A DHW pump is a universal unit that ensures constant circulation of water in hot water supply systems, which will be discussed, heating, cooling and air conditioning. Equipment of this type is used in equipping apartment and private buildings, various industries, agriculture and the national economy.

Modern technologies allow manufacturers to produce compact and at the same time high-performance installations with low energy consumption in continuous operation. Thanks to this, hot water supply is available for optimization performance characteristics buildings and premises for any purpose.

1 Description and purpose

The basic function of a DHW pump is to ensure uniform movement of water under given pressure regardless of the instantaneous flow rate when the tap is turned on. As a rule, this is a circulation unit for completing closed-loop systems. The recirculation pump is indispensable in the supply system hot water. Depending on the actual need, it regulates and maintains the specified temperature of the pumped medium.

All modern installations are equipped with a system of sensors and regulators that prevent excessive heating or cooling of water. This is of no small importance for creating an optimized microclimate, meeting user needs and minimizing the risks of premature equipment failure as a result of uncontrolled overloads. The flexibility of customizable parameters also allows you to control temperature indicators depending on external conditions and even the time of day.

The most popular and energy efficient is a recirculation pump with a built-in thermostatic circuit. Turning the unit on and off is regulated by specified settings, which guarantees a reduction in the percentage of heat loss.

The operating principle of a DHW system equipped with a pump is simple. Essentially, this is a closed pipeline, the branches of which are connected directly to taps or other water intake points. Secured pumping station pressure promotes constant circulation of hot water in the system, so that it is always available in the immediate vicinity of each tap. The result is that there is no need to drain a certain amount of drinking cold water into the sewer.

As water is consumed from the tank, the pump automatically refills it, where the unused liquid remaining in the system circuit is also returned.

1.1 Classification

The electric pump for hot water systems is equipped with a wet or dry rotor, which is what the traditional classification of equipment of this class is based on.

Equipment with a wet-type rotor is installed directly in the pumped medium. The advantages of this method include automatic cooling without the need to stop working. Pronounced advantages are low cost, no need for frequent maintenance, ease of installation. However, if your choice falls on a device with a wet rotor, you need to remember 2 points:

• The efficiency of the unit is only 45%;
• installation is only possible in a horizontal position.

Unlike the previous version, pumps with a dry rotor are cooled thanks to the included fan. The tightness of the housing ensures that the working parts do not come into contact with water, which is why such models are durable and reliable. Such models are effective when pumping large quantity liquids, the efficiency level reaches 70%.

Types of air-cooled pumps:

• , the installation of which requires the construction of a foundation, the engine is moved outside the housing and connected to the main unit using a coupling;
• monoblocks - all working parts are located inside the housing, the drive shaft is equipped with a wheel;
• inline - 2-ring and more tightly sealed analogues of cantilever pumps, made of anti-corrosion materials.

1.2 Benefits

A circulation pump for domestic hot water is:

• guarantee of maintaining the set temperature in the system;
• wide range of customizable parameters;
• possibility of aggregation to pipes of any type and size;
• no need to install the boiler at the lowest point of the system;
• Ease of Management;
• economical energy consumption.

2 Selection options

The most important thing when buying a domestic hot water pump is to choose a model with the characteristics that best suit your needs. Only in this case will the water supply be as efficient as possible. In general, the selection of a circulation pump for a boiler or system with another heating element based on flow rate, pressure, temperature and design features.

Flow is a basic characteristic of pumping equipment. To calculate it, it is enough to know what power the heat source has, the indicators and temperature difference in the supply and return pipelines.

The pressure in the system depends on the power of the selected unit and the correctness of its connection. Select an electric pump for closed-loop systems in apartment building possible without taking this characteristic into account. And if DHW pump designed for a private home, it deserves attention.

The water temperature in the hot water system is 60-65 o C, but it is important that the equipment still has a small margin of safety.

The material used to manufacture the DHW pump determines its durability. We recommend giving preference to models made of brass, bronze or of stainless steel due to corrosion resistance and low susceptibility to resolution due to contact with oxygenated or other impurities water.

