Description:
Currently, along with centralized heat supply systems, decentralized systems have become quite widespread. Decentralized autonomous systems conventionally mean small systems with an installed thermal power of no more than (20 Gcal/g) 23 MW.
Technological diagrams of district heating, heat supply and heating systems
S. A. Chistovich, Academician of RAASN, President of the Union of Power Engineers of North-West Russia
Academician S. A. Chistovich is an outstanding specialist, one of the creators of the domestic district heating and heat supply system, which has received worldwide recognition. On his anniversary, Academician S. A. Chistovich is actively engaged in scientific and teaching activities, including completing work on the monograph “Automated district heating, heat supply and heating systems”, which is expected to be published at the end of the year.
1. Centralized and decentralized systems
Currently, along with centralized heat supply systems, decentralized systems have become quite widespread.
Decentralized autonomous systems conventionally mean small systems with an installed thermal power of no more than (20 Gcal/g) 23 MW.
Increased interest in autonomous heat sources (and systems) in last years was largely determined by investment and credit policy, since the construction of a centralized heat supply system requires the investor to make significant one-time capital investments in the source, heating networks and internal systems of the building, with an indefinite payback period or on an almost irrevocable basis. With decentralization, it is possible to achieve not only a reduction in capital investments due to the absence of heating networks, but also to shift the costs to the cost of housing (i.e., to the consumer). It is this factor in Lately and has led to increased interest in decentralized heat supply systems for new housing construction projects. The organization of autonomous heat supply allows for the reconstruction of facilities in urban areas with old and dense buildings in the absence of free capacity in centralized systems. Decentralization based on highly efficient heat generators of the latest generations (including condensing boilers) with automatic control systems allows you to fully satisfy the needs of the most demanding consumer.
The listed factors in favor of decentralization of heat supply have led to the fact that it has already begun to be considered as a non-alternative technical solution, devoid of disadvantages. Therefore, it is necessary to consider in detail those problems that appear with a more careful approach to this issue, to analyze individual cases of using decentralized systems, which will allow choosing rational decision in complex.
The feasibility of using such systems in comparison with centralized systems should be assessed according to a number of indicators:
– commercial (financial) efficiency, taking into account the financial consequences of the project for its direct participants;
– economic efficiency, taking into account the costs and results associated with the project that go beyond the direct financial interests of its participants and allow for cost measurement;
– fossil fuel costs – the assessment for this natural indicator should take into account both projected changes in the cost of fuel and the development strategy of the fuel and energy complex of the region (country);
– impact of atmospheric emissions on the environment;
– energy security (for a populated area, city, region).
When choosing a source of autonomous heat supply, it is necessary to take into account a number of factors. First of all, this is the area where the heat supply facility is located to which heat must be supplied (a separate building or a group of buildings). Possible heat supply zones can be divided into four groups:
District heat supply zones from city (district) boiler houses;
Zones of centralized supply from city thermal power plants;
Autonomous heat supply zones;
Mixed heat supply zones.
The nature of the development at the location of the buildings (number of floors and building density: m 2 /ha, m 3 /ha) has a significant influence on the choice of heat supply source.
An important factor is the condition of the engineering infrastructure (the condition of the main technological equipment and heating networks, the degree of their moral and physical deterioration, etc.).
Equally important is the type of fuel used in a given city or town (gas, fuel oil, coal, wood waste, etc.).
Determining economic efficiency is mandatory when developing a project for creating autonomous systems for buildings located in the area of centralized heat supply.
The installation of autonomous sources in this case, while being financially attractive for investors (direct participants in the project), worsens the economic efficiency of the city's centralized heat supply system:
– the connected heat load to the city boiler house decreases, which leads to an increase in the cost of supplied thermal energy;
– in heating systems, in addition, the share of electricity produced in the combined cycle (based on thermal consumption) decreases, which worsens the energy efficiency of the station.
Determining the cost of organic fuel allows, through direct measurements, to objectively assess energy losses in the entire technological chain from the source to the final consumer.
The overall efficiency of fuel use in the system is calculated by multiplying the coefficients characterizing heat losses in all elements of the heat supply system connected in series. In combined production (at a thermal power plant, in a cogeneration plant), a coefficient is introduced that takes into account heat savings compared to the separate production of thermal energy in a boiler house and electrical energy in a condensing power plant.
Initial dependencies for determining the overall coefficient beneficial use fuels for various options for heat supply systems are given in table. 1.
| Table 1 Initial dependencies for determining the total efficiency factor actions of various options for heat supply systems |
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In the table: η 0 – coefficient characterizing the size of excess losses through the building envelope; η 1 – efficiency factor of thermal source fuel; η 2 – coefficient characterizing heat loss in in-house engineering systems (heating and hot water supply); η 3 – coefficient characterizing excess heat consumption due to excess heat supply and imperfection of its distribution between heated rooms; η 4 – heat loss coefficient in intra-block heating networks; η 5 – the same in city distribution and intra-block heating networks; η k – coefficient determined by the amount of fuel savings due to the combined production of fuel and electrical energy; μ e – the share of fuel savings attributed to the production of thermal energy. |
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The amount of excess heat loss through the external enclosures of the building (1 – h 0), knowledge of which is necessary when calculating the heat balance, does not depend on the type of heat supply systems and therefore may not be taken into account when comparing centralized and decentralized systems.
