Collector type
Total heat loss coefficient U L, W/(m 2 °C)
Absorption capacity of the heat-receiving surface α	0,95	0,90	0,95
The degree of emissivity of the absorption surface in the range of operating temperatures of the collector ε	0,95	0,10	0,95
Glazing transmittance τ p	0,87	0,87	0,72
Efficiency factor F R	0,91	0,93	0,95
Maximum coolant temperature, °C
Note. I - single-glass non-selective collector; II - single-glass selective collector; III - double-glass non-selective collector.

Appendix 3

Technical characteristics of solar collectors

	Manufacturer
	Bratsk plant heating equipment	Spetsgelioteplomontazh GSSR	KievZNIIEP	Bukhara solar equipment plant
Length, mm	1530	1000 - 3000	1624	1100
Width, mm			1008
Height, mm		70 - 100
Weight, kg	50,5	30 - 50
Heat-receiving surface, m		0,6 - 1,5		0,62
Working pressure, MPa		0,2 - 0,6

Appendix 4

Technical characteristics of flow-through heat exchangers type TT

	Outer/inner diameter, mm		Flow area		Heating surface of one section, m 2	Section length, mm	Weight of one section, kg
			inner pipe, cm 2	annular channel, cm 2
	inner pipe	outer pipe
TT 1-25/38-10/10	25/20	38/32	3,14	1,13		1500
TT 2-25/38-10/10	25/20	38/32	6,28	6,26		1500

Appendix 5

Annual arrival of total solar radiation on a horizontal surface (N), kW h/m 2

Azerbaijan SSR
Baku	1378
Kirovobad	1426
Mingachevir	1426
Armenian SSR
Yerevan	1701
Leninakan	1681
Sevan	1732
Nakhchivan	1783
Georgian SSR
Telavi	1498
Tbilisi	1396
Tskhakaya	1365
Kazakh SSR
Almaty	1447
Guryev	1569
Fort Shevchenko	1437
Dzhezkazgan	1508
Ak-Kum	1773
Aral Sea	1630
Birsa-Kelmes	1569
Kustanay	1212
Semipalatinsk	1437
Dzhanybek	1304
Kolmykovo	1406
Kirghiz SSR
Frunze	1538
Tien Shan	1915
RSFSR
Altai region
Blagoveshchenka	1284
Astrakhan region
Astrakhan	1365
Volgograd region
Volgograd	1314
Voronezh region
Voronezh	1039
Stone steppe	1111
Krasnodar region
Sochi	1365
Kuibyshev region
Kuibyshev	1172
Kursk region
Kursk	1029
Moldavian SSR
Kishinev	1304
Orenburg region
Buzuluk	1162
Rostov region
Tsimlyansk	1284
Giant	1314
Saratov region
Ershov	1263
Saratov	1233
Stavropol region
Essentuki	1294
Uzbek SSR
Samarkand	1661
Tamdybulak	1752
Takhnatash	1681
Tashkent	1559
Termez	1844
Fergana	1671
Churuk	1610
Tajik SSR
Dushanbe	1752
Turkmen SSR
Ak-Molla	1834
Ashgabat	1722
Hasan-Kuli	1783
Kara-Bogaz-Gol	1671
Chardzhou	1885
Ukrainian SSR
Kherson region
Kherson	1335
Askania Nova	1335
Sumy region
Konotop	1080
Poltava region
Poltava	1100
Volyn region
Kovel	1070
Donetsk region
Donetsk	1233
Transcarpathian region
Beregovo	1202
Kyiv region
Kyiv	1141
Kirovograd region
Znamenka	1161
Crimean region
Evpatoria	1386
Karadag	1426
Odessa region
	30,8	39,2	49,8	61,7	70,8	75,3	73,6	66,2	55,1	43,6	33,6	28,7
	28,8	37,2	47,8	59,7	68,8	73,3	71,6	64,2	53,1	41,6	31,6	26,7
	26,8	35,2	45,8	57,7	66,8	71,3	69,6	62,2	51,1	39,6	29,6	24,7
	24,8	33,2	43,8	55,7	64,8	69,3	67,5	60,2	49,1	37,6	27,6	22,7
	22,8	31,2	41,8	53,7	62,8	67,3	65,6	58,2	47,1	35,6	25,6	20,7
	20,8	29,2	39,8	51,7	60,8	65,3	63,6	56,2	45,1	33,6	23,6	18,7
	18,8	27,2	37,8	49,7	58,8	63,3	61,6	54,2	43,1	31,6	21,6	16,7
	16,8	25,2	35,8	47,7	56,8	61,3
Boiling point, °C	106,0	110,0	107,5	105,0	113,0
Viscosity, 10 -3 Pa s:
at a temperature of 5 °C		5,15		6,38
at a temperature of 20 °C					7,65
at a temperature of -40 °C	7,75	35,3		28,45
Density, kg/m 3				1077	1483 - 1490
Heat capacity kJ/(m 3 °C):
at a temperature of 5 °C	3900	3524
at a temperature of 20 °C				3340	3486
Corrosivity	Strong	Average	Weak	Weak	Strong
Toxicity	No	Average	No	Weak	No