2.1 DHW recirculation pump Wilo Star-Z Nova (video)

To ensure the circulation of hot water supply in large premises and apartment buildings, DHW circulation pumps are used to regulate the water supply in a closed circuit. Due to the ability to circulate and recirculate water several times in one circuit, the pump is also called a recirculation pump.

The need to use a pump

The circulation pump for hot water supply is used for the full operation of the entire heating system of the house, as well as cooling and air conditioning systems. The equipment is designed to prevent the accumulation of stagnant water in pipes. In the production of pumps for recirculating hot water, designs are thought out that are protected from breakage and sedimentation of calcified residue. To provide the necessary conditions for pumping hot water through a pipeline, the pump has a recirculation principle of operation, which allows increasing pressure throughout the system.

Due to the fact that the DHW circulation pump operates silently and energy-saving technologies are used, it can operate for up to 13-15 years, according to average data. The models produced are configured in such a way as to ensure uninterrupted operation of the system and are equipped with a temperature control function along the circuit.

The need to use a circulation pump for hot water is explained by the fact that at temperatures above 60°C all pathogenic bacteria die. Even with a 25 W pump you can kill pathogenic bacteria such as Legionella. The installed equipment will not only be durable, but will also preserve the health of all family members.

The structures that are installed in the hot water system are made of brass and stainless steel, cast iron, bronze; they can withstand exposure to water with a large amount of salts. Conventional pumps may not be suitable, so manufacturers provide the population with circulation systems different types. Some models are equipped with thermostats; they maintain the set temperature for the entire operating period or for a certain period of time. Small water supply systems are equipped with a rotor that is easy to clean from calcium deposits.

Application area

The circulation pump can independently improve the functions of the pipeline circuit and ensure uninterrupted pressure supply. The devices are used for finishing houses or apartments with warm floors, since circulating hot water, pumping and pumping, requires more power.

The use of circulation pumps in large buildings and multi-storey buildings, where there is an extensive network of circuits along the entire perimeter, tens of meters long. Heaters are inferior in functionality in that the water in them quickly cools down and the necessary energy is lost; in practice, it drops from 55-60 degrees to 40-45.

Natural and forced hot water systems have their pros and cons, which depend on the application for a particular area. Natural circulation water in the heating system is carried out due to gravitational forces, they cannot be regulated and used in hot water supply.

The forced system, exactly the opposite, is designed to work with DHW circulation pumps, as it is adjustable. Thermal energy V in this case used to its full capacity, providing a high degree of comfort. In this way it is possible to minimize the difference temperature conditions water leaving and entering the boiler.

There are also models for industrial use that have large dimensions and significantly increased power.

Principle of operation

In a hot water supply system, the circulation pump has a design similar to those used for heating systems. The main goal of creating equipment is to increase pressure through the pipeline and maintain the required temperature.

Hot water supply is provided in stages:

1. A closed-type pipeline is connected to the boiler, which runs throughout the house;
2. First, hot water is drawn into the container, after which the pump creates the pressure necessary for the pipeline circuit;
3. Water with a temperature of 50-60 degrees circulates through pipes near the apartment taps. Thus, a person immediately receives water under pressure in the shower or tap in the kitchen.

If the water has not been completely used up, it is returned to the boiler or boiler again through the return pipeline. If the system does not function according to sanitary standards, the water flow will become slower, this will cause insufficient heating.

Types of pumps

In order to choose electric pumps for a hot water supply system, you should know their types.

Classification by rotor type:

• Models with a “wet rotor” are popular because they are durable and silent during operation. In addition, the pressure part of the unit is located in the pumped medium, in which the rotor is constantly lubricated and cooled if necessary. A wet rotor pump does not require constant diagnostics and is inexpensive. The downside of the unit is its low efficiency of up to 45% and the fact that it is mounted only horizontally; it can increase the pressure to a maximum of 3 atmospheres;
• Models with a “dry rotor” differ from the previous version in that the main power unit is located outside the pumped medium. The disadvantage of this mechanism is problems with lubrication and cooling, since it always remains dry. The solution to the problem is to regularly inspect the equipment and install a fan. A more powerful device, compared to a wet rotor, can increase the pressure through the pipeline to 5-10 atmospheres, which explains its high cost.