Modern apartment heat generators using gas fuel have an efficiency: h 1 = 0.92–0.94%.
The efficiency factor of fuel use in a city boiler house attributed to the final consumer is determined from the expression (Table 1):
h c = h 1 h 2 h 3 h 4 h 5 .
The value of this coefficient, according to numerous field tests, is no more than 50–60%. Thus, from the point of view of fuel efficiency, the use of residential heat generators running on gas is much more profitable.
The efficiency of fuel use at a thermal power plant is higher than in a city boiler house due to the combined production of thermal and electrical energy. When all savings are attributed to the production of thermal energy (h = 1.0), the overall coefficient for CHP is 0.80–0.90%.
When supplying heat from a house mini-CHP, the overall efficiency, due to the absence of losses during transportation and distribution of the coolant and all savings attributed to the production of thermal energy, can reach one hundred percent or more.
From the above it follows that gas apartment heat generators, as well as cogeneration plants that can operate on both gas and diesel fuel, have the highest fuel utilization rates. Autonomous boiler houses (roof-mounted or attached to houses) are somewhat inferior to apartment heat generators due to heat losses in intra-house communications. City boiler houses that produce only thermal energy have the lowest fuel efficiency.
A comparison of centralized and decentralized systems from the perspective of their impact on the environment in areas where people live indicates the undeniable environmental advantages of large thermal power plants and boiler houses, especially those located outside the city limits.
Emissions with flue gases (CO 2 , NOx) from small autonomous boiler houses built in places where thermal energy is consumed pollute the surrounding air, the concentration of harmful substances in which in large cities, due to the saturation of motor transport, already exceeds permissible sanitary standards.
At comparative assessment Energy security of the functioning of centralized and decentralized systems must take into account the following factors.
– Large heat sources can operate on various types fuels (including local and low-grade), can be switched to burning reserve fuel when the supply of network gas is reduced.
– Small autonomous sources (rooftop boilers, apartment heat generators) are designed to burn only one type of fuel – network natural gas, which, naturally, negatively affects the reliability of heat supply.
– Installation of apartment heat generators in multi-storey buildings, if their normal operation is disrupted, creates a direct threat to the health and life of people.
– In looped heating networks of centralized heating, the failure of one of the heat sources allows you to switch the coolant supply to another source without turning off the heating and hot water supply of buildings.
It is necessary to point out that the state strategy for the development of heat supply in Russia clearly defines the rational scope of application of centralized and decentralized systems. In cities with high building density, district heating systems from large thermal power plants, including those located outside the city limits, should be developed and modernized.
In order to increase the reliability of the operation of these systems, it is advisable to supplement them with sources of distributed generation of thermal and electrical energy operating on common city networks.
In cities or certain areas of cities with low heat density, it is advisable to use decentralized heat supply systems with the preferred use of cogeneration units. The use of autonomous heat supply systems is the only possible solution in geographically remote and hard-to-reach areas.
2. Cogeneration and trigeneration plants (micro- and mini-CHP)
Small CHP plants include thermal power plants with a single electrical power from 0.1 to 15 MW and thermal power up to 20 Gcal/h. Small thermal power plants can be supplied complete, including in a container version, or created by reconstructing steam or hot water boiler houses with retrofitting them with electric generating units.
To drive electric generators of small thermal power plants, diesel, gas piston, dual-fuel piston internal combustion engines, gas turbines, steam turbines with back pressure or condensation type with intermediate steam extraction and the use of water heated in the condenser for process needs, rotary or screw steam engines are used.
Exhaust gas recovery boilers and chilled water heat exchangers operating in basic mode or only to cover peak loads are used as heat generators.
Trigeneration plants In addition to the combined generation of electrical and thermal energy, they produce cold.
Vapor compression or absorption refrigeration machines can be used to produce cold. During the heating season, refrigeration machines can switch to heat pump mode. The compressor drive of vapor compression machines is carried out from electric generators of small thermal power plants. Absorption trigeneration plants operate on thermal energy utilized by these stations (exhaust gases, hot water, steam).
Cogeneration and trigeneration plants can be created using exhausted engines of vehicles (airplanes, ships, cars).
The units can operate on various types of fuel: natural gas, diesel fuel, gasoline, propane-butane, etc. Wood waste, peat and other local resources can also be used as source fuel.
The main advantages of small thermal power plants:
1. Low losses during transportation of thermal energy compared to centralized heat supply systems.
2. Autonomy of operation (independence from the energy system) and the possibility of selling excess generated electricity to the energy system and covering the deficit of thermal energy when a small thermal power plant is located in a district heating supply zone.
