How to choose a circulation pump: types, calculation of parameters
Today you rarely see a home heating system built according to the classical gravitational scheme. Almost everywhere a circulation pump is used for heating. This device is useful and functional, but reduces the overall requirements for the accuracy of designing a pipeline network. At the same time, without a forced circulation source, it is impossible to operate such technologically advanced heating systems in a private house or apartment as a warm floor.
The device and principle of operation of the circulation pump
Circulation pump device — implementation of a standard scheme centrifugal machine. The main structural components include:
- pump housing;
- a rotor that transmits rotation from the engine shaft to the turbine block;
- turbine impeller with inclined blades, which is also called the impeller;
- means of sealing, isolation from water or coolant;
- the main electrical circuit that switches operating modes and monitors engine parameters.
Circulation pumps can have a different body shape and the location of the outlet and inlet nozzles. This is done so that the device can be easily mounted, serviced in the operating conditions for which it is designed. In particular, the selection of the pump can be made according to the type of connection: with a flange, threaded connection, nut.
The circulating pump has small dimensions. It is often built directly into the internal cavity of the body of domestic gas heating boilers. Safety devices can be installed with the pump. The small size of the supercharger is easy to understand, given the purpose of the circulation pumps. They do not require a record liquid supply power. In fact, they move water literally in a horizontal direction.
The task of circulation pumps is to overcome the hydraulic resistance of pipelines. If the underfloor heating collector group is considered, the blower is busy creating a flow of very small volume as such, since no significant gravitational forces exist in this type of heating circuit.
The principle of operation of the circulation pump can be illustrated in several ways.
- The coolant enters the inlet pipe.
- When the engine is turned on, the torque is transmitted through the rotor to the turbine wheel.
- Rotating, the wheel moves water with inclined blades, which moves to the edge of the disk under the action of mechanics (distribution of forces along an inclined plane), as well as due to centrifugal force.
- As you approach the edge of the disk, the speed of the water flow increases, as does its pressure.
- The liquid is ejected into the outlet pipe.
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As water or coolant moves to the edge of the turbine wheel, a rarefaction occurs in the inlet pipe, it captures a new portion of the working fluid for transportation.
Important! The circulation pump of a gas or solid fuel boiler is able to effectively serve a certain length of pipelines, pumping the volume of coolant declared in the characteristics. If you need more performance and pressure, it is not necessary to buy a separate, external supercharger. An additional pump can be installed in the system, which will create the necessary flow or help raise water to the second floor. They do the same when building a distributed, zoned floor heating system.
Both a conventional home heating system and a two-pump heating system can use different types of blowers. The main difference between the models offered on the market is in the engineering solution of the rotor-turbine zone.
Glandless circulation pumps — the most common type of blowers for the heating system of a private house or apartment. The devices are so named due to the fact that the operation of the nodes occurs directly in the coolant.
- The rotor is placed in a special glass with sealing or vortex protection against leakage.
- During operation, rotor parts, including plain bearings, are in water or coolant.
- There is a continuous lubrication and cooling of parts of the structure.
Thanks to these operating features, wet systems are stable, maintenance-free, low noise.
To prevent air from entering the rotor area, the pump is equipped with exhaust outlets. The upper one is designed for the operation of an automated system, and gas is released through the front of the housing during commissioning or adjustment.
Important! The operation of the pump with a wet rotor, provided that air enters the pipelines, causes a sharp increase in wear of moving parts, overheating, jamming or irreparable damage to the equipment. The presence of abrasive particles in the coolant is not recommended. Therefore, a wet rotor water pump should only be installed in a closed heating system.
Dry rotor pumps
The dry rotor pump is available with careful isolation of the turbine block from leaks. The system has a number of advantages and disadvantages.
- The advantage of dry systems is better cooling — most of the nodes in the heating system do not come into contact with the hot coolant.
- Dry pumps are noisier.
- The overall level of reliability of pumps with a dry rotor is lower due to the large number of seals, the lack of constant lubrication.
However, the main advantage of dry type blowers is that they are not afraid of airing.. They are also less disturbed by the abrasive suspension in the water — only the turbine suffers from it, in which the resource for failure is much higher than that of the rotor block with its plain bearings. Therefore, such superchargers should be chosen if an open heating system with a circulation pump is being built.