Based on speed switching, hot water pumps are classified:

• With one speed, the devices fit any living conditions, have low productivity. Easily integrated into the system and do not require special maintenance;
• Multi-speed units can be configured in such a way that operation algorithms can be switched. They are most often installed for plumbing systems.

The selection of a circulation pump is carried out in accordance with the requirements:

1. First, you should select the required pump based on its performance, calculating its performance with minimal use;
2. The unit is selected depending on required pressure, with wet or dry rotor;
3. The pump should be selected according to the parameters of the heated room and the temperature of the pipeline fluid;
4. The device is selected based on noise level, giving preference to silent options;
5. In contrast to which room will be connected to the hot water supply, equipment with different levels of complexity is purchased.

The main task of the pump is to DHW circulation is to ensure constant pressure through the pipeline, so that the return water temperature can be known.

For further operation of the pump, the following selection criteria are important:

• Water pressure speed, which makes it possible to estimate the pressure on centrifugal water flows and return;
• Amount of water consumed;
• Heat transfer of the DHW system, determined by the area of ​​the room and heat losses.

When choosing a circulation pump, preference is given to devices with a “dry rotor”, despite their high cost. Compared to a “wet rotor” in a DHW pump, “dry” ones have a productivity of up to 75%.

Installing a circulation pump

Before installation recirculation pump for hot water supply, you should be sure that it will be carried out in accordance with the instructions from the manufacturer and the house design diagram, and all liquid from the pipeline must also be drained.

The equipment is installed step by step:

1. The first step is to select the installation location; it should be on the return line, in front of the boiler. The location on the return line prevents oxygen from entering the station, which can lead to equipment shutdown. The coolant will rest against the boiler, creating a vacuum space, ensuring it is completely filled with water;
2. Then there is a choice of bypass or bypass, which is designed for uninterrupted operation of the pump in the event of a power outage and water supply to the taps. It is important that the diameter of the main pipeline is larger than the diameter of the bypass pipe. It is imperative that the pump shaft is installed in a horizontal straight line so that it is completely in the water;
3. A check valve should be installed in front of the storage tank, and shut-off valves will also be required before and after the station;
4. The installation of a filter must be considered for the system to avoid small particles from entering the pump design. To be able to release air jams, an automatic or manual valve must be installed;
5. The pump is connected to a UPS to avoid power outages;
6. Before starting the electric motor, additional pressure movement valves and distribution manifolds are installed.

Starting the system and doing a test run is only allowed after the pump is installed in the DHW system and the water circuit is being filled. Regardless of the heating area in the house, a DHW circulation pump is installed for private and multi-storey buildings.

First of all, it is necessary to remember that circulation and booster pumps are completely various devices. The circulation pump does not change static pressure system, but only ensures the movement of coolant through the pipes.

The main characteristic of any circulation pump is the operating curve, which in the case of the DHW recirculation option usually consists of a single curve, since it usually does not have switching speeds (Fig. 1). The graph shows that as the volume of pumped liquid increases, the pressure drops. And vice versa, as the height of the rise increases, the flow decreases. At the extreme point with maximum pressure, the flow is zero, at the point with maximum flow, pressure is zero.

It is very convenient to illustrate the physical meaning of this curve using the example of an open system (Fig. 1 and 2). If the length of the pipe H is equal to H max, water will not flow out of it, since at this pressure value the flow V 0 is zero. If you shorten the pipe to length H1, water will flow out of it at a speed of V1. By removing the pipe altogether, we get a flow at the outlet Vmax, since the pressure H0 = 0.

The situation described above is only true for open systems. IN closed system the pressure created by the circulation pump is not intended to overcome the height of the liquid rise, but to compensate for the pressure loss caused by the resistance of pipes and fittings.

Operating point of the DHW circulation circuit

In a circulation circuit, pressure loss and volumetric flow are closely related. There is an equilibrium between the pressure loss in the system, which must be converted into head loss, and the pump head. This means that the system losses coincide with the pump head at the operating point.