Notes e. Coolants based on potassium carbonate have the following compositions (mass fraction):

Recipe 1 Recipe 2

Potassium carbonate, 1.5-water 51.6 42.9

Sodium phosphate, 12-hydrate 4.3 3.57

Sodium silicate, 9-hydrate 2.6 2.16

Sodium tetraborate, 10-hydrate 2.0 1.66

Fluoreszoin 0.01 0.01

Water Up to 100 Up to 100

What are thermal solar collectors used for? Where can they be used - areas of application, application options, pros and cons of collectors, technical characteristics, efficiency. Is it possible to do it yourself and how justified is it? Application schemes and prospects.

Purpose

The collector and the solar battery are two different devices. The battery uses the conversion of solar energy into electrical energy, which is stored in batteries and used for household needs. Solar collectors, like a heat pump, are designed to collect and accumulate environmentally friendly energy from the Sun, the conversion of which is used to heat water or heating. Solar thermal power plants, which convert heat into electricity, have become widely used on an industrial scale.

Device

Collectors consist of three main parts:

• panels;
• fore camera;
• storage tank.

The panels are presented in the form of a tubular radiator placed in a box with an outer wall made of glass. They must be placed in any well-lit place. Liquid enters the panel radiator, which is then heated and moved to the front chamber, where cold water is replaced by hot water, which creates constant dynamic pressure in the system. In this case, cold liquid enters the radiator, and hot liquid enters the storage tank.

Standard panels are easy to adapt to any conditions. Using special mounting profiles, they can be installed parallel to each other in a row in an unlimited number. Holes are drilled in aluminum mounting profiles and secured to the panels from below with bolts or rivets. Once completed, the solar absorber panels, together with the mounting profiles, form a single rigid structure.

The solar heating system is divided into two groups: air-cooled and liquid-cooled. Collectors capture and absorb radiation, and convert it into thermal energy, are transferred to the storage element, from which the heat is distributed throughout the room. Any of the systems can be supplemented with auxiliary equipment ( circulation pump, pressure sensors, safety valves).

Principle of operation

IN daytime thermal radiation is transferred to the coolant (water or antifreeze) circulating through the collector. The heated coolant transfers energy to the water heater tank, located above it and collecting water for hot water supply. In the simple version, water circulation is carried out naturally due to the difference in density of hot and cold water in the circuit, and to ensure that the circulation does not stop, a special pump is used. The circulation pump is designed to actively pump liquid through the structure.


In a more complicated version, the collector is included in a separate circuit filled with water or antifreeze. The pump helps them begin to circulate, transferring stored solar energy into a thermally insulated storage tank, which allows heat to be stored and taken back when needed. If there is not enough energy, the electric or gas heater provided in the design of the tank automatically turns on and maintains the required temperature.

Kinds

Those who want to have a solar heating system in their home must first decide on the most suitable type of collector.

Flat type collector

Presented in the form of a closed box tempered glass, and has a special layer that absorbs solar heat. This layer is connected to tubes through which the coolant circulates. The more energy it receives, the higher its efficiency. Reducing heat losses in the panel itself and ensuring the greatest heat absorption on the absorber plates allows for maximum energy collection. In the absence of stagnation, flat collectors can heat water up to 200 °C. They are designed for heating water in swimming pools, domestic needs and heating the house.

Vacuum type manifold

It consists of glass batteries (a series of hollow tubes). The outer battery has a transparent surface, and the inner battery is covered with a special layer that traps radiation. The vacuum layer between the internal and external batteries helps save about 90% of the absorbed energy. Heat conductors are special tubes. When the panel heats up, the liquid located at the bottom of the battery is converted into steam, which rises and transfers heat to the collector. This type of system has greater efficiency compared to collectors flat type, since it can be used for low temperatures and in low light conditions. A vacuum solar battery allows you to heat the coolant temperature to 300 °C, using a multilayer glass coating and creating a vacuum in the collectors.

