Hot and cold water system. Hot water supply
hallmark centralized hot water supply is a continuous supply hot water to water supplies. AT modern systems In the heat supply sector, the most widespread is the preparation of hot water in local or central heating points, from which water enters the hot water supply systems.
Rice. 3.1. Dead-end scheme of hot water supply with upper wiring and a storage tank: 1 - tap water; 2 - sectional water heater; 3 - upper storage tank with a float valve; 4 - to water folding devices; RT - temperature controller;
t 1 , t 2 , t x - respectively, the temperature of the water in the supply and return pipelines and cold water
Hot water supply from the MTP is organized mainly with district or quarterly heat supply.
At enterprises with constant and large water intake, as well as in small low-rise residential buildings with periodic water intake, simple and cheap dead-end circuits with top wiring and a battery are common (Fig. 3.1). Hot water in such systems is prepared in advance before the start of water intake. A large supply of water in the accumulator allows you to maintain a high temperature even during long breaks in water consumption.
In large residential buildings with uneven consumption of hot water and without accumulation, dead-end wiring is unacceptable, since a prolonged cessation of water intake can lead to unacceptable cooling of the water and the need to drain it. The cooling of water in the distribution pipelines is prevented by continuous or short-term natural or forced circulation of the coolant in the local system.
Natural circulation is most effective in overhead systems, since with a closed loop device (Fig. 3.2), continuously operating circulation occurs naturally. The natural movement of water occurs due to the different densities of hot and cooled water. Usually, the difference in the density of water in the system is small, so the necessary circulation pressure is ensured by careful thermal insulation of the riser 1 and the laying of distributing pipelines 3, 4, 5 without thermal insulation. As a result, the difference in water temperatures in the circuit (at the outlet of the heater and at the inlet to it) reaches its maximum value.
In buildings with large attic spaces, it is advisable to install storage tanks instead of air collectors.
Due to the relatively small value of the natural circulation pressure, the limits of the application of natural circulation are limited. In buildings with a length of distributing pipelines exceeding the permissible limits, forced circulation using pumps is used. It is allowed in systems with lower piping (Fig. 3.3).
Hot water systems with continuous circulation operate with constant water heating, which is necessary condition use of towel warmers. Therefore, in residential buildings, hot water supply should be designed with circulation and heated towel rails. Towel dryers are placed in bathrooms and shower rooms on pipelines, in which a constant flow of hot water is ensured. Often heated towel rails are connected to circulation risers.
The need for circulation is determined from the condition of ensuring the minimum allowable water temperature at the most remote and highly located point of the water intake. At the same time, in residential buildings up to five floors without heated towel rails, water circulation should be provided only in the supply pipelines. In buildings of larger and any number of storeys, but with heated towel rails on hot water pipelines, circulation should be provided in the supply pipelines and distributing risers at the same time.
Rice. 3.3. Hot water supply scheme with lower wiring and forced circulation: 1 - heated towel rail; 2, 3 - supply and circulation lines; 4 - sectional water heater; 5 - plumbing; 6 - circulation pump; B - water meter
Hot water supply systems with lower wiring and accumulation can only have a lower location of storage tanks (Fig. 3.4). The lower tanks are under static water pressure from the highest draw point. The heat reserve in the tanks is created when the water intake is reduced or stopped, when the performance of the pump and heater exceeds the load of hot water supply. During such periods, admission cold water from the water supply to the closed system decreases or stops completely, and the continuous operation of the heater is used to accumulate thermal energy in the system.
In the absence of water intake, all hot water from the heater enters the system (for circulation) and into the tank, displacing cold water from top to bottom. The water displaced from the tank mixes with the cooled circulating water and is again pumped through the heater into the tank and into the system. With partial drawdown, the loss of water in the system is replenished from the water supply, and the flow of hot water into the tank is reduced by the amount of the steady drawdown. This process of gradually filling the accumulator with hot water is called charging. When the hot water drawdown becomes equal to the capacity of the charging pump and the heater, the accumulator charging stops and due to the pressure drop in the circulation pipe, the non-return valve closes, stopping the water circulation. With a maximum drawdown exceeding the capacity of the installation, the pressure in the distributing pipelines becomes less than the pressure in the water supply system. Then, under the pressure of cold tap water, the missing amount of hot water will be forced into the system from the tank from the bottom up, while the battery is discharged.