3. Increasing the reliability of heat supply:
– interruptions in the supply of electrical energy to the boiler room do not lead to the cessation of operation of the heat source;
– when a small thermal power plant is located in a centralized heat supply zone, the minimum permissible heat supply to buildings is ensured in the event of accidents on heating networks.
4. Possibility of heat and power supply to autonomous (not connected to a single electrical system) objects: remote, hard-to-reach, dispersed over a large area, etc.
5. Providing emergency heat and electricity supply with mobile power plants.
Features of small thermal power plants of different types.
The advantage of diesel units, as well as gas engines with spark ignition, is the high coefficient useful action for the generation of electricity, practically independent of the unit power of the engine. Also, the installations are insensitive to changes in thermal load. For this reason, they are widely used in land and water transport, where the load can vary from idling to using maximum power.
The possibilities of heat recovery in such installations decrease with a decrease in the heat load, since the temperature of the exhaust gases also decreases somewhat. If at full load the exhaust gas temperature is 400–480 °C, then at an engine load of 50% of the rated power it drops to 175–200 °C. This necessitates the installation of a peak boiler or equipping the exhaust gas heat recovery boiler with a fire furnace. To ensure reliable engine operation, the temperature in the primary circuit of the water cooling system is maintained at 90–95 °C.
The ratio of electricity generation to heat generation in the cogeneration plants under consideration is usually in the range of 1:1.2.
The advantage of dual-fuel piston units compared to diesel and gas engines is the ability to switch to diesel fuel in the absence of natural gas.
Compared to reciprocating (diesel and gas-engine CHPPs), gas turbine CHPPs, made according to the classical scheme (gas turbine - boiler - waste heat exchanger), have a significantly smaller specific gravity and dimensions (kg / kW and m 3 / kW). That is why gas turbine units replaced piston engines in aviation, and this made it possible to raise aircraft manufacturing to a qualitatively new level. At the same time, their efficiency in generating electricity decreases noticeably with decreasing load. Thus, when the load is reduced to 50%, the electrical efficiency of a gas turbine is reduced by almost half.
The highest efficiency value (at rated load) is about 40% for gas turbines and gas piston engines. The share of electrical load in relation to thermal load in gas turbine CHP plants of complete delivery is 1: (2–3).
When installing gas turbines pre-connected to existing water-heating boilers, i.e. with exhaust gases discharged into the boiler furnace, the share of electrical load and heat load usually does not exceed 1:7. An increase in electricity generation based on thermal consumption can only be achieved under the condition of a serious reconstruction of boiler units.
Equipping steam heating and industrial boiler houses with steam turbine units makes it possible to usefully use the difference in steam pressure in the boiler and required in front of the heat exchangers to generate electricity, both to cover the entire need for one’s own needs, and for transfer to the outside.
Steam turbines for small thermal power plants, depending on the nature of the connected heat load, are produced in two types: with back pressure and condensing turbines with intermediate steam extraction. Steam from the intermediate extraction with a pressure of 0.5–0.7 MPa is used for process needs and for heating network water in the heat supply system. Water heated in the condenser can also be used for technological needs and, in addition, in low-potential water heating systems.
In addition to turbines, steam heating and industrial boiler houses can be equipped with other types of power units: steam rotary or auger screw machines.
The advantages of these machines compared to steam turbines are low sensitivity to steam quality, simplicity and reliability in operation. Disadvantage: lower efficiency.
3. Technological diagrams of centralized heating systems and their characteristics as control objects
The centralized heating system (DHS), as is known, is a complex of various structures, installations and devices, technologically interconnected by the common process of production, transport, distribution and consumption of thermal energy.
In general, the SCT consists of the following parts:
Source or sources for the generation of thermal energy (CHP, ATPP, boiler houses, small cogeneration or trigeneration plants);
Transit lines and main heating networks with pumping (less often throttling) and shut-off substations for transporting thermal energy from generating facilities to large residential areas, administrative and public centers, industrial complexes, etc.;
Distribution heat networks with district heating points (RTP), central heating points (CHP) for distribution and supply of heat to consumers;
Heat consuming systems with individual heating points (IHP) and in-house engineering systems (heating, hot water supply, ventilation, air conditioning), heat distribution installations of industrial enterprises to meet the needs of consumers for supplied energy.
The operation mode of the central heating system is dictated by the operating conditions of heat consuming objects: variable heat losses to the environment of buildings and structures, modes of hot water consumption by the population, operating conditions of technological equipment, etc.
The system consists of a large number of interdependent elements connected in series and in parallel, having various static and dynamic characteristics: installations for energy generation (boilers, turbines, etc.), external heating networks and intra-house communications, equipment of heating points, indoor heating devices, etc.