Heat pump

Solar thermal systems work most efficiently with a device such as a heat pump. Designed to collect energy from the environment, regardless of weather conditions, and can be installed inside the house. The source of energy here can be water, air or soil. A heat pump can operate using just solar collectors if there is enough solar power. When using a combined heat pump and solar collector system, the type of collector does not matter, but the most suitable option there will be a solar vacuum battery.

What's better

A solar heating system can be installed on any type of roof. Flat-plate collectors are considered more durable and reliable, in contrast to vacuum collectors, whose design is more fragile. However, if a flat collector is damaged, the entire absorption system will have to be replaced, whereas for a vacuum collector only the damaged battery must be replaced.


The efficiency of a vacuum manifold is much higher than that of a flat manifold. They can be used in winter time and they produce more power in cloudy weather. The heat pump has become quite widespread, despite its high cost. The energy production rate of vacuum collectors depends on the size of the tubes. Normally, the dimensions of the tubes should be 58 mm in diameter with a length of 1.2-2.1 meters. It is quite difficult to install the collector yourself. However, having certain knowledge, as well as following detailed instructions the installation and selection of the location of the system specified when purchasing the equipment will significantly simplify the task and help bring solar heating into the house.

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

Abroad wide use received air heating systems, where building structures or a special stone backfill under it are used as batteries. In our country, the Physicotechnical Institute of the Academy of Sciences of the UzSSR and TbilZNIIEP are working in this direction, but the results of the work are clearly insufficient and no well-functioning solutions have been created, although air systems 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 have been developed by IVTAN, Physicotechnical Institute of the Academy of Sciences of the UzSSR, TashZNIIEP, TbilZNIIEP, KievZNIIEP and etc. and in some cases erected.

A large amount of information on active systems solar heating given in a book published in 1980. The following describes the KievZNIIEP developed, built and tested two individual residential buildings with autonomous solar heating systems: 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. Kolesnoye, 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 heating: effective masonry with insulation was used for external walls and triple glazing of window openings; heating system coils are combined with interfloor ceilings; a basement is provided for equipment placement; Additional insulation of the attic and recovery of exhaust air heat were carried out.

In terms of architectural layout, the house is designed on two levels. On the ground floor there is a front room, a living room, a bedroom, a kitchen, a bathroom and storage rooms, and on the second floor there are two bedrooms and a bathroom, and there is an electric stove for cooking. The solar heating system equipment (except collectors) is located in the basement; The system is backed up by electric water heaters, which allows for a single energy input into the building and improves the comfortable quality of housing.

Solar heating system for a residential building (Fig. 4.1) consists of From three circuits: heat receiving circulation And heating and hot water supply circuits. The first of them includes solar water heaters, a coil-heat exchanger of the storage tank, a circulation pump and a “pipe-in-pipe” heat exchanger for operating the system in the summer in natural circulation mode. The equipment is connected by a pipeline system with fittings, instrumentation and automation devices. The storage tank with a capacity of 16 m3 contains a two-section coil heat exchanger with a surface area of ​​4.6 m2 for the circulation circuit coolant and a single-section heat exchanger with a surface area of ​​1.2 m2 for the hot water supply system. The heat capacity of a tank with a water temperature of +45 °C provides a three-day heating requirement for a residential building. A “pipe-in-pipe” heat exchanger with a surface area of ​​1.25 m2 is located under the ridge of the house’s roof.

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

The hot water supply 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, heat from the collectors is transferred by the coolant (45% aqueous solution of ethylene glycol) to the water in the storage tank, which is sent by a pump to the heating panel coils, and then returned to the storage tank.

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

In summer, the system meets the needs of hot water supply from a “pipe-in-pipe” heat exchanger with natural circulation of coolant in the heat receiving circuit. The transition to incentive circulation is carried out using an electronic differential regulator RPT-2.

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

The residential building is of the attic type. On the ground floor there is a common room, a kitchen, a laundry room, and a utility room, and on the second there are three bedrooms. IN ground floor There is a garage, a cellar and a room for equipment of the solar heating system. The house is connected to an outbuilding, which includes summer kitchen, shower, canopy, inventory and workshop.