Since each pump pressure value corresponds to a single flow rate, the volume of water circulating in the system is directly related to the resistance of pipelines and fittings. To determine the operating point, it is necessary to superimpose the curve of the DHW circuit on the graph of the circulation pump.

There are often cases when neither the system curve nor its operating point are known. In this case, the required values ​​of pressure loss in the system and the required volume of hot water for circulation can be determined arithmetically by calculating the resistance of individual sections of the system.

It must be taken into account that it will be possible to achieve the design characteristics only if all circulation branches connected to one pump are hydraulically balanced using control valves, mechanical or thermostatic. The purpose of balancing is to maintain optimal speed flow throughout the entire system, regardless of the length of the pipes and their diameter, in order to prevent an excessive decrease in the temperature of the water returning to the boiler. Ideally, the difference between the supply pipe at the outlet and the recirculation line at the inlet of the water heater should be 2-3 K for small systems less than 200 m in length and 7-10 K for large ones (more than 200 m in length).

In the standard case, with equal diameters of all circulation pipelines, in branches located closer to the pump, the resistance must be increased to such an extent that it corresponds to the pressure loss in distant branches. Far from the pump, on the contrary, it is necessary to create an increased flow so that the circulating water does not have time to cool down too much.

The diameter of the circulation pipe depends on the diameter of the supply pipe. Unfortunately, the Russian SNiP 2.04.01-85* “Internal water supply and sewerage” does not have clear recommendations in this regard, so let’s turn to the German DIN 1988, part 3 (Table 1).

Operating point calculation

Now let's start determining the operating point of the system. For this we need flow V c and pressure loss (pressure) Δp c. The flow that needs to be provided depends on the total volume of water circulating in all branches. To prevent excessive cooling of the liquid, the pump must provide such a speed that all the water in the pipes does not have time to cool too much. It should also be taken into account that maximum speed should not exceed 0.5 m/s for copper pipes and 1 m/s for pipes made of other materials.

The pressure is determined by the sum of the resistances of the longest circulation branch, if we count from the connection of the circulation pipeline to the supply line to the entrance to the water heater. The operating point should be selected so that the temperature of the hot water in the pipes does not fall below 55-60 °C to prevent the growth of bacteria.

There are different calculation methods. We offer here one of them, quite simple, based on some averaged data. Among the disadvantages of this method, we can only note the possibility of using it for relatively small systems with a circulation pipe diameter of different areas from DN 10 to DN 20 and, accordingly, the pump flow area is no more than 3/4'.

First, let's determine the heat loss in the pipelines. If there is no data from the manufacturer of pipes and thermal insulation, for a well-insulated pipe we accept: q tp.neot = 11 W/s per 1 m of pipe laid in an unheated room (for example, a basement), and also q tp.ot = 7 W/s per 1 m of pipe laid in a heated room (for example, a plumbing box, kitchen, bathroom). Heat loss from fittings (valves, meters, etc.) can be ignored due to their insignificant impact on the overall result. Thus, total losses heat in the system are:

Qtp = Σl tp.neot q tp.neot + Σl tp.ot q tp.ot, (1)

where Σl tp.neot and Σl tp.ot are the total length of pipelines laid in cold and heated rooms, respectively.

The maximum permissible temperature difference between the supply and circulation lines is taken to be Δt tp = 2 K. From these data we can now calculate the required flow:

where ρ is the density of water equal to 1 kg/l; c is the specific heat capacity of water, equal to 1.2 W*h/(kg*K). This way you can find the required water speed in individual branches.

If there is only one branch, then the flow in it is equal to the total flow. But this rarely happens, since the circulation line covers all water points, therefore, it is replete with branches.