It must be borne in mind that, unlike other water supply systems (water supply, gas supply and heat supply), the operating mode of heating networks is characterized by two parameters that are different in nature. The amount of thermal energy released is determined by the temperature of the coolant and the pressure drop, and therefore the water flow in the heating network. At the same time, the dynamic characteristics of the paths: the pressure transmission path (flow changes) and the temperature transmission path are sharply different from each other.
In addition to the internal relationships between the elements of the central heating system, there are external functional connections with other engineering systems of cities and industrial complexes: fuel supply systems, electricity supply and water supply.
Analysis of the existing technological structure for constructing centralized heat supply systems, heating network diagrams, circuit diagrams subscriber inputs and subscriber heating systems, designs of the technological equipment used show that they do not fully meet modern requirements for automated control objects.
In large heat supply systems, numerous subscriber installations are connected to the main heating networks, as a rule, without intermediate control units. As a result, the system turns out to be insufficiently maneuverable, remains inflexible, and an excessive amount of water has to be passed through the networks, focusing on subscribers with the worst conditions.
Urban heating networks were designed for cost-saving reasons and, as a rule, were dead-end. There were no backup connections between sections of heating networks, allowing for the organization of heat supply to some consumers in the event of damage (out of service) of a section. In a number of cases, the possibility of operating heat networks from several sources combining common heat networks was not provided for.
The disadvantage of the applied method of distributing thermal energy across numerous heating points is especially evident during periods of sharp cold weather, when consumers do not receive it required quantity due to the fact that the temperature of the water supplied from the heat source is significantly lower than that required according to the control schedule.
The basements of residential buildings allocated for the placement of heating points are of little use for the installation and normal operating conditions of local automatic control systems.
For individual automatic control of heat transfer from heating devices, vertical single-pipe water heating systems, most common in mass residential construction, are not optimal. Due to the high residual heat transfer of heating devices (when the regulator is closed), the significant mutual influence of devices during the operation of regulators and other factors, the possibilities for effective individual regulation in these systems are very low.
Finally, it should be noted that typical technological schemes district water heating boiler houses do not meet the requirements complex automation heat supply systems. These schemes are focused on a high-quality schedule for the supply of thermal energy, i.e., maintaining a constant water flow in the supply pipeline (or a constant pressure on the boiler room collectors).
In automated heat supply systems with local automatic regulation among consumers, as well as in conditions collaboration several sources to common heating networks, the hydraulic mode in the network at the exit from the boiler room should be variable.
From the above it follows that all heat supply links (source, heating networks, heating points, subscriber heating systems) were designed without taking into account the requirements for automating their operating modes. Therefore, the creation of automated heat supply control systems must be accompanied by the modernization of these systems along the entire technological chain: production – transportation – distribution and consumption of thermal energy.
Approximate technological control schemes in heating and centralized heating systems of cities are given in Table. 2.
| table 2 Technological control schemes in heating systems and district heating |
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4. Ways to improve the control of technological modes of heat supply systems with distributed generation of thermal and electrical energy
Significant physical deterioration pipelines and equipment, the outdated structure of constructing centralized heat supply systems put forward, along with the task of quickly replacing worn-out equipment, the urgent task of optimizing circuit-technical solutions and operating modes of these systems.
Considering the extremely neglected state of heat supply systems in Russia, their complete modernization in order to ensure the ability to operate in the design mode with a coolant temperature of 150 °C (with the upper cut-off of the graph at 130 °C) over the next 20–30 years is practically impossible in most cities. It will require the relocation of hundreds of thousands of kilometers of heating networks, the replacement of worn-out equipment at tens of thousands of heat sources and at hundreds of thousands of subscriber heat-consuming installations.
Based on the analysis of the state of heat supply in various regions of the country, proposals for optimizing schemes, technical solutions and operating modes of centralized heat supply systems are as follows:
Orientation of centralized heat supply systems to cover the base heat load with a maximum coolant temperature at the exit from the CHP (city boiler house) of 100–110 °C;
Application of energy-saving technologies, circuit solutions, materials and equipment during the reconstruction of heat supply systems;
Construction of local peak heat sources, as close as possible to heat consumption systems;
Conversion of district city boiler houses (in some cases, block ones) into mini- and micro-CHPs;
Application of binary (steam-gas) thermodynamic cycles to improve the efficiency of urban thermal power plants;
Creation of automatic control systems for heat supply, including automation of processes of production, transportation, distribution and consumption of thermal energy.
When heat supply systems are oriented to cover the base heat load, capital costs for the reconstruction of heating networks are significantly reduced (due to a smaller number of compensators, the possibility of using cheaper and non-corrosion pipes made of polymer materials, etc.). With the allocated funds, it is possible to reconstruct a significantly larger volume of heating networks, increasing their reliability and reducing losses during coolant transportation.
The use of energy-saving technologies, materials and equipment makes it possible to reduce specific heat consumption by 40–50%, namely:
– insulation of building envelopes;
– transition from vertical single-pipe heating systems to horizontal ones with apartment-by-apartment heat metering;
– installation of apartment water meters in cold and hot water supply systems, installation of automated heating points, etc.
