Two-stage hot water supply scheme principle of operation. Centralized hot water systems

There are three main schemes for connecting heat exchangers: parallel, mixed, serial. The decision to apply this or that scheme is made by the design organization on the basis of the requirements of SNiP and the supplier of heat coming from their energy capacities. In the diagrams, the arrows show the passage of heating and heated water. In the operating mode, the valves located in the jumpers of the heat exchangers must be closed.

1. Parallel circuit

2. Mixed scheme

3. Sequential (universal) circuit

When the DHW load significantly exceeds the heating load, hot water heaters are installed on heating point according to the so-called single-stage parallel scheme, in which the hot water heater is connected to the heating network in parallel with the heating system. The constancy of the temperature of tap water in the hot water supply system at the level of 55-60 ºС is maintained by the RPD direct-acting temperature controller, which affects the flow of heating network water through the heater. When connected in parallel, the consumption of network water is equal to the sum of its costs for heating and hot water supply.

In a mixed two-stage scheme, the first stage of the DHW heater is connected in series with the heating system on the heating water return line, and the second stage is connected to the heating network in parallel with the heating system. At the same time, tap water is preheated by cooling the network water after the heating system, which reduces the heat load of the second stage and reduces the total consumption of network water for hot water supply.

In a two-stage sequential (universal) scheme, both stages of the DHW heater are connected in series with the heating system: the first stage - after the heating system, the second - before the heating system. The flow regulator, installed in parallel with the second stage of the heater, maintains a constant total flow of network water to the subscriber input, regardless of the flow of network water to the second stage of the heater. At hours maximum loads DHW all or most of the network water passes through the second stage of the heater, cools in it and enters the heating system with a temperature below the required one. In this case, the heating system receives less heat. This undersupply of heat to the heating system is compensated during hours of low hot water supply loads, when the temperature of the network water entering the heating system is higher than required at this outdoor temperature. In a two-stage sequential scheme, the total consumption of network water is less than in mixed scheme, due to the fact that it uses not only the heat of network water after the heating system, but also the heat storage capacity of buildings. Reducing network water costs helps to reduce unit cost external heating networks.

The scheme for connecting hot water heaters in closed heat supply systems is selected depending on the ratio of the maximum heat flow to hot water supply Qh max and the maximum heat flow to heating Qo max:

Main water heating schemes for DHW systems buildings

Circuit classification

For water folding devices of public, various industrial and residential buildings, the following water temperature (hot) is provided:

• Not more than 70°С - too hot water will result in burns.
• Not less than 50°C for DHW systems that are connected to closed heat supply systems. At low temperatures, animal and vegetable fats do not dissolve in water.

Network water, which circulates in pipelines, in closed systems heat supply is used only as a heat carrier (not taken for consumers from the heating network).

Network water is carried out in heat exchangers(in closed systems) heating of tap cold water. As a result, heated water is supplied through the internal water supply to the water-folding devices of industrial, various residential and public buildings.

Network water, which circulates in pipelines, is used in open systems not only as a heat carrier. Water is completely or partially taken from the heating network by the consumer.

Consider only the DHW systems of different buildings that are connected to closed heat supply systems. The main schemes of such systems are shown below.

Schematic diagram of a DHW system with a parallel one-stage connection of hot water heaters.

Now the most common and simple is the scheme with a parallel single-stage connection of hot water heaters. At least two heaters are connected in parallel to the same heating network as existing systems building heating. From the external water supply network, water is supplied to the hot water heaters. As a result, it will heat up in them. network water which comes from the supply pipeline.

Network chilled water is fed into the return pipeline. After the heaters, the tap water heated to a certain temperature is sent to the water fittings of various buildings.

In the event that the water folding devices are closed, then a certain part of the hot water will again be supplied to the hot water heaters through the circulation pipeline.

The main disadvantage of such a scheme is high flow water (network) for the DHW system and, therefore, in the entire existing heating system.

Experts recommend using such a scheme with a parallel single-stage connection of DHW heaters if the ratio of the maximum heat consumption for DHW of different buildings to maximum flow the heat required for heating is less than 0.2 or more than 1. As a result, the scheme is used with a normal temperature curve of water (mains) in heating networks.