Sharp fluctuations in the load of hot water supply cause continuous changes in the processes of charging and discharging, therefore, circuits with a lower arrangement of batteries must be fully automated.
Hot water supply schemes with direct water intake from heating networks differ from those considered in that group mixers are installed at heating points instead of heaters (Fig. 3.5 and 3.6). Mixers are designed to lower the temperature of the network water from the supply pipeline by mixing in colder water coming from the heating system. The required hot water temperature is regulated by changing the water supply from the supply pipe using a temperature controller. To eliminate the flow of water from the supply pipeline to the return pipeline, a check valve is installed on the return pipeline.
For the normal operation of hot water supply systems, it is necessary that the pressure after the mixers is sufficient for water to flow to the highest and most remote points of water intake. In the warm season, when drawing water from the supply line, this pressure must be provided at points a(Fig. 3.5) with valve 5 open, with water drawn from the return line - at points b with valve 5 closed. In the diagram in fig. 3.5 required pressure points a and b is selected from the condition of free filling of the storage tank with hot water.
In the diagram in fig. 3.6 circulation in summer and winter period s is created in various ways. In summer, when drawing water from the supply line, the valve a closes. Since a large pressure difference between the supply and return lines causes excessive water circulation, in order to absorb excess circulation pressure, the water flow is directed through the summer washer by closing the valve b. In winter, water is drawn from both pipelines simultaneously or only from the reverse, for this the valve a should be open. For water to circulate in a hot water supply system, it is necessary that the pressure at the point in there was less pressure at the point G, which is achieved by installing a winter washer. For decreasing hydraulic resistance of the circulation pipeline, the summer washer is turned off and all circulation water flows through the line with an open valve b.
Hot water supply according to the scheme in fig. 3.5 is used in houses with large and periodic water intake, and without circulation it is used in the same place as the circuit shown in fig. 3.1.
Hot water heaters in closed heating systems are much more expensive than mixers. But with direct large water intake from heating networks, the costs of preparing make-up water at a thermal station and pumping heat carrier in networks sometimes exceed the savings obtained from replacing heaters in heating points with mixing devices. Using the combined circuit shown in fig. 3.7, gives a tangible savings in network water consumption due to the addition of tap water to the local system, heated in the heater by return water from the heating system. When the temperature of the network water in the return pipeline rises to 70 ° C, the water intake from the supply pipeline can be completely stopped. In this case, hot water supply is entirely provided by tap water heated in a heat exchanger. In terms of capital costs, this scheme is more expensive than schemes with direct water intake, but it allows to reduce the volume of water treatment by 35–40% and the consumption of electricity for the circulation of network water by 20%.
There are various schemes for connecting hot water risers. The "classic" scheme with a circulation riser for each supply riser (Fig. 3.8, a) has the highest metal content. In the scheme with paired looped risers (Fig. 3.8, b) water-cutting appliances and heated towel rails are connected to the supply and circulation risers. According to this scheme, during the hours of maximum drawdown, both risers are supply, the rest of the time one of the risers performs the functions of circulation. Switching the riser from the supply mode to the circulation mode is carried out by an automatic device in the heating substation. The scheme has not gained popularity due to poor heating of heated towel rails and a low temperature of water intake from the circulation riser at circulation mode work. A common disadvantage of schemes a and b is the low rate of water circulation, which contributes to the accelerated corrosion of heated towel rails.
In residential buildings, several supply risers can be connected to the circulation riser (Fig. 3.8, in, G), proportionally to their number, the speed of water in the circulation riser increases. Schemes for metal costs are more economical and when the circulation risers are loaded with heated towel rails, the corrosion of heated towel rails is somewhat reduced.
In buildings with a height of more than 50 m, hot water supply systems should be divided into zones, since while maintaining the circulation schemes traditional for mid-rise buildings, it becomes difficult to regulate the same pressure in water fittings on different floors. The height of the zones is determined according to the design standards for the internal water supply. In the most common schemes (Fig. 3.9, a) each zone is provided with hot water from its own set of equipment in the MTP or TsTP. Such schemes are reliable, but have a high initial cost and high operating costs.