Thus, the impact of heat loss from the external network during the coldest period of the heating season will be compensated.
Energy saving allows you to save not only a significant amount of fuel and energy resources, but also to provide conditions for thermal comfort with a “basic” heat supply from the heating network.
The construction of peak (local) heat sources that are as close as possible to heat consumption systems will make it possible, at low outside air temperatures, to increase the temperature of the coolant coming from the heating network to the parameters required for heated premises.
Retrofitting a district heating system with a peak source dramatically increases the reliability of its operation. In the event of an accident in the external network, the peak source is transferred to an autonomous mode of operation in order to prevent freezing of the heating system and continue the operation of a heat consuming facility located in an area disconnected from the heating network. During preventive shutdowns of heat supply in summer time buildings connected to the peak source will also be supplied with heat.
The construction of peak sources will essentially mean a transition from the centralized heat supply system that has existed for many decades in our country to a “centralized-local” one, which has higher reliability and a number of other advantages.
In contrast to autonomous and individual heat supply sources (installed in densely built-up areas of northern cities), operating year-round and harmful to the environment (even when running on gas), the total emissions into the atmosphere from peak sources, which produce only 5–10 % of the total annual heat supply will be negligible.
At modern level In gas heating equipment, centralizing the production of one's own thermal energy, as a rule, does not make economic sense. The efficiency of modern gas heat generators is high (92–94%) and practically does not depend on their unit power. At the same time, an increase in the level of centralization leads to an increase in heat losses during coolant transportation. Therefore, large district boiler houses turn out to be uncompetitive compared to autonomous sources.
A sharp increase in the efficiency of district boiler houses can be achieved by reconstructing them into mini-CHPs, in other words, by retrofitting them with electricity generating units and switching the operation of boiler houses to cogeneration mode.
It is known that the operating efficiency of cogeneration plants is higher, the greater the number of hours per year that electricity is generated on the basis of thermal consumption. The year-round heat load in cities (excluding the technological load of industrial enterprises) is hot water supply. In this regard, calculating the power of a cogeneration plant (in district heating systems from boiler houses) to cover the hot water supply load ensures its year-round operation and, therefore, the most efficient use. On the other hand, specific capital costs for the creation of electricity generating installations decrease with an increase in their unit capacity.
Therefore, for the reconstruction of boiler houses in mini-CHPs, it is first of all advisable to choose the largest of them with a developed hot water supply load.
A significant increase in the operating efficiency of urban thermal power plants can be achieved by installing a gas turbine in front of the steam turbine part of the station. Transferring the operation of a steam turbine thermal power plant to a steam-gas (binary) cycle increases the efficiency of electricity generation from 35–40 to 50–52%.
Sustainable and effective work Centralized heat supply systems from city thermal power plants and district boiler houses, converted into mini-CHPs, with peak heat sources operating in automatic mode and automated heating points, are impossible without an automated heat supply control system. Therefore, the creation of an automated control system is a prerequisite for the reconstruction of the heat supply system.
The main purpose of ventilation - maintaining acceptable conditions in the room - is achieved organization of air exchange. Air exchange is usually understood as removing polluted air and supplying clean air into the room.Air exchange is created by the operation of supply and exhaust systems. Traditionally, preference is given to the simplest ventilation methods that provide the specified conditions. When designing ventilation systems, they strive to reduce their productivity by reducing the flow of excess heat and other harmful emissions into the air of the room. An imperfect technological process may result in the inability to provide the required air parameters in the work area using ventilation means.
Ventilation system called a set of devices for processing, transporting, supplying or removing air.
By purpose ventilation systems are divided into supply and exhaust. Cable systems supplies air to the room. Systems that remove air from a room are commonly called exhaust. By their combined action, the inflow and exhaust systems organize supply and exhaust ventilation of the room.
In technical literature you can often find the concept ventilation unit. This term is applied to ventilation systems that use a fan as a draft stimulator. A ventilation unit is a part of a ventilation system that does not include a network of air ducts and channels through which air is transported, as well as devices for supplying (air distributors) and removing air (exhaust grilles, local suction units). Supply ventilation unit consists of an air intake device, an insulated valve, a filter for cleaning air from dust, an air heater and a ventilation unit consisting of a fan and an electric motor. Some air handling units may not have a filter. Exhaust ventilation unit includes devices for cleaning ventilation emissions from polluting substances and a ventilation unit. If purification of the air removed into the atmosphere is not required, which is typical for civil buildings and some industrial premises, there is no purification device and the ventilation unit consists of a ventilation unit. Recently they began to use supply and exhaust ventilation units, combining supply and exhaust units in one unit. This became possible due to the development and industrial production panel-frame supply and exhaust units, the design of which provides for the possibility of such a combination. The main reason for using supply and exhaust units is the need to utilize the heat of the exhaust air. The supply and exhaust unit often uses a common surface heat exchanger, transferring the heat of the exhaust air to the cold supply air. In addition, supply and exhaust units require less space for placement than separate supply and exhaust units.