Autonomous solar heating system (Fig. 4.2) is a combined solar-heat pump installation designed to provide heating needs (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: heat-receiving circulation circuits, heat pump circuits, 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 built-in heat exchanger with a surface area of ​​6 m2. Solar collectors designed by KievZNIIEP with double-layer glazing with a total area of ​​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 % 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-condenser 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. The compressor is a sealless piston compressor, the condenser and evaporator are shell-and-tube with water cooling.

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

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

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

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

Rice. 4.3. Schematic diagram heat supply systems in Gelendzhik 1 - solar collector; 2 - reheating heat exchanger with coolant from the heat pump condenser circuit; 3 - reheating heat exchanger with coolant 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 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 "Friendly Beach" in Gelendzhik (Fig. 4.3).

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

Sea water is a low-grade heat source for heat pumps. To ensure 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 heat supply scheme from the boiler house, the use of non-traditional heat sources -

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

Another typical example of the use of new energy sources is the heat supply project for a manor house using

Solar heat pump installation. The project provides for year-round full satisfaction of the heating and hot water supply needs of an attic-type manor house with a living area of ​​55 m2. The low-grade heat source for the heat pump is soil. The estimated economic effect from implementing the system is at least 300 rubles. per apartment compared to the traditional option of heat supply from a solid fuel unit.

Classification and main elements of solar systems

Solar heating systems are systems that use solar radiation as a source of thermal energy. Their characteristic difference from other systems is low temperature heating 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 those in which the building itself or its individual enclosures (building-collector, wall-collector, roof-collector, etc.) serve as an element that receives solar radiation and converts it into heat (Fig. 3.4)) .

Rice. 3.4. Passive low-temperature solar heating system “wall-collector”: 1 – solar 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 mass; 7 – black beam-receiving surface of the wall; 8 – blinds.

Active are solar low-temperature heating systems in which the solar receiver is an independent separate device 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 purposes);

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

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

- according to the technical solution of circuits (one-, two-, multi-circuit).

Air is a widely used coolant that does not freeze over the entire range of operating parameters. When using it as a coolant, it is possible to combine heating systems with a ventilation system. However, air is a low-heat 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 to it. In addition, it must be taken into account that water oxygenated, causes corrosion of pipelines and apparatus. But the metal consumption in solar water systems is much lower, which greatly contributes to their wider use.

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

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

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

A schematic diagram of the solar heating system is shown in Fig. 3.5. 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.

Rice. 3.5. Schematic diagram of the solar heating system: 1 – solar collector; 2 – storage tank; 3 – heat exchanger; 4 – building; 5 – heater; 6 – heating system backup; 7 – hot water supply system backup; 8 – circulation pump; 9 – fan.

The solar heating system operates as follows. The coolant (antifreeze) of the heat receiving circuit, heating up in the solar collectors 1, enters the heat exchanger 3, where the heat of the antifreeze is transferred to the water circulating in the interpipe 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. From the storage tank, water is taken by the hot water supply pump 8, brought, if necessary, to the required temperature in the backup 7 and enters the hot water supply system of the building. The storage tank is recharged from the water supply.

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

The selection and arrangement of elements of a solar heating system in each specific case are determined by climatic factors, purpose of the facility, heat consumption regime, and economic indicators.

Concentrating solar receivers

Concentrating solar receivers are spherical or parabolic mirrors (Fig. 3.6), made of polished metal, at the focus of which a heat-receiving element (solar boiler) is placed, through which the coolant circulates. Water or non-freezing liquids are used as a coolant. When using water as a coolant at night and during cold periods, the system must be emptied to prevent it from freezing.

To ensure high efficiency of the process of capturing and converting solar radiation, the concentrating solar receiver must be constantly directed strictly at the Sun. For this purpose, the solar receiver is equipped with a tracking system, including a direction sensor to the Sun, an electronic signal conversion unit, and an electric motor with a gearbox for rotating the solar receiver structure in two planes.

The advantage of systems with concentrating solar receivers is the ability to generate heat at a relatively high temperature (up to 100 ° C) and even steam. The disadvantages include the high cost of the structure; the need to constantly clean reflective surfaces from dust; work only during daylight hours, and therefore the need for large batteries; large energy costs for driving the solar tracking system, commensurate with the energy generated. These disadvantages hinder the widespread use of active low-temperature solar heating systems with concentrating solar receivers. Recently, flat solar receivers have been most often used for solar low-temperature heating systems.

Flat-plate solar collectors

Flat solar collector – a device with a flat configuration absorbing panel and flat transparent insulation to absorb energy solar radiation and converting it into heat.