Schematic diagram of a hot water supply system with two-stage serial connection of DHW heaters

In this scheme, DHW heaters are divided into two stages. The first ones are installed on the return pipeline of the heating network after the heating systems. These include DHW heaters of the lower (first) stage.

The rest are installed on the supply pipeline in front of the ventilation and heating systems of buildings. These include DHW heaters of the upper (second) stage.

From the external water supply network, water with t t-1 will be supplied to the DHW heaters of the lower stage. In them, it will be heated by water (network) after the ventilation and heating systems of buildings. Network chilled water will enter the network return pipeline and will be directed to the heat supply source.

The subsequent heating of water is carried out in the DHW heaters of the upper stage. Network water acts as a heating medium - it is supplied from the supply pipeline. Network chilled water will be directed to the ventilation and heating systems of buildings. Hot water flows through the internal plumbing to the installed water fittings. In such a scheme, with closed water intake devices, part of the heated water is supplied to the DHW heaters of the upper stage through the circulation pipeline.

The advantage of such a scheme is the absence of the need for a special water flow (network) for the DHW system, because tap water is heated thanks to network water from ventilation and heating systems. The disadvantage of the scheme with a serial two-stage connection of DHW heaters is the mandatory installation of an automation system and local additional regulation of all types of heat loads (heating, ventilation, hot water supply).

The scheme is recommended to be used if the ratio of the maximum heat consumption for hot water supply to the maximum heat consumption required for heating buildings will be in the range from 0.2 to 1. The scheme requires a certain increase in the water temperature curve (network) in thermal networks.

Schematic diagram of a DHW system with a mixed two-stage connection of DHW heaters

A scheme with a mixed two-stage connection of DHW heaters is considered more universal. This scheme in thermal networks is used at an increased and normal temperature curve of water (network). It is used for any ratio of the maximum heat consumption for DHW to the maximum heat consumption required for quality heating buildings.

A distinctive feature of the scheme from the previous one is that the DHW heaters of the upper stage are connected to the supply pipeline of the network in parallel (not in series) to the heating system.

Tap water is heated by heating water from the supply pipe. Network chilled water is fed into the return pipeline of the network. As a result, it is mixed there with water (network) from ventilation and heating systems and enters the DHW heaters of the lower stage.

Compared to the previous scheme, the disadvantage is the need for additional water consumption (mains) for the upper stage DHW heaters. As a result, water consumption in the entire heating system increases.

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Types and advantages of DHW flow circuits
DHW using a flow circuit and plate heat exchangers is the most efficient and hygienic way to prepare hot water. Compared to battery circuits, it has significant advantages.

For flowing hot water, a parallel single-stage scheme, sequential and mixed two-stage schemes are used.

Parallel one-stage circuit with one heat exchanger connected to the supply pipeline of the heating network in parallel with the heating system ( rice. one) is simple and inexpensive.

The two-stage DHW scheme is used to reduce the water temperature in the return pipeline and the total water flow from the heating network. To do this, the heat exchange surface of the DHW heat exchanger is divided into two sections, called steps. Cold in the first stage tap water heated by water leaving the heating system. Then, the water heated in the first stage of the heat exchanger is heated together with the recirculation water to the required temperature (55-60 °C) by heating water from the supply pipeline of the heating network.

With a sequential DHW scheme, the second stage is connected before the heating system to the supply pipeline ( rice. 2). First, hot network water passes through the second stage of the DHW, then enters the heating system. Thus, it may turn out that the temperature of the heat carrier will not be sufficient to cover the heat losses of the building. Then, during the withdrawal of a large amount of hot water during peak hours, the building connected to the IHS may not heat up enough. Due to the storage capacity of the building structure, this does not affect the comfort in the rooms if the period of insufficient heat supply does not exceed about 20 minutes. For the summer non-heating period, there is a switchable bypass, through which the network water after the second stage enters the first stage of the DHW, bypassing the heating system.

The mixed two-stage DHW scheme is distinguished by the fact that its second stage is connected to the supply pipeline of the heating network in parallel to the heating system, and the first stage is connected in series ( rice. 3). The network water leaving the second stage of the hot water supply is mixed with the return water from the heating system and also passes through the first stage.