When hot water is supplied through a common supply pipeline (Fig. 3.9, b) the pressure in the upper zone is regulated by a pressure regulator on the circulation riser or a booster pump on the supply riser. In the lower zone, the required pressure is controlled by installing a pressure regulator on the supply riser. The disadvantage of this scheme is the difficulty of setting up circulation modes with a large difference in water pressure in the zones.
The most promising hot water supply scheme with natural circulation within each zone and water heating in small heaters installed on the supply risers. In this case, hot water should be supplied from the central heating station in a dead-end scheme.
DHW from the central heating station is calculated to serve 2 - 20 buildings. Group heaters (in closed heat supply systems) and mixing devices (in open heat supply systems) in the CHP are connected to the heating networks according to the same schemes as in the MTP. From the central heating station, hot water is supplied through quarterly networks to the MTP of each building in the quarter. In the MTP, the hot water supply systems of buildings with supply and circulation risers cut into the corresponding pipelines laid from the central heating station, usually in the basements of houses.
Rice. 3.9. Scheme of hot water supply of high-rise buildings:
a- separate; b– joint
The most serious shortcomings of group preparation of hot water in the central heating substation are associated with the direct connection of the risers of local hot water supply systems to quarterly pipelines from the central heating substation. Direct connection creates a large number of jumpers between the supply and circulation pipelines, which makes it difficult to evenly distribute hot water along the risers in the building and between buildings. Due to the inequality of the hydraulic resistance of the near and far lintels, the water flow decreases as the buildings move away from the central heating station along the lintels, and sometimes significantly. To restore the calculated hot water consumption in each building, it is required to install additional control valves in the MTP, for example, flow regulators, washers. This, in turn, complicates the system setup and maintenance.
The desire to increase the number of serviced buildings and the range of central heating also leads to a significant decrease in the temperature of hot water at the most remote consumers. Low temperature water contributes to the growth of its consumption by draining the cooled water and reducing the consumption of cold water for mixing with hot water. To prevent significant cooling and draining of water from the system of the most remote buildings, it is recommended to provide them with additional autonomous water circulation using local circulation pumps, which at the same time increases the hydraulic stability of hot water supply.
Based on the noted phenomena, the choice of group preparation of hot water in each specific case must be confirmed by technical and economic calculations.
Centralized hot water supply in systems with steam coolant it is mainly used in workers' settlements, rural settlements that have their own steam boilers or receive heat from nearby industrial complexes. Hot water is produced either at the point of consumption or directly in the boiler rooms. Tap water is heated in sectional or capacitive surface-type steam-water heaters.
Hot water supply system (DHW) - a set of devices that provide heating of cold water and its distribution to water-folding devices.Domestic hot water systems subdivided into centralized and local (decentralized).
In centralized
systems, one heating unit in a boiler room or central heating station supplies hot water to one or more large buildings within a residential microdistrict, block or village. All centralized DHW systems are designed with circulation pipelines to provide consumers with hot water, since without them, in the absence of water intake, the water in the supply lines cools quickly and the consumer is forced to drain it, losing water and heat. In addition, heated towel rails are installed in hot water systems, which are necessary for drying clothes and heating bathrooms and cannot work in the absence of circulation.
Circulation pipelines and circulation pumps create a continuous movement of water (circulation) through closed loop heat exchanger - supply pipeline - tap water - circulation pipeline - heat exchanger, maintaining the temperature of hot water at tap 50-60 gr.S. At this temperature, most of the pathogenic bacteria contained in water die (pasteurization effect), edible fats, oils and household contaminants emulsify well - they dissolve in water and are washed off by its flow when washing dishes and washing clothes. To enhance these processes, the industry produces a variety of soaps, synthetic detergents, scouring powders and emulsifiers.
For body washing, people usually use hot water at a temperature of 35-40 degrees C in baths and up to 45 degrees C in baths, diluting hot primary water with cold water using mixing taps and devices.