At nodal points, the duct is divided into a main duct and an additional one. The flow in the main part is equal to:

and in the additional one:

or V add = V c - V main. (5)

The pressure component of the operating point is determined, as indicated earlier, by the longest branch with a coefficient for bends and joints K = 1.2-1.4. The more tortuous the pipe, the higher the coefficient value should be taken. The duct in this case at each node is divided into main and additional. If, after branching, none of the pipes goes directly to the water collection point, the one with the smaller volume of water is considered additional. They also take into account the resistance of various fittings that are not included in the calculation of heat loss - valves, flaps, etc.:

Δp c = KΣl tr R tr + ΣR arm. (6)

The pressure and flow calculated in this way represent the operating point of the system. Let's look at an example (Fig. 3). In table Table 2 shows the main characteristics of the hot water supply system of a three-story building with five risers: the length of metal-plastic pipelines laid in the basement and in heated rooms, the internal diameter of the pipes, the type of flow when dividing at nodal points, and the heat loss in each segment is calculated. After this, we find the common duct according to (2):

at Δt tp = 2 K.

Calculation of the required flow rate on each pipe section based on those determined in the table. 2 heat loss is given in table. 3. Heat losses of the main and additional sections are summed up in the “Total heat losses” column, and the corresponding flow values ​​are calculated using formulas (3) and (4).

In table 4, based on SP 41102-98, the speed of movement of the coolant and pressure loss due to friction are calculated (if the pipes are plastic or copper, then you need to use SP 40101-96 or SP 40108-2004, respectively). The longest branch: 10-8, 8-7 , 7-6, 6-1, the pressure loss in it is 1271.27 Pa. Using formula (6) we find the pressure at the operating point:

Δp c = KΣl tr R tr + ΣR arm = 1.4 × 1271.27 + 200 = 1979.78 Pa,

at K = 1.4 and R arm = 200 Pa. Converted to meters of pressure 1979.78 Pa = 0.2 m.

According to those available in the table. 4, it is also necessary to adjust the control valves.

So, a pump with an operating point V c = 189.17 l/h, Δp c = 0.2 Pa is suitable for this system. Almost any of the DHW circulation pumps available on the market can easily cope with such minor parameters.

1. Brochure VORTEX Brauchwasserpumpen. Technische Broschu..re. Trinkwasserzirkulation mit VORTEX Pumpen // 09de0090 11/09.

2. SP 41102-98. Design and installation of pipelines for heating systems of buildings using metal-polymer pipes.

3. SP 40101-96. Design and installation of pipelines made of random copolymer polypropylene.

4. SP 40108-2004. Pipeline design and installation internal systems water supply and heating of buildings from copper pipes.

An autonomous hot water supply (DHW) system often uses a circulation pump. If the heat source is a boiler, and a significant portion of hot water accumulates in the boiler, then the pump constantly pumps water from the storage tank to the heat exchanger and back. If you mean a hot water recirculation pump, then it eliminates the biggest disappointment autonomous systems DHW - makes it so that when you open the tap you don’t have to wait long for hot water to reach the consumer through the pipes.

Principle of operation

A recirculation pump is not at all necessary, but it significantly increases comfort and even the quality of hot water. Its main task is to pump water through a pipeline in a closed loop from the boiler to the intake points and back. For this purpose, devices with low productivity, low noise and low energy consumption are specially developed. The main requirement for pumps is resistance to high temperatures, stable operation provided that the water is heated to 65°C.

Taken together, recirculation pumps for hot water are still different from pumps for heating. The latter are designed for temperatures up to 90°C and with significantly higher productivity. Interchangeability is irrelevant in this case. If desired, the heating pump can be used in DHW recirculation, but the pump cannot be used the other way around.

A circulation pump is especially in demand in houses with an area of ​​more than 200 square meters, where the boiler is located in separate room or basement, and there are several water intake points spread throughout the house. Wait for the pipes to drain cold water, it will take a long time, which significantly increases consumption. If the water in the boiler heats up to 65-80°C, then almost all pathogenic bacteria die, but in the pipes where the water cools, they are able to actively multiply.

Regular pumping of water through pipes eliminates these problems in the bud. However, due to heat loss in the pipes, the load on the boiler or water heater increases, so the installation of a recirculation pump has a lesser impact on savings and is primarily responsible for the comfort of residents.