If the entire volume of the room or its work zone in the presence of dispersed sources of harmful emissions. Ventilation is called general exchange supply and exhaust ventilation. Removing air directly from equipment that produces harmful emissions or supplying air directly to workplaces or to a certain part of the room is called local ventilation. Local exhaust ventilation is more effective than general exhaust ventilation, since it removes harmful emissions with a higher concentration compared to general exhaust ventilation, but is more expensive, since it requires more air ducts and equipment local suctions.
According to the method of organizing room ventilation differentiate centralized And decentralized ventilation systems. In centralized ventilation systems, supply and exhaust ventilation units serve a group of rooms or the building as a whole. In case of room ventilation large area A decentralized ventilation scheme with several supply and exhaust units may be preferable. This method of organizing ventilation allows you to do without an extensive network of air ducts. A typical ventilation unit for this type of ventilation is Hoval, Operating Modes LHW.
By the method of stimulating air movement systems are divided into mechanically driven systems(using fans, ejectors, etc.) and systems with gravitational pull(action of gravity, wind).
Air can be supplied (or removed) to ventilated rooms through an extensive network of air ducts (such systems are called duct) or through openings in fences (this ventilation is called ductless).
In the premises of civil or industrial buildings it is arranged supply and exhaust ventilation.
Mechanically driven duct systems are the most widely used. A supply ventilation system with mechanical drive can be made with recycling. Recirculation is the mixing of exhaust air with supply air. Recirculation can be complete or partial. Partial recirculation is used in conventional ventilation systems in work time, since the room requires an influx of outside air. The minimum amount of outside air should not be less than the sanitary norm. The use of recirculation allows you to save heat consumption in winter.
The following systems can be installed in civil and industrial buildings.
Supply and exhaust ventilation is direct-flow. It is used primarily in industrial premises where the use of recycling is prohibited. The reason for the ban may be the release of toxic vapors and gases, pathogenic bacteria, etc. into the indoor air. Heat consumption for heating supply air maximum
Supply and exhaust ventilation with partial recirculation. It is used for ventilation of civil and industrial premises with excess heat without the release of toxic vapors and gases, pungent odors, etc. into the air.
Supply and exhaust system with full recirculation. Used when the ventilation system operates in air heating after hours. It is a special type of ventilation used in spaceships, space stations, submarines, etc.
Emergency ventilation systems For one-story buildings often consist of a supply chamber that supplies the room with a sudden intake large quantity toxic or explosive substances unheated outside air. Contaminated air is removed through a special opening in the enclosure or an exhaust shaft.
Supply ductless ventilation system with mechanical drive carried out by installing a fan, usually axial, in the supply opening. It is used for ventilation of production and auxiliary premises with a small number of workers and in the absence of permanent workplaces. Ventilation can be carried out periodically both in warm and cold periods of the year. Sometimes used as additional ventilation to main operating systems. Air is removed through an open opening.
Supply and exhaust general exchange ductless ventilation with natural impulse in relation to industrial buildings received the name aeration. Aeration is carried out through special aeration supply and exhaust openings with control devices that allow you to change the amount of air exchange or completely stop it. Widely used to remove excess heat from industrial premises.
Supply local duct ventilation used in industrial premises. Serves to supply air supply through a network of air ducts to workplaces that are constantly polluted or exposed to thermal radiation. Better known as air showering outside air. The supply air is pre-treated (heated or cooled adiabatically, or using artificial refrigeration)
Supply local ductless ventilation with mechanical drive is a type of air showering of workplaces with internal room air. Produced by a special ventilation unit called aerator, a stream of air from which is directed towards workplace. Stuffing with internal air can be used if the air in the room is not significantly polluted.
Supply local ductless ventilation with natural impulse It is rarely used on its own. It is carried out by installing an additional aeration opening near a permanent workplace, the air flow from which enters directly into the workplace. Used in combination with aeration.
Exhaust general-exchange ductless with mechanical drive, usually carried out roof fans installed in holes in the roof. The influx enters through open windows or special aeration openings in the walls.
Exhaust general-exchange duct with natural impulse typical for residential and civil buildings. The influx into the premises enters through the window ledges and other leaks in the enclosing structures. In the technical literature this ventilation system is called: supply and exhaust ventilation system with gravitational force and unorganized inflow.
Local duct exhaust with mechanical drive is used in industrial buildings to remove harmful substances from places of their release through special shelters - local suctions. Before being released into the atmosphere, the removed air is usually cleaned of harmful impurities.
A direct-flow supply and exhaust system with a general exchange inflow and local exhaust is used in industrial premises without the release of harmful vapors and gases into the air (for example, woodworking shops).
Local duct exhaust with natural induction is also used in industrial buildings to remove heated polluted air from process furnaces, equipment, etc.