Flat solar collectors (Fig. 3.7) consist of glass or plastic covering(single, double, triple), heat absorbing panel, painted black on the side facing the sun, insulation on back side and housing (metal, plastic, glass, wood).

Any metal or plastic sheet with channels for coolant can be used as a heat-receiving panel. Heat-receiving panels are made of aluminum or steel of two types: sheet-pipe and stamped panels (pipe in sheet). Plastic panels, due to their fragility and rapid aging under the influence of sunlight, as well as low thermal conductivity, are not widely used.

Rice. 3.6 Concentrating solar receivers: a – parabolic concentrator; b – parabolic cylindrical concentrator; 1 – sun rays; 2 – heat-receiving element (solar collector); 3 – mirror; 4 – tracking system drive mechanism; 5 – pipelines supplying and discharging coolant.

Rice. 3.7. Flat solar collector: 1 – sun rays; 2 – glazing; 3 – body; 4 – heat-receiving surface; 5 – thermal insulation; 6 – seal; 7 – own long-wave radiation of the heat-receiving plate.

Under the influence of solar radiation, heat-receiving panels heat up to temperatures of 70-80 ° C, exceeding the ambient temperature, which leads to an increase in convective heat transfer of the panel in environment and its own radiation into the sky. To achieve more high temperatures The coolant surface of the plate is covered with spectral-selective layers that actively absorb short-wave radiation from the sun and reduce its own thermal radiation in the long-wave part of the spectrum. Such designs based on “black nickel”, “black chrome”, copper oxide on aluminum, copper oxide on copper and others are expensive (their cost is often comparable to the cost of the heat-receiving panel itself). Another way to improve the performance of flat plate collectors is to create a vacuum between the heat-receiving panel and the transparent insulation to reduce heat loss (fourth generation solar collectors).

Operating experience solar installations based on solar collectors revealed a number of significant shortcomings of such systems. First of all, this is the high cost of collectors. Increasing the efficiency of their work due to selective coatings, increasing the transparency of glazing, vacuuming, and also installing a cooling system turn out to be economically unprofitable. A significant disadvantage is the need to frequently clean the glass from dust, which practically excludes the use of the collector in industrial areas. At long-term operation solar collectors, especially in winter conditions, there is a frequent failure of them due to the uneven expansion of the illuminated and darkened areas of the glass due to the violation of the integrity of the glazing. There is also a large percentage of collectors failing during transportation and installation. A significant disadvantage of operating systems with collectors is also the uneven loading throughout the year and day. Experience in operating collectors in Europe and the European part of Russia with a high proportion of diffuse radiation (up to 50%) has shown the impossibility of creating a year-round autonomous hot water supply and heating system. All solar systems with solar collectors in mid-latitudes require the installation of large-volume storage tanks and inclusion in the system additional source energy, which reduces the economic effect of their use. In this regard, it is most advisable to use them in areas with high average intensity of solar radiation (not lower than 300 W/m2).

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 day near 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 of cold water from the garden water supply to +60°C.

Solar energy can easily be used to heat indoor air in winter. In spring and autumn, when it is often sunny but cold, solar heating of the premises 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 (cottages, bungalows), heating with solar energy is especially useful in winter, because... eliminates excessive cooling of the walls, preventing destruction from moisture condensation and mold. In this way, annual operating costs are largely reduced.

When heating houses using solar heat, it is necessary to solve the problem of thermal insulation of premises based on architectural and structural elements, i.e. while creating effective system For solar heating, houses that have good thermal insulation properties should be built.

Heat cost
Auxiliary heating

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

Most of the energy we have at our disposal during summer period, is lost due to the lack of constant demand for it (in fact, the collector system is to some extent a self-regulating system: when the temperature of the medium reaches an equilibrium value, heat perception stops, since the heat losses 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. the efficiency of heat transfer from the heat receiver (from the heat-receiving surface of the solar collector to the liquid, i.e., on the efficiency value of the heat receiver);
5. transmittance of transparent thermal insulation, which determines the level of heat loss;
6. 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 entrance to the solar collector;
7. outside air temperature.

The efficiency of the solar collector, i.e. the ratio of used energy to incident energy will be determined by all these parameters. At favorable conditions it can reach 70%, and in case of unfavorable conditions it can drop to 30%. An accurate efficiency value can be obtained in a preliminary calculation only by fully modeling the behavior of the system, taking into account all the factors listed above. Obviously, such a problem can only be solved using a computer.