AT last years in buildings with a height of five floors or more, part of the supply risers (for example, from 3 to 7 risers of one section of a residential building) are combined into one water-collecting unit, called a sectional unit, with a single circulation pipeline. In buildings higher than 50 m (over 16 floors) the DHW system is divided vertically into separate zones with independent wiring and separate risers for each zone, sometimes even with the device of special technical floors. This is due to the limitation of the allowable pressure in front of the water folding and water shut-off valves to 0.6 MPa.
Local (dead-end) DHW systems
suit in individual houses(dacha, cottage, interlocked)or apartments. Their radius of action is small, hot water preparations are produced in small heat generators (electric, gas water heaters, small boilers, etc.). Often such a heat generator is common to both the heating system and the DHW system; they are called bipolar. A double-circuit boiler is enough to prepare hot water for a family of 3-4 people. For large families, sometimes a capacitive boiler is attached to the boiler.
On the
industrial and municipal
enterprises (baths, laundry, dry cleaning, swimming pools), along with high-speed water supply installations, steam-water heaters of hot water have found their application.
For internal pipelines of cold and hot water, SNiP 2.04.01-85 * recommends the use of plastic pipes and fittings made of polyethylene, polypropylene, polyvinyl chloride, polybutylene, metal-polymer, fiberglass and other plastic materials for all water supply networks, except for an independent fire water supply network.
The laying of plastic pipes is carried out mainly hidden - in baseboards, strobes, shafts and channels in the floor fill. Open laying of connections to sanitary appliances is allowed, as well as in places where mechanical damage to plastic pipelines is excluded. For all internal water supply networks, it is allowed to use copper, bronze and brass pipes, fittings, as well as with an internal and external protective coating against corrosion.
In order to avoid rapid destruction from internal corrosion, DHW systems are made of galvanized pipes with a slope of distribution pipes to risers of at least 0.002. For pipe diameters over 150 mm in open heat supply systems, the use of non-galvanized black pipes is allowed.
For agricultural enterprises it is allowed to apply asbestos-cement pipes. In hot water and cold water systems, fittings of ordinary general industrial use are used, designed for operating pressures up to 0.6 MPa. Pipes are connected by threading or welding in an environment of gaseous carbon dioxide. To compensate for thermal elongations, either natural pipe turns or special compensators are used.
Stop valves are installed on branches to individual buildings and structures, on branches to sectional units and on branches from risers to each apartment. To repair individual risers at their upper and lower points, a shut-off valves with plugs for draining water from risers and letting air into them.
All pipelines of the DHW system, with the exception of apartment connections and heated towel rails, must have thermal insulation. The thickness of the thermal insulation layer of the structure must be at least 10 mm , and its thermal conductivity is not less than 0.05 W (m x gr. C).
Water consumption rate (in liters per inhabitant), for example, in an apartment-type residential building with centralized hot water supply (with bathrooms 1500- 1700 mm equipped with showers) and in a residential building with increased requirements for landscaping (with a building height of 12 floors and above) is from 250 to 400 liters per day.
The physiological (drinking) need of a person ranges from 5 l / day (in a calm state) to 10 l / day (during heavy physical work).
Determination of heat flows for hot water supply is carried out according to SNiP 2.04.02-84.
Main heating appliances
. In centralized hot water systems, water is heated in hot water boilers, open tanks or closed water heaters equipped with coils.
Most often use a hot water supply system from a steam boiler and from a heating network.
Domestic hot water system with steam boiler
and horizontal water heater operates as follows. From the steam collector, steam through the steam pipeline enters the coil of a horizontal capacitive water heater, where it condenses, heating the water in the water heater. Condensate from the coil through the condensate pipeline returns to the boiler. The water in the water heater is under the pressure of the city water supply and is heated up to 70 degrees C. Through the supply pipeline, it enters the upper bottling, from where it is fed through hot water risers through hot water inlets to sanitary appliances. Part of the water is returned through the return pipeline to the water heater through the lower fitting, which prevents the water from cooling in the supply line. As hot water is drawn, cold water from the water supply line enters the water heater. A safety lever valve with a drain pipe and a thermometer are installed on the water heater, and a safety ejection device, a pressure gauge, a thermometer and a water gauge glass are installed on the boiler.
The domestic industry produces steam-to-water high-speed water heaters MVN - 1436 and MVN - 1437 and water-water sectional MVN - 2052-62, designed for heating water in heating and hot water supply systems.