Thus, the comfort in the premises of a building with a mixed two-stage DHW scheme does not decrease, however, more network water is consumed than with a sequential DHW scheme ( rice. 4).

* Based on the book by N.M. Singer and others. "Improving the efficiency of heat points." M., 1990.

The two-stage scheme is most widespread in residential buildings with significant loads on the hot water supply in relation to heating. In buildings with very low or high thermal values, compared to heating (1

IN Western countries in Lately more and more people are thinking about the use of a flow-through method of hot water supply, especially after recognizing the serious danger of infection with legionella - bacteria that multiply in a stagnant warm water. Strict standards already adopted in European countries, provide for regular thermal disinfection of storage tanks and hot water pipelines connected to them, including recirculation pipelines. Disinfection is carried out by raising the temperature in the entire system for a certain time to 70 ° C and above. The complication of accumulator circuits necessary for this especially reveals the advantages of DHW flow systems with plate heat exchangers. They are simple and compact, require less investment, while providing lower return temperatures and lower heating water costs.

More low temperature water in the return pipeline of heating networks reduces heat loss and increases the efficiency of electricity generation at combined heat and power plants. Lower consumption of network water requires smaller diameters of pipelines of heating networks and lower consumption of electricity for its pumping.

Control options
Many firms are currently working on automatic regulators that would provide comfortable temperature hot water with an accuracy of 1-2 °C or less. IN storage tanks heating uniformity is achieved by natural or artificial mixing of the incoming water with the water in the tank.

For this purpose, in DHW flow systems, especially with low and rapidly changing flow rates, when regulating the temperature of hot water, it is required to take into account, in addition to temperature, as a second value, the flow rate. Leading manufacturing companies have developed regulators for a small - for one consumer - consumption, operating without auxiliary energy. These controllers take into account both the flow and the temperature of the hot water. Unlike conventional thermostatic regulators, in the absence of hot water flow, these devices can generally stop the supply of heating coolant, which protects the DHW heat exchanger from the formation of lime deposits.

In systems of flowing hot water with a large consumption of hot water, flow fluctuations, compared with its general meaning, less, and satisfactory temperature control accuracy can be achieved by using both thermostatic and electronic controllers. However, in electronic regulators, it is necessary to smooth the control curve by the right choice of the control law and the characteristics of the control valve itself - the stroke speed of the regulator drive, the diameter of the valve Du, its hydraulic resistance k VS - in order to exclude oscillation phenomena in the entire range of its operation. The constant opening and closing of the regulator at a high frequency exposes the DHW plate heat exchanger to high thermal and hydraulic loads, which will lead to its premature failure due to the occurrence of external or internal leaks.

In order to prevent fluctuations with large differences in hot water flow or with significant fluctuations in the temperature of the heating water, for example 150-70 °C, it is advisable to install two parallel regulators of different diameters, which - by themselves - optimally provide a certain range of heating water flow ( rice. five).

As noted above, in the absence of hot water analysis, for example in systems without recirculation or with regular shutdowns of the water supply, it is necessary to protect the heat exchanger from carbonate deposits by stopping the supply of heating water. At high flow rates, this can be achieved using combined regulators with two temperature sensors - heated and heating water - at the heat exchanger outlets ( rice. 6). The second sensor, set, for example, to 55 °C, stops the supply of coolant to the heat exchanger even if the hot water temperature sensor is installed far from the heat exchanger and is not affected by the heating medium due to the lack of water intake. At a temperature in the heat exchanger of 55 °C, the process of deposition of hardness salts slows down significantly.

The closer the sensors are installed to the medium whose parameters are being controlled, the better control can be achieved. Therefore, it is desirable to install temperature sensors, if possible, deeper into the corresponding fittings of the heat exchanger. To do this, you can use plate heat exchangers with fittings on both sides of the plate pack, where a temperature sensor is inserted into one of the fittings, and the other serves to select the coolant. Then the sensor is washed by the coolant even before it exits the heat exchanger, and in the absence of coolant circulation, the sensor records the temperature of the medium under the influence of thermal conductivity and natural convection, which would not have occurred if it was installed outside the heat exchanger.