Since the flux density of solar radiation is constantly changing, the total amounts of radiation per day or even per month can be used for calculation estimates.

In table 1 shows as an example:

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 inclination angle of 34° (for Kew, near London).

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

The table shows that a surface with an optimal inclination angle receives (on average during 8 winter months) approximately 1.5 times more energy than a horizontal surface. If the amounts of solar radiation arriving on a horizontal surface are known, then to convert them to an inclined surface they can be multiplied by the product of this coefficient (1.5) and the accepted value of the efficiency of the solar collector 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 heating 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, let's look at an example.

If we use the above data and consider a house for which the heat loss rate is 250 W/°C, the location has an annual degree days of 2800 (67200°C*h). and the area of ​​solar collectors is, for example, 40 m2, then the following distribution by month is obtained (see Table 2).

Table 2. Calculation of the effective contribution of solar energy

Month	°C*h/month	Amount of radiation on a horizontal surface, kW*h/m2	Useful heat per unit collector area (D*0.6), kW*h/m2	Total useful heat (E*40 m2), kW*h	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 example discussed above, a solar heating system is used instead of a traditional heating system that consumes, for example, gas fuel and produces 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 calculations in Table 2 for a collector area of ​​40 m2), multiply by 1.67 rubles/kWh, which gives

8358*1.67 = 13957.86 rubles.

Auxiliary heating
One of the questions most often asked by people who want to understand the use of solar energy for heating (or other purposes) is, “What do you do when the sun doesn't shine?” Having understood the concept of energy storage, they ask the next question: “What to do when there is no more thermal energy left in the battery?” The question is natural, and the need for backup, 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 the solar heating system is not sufficient to keep the building going through a period of cold, cloudy weather, then the consequences, even just once during the winter, can be severe enough to require the provision of a conventional full-size heating system as a backup. Most solar heated buildings require a full redundant system. Currently in most areas solar energy should be considered as a means of reducing the consumption of traditional types of energy, and not as a complete substitute for them.

Conventional heaters are suitable backups, 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 unfavorable conditions. Since the combination of very cold days and long periods of cloudy weather rarely occurs, the additional size of the solar power system (collector and battery) required for these cases will be too expensive for relatively little fuel savings. Additionally, the system will operate at less than rated power most of the time.

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

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

However, bold attempts have been made to store enough solar thermal energy to cover the entire heating demand and eliminate the auxiliary heating system. With the rare exception of systems such as G. Hay's solar house, long-term heat storage is perhaps the only alternative to an auxiliary system. G. Thomason came close to 100% solar heating in his first home in Washington; only 5% of the heating load was covered by a standard liquid fuel 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 (the power plant consumes 10500...13700 kJ 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 required to heat the building may justify its use. In addition, an electric heater is a less material-intensive device due to the relatively small amount of material (compared to a heater) used for the manufacture of electric coils.

Because Efficiency of solar the collector increases significantly if it is operated at low temperatures, then the heating system should be designed to use as low temperatures as possible - even at 24...27°C. One of the benefits of Thomason's 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 expected to use lower temperatures, for example by lengthening the finned radiators with hot water, increasing the size of the radiation panels or increasing the volume of air at a lower temperature. Designers most often opt for heating the room using warm air or using enlarged radiant panels. An air heating system makes best use of low-temperature stored heat. Radiant heating panels have a long lag time (between turning on the system and heating the air space) and usually require higher operating temperatures of the coolant 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 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 overall costs by eliminating downtime of the components, many designers have chosen to integrate the solar collector and battery with the auxiliary system. Common components are the following:

Fans;
- pumps;
- heat exchangers;
- controls;
- pipes;
- air ducts.

The pictures in the System Engineering article show various schemes such systems.

A pitfall of 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 the systems is almost irresistible and may be the most common reason for the failure of a solar heating system. Typically, the auxiliary heater should not heat the solar thermal storage compartment. If this happens, the solar heat harvesting phase will be less efficient since the process will almost always occur at higher temperatures. In other systems, reducing the temperature of the battery by using heat from the building increases the overall efficiency of the system.

The reasons for other shortcomings of this scheme are explained by 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 when there is no sun for several days. Even in systems designed this way, heat loss from the container amounts to 5...20% of the total heat absorbed by the solar heating system. With a battery heated by auxiliary equipment, the heat loss will be significantly higher and can only be justified if the battery container is located inside a heated area of ​​the building