Water heaters
MVN-1436 and MVN-1437
consist of a body, pipe system, front and rear water chambers and a cap. The case, chambers and a cap - steel. The pipe system consists of steel support grids and a bundle of brass tubes with a diameter of 16x1 mm or 16x0.75 mm. Heaters are made short - 2040 mm and long - 4080 mm . Water heaters with a diameter of 273 and 325 mm - two-way, with a diameter of 377 mm or more - four-way.
Water heaters work as follows. Heated water enters through the lower branch pipe of the front inlet chamber, passes through brass tubes, is heated and enters the network with an outside temperature through the upper branch pipe. The steam that heats the water is fed into the annulus.
Hot water water heaters МВН-2052-62
make collapsible single and multi-section, long and short. Sections are interconnected with bolts. The section consists of a body (seamless pipe) with steel tube sheets welded to it and a bundle of brass tubesdiameter 16x0.75 mm. Branch pipes with flanges are welded to the body for connecting sections along the annular space. Water heaters are designed for a maximum water temperature of 150 gr. C and a working pressure of heating and heated water up to 1 MPa.
Scheme with steam speed water heater
used for hot water supply systems of large residential buildings, baths, laundries and other large consumers of hot water. In the water heater, the water entering the house network through the inlet is heated to the required temperature. The high-speed water heater is flowing, the consumed water flows at a significant speed through the heating tubes - tubular heating elements, which in turn are heated by water from the heating network passing inside the water heater body and washing them. From the water heater, hot water is supplied to the hot water supply system through a pipeline. A regulator is installed on the supply pipeline of the heating network, which automatically maintains a constant flow of water from the heating network, and an air vent. Cold water in the water heater comes from the water supply. On the control unit at the input there are valves for shutting off the pipeline of the heating system and individual parts of the unit. The water consumption in the network is taken into account using a water meter.
To prevent water from the heating system from entering the heating pipeline, check valves are installed. Manometers and thermometers are installed at separate points of the control unit to measure the pressure and temperature of the water. Three-way control valves are installed under the pressure gauges, which are screwed into the pipe fittings. High-temperature water from the heating network from the input is mixed with a part of the cooled water from the return line of the heating system by an elevator, which has valves that regulate the temperature of the mixed water. Mixed water enters the main riser of the heating system and returns to the return pipeline of the heating network through the return pipeline from the heating system. The mud trap is used to catch dirt from return pipeline heating systems. A heat meter is used to account for the heat consumed. A pressure regulator is installed on this line.
Hot water systems are:
- with a dead-end pipeline, where, with a small analysis of hot water or no water intake, the water cools quickly. Therefore, such a scheme is used in low-rise residential buildings with a short network, or in systems where water is constantly taken apart (baths, laundries, etc.)
- with circulation risers; such schemes are used where water cooling in pipes is not allowed, for example, in multi-storey residential buildings, hotels.
Single-pipe systems of centralized hot water supply
currently widely used in residential buildings. In these systems for buildings of 5-9 floors, risers within the section at the top are interconnected, with all risers, except for one, being connected to the supply line, and one outlet riser to the circulation line. To the holiday riser, as well as to the supply, devices for drawing hot water are attached. To ensure uniform circulation of water in the hot water supply systems of buildings connected to one central heating point, a diaphragm is provided on the outlet riser.
For residential buildings over 9 floors, all hot water risers are connected to the supply line and an independent circulation riser is laid, which is connected at the top to the jumper between all supply risers, and at the bottom to the circulation line. In supply systems, the circulation line is calculated from the condition for supplying the calculated amount of hot water. Air removal from hot water systems is carried out through an air collector or by connecting a branch to the devices on the last floor at the top mark of the riser. At the base of each riser and on the jumpers between the risers, a shut-off valve is installed.
At ring pattern
risers are accepted of the same diameter over the entire height of the building and are usually equal for buildings up to 5 floors inclusive 25 mm , and for higher-rise buildings - 32 mm.