To use a recirculation pump, the DHW distribution throughout the house must be carried out in the form of a closed circuit connected to the boiler. All water intake points are already connected from it. If you take water from the top of the boiler, then this will be considered the beginning of the circuit, then the pump is installed at the second entrance to the boiler, located in the lower part of the storage tank at the same level as the entrance to the cold tap water supply.

The circulation pump must be installed together with check valve, which will prevent the reverse flow of water in the circuit, because in this case only cold water will flow through the pipes, tied to the bottom of the boiler and the inlet water supply.

Characteristics

The list of main characteristics of circulation pumps:

• productivity, m3/hour (liter/min);
• pressure, generated pressure, meters or Pa;
• power consumption, W;
• control method (by timer or temperature sensor).

The recirculation pump requires little power and performance. It is necessary to pump water only in tubes with a small internal volume, and at low speed. A device with a capacity of only 0.2-0.6 cubic meters per hour is sufficient to constantly maintain the temperature of water in pipes up to 40-50 meters long.

Pump consumption is also low and ranges from 5 to 20 W. This is enough for stable operation and completion of the assigned task.

It is more important to select the correct pressure generated by the pump. More often, in a house or, especially, an apartment, the wiring is carried out one floor at a time, then a pressure equivalent to 0.5-0.8 meters of water column is sufficient. However, if it is necessary to ensure trouble-free circulation of water in a house with several floors, then the pump must cope with the rise of water to a given height, and with a margin. Pump performance directly depends on the actual installed load.

Design

Centrifugal pumps are used to circulate water. The main elements in them are the shell housing, the impeller and the engine. Water is supplied to the center of the impeller. The engine spins it, and under the influence of centripetal force, water moves with pressure along the outer edge of the shell to the outlet pipe.

For a recirculation pump, the advantages are noiselessness and small dimensions. Therefore, small pumps are used mainly with a wet rotor type. The rotor is the internal moving part of the engine, mounted on the same shaft as the impeller. Under the influence of variable magnetic field From the stator coil, the rotor acquires rotational motion.

The wet rotor is completely immersed in the pumped medium. Water acts as a heat sink and at the same time as a lubricant for the support bearings. The presence of water around the moving parts of the engine reduces noise and vibration during pump operation.

Control method

It is quite acceptable to constantly maintain the circulation of hot water in the pipes, but this is uneconomical and unjustified. Hot water is not used constantly. At night, while all the residents are sleeping, it is useless to keep the water hot in the pipes, the same applies to the time when everyone is at work or school.

If the pipes are laid out correctly, then thermal insulation is required, so that once hot water gets into the pipes, it does not cool down instantly. Therefore, there is no need to constantly pump water from the boiler into the pipes and back; periodic operation of the pump is sufficient, which reduces the load on it and the hot water system as a whole. There is no need to talk about saving electricity, since the consumption of the recirculation pump is low.

Two main control methods are used:

• according to temperature sensor readings;
• according to a timer (schedule).

Both options are in demand, although they differ significantly in their operating principles.

By temperature sensor

Grundfos UP 15-14 BT 80

In this case, the pump control unit relies on the readings of a temperature sensor immersed in water inside the circuit pipes. The pump resumes operation as soon as the water has cooled to a certain threshold temperature. This approach significantly reduces the load on the equipment and constantly keeps the water in the pipes heated. In addition, the safety of the hot water supply increases. Having set a sufficiently high response threshold, water is pumped more often through the boiler, where it is additionally heated and disinfected.

By timer

Grundfos UP 15-14 BU

The control unit alternately turns the pump on and off based on the time delays set in the settings. Knowing exactly the parameters of the hot water system, the length of the pipes and their internal volume, thermal insulation and average heat loss, you can select optimal time, during which the water will not have time to cool. The pump is turned on by a timer signal and pumps all the water. In this case, the duration of operation is also calculated based on the volume of pipes and pump performance.

Another advantage of the timer is the ability to schedule the operation of the recirculation pump for a day or even a week. It is in this case that downtime is taken into account when hot water don't use it.

Installation diagrams

Depending on the number of connection points and the length of the pipes, the method of connecting the circulation pump and pipe routing is selected:

• serial connection with one circuit;
• parallel connection with the collector.