Two-stage DHW schemes are distinguished by the fact that in the first stage of heating, heat is taken from the return water of the heating system. Due to the discrepancy between the heat loads of heating and hot water in winter or night mode, it may turn out that hot water is heated above the required 55-60 °C. For example, with a heat carrier with a temperature of 70 ° C (calculated point), DHW water can be heated up to 67-69 ° C even in the first stage. To exclude overheating and intense carbonate deposits at these temperatures, it is possible to install a three-way control valve at the inlet or outlet of the heat exchanger ( rice. 7). Its task, depending on the temperature of the coolant at the outlet of the heat exchanger, is to pass heating water through the heat exchanger or past it - along the bypass. The three-way valve sensor is installed in the return pipe. It simultaneously with the regulation of the temperature of the heating medium indirectly limits the temperature of hot water. At the same time, heat extraction from the return pipeline is not limited, but optimized, increasing the reliability and comfort of hot water supply.

In favor of a brazed heat exchanger
In Western countries, in the vast majority (over 90%) of cases, brazed plate heat exchangers are used for hot water purposes. This is due to the relative cheapness and ease of maintenance of these devices.

As a rule, Russian and Ukrainian customers who have experience in operating high-speed shell-and-tube heat exchangers, which often require cleaning, prefer gasketed plate heat exchangers. However, it should be taken into account that these devices are equipped with gaskets made of polymer (rubber) materials, which are subject to aging - crack, become brittle. After five years of operation during the repair of a collapsible plate heat exchanger often it is no longer possible to ensure its satisfactory density. And the purchase of a new set of seals comes at a price, sometimes almost comparable to the price of a new heat exchanger.

If the seals are attached to the plates with adhesive, then replacing them involves such work as destroying the existing seals in liquid nitrogen and gluing new ones. For their implementation, it is necessary special devices and highly qualified staff. Heat exchanger manufacturers provide customer service, but the heat exchanger often needs to be sent to a specialized facility. All this led to the widespread use in Western countries of brazed plate heat exchangers for hot water purposes.

Note: doubts about the possibility of using brazed heat exchangers in the countries of the post-Soviet space, associated with poor quality coolant are not justified - hard water is found all over the world. It is only necessary to correctly adjust the DHW and limit the temperature of the heat exchanger walls, as described in the previous section.

Brazed plate heat exchangers are subjected to chemical washing. If insufficient heating of hot water or return cooling is noticed, and chemical composition water is characterized by a high content of hardness salts, it is necessary to regularly flush the heat exchanger with special solutions that do not destroy either the walls of the heat exchanger or the copper solder. The customer can carry out flushing on his own: this work is simple, flushing units and reagents are affordable and pay for themselves quickly.

At ultra-high heating water temperatures (for example, if temperature chart 150/70 °C), when it is not excluded that the temperature of the heat exchanger wall exceeds the temperature at which intensive scale formation occurs, a preliminary decrease in the temperature of the heat carrier before the heat exchanger is required. There are two ways to do this - pumping scheme injection or elevator scheme. In the first case, a separate sensor is required to turn on the pump, a significant amount of electricity is consumed; the equipment used is subject to wear and tear. elevator scheme extremely simple, with a thermostatic drive it does not depend on electrical network and more economical in implementation and operation ( rice. 8). Connecting the suction pipe of the elevator to the return pipe of the heating system gives additional effect lowering the temperature in the return pipeline of heating networks.

Point solution
A two-stage DHW scheme requires two heat exchangers - for the first and second stages. The choice of heat exchangers by power, that is, a partition total power by steps, is a difficult task that requires several iterations in the calculations (they are the responsibility of the supplier). The absence of mass-produced DHW units with a two-stage scheme is due to certain deadlines supplies.

Two brazed heat exchangers need to be tied together with pipelines. The piping takes up space and accounts for a significant portion of the cost of a two-stage DHW module. Therefore, manufacturers began to produce brazed heat exchangers with an intermediate dividing wall and six fittings.