Water heaters,
heating water for domestic needs, there are: electric, gas, solid fuel, indirect heating of hot water from the heat carrier of the heating system. Water heaters are divided into:
- flow, where water is heated as it moves past the heat transfer elements (electric heating elements, copper pipes, plate heat exchangers)
- accumulative, where water is heated in the accumulative parts of the device using heat transfer elements.
All water heaters can be divided into the following types: gas flow ( geysers), gas storage, electric flow, electric storage (with and without a built-in coil), electric storage with a firebox for solid fuel, indirect heating.
An open water supply system, its advantages and disadvantages in comparison with the opposite, a closed system, is considered in detail. The elements of an open system and the features of its operation are listed.
Tip: an open water supply system of this type is advisable only in places of continuous hot water analysis, or in short-distance networks.
Picture 1: open system hot water supply
Circulating water supply system
Where continuous provision of hot water to points of consumption is preferable, and the discharge of water is undesirable, circulating systems are used. The water in the pipeline of such a system does not stop and does not cool down, but is continuously pumped through the water heating installation, which makes it possible to maintain its temperature at a given level at each individual point of water consumption.In buildings up to 4 floors, water circulates only in the distribution pipes, and more than 4 floors - also in the pipes of the risers. At the same time, the water temperature in water points where the centralized heating system is connected to the local system is not lower than 60 degrees (for open water supply systems) or 50 degrees (for closed water supply systems). In both cases, the water temperature should be within the range of up to 75 degrees. (See also: )
Figure 2: circulation system hot water supply
Differences between open and closed water supply systems
AT closed system water from heating networks is used as an energy carrier for heating cold water coming from the water supply to the hot water supply system in a heat exchanger. In open systems, hot water is supplied directly from the heating network. The temperature of such water is up to 75 degrees, and it is intended to meet the hygienic and domestic needs of the population (bathing, washing, etc.). Therefore, the open and closed water supply systems differ and are classified depending on the method of water supply. Water taken directly from the heating network is called household water.Figure 3: Closed hot water system
Maintenance of open water supply systems includes disinfection, and, in agreement with the state supervision authorities, it can be carried out not only with the help of chlorination, but also by simple washing with hot water at a temperature of about 90 degrees.
Advice! The water heater also needs to be cleaned periodically, because under the influence high temperatures unfavorable conditions for water quality may be created. (See also: )
Figure 4: Open hot water system
An open hot water system is extremely simple: it consists of a water heating installation, circulation pump and pipelines for its transportation to water points. The location of the distribution line inside the building can be of several options:
- Top wiring system - most often used in the case of installing top water heaters (tanks), which is possible if there is an upper technical floor in the structure. In this case, the circulation line is laid in the basement.
- System with bottom wiring - more convenient in terms of Maintenance, the water heating installation is located in the basement. (See also: )
Water quality requirements
The quality of water in an open system is the same as in radiators. Therefore, the requirements that an open hot water supply system imposes on the quality of the coolant are higher than for closed systems, in which water for consumption practically does not differ in quality from cold tap water.Figure 5: Quality water
Arrangement of an open water supply system
Equipment for arranging an open water supply system should be selected taking into account the principle of its operation. In other words, the water supply from the lower tank must be accompanied by the same water pressure in the taps of all floors, from the first to the last, and it is not always possible to achieve this only using a pump of the required capacity.Important! It is necessary to take into account the friction force on the pipeline walls, which reduces the speed of water movement. This influence seems insignificant, but in practice an open-type water supply system is effective only when all the nuances are taken into account.
The water pressure in the system is determined by the following factors:
- Geodetic injection height;
- dynamic pressure;
- Losses in pipelines.
Figure 6: System pressure measurement
Efficiency of hot water systems
The efficiency of the system is determined by the maximum transfer of thermal energy to the consumer with a minimum coolant consumption. The water supply system is open and closed, in the absence of water intake for hot water supply, the efficiency indicators will not differ, with the exception of the option with a heat pump (which is the most efficient in any conditions). Closed and open systems have different advantages. In a closed system, it is possible to provide hydraulic decoupling of heat networks, and in an open system, the cost of hot water supply for the end user is much lower. In addition, it is characterized by a higher level of reliability and increased efficiency in the future (provided that the coolant is water of drinking quality).The use of materials is allowed only if there is an indexed link to the page with the material.