In the first case, all water intake points are connected in series and in one circuit. This is beneficial if you can easily combine bathrooms and kitchen into one water pipe without unnecessary material costs and a fairly short route. There is only one feature that concerns the pressure pump rather than the circulation pump. If several water intake points are open at the same time, the pressure in each of them will be divided equally. Alternatively, this can be solved by installing a gearbox on each tap and choosing a more powerful pump.

Parallel connection solves the problem with pressure and distribution of water using a manifold group and compact placement of gearboxes. In this case, recirculation pumps must be installed in each individual circuit or one more efficient pump must be selected for all groups at once. Such wiring is necessary if there are several bathrooms in the house, spaced far from each other and from the kitchen, or when, with a serial connection, the total length of the route becomes too long.

To increase the efficiency of heating and hot water supply systems, they are equipped with a recirculation pump, the task of which is not only to increase the pressure of the medium transported through them, but also to ensure its circulation in a continuous mode. In some cases (in particular, when installing autonomous hot water supply and heating systems), only a recirculation pump can cope with this task.

Before equipping a hot water supply or heating system with a recirculation pump, you should understand how this equipment works. It is also advisable to study the principle of operation of the circulation pump.

Purpose and scope

Hot water recirculation pumps have a very important function. With the help of such devices, closed pipelines through which hot water is transported operate in the required mode. By pumping liquid into the pipeline due to the rotation of special elements, recirculation electric pumps increase the pressure of the liquid medium they pump and, accordingly, the speed of its movement.

Most often, heating systems are equipped with recirculation pumps, which increases not only the efficiency, but also the cost-effectiveness of the latter. Most of these systems, as is known, operate using a coolant, which, moving through a pipeline, releases heat into the room. Heating of the coolant (in this case, before it is supplied to the pipeline) is provided by a boiler, boiler or water heater. After passing through the entire heating circuit, the water must return to the heating equipment, where it is again given the required temperature.

Without the use of special pumping equipment, water circulation in the heating system will flow slowly, and in some cases may not flow at all, since the pressure of the coolant flow, which is not further increased in any way, will be dampened by the pipeline elements. The result of this is unevenly heated heating pipes and, accordingly, an uncomfortable temperature in the premises of the house.

A circulation pump for hot water supply increases the pressure and pressure of hot liquid moving through a closed pipeline circuit. The use of circulation pumps for hot water is especially important in the pipeline systems of houses with an area of ​​more than 200 m2, in which there are several water intake points, and the boiler is installed in a separate room or in the basement. Water in such pipelines (as a rule, quite long), if they do not have a recirculation system using a special pump, cools down quite quickly. This leads to the fact that when you open the tap you have to wait a long time until liquid heated to the required temperature flows out of it.

In addition, when some taps at water intake points are opened immediately, the water pressure in them drops, because the pressure of the liquid moving through the pipeline by gravity is not additionally supported by anything. To solve exactly these problems that private owners and residents face apartment buildings, a domestic hot water pump is designed to provide forced movement, as well as the creation of stable water pressure and pressure in the hot water supply system.

Using a circulation pump for heating and hot water supply to a private home, in addition to the above advantages, allows you to save on energy costs. Since in systems with recirculation, water from the boiler is transported through pipes forcibly and reaches all water intake points and heating radiators much faster, its temperature during such transportation decreases slightly. A boiler, if forced water recirculation is provided in the pipeline it serves, requires less time to heat it, and accordingly, the consumption of energy carriers used to operate the heating equipment is reduced.

Pumps for circulating hot water are actively used to equip “warm floor” systems, the design of which assumes the presence of an extended pipeline circuit of a complex configuration, consisting of small-diameter pipes. In such cases, the circulation pump ensures constant movement of the coolant through the pipes.

Design Features

For DHW circulation, centrifugal pumps with a “wet” rotor are mainly used. The operating principle of such a circulation pump is quite simple.