The piping of heat points based on them is simplified, but problems with the calculation and the lack of mass production remain.

In addition, during operation, there are periods when the first or second stages of the system are not loaded at all. Yes, in summer period the second stage would be enough, and at the calculated heating point - the first.

The author of this article has developed and patented a solution for a mixed two-stage DHW scheme, including one commercially available brazed plate heat exchanger ( rice. nine). Its essence lies in the use of a special fitting inserted into one of the serial fittings. Through this fitting, both return water from the heating system and hot network water from the heating network are supplied. The heat exchange surface is fully engaged in any mode.

In order for any residential building to function normally, it is necessary to install a water supply system. Its competent device will ensure timely supply and sufficient water pressure. This article will discuss in detail the hot water supply scheme, connection types and its features in an apartment building.

What is the peculiarity of the water supply of an apartment building?

Providing water to a building with a large number of storeys is very difficult. After all, the house consists of many apartments with separate bathrooms and plumbing fixtures. In other words, water supply schemes in apartment buildings- this is a kind of complex with separate piping, pressure regulators, filters and accounting equipment.

Most often, residents of high-rise buildings use water central water supply. With the help of a water pipe, it is supplied to individual plumbing fixtures under a certain pressure. Water is often treated with chlorination.

The composition of the central water supply system

Centralized water supply schemes in multi-storey buildings consist of a distribution network, water intake facilities and treatment plants. Before getting into the apartment, water travels a long way from pumping station to the reservoir. Only after cleaning and disinfection, the water is sent to distribution network. With the help of the latter, water is supplied to appliances and equipment. Pipes central scheme hot water supply high-rise building can be made of copper, metal-plastic and steel.

The latter type of material is practically not used in modern buildings.

Types of water supply schemes

The water supply system is of three types:

• collector;
• consistent;
• combined (mixed).

Recently, when it is increasingly common in apartments a large number of sanitary equipment, use collector wiring diagram . It is the best option for the normal functioning of all devices. The collector-type hot water supply circuit eliminates pressure drops in different points connections. This is the main advantage of this system.

If we consider the scheme in more detail, we can conclude that there will be no problems with the use of plumbing equipment for its intended purpose at the same time. The essence of the connection is such that each individual water consumer is connected to the collectors of the cold and hot water supply riser in isolation. Pipes do not have many branches, so the likelihood of leakage is very small. Such water supply schemes in multi-storey buildings are easy to maintain, but the cost of equipment is quite high.

According to experts, the hot water collector scheme requires the installation of more complex installation plumbing fixtures. However, these negative sides are not so critical, especially considering the fact that the collector circuit has many advantages, for example - concealed installation pipes and taking into account the individual characteristics of the equipment.

Sequential scheme of hot water supply multi-storey building - this is the easiest way to wire. Such a system has been tested by time, it was put into operation in the days of the USSR. The essence of its device is that the pipeline of cold and hot water supply is carried out parallel to each other. Engineers advise using this system in apartments with one bathroom and a small amount sanitary equipment.

In the people, such a hot water supply scheme for a multi-storey building is called a tee. That is, branches come from the main highways, which are connected to each other by tees. Despite the ease of installation and cost savings consumable, this scheme has several major drawbacks:

1. In the event of a leak, it is difficult to find damaged areas.
2. The impossibility of supplying water to a separate plumbing fixture.
3. Difficulty of access to pipes in case of breakage.

Hot water supply of an apartment building. Scheme

Pipe layouts are divided into two types: to the riser of hot and cold water supply. Briefly they are called HVS and DHW. The hot water system deserves special attention. apartment building. Scheme DHW networks consists of two types of postings - lower and upper. Looped wires are often used to maintain high temperature in the pipeline. The gravitational pressure forces the water to circulate in the ring, despite the lack of water intake. In the riser, it cools and enters the heater. Water with a higher temperature is supplied to the pipes. So there is a continuous circulation of the coolant.