Mixed ventilation system. Local supply and exhaust systems are rarely used independently. They are often components mixed ventilation system, in which air showering, local gravitational exhaust, and local mechanical exhaust can take place. A mandatory component is also general mechanical or natural air exchange. Mixed system ventilation is used for two reasons:
1) the effectiveness of local suction is not absolute; some part of the harmful emissions from hidden sources enters the air of the room;
2) it is economically infeasible, and technically it is often simply impossible to install local exhaust from all sources of harmful emissions, so harmful emissions enter the room air from sources unprotected by local suction.
The task of general air exchange during mixed ventilation is to remove harmful emissions entering the volume of the room from unprotected and, partly, from sources protected by local suction.
The presence of the above various design solutions for ventilation allows you to choose the most suitable for each case. best option.
Split ventilation systems. These systems remove excess heat using a refrigeration machine, consisting of two units: external and internal. The following are mounted on the outside: a refrigeration machine, a condenser and an air cooling fan. In the internal one there is an evaporator and a fan that circulates air through the evaporator. The supply of sanitary air standards is ensured either by installing a special supply and exhaust ventilation system, or by using partial recirculation.
European requirements for energy efficiency of buildings require modern thermal insulation glazing and sealing outer shell, the question inevitably arises about forced ventilation premises.
The central unit of a domestic ventilation unit can be mounted under the roof, such as this model RecoVair.
In the future, controlled home ventilation may become a decisive factor in creating a comfortable microclimate in new buildings and energy-modernized buildings.
Global climate change and skyrocketing prices for fossil energy resources are tightening the requirements for reducing losses through the ventilation system of buildings.
Therefore, home owners strive to increase the thermal protection of windows and update doors. As a result, buildings become more airtight. In an effort to avoid wasteful use of thermal energy, residents ventilate their premises less frequently. High humidity leads to the appearance of mold, which in turn leads to damage building structures.
And this is a sustainable trend generated by reducing heating costs. Today, even in prosperous Germany, 22% of houses and 7 million apartments are affected by mold, while the burden of eliminating the consequences falls on the shoulders of homeowners or renters.
Optimal air exchange
According to European building regulations, when planning ventilation and technical measures, the degree of tightness of buildings is taken into account, in determining which a special calculation system is used. A specific hermetic shell requires an appropriate air exchange regime necessary to protect building structures.
Today, this requirement is implemented through a number of measures, including automatic opening of windows. However, the most practical solution is to use controlled forced ventilation with heat recovery, the installation of which takes into account the interaction of heating and ventilation equipment.
Noticeable savings on heating
In the near future, heating equipment will be oriented towards specific energy consumption values specified in the building's energy passport.
Today, when calculating the heating load and determining heat loss, the role of controlled ventilation is often not taken into account, which can lead to insufficient investment in heating equipment.
For example, when equipping a home with a heat pump, this may mean using a smaller generator, as well as reducing the heat-transfer surface of the collector or probe.
Controlled ventilation contributes not only to energy saving and compliance with sanitary and hygienic standards, but also to maintaining the integrity of building structures. Under the new European energy saving regulations, such installations could become part of standard equipment in both new and retrofitted buildings in the future.
Possible options for a controlled ventilation system may have different designs.
1. Centralized supply and exhaust ventilation
Centralized ventilation is provided by a highly efficient direct-flow fan with adjustable air flow. In this case, exhaust air is removed, and fresh air enters the building.
Central control ensures highly efficient heat recovery: the heat from the exhaust air passes through the heat exchanger and is transferred to the supply air. The better the thermal insulation of the building, the faster such an installation pays off.
Reusing up to 95% of thermal energy provides highly efficient energy savings. In this case, the heat exchanger must be equipped with a function to prevent the formation of condensation and freezing. Central ventilation systems are equipped with filters that trap dust.
2. Decentralized air handling unit
Such systems provide air exchange in one or two rooms. Being a cheaper alternative to centralized systems, this solution creates a number of problems, for example, the need for individual control in the bathroom or bedroom.
Typically, soundproofed heat recovery units are installed near windows and in combination with heating devices supply air is heated. Air filtration capabilities vary depending on the features of the specific model.
3. Centralized exhaust unit
The centralized version uses an exhaust fan with a grille or poppet valve. It removes used air from the kitchen and bathroom, causing a slight decrease in pressure, which leads to the entry of fresh air through passively operating anemostats in the external walls.
In this system, the heat recovery function is advisable through the use of heat pump or regulation of the volume of exhaust air, which ensures optimal mode air exchange and energy saving. Installation work in this case is limited to organizing a channel for air removal, while the inflow is carried out without special pipelines.
4. Decentralized exhaust unit
A soundproof exhaust fan is mounted on the outside wall of the kitchen or bathroom and allows exhaust air to escape to the outside. Thanks to a slight decrease in pressure, fresh air enters the anemostats in the external walls. The installation costs are lower compared to centralized systems, but there is no heat recovery.
Controlled ventilation with heat recovery provides 20 percent savings in thermal energy directed to or any other building.
Option for a separate room.