• Water entering the chamber of the recirculation pump through the inlet pipe is captured by the blades of the impeller, which is rotated by the drive motor shaft.
• Centrifugal force begins to act on the water, which throws it towards the walls of the working chamber, where increased pressure is created.
• Under the influence of pressure generated by centrifugal force, the liquid is pushed into the pressure line of the recirculation pump.
• The suction of the next portion of hot water into the working chamber occurs due to the fact that air rarefaction is created in the central part of such a chamber during the processes described above.

Design of a centrifugal circulation pump with a “wet” rotor

It should be borne in mind that for heating and hot water supply a conventional centrifugal pump for water, since the operating conditions of such equipment do not provide for a high temperature of the pumped liquid. For the manufacture of pumps that recirculate hot water, materials are used that are resistant to increased loads and impacts. high temperatures. In addition, such electric pumps, which operate primarily indoors, must be low-noise so as not to make living conditions in a private or apartment building uncomfortable. No less important characteristics of electric pumps for DHW circulation are compactness and efficiency in terms of electricity consumption.

Picking up pump equipment which will have to work with hot water, you should also keep in mind that pumps for DHW recirculation differ in operating conditions from the devices used to equip the heating system. Thus, pump models for a boiler room are designed to pump water whose temperature reaches 90°, while devices that circulate hot water can work with a liquid medium heated to 65°. As such, they are not interchangeable, although if necessary, an electric heating pump can be used to circulate hot water in DHW systems. However, replacing such devices in reverse order it is forbidden.

Main characteristics

When choosing a circulation pump for domestic hot water or heating, you should pay attention to the following characteristics:

• productivity - the amount of liquid that a recirculation electric pump is capable of pumping per unit of time (m 3 / hour or liter / min);
• pressure or pressure of the liquid medium created by the pump (meters of water column or Pa);
• power consumed by the recirculation pump (W);
• method of controlling the device (using a timer or temperature sensor).

Since recirculation pumps pump small volumes of liquid, which moves in heating pipes or water pipes at low speed, such devices do not require high power and performance. Thus, to maintain the water temperature in domestic heating and water consumption systems, the length of which does not exceed 40–50 meters, a recirculation pump with a capacity of 0.2–0.6 m 3 /hour will be quite sufficient.

In terms of electricity consumption, boiler and hot water pumps are also economical, since their power, depending on the model, ranges from 5 to 20 W. This is quite enough for the electric water pump to be able to ensure efficient circulation through the hot water pipes in a private house.

It is very important to choose the right circulation pump according to such a parameter as the pressure of the liquid flow that it is capable of creating.

To choose the right pump according to this characteristic, you can follow the following recommendations when selecting recirculation equipment for heating and hot water systems of both a small residential building and a large cottage with several floors.

• If the pipes through which the pump must circulate the liquid medium are located at the same level, then we select equipment with a pressure value of 0.5–0.8 meters of water column.
• If the house has several floors, DHW recirculation must be ensured at several levels of the pipeline, which means that the height to which the liquid must be raised must be taken into account.

In order to make recirculation of the liquid medium more efficient in heating and hot water systems, pumps should be selected with some reserve in the pressure generated.

Equipment control methods

Since the consumption of hot water by the residents of the house is carried out periodically, as needed, there is no point in having the DHW recirculation pump operate in constant mode. The operation of a water recirculation pump in periodic on and off mode reduces the load on both the equipment itself and the pipeline as a whole. There are two ways to ensure the operation of recirculation pumps in periodic mode:

• using temperature sensors;
• using a timer (turning on and off the electric pump according to a schedule).

The difference between such recirculation pump controls lies in both their design and operating principle.

Control via temperature sensor

This method of controlling the operation of a recirculation pump involves the use of a temperature sensor, the working part of which is in constant contact with the liquid transported through the pipeline. When the water temperature in the DHW system or in heating system decreases to a critical value, the sensor automatically turns on the recirculation electric pump, and when the liquid temperature rises to the required level, turns it off. The use of a temperature sensor to control the operation of the recirculation pump allows you to maintain a stable temperature of the liquid in the serviced pipeline. It is also convenient when using a temperature sensor that it can be adjusted to any temperature value at which it will operate.