Dead-end highways are also not uncommon, but most often they can be found in utility rooms industrial facilities and in small residential buildings with a low number of storeys. If the water intake is planned intermittently, then a circulation pipeline is used. Engineers advise using hot water supply in apartment buildings (the scheme was discussed above) with a number of floors no more than 4. A pipeline with a dead-end riser is also found in hostels, sanatoriums and hotels. Pipes of a dead-end network have a lower metal consumption, therefore they cool down faster.

DHW networks include a horizontal main pipeline and distribution risers. The latter provide piping for individual objects - apartments. Hot water supply is mounted as close as possible to the plumbing equipment.

For long buildings main pipes schemes with circulation and looped supply pipelines are used. A prerequisite is the installation of a pump to maintain circulation and constant water exchange.

Two-pipe DHW scheme - Photo 07

Modern builders and engineers are increasingly resorting to the use two-pipe systems DHW. The principle of operation is that the pump takes water from the return line and supplies it to the heater. Such a pipeline has a higher metal content and is considered the most reliable for consumers.

Fig.1. Typical scheme boiler connections.

Fig.2. Typical diagram of a flow heat exchanger with regulation on the primary side of the heat exchanger.

Fig.3. Typical scheme for the preparation of hot water with temperature control on the secondary side of the heat exchanger.

Fig.4. Typical scheme for the preparation of hot water supply with receipt different temperature from one heat exchanger on the secondary side of the heat exchanger.

Fig.5. Typical DHW preparation scheme combined type when using constant peak DHW analysis.

Fig.6. A typical scheme for the preparation of combined-type DHW using periodic peak analysis of DHW.

DHW scheme accumulative type

As a rule, such a scheme is used for hot water supply of cottages. The analysis of hot water in the house has a periodic peak character, i.e. it is more intense during breakfast, lunch and dinner. As storage capacity boiler is used.

A boiler is a container designed for the preparation, accumulation and storage of hot water. External thermal insulation the boiler is made of polyurethane foam, inner surface the boiler is covered with glass enamel, which prevents the formation of lime scale, simplifies cleaning and ensures increased hygiene of the produced DHW. A magnesium anode is also installed inside the boiler, it protects it from stray currents.

A sleeve for installing a thermostat is welded into the body of the boiler. The temperature regulator sets the water heating temperature, according to the norms, the water temperature should not exceed 55-60 ° C, with more high temperature possible skin burns. The volume of the boiler depends on the number of people living and hot water outlets.

The heating element of the boiler can be electric, water, and both types of heaters are also possible. These are the so-called boilers with combined heating. Boilers with electric heating are used where there is no hot coolant, water is heated by a built-in electric heater, and water-heated boilers are used where there is hot coolant and water heating is carried out through a built-in heat exchanger in the form of a coil. Combined boilers have the opportunity to winter period time to heat water with a hot coolant from the boiler room, and in summer - with electricity. This combination of boiler heating is used in the West, since the cost of energy carriers is the same there. Boiler water from the boiler house is used as a hot heat carrier.

A typical scheme for connecting a boiler to a heat carrier and cold water supply (hereinafter referred to as cold water supply) is shown in fig. 1. The operation of the circuit for preparing hot water, shown in fig. 1, carried out in the following way.

As described above, a sleeve is welded into the body of the boiler, in which an adjustable thermostat sensor is installed. This thermostat measures the temperature of the water in the boiler. If the measured temperature in the boiler is below the set thermostat setting, then its contacts go into the “request” state for DHW preparation. This signal switches the boiler and pump K2 into operation. When the water temperature in the boiler reaches the set thermostat setting, its contacts go into the “request hang-up” state for hot water preparation, while the boiler and pump K2 go into the off state.

The input of cold water into the boiler is carried out through check valve, it prevents the "leaving" of the DHW during the disappearance of the cold water. An emergency relief valve K4 is installed at the inlet to the boiler up to its shut-off valves, which protects the boiler from high pressure, and an expansion tank is installed closed type K5, to compensate for thermal expansion of water. DHW is recirculated from the last tap.

For normal operation recirculation line, it has a K3 pump. During hot water drawdown, the water flow V1 comes from the cold water supply, when there is no hot water drawdown, the water flow V2 comes from the recirculation line. If the farthest point of DHW disassembly is at a distance of no more than 7-8 m, then the line re DHW circulation can be neglected.