Through a hole in the external wall, an energy-saving direct-flow fan EcoVent pumps in atmospheric air. Highly efficient and large-sized aluminum plate heat exchanger provides reuse over 70% thermal energy.
Creating ventilation systems during the reconstruction of existing buildings is not an easy task, especially when it comes to architectural monuments of the early 20th century. As a rule, traditional schemes and solutions are not suitable here: the architecture, layout and state of internal communications of the building impose many restrictions. In such situations, modern developments in the field of decentralized, highly efficient ventilation systems come to the aid of designers.
The five-story building of the Ministry of Health of the Russian Federation located in the center of Moscow with total area 21,000 m2 is an architectural monument. During its construction, no ventilation system was provided. However, a modern administrative building in the center of a metropolis cannot function normally without such a system.
In 2009, a decision was made to reconstruct the building. The customer's requirements were formulated. The main requirements for ventilation system steel: installation of equipment in the shortest possible time and minimal consumption of heat and electricity by the system at the site.
During the inspection of the building, it was found that due to the peculiarities of the layout, it was impossible to lay vertical ventilation shafts. In addition, there is no space to accommodate the main equipment of central ventilation systems. Finally, the insufficiency of the existing energy limits and the impossibility of supplying additional sources of electricity and heat were revealed. Such severe restrictions immediately made many traditional solutions unsuitable.
As one of the options, a scheme was considered in which air, under the influence of exhaust fans installed in the corridors, would flow through transfer grilles window frames. As a result, this scheme had to be abandoned, since the air entering the premises did not meet the requirements for cleanliness and temperature.
However, the vector the right decision was obvious - we need to look for decentralized ventilation systems, but more integrated than ductless systems used in large warehouse spaces.
Mini air supply and exhaust units with metal plate heat exchangers fit quite well into the accepted concept. But after carefully studying the principle of their operation, I had to abandon their use. The fact is that at an air temperature below about -8 °C, the control system of such installations opens a bypass channel and cold air, bypassing the recuperator, enters directly into the room, which was not suitable for this facility. Some installations of this type, as an alternative to the bypass channel, are equipped with an electric heater to preheat the air in front of the recuperator, however, in conditions of energy shortages, such a solution was unacceptable.
After a detailed study of the latest developments in the field of ventilation technology, it was decided to use systems with membrane plate heat exchangers. On the Russian market, similar equipment is represented by air handling units from several manufacturers: Mitsubishi Electric (Lossnay) and Electrolux (STAR). Lossnay installations were installed at this site.
The plates of recuperators of such systems are made of a special porous material with selective throughput. An important advantage of a membrane recuperator is the ability to transfer not only heat, but also moisture from the exhaust air to the supply air.
The efficiency of such a recuperator reaches 90%, and even at low outside air temperatures, the supply and exhaust unit can supply air with a temperature of 13–14 °C into the room without additional heating, which, in case of excess heat generation in the offices, also allows air conditioning of the rooms in the winter.
The absence of condensation due to moisture transfer allows installations to be placed in any position without problems, while traditional plate heat exchangers require the organization of a drainage system, which significantly narrows the scope of their application.
The design solution using installations with a membrane recuperator provided for the placement of supply and exhaust manifolds on a floor-by-floor basis in corridors with exits at the ends of the building. The installations themselves, due to their low height, were mounted directly in the offices behind suspended ceiling. Since the noise level of such equipment is extremely low, there was no need for additional noise insulation measures. This, as well as the absence of the need to organize a condensate drainage system, made it possible to significantly reduce installation time.
The automation of such systems allows you to program their operation for a week with night and day modes. This function can be useful when using units for ventilation of office premises. In this case, programming the installations to turn off at night allows you to further save energy. For installations serving conference rooms, a scheduled on and off program can be prescribed. In addition, the built-in automation has the functions of protecting the heat exchanger from freezing (when the supply air temperature drops significantly, usually below –20 °C), selecting the fan speed and monitoring filter contamination based on operating time.
Already at the design stage it became clear that the chosen solution was the best for the given object and had many advantages. Only one drawback was identified: a significant number of ventilation units, and there are more than 150 of them according to the project, can cause certain difficulties with their maintenance, which in this case comes down to replacing filters and cleaning recuperators. The frequency with which these procedures must be performed depends on the cleanliness of the air entering the installation. It was decided to pre-clean the outside air with additional filters installed in the floor-by-floor supply manifolds, which made it possible to double the service life of the standard supply filters and the service interval of the recuperators.
Thanks to the minimal number of air ducts and the ease of installation of the units themselves, the installation work was completed even faster than planned.
At the moment, the systems operate without emergency modes and operate stably at low temperatures of the real winter that occurred this year, which confirms the correctness of the chosen design solution.
In conclusion, it should be noted that the described approach can be applied not only in regions with a temperate climate, but also in more severe climatic conditions. However, in this case it is no longer possible to do without installing external electric heaters.
The article was prepared by the company's technical department