When using a DHW recirculation line Special attention it is necessary to pay attention to the installation of hot water pipes and recirculation pipes. The installation of these pipes must be carried out in accordance with the rules for the installation of heating systems, i.e. the technological slope of these pipes towards the last water tap must be observed. If the hot water and recirculation pipe passes through the "gate", i.e. bypasses the doorway, then automatic air vents must be installed in the upper part of these “gates”, i.e. it is necessary to provide for the removal of air from the pipes in all possible places of its accumulation. Otherwise, the recirculation line will not work or will not work properly.

DHW scheme flow type

The flow type hot water supply scheme is usually used in production for production lines that use constant hot water analysis.

Heat exchangers are used as a heating element for domestic hot water different types(plate, tubular, etc.), however, plate-type heat exchangers have gained great popularity.

Plate heat exchangers are smaller and more efficient than a boiler, they are used in almost all areas of industry where a heat exchange process is required. The design of the plate heat exchanger contains a set of corrugated plates made of corrosion-resistant material with channels for two fluids involved in the heat exchange process. The plate package is placed between the base plate and pressure plate and secured with tie bolts. Each plate of a plate heat exchanger is provided with a heat-resistant rubber gasket that seals the connection and directs the various fluid flows into the appropriate channels.

The required number of plates is determined according to the temperature, the water flow and the allowable head loss. Plate heat exchangers are collapsible and brazed, they are made of of stainless steel which allows them to be used for many years.

A typical scheme for connecting a plate heat exchanger to a heat carrier and cold water is shown in fig. 2. The operation of the circuit for preparing hot water is as follows. On the primary side of the heat exchanger, a pump with its own mixer and servo drive is installed. The DHW temperature is measured by the K8 PID controller; at a low DHW temperature, the PID controller sends a signal to open the mixer, and at an increased temperature, to close it.

The principle of PID control is as follows. The measured DHW temperature is compared with the setpoint (for example, the setpoint is 55-60°C), and the higher the difference between the measured temperature and the setpoint, the longer the K8 device gives a signal to close the mixer. After the set measurement time has elapsed, the K8 device again measures the DHW temperature and compares it with the setpoint, the temperature difference has decreased and the device gives a shorter signal to close the mixer.

Using the dynamic approximation method, the measured DHW temperature and the setpoints coincide, the PID controller will stop issuing control signals to the mixer. The same regulation takes place when the measured DHW temperature is lower than the setpoint, in which case the PID controller will send a signal to the servomotor to open the mixer.

For any outrage DHW temperature The PID controller will resume its operation to obtain the required DHW temperature. With this regulation, the hot water coming from the boiler and the return water coming from the heat exchanger are mixed, thus maintaining a constant DHW temperature. The input of cold water to the heat exchanger is carried out through a check valve, it prevents the “leaving” of hot water during the disappearance of cold water. At the inlet to the heat exchanger, up to its shut-off valves, an emergency relief valve K4 is installed, which protects the heat exchanger from high pressure, and a closed-type expansion tank K5 is installed to compensate for thermal expansion of water.

DHW is recirculated from the last tap. DHW preparation schemes on heat exchangers should only work with a recirculation line; in rare cases, a recirculation line is not used. To operate the recirculation line, a K3 pump is installed on it. During hot water drawdown, the water flow V1 comes from the cold water supply, when there is no hot water drawdown, the water flow V2 comes from the recirculation line. We have considered a scheme for preparing hot water on a heat exchanger with temperature control on the primary side of the heat exchanger. On the basis of this scheme, there are also its varieties, i.e. with temperature control on the secondary side of the heat exchanger. This circuit is shown in fig. 3.

The advantage of this scheme is that the diameter of the pipes on the secondary side of the heat exchanger is usually smaller than the diameter of the pipes used on the primary side of the heat exchanger. This reduces the cost of the servo and slightly simplifies installation. In addition, the circuit with DHW temperature control on the secondary side of the heat exchanger allows you to get several different temperatures from one heat exchanger (Fig. 4).

The installation of DHW pipes must be carried out in accordance with the rules for the installation of heating systems, i.e. the technological slope of these pipes towards the last water tap must be observed. If the hot water and recirculation pipe passes through the "gate", i.e. bypasses the doorway, then automatic air vents must be installed in the upper part of these “gates”, i.e. it is necessary to provide for the removal of air from the pipes in all possible places of its accumulation. Otherwise, the recirculation line will not work or will not work properly.

Combined hot water supply scheme

The DHW scheme of a combined type (i.e. instantaneous + storage water heaters) is usually used in production for process lines that use constant and periodic peak analysis of DHW (Fig. 5 and 6).

A flow heat exchanger is used as a DHW heating element. The boiler is used as a thermal energy storage for peak analysis of hot water. A heat exchanger is not used in the boiler because it is more inert than a flow type heat exchanger. The scheme shown in fig. 5 corresponds to the operation of a flow heat exchanger with regulation on the primary side of the heat exchanger (see fig. 2), and the circuit shown in fig. 6 corresponds to the operation of a flow heat exchanger with regulation on the secondary side of the heat exchanger (Fig. 3).

With regulation on the secondary side of the heat exchanger, it is also possible to obtain different temperatures DHW, for this it is enough to improve the circuit, as shown in Fig. 4. If the circuits (Fig. 5, 6) are provided with bypass valves, then it will be possible (with a deterioration in the quality of hot water supply) for a “hot” revision of the flow and storage heat exchanger. The requirements for the installation of DHW pipes remain the same.

Installation of a hot water supply system is a laborious process that requires certain knowledge and skills. In addition, each case has its own nuances. They must be taken into account so that the hot water supply is connected correctly.

Types of heating systems

Depending on the acceptable way water supply, from the source of water, from the availability of sales various schemes connections, etc., all heating network can be divided into two types:

• thermal networks of closed type;
• heating systems of open type.

Let us consider in more detail what installation scheme exists within each of them.

Scheme of a closed type heating network

Similar complexes are mounted to centralized heating networks by means of hydro heat exchangers. There are several schemes for such a connection of hot water supply, and each has its own characteristics.

• parallel type.

This circuit is quite simple and includes only one regulator. temperature regime. Water heating equipment and the network itself are focused on optimal DHW consumption . But this scheme has significant disadvantage- the thermal efficiency of water is not fully realized. For example, the heat of network water does not come into play, although its temperature is quite high and it could well take on most of the DHW load.

• Foreground type.

Connecting hot water in this way involves connecting the water heater in series to the heating network. Such a scheme has undeniable merits, in particular, a stably maintained thermal regime in the network, which is carried out in an automated way. This makes it possible to save on energy resources in heating season. In addition, if the temperature in the room is slightly below the norm, then it is possible to heat it by supplying network water to heating radiators. The disadvantage of this scheme is the same as the previous one.

• Two-stage sequential type.

In this case, the network water is divided into two parts, one of which is driven through flow regulator, and the second - through the heater of the second level, after which both flows merge and fill the heating system.

• two stage mixed type.

With such a hot water connection scheme, the first stage heating device is connected via network water and closed in the return line, and the second stage device is connected in parallel with respect to the heating system. The main advantage here is the low heat consumption compared to the total amount of hot water.

• Two-stage mixed type with water flow limiter.

The main advantage here is the ability to use the ability of buildings to accumulate heat. In this scheme, the flow regulator is mounted at the point of transition of network water to the second level of the heater.

Scheme of an open type heating network

Such complexes are regulated by temperature autoregulator, and the connection is the same as in closed systems. There are several schemes for such a connection of hot water supply, and each has its own characteristics.

• Typical connection using a thermostat. In such a scheme, hot water will be mixed in the depths of the thermoregulatory device. In this case, the DHW circulation line will be mounted behind the drainage point and behind the throttle plate.
• Combined connection of hot water supply with water intake from the return line. A very convenient scheme for reducing fluctuations in water flow and pressure levels in the pipeline. The heating device is mounted in the system in a serial way.
• Combined connection of hot water supply with water intake from the supply line. Applicable if the water source has low power, and for a boiler house or station it is necessary high pressure, however, a stable temperature in the pipeline. This is a very economical way.