Advice! The danger of an open heating system for a circulation pump is the likelihood of airing, hydraulic surges and the formation of an abrasive suspension in the coolant. Due to contact with air, water is constantly saturated with oxygen, oxidation processes are accelerated, especially if steel pipes or heating radiators are used. The amount of rust increases in the coolant. In such conditions, the use of a pump with a dry rotor is recommended.
Variable speed pumps
The speed of the pump in the heating system plays a big role. By changing it, you can achieve:
- optimal mode of operation of heating equipment;
- stabilization of the temperature of all radiators, regardless of the distance of their location from the boiler;
- reducing the temperature of the coolant with a constant heating efficiency, since at a higher circulation rate, each passage of water loses less energy.
There are various technical solutions for pumps on the market today. Home heating can use a single-speed model, the performance of which must be selected in accordance with the characteristics of the boiler and the total volume of the heat carrier. Offered two, three, four speed models. Their work is based on changing the switching circuit of the motor pole pairs.
A more technologically advanced, but also noticeably expensive solution is frequency control. This type of pump does not provide step switching, but smooth speed control. This allows you to very finely tune the operation of the heating circuit.
The use of circulation pumps in home heating
Since some features of the operation of water circulation pumps in various heating schemes have already been mentioned above, the main features of their organization should be touched upon in more detail. It is worth noting that in any case, the supercharger is placed on the return pipe, if home heating involves raising the liquid to the second floor, another copy of the supercharger is installed there.
The most important feature of a closed heating system is sealing. Here:
- the coolant does not come into contact with the air in the room;
- inside the sealed piping system, the pressure is higher than atmospheric pressure;
- the expansion tank is built according to the hydraulic compensator scheme, with a membrane and an air area that creates back pressure and compensates for the expansion of the coolant when heated.
On a note! For a closed circuit, you can make an expansion tank with your own hands. Its capacity is calculated using simple formulas, it depends on the total volume of water in the system.
The advantages of a closed heating system are many. This is the ability to carry out desalination of the coolant for zero sediment and scale on the boiler heat exchanger, and filling in antifreeze to prevent freezing, and the ability to use a wide range of compounds and substances for heat transfer, ranging from a water-alcohol solution to machine oil.
The scheme of a closed heating system with a single-pipe and two-pipe type pump is as follows:
When installing Mayevsky nuts on heating radiators, the circuit setting is improved, a separate air exhaust system and fuses in front of the circulation pump are not needed.
Important! A closed heating system built without tilting pipes, observing the level of the main lines of movement of the coolant, does not work without a circulation pump. It also does not function when the power is turned off.
Open heating system
The external characteristics of an open system are similar to a closed one: the same pipelines, heating radiators, expansion tank. But there are fundamental differences in the mechanics of work.
- The main driving force of the coolant is gravitational. Heated water rises up the accelerating pipe; to increase circulation, it is recommended to make it as long as possible.
- The supply and return pipes are placed at an angle.
- Expansion tank — open type. In it, the coolant is in contact with air.
- The pressure inside an open heating system is equal to atmospheric pressure.
- The circulation pump installed on the feed return acts as a circulation amplifier. Its task is also to compensate for the shortcomings of the piping system: excessive hydraulic resistance due to excessive joints and turns, violation of tilt angles, and so on.
An open heating system requires maintenance, in particular, a constant topping up of coolant to compensate for evaporation from an open tank. Also, corrosion processes are constantly taking place in the network of pipelines and radiators, due to which the water is saturated with abrasive particles, and it is recommended to install circulation pump with a dry rotor.
The scheme of an open heating system is as follows:
An open heating system with the correct angles of inclination and a sufficient height of the accelerating pipe can be operated and when power is off (stopping the circulation pump). To do this, a bypass is made in the pipeline structure. The heating scheme looks like this:
In the event of a power outage, it is enough to open the valve on the bypass bypass loop so that the system continues to work on the gravitational circulation scheme. This unit also makes the initial start-up of the heating easier.
Underfloor heating system
In the underfloor heating system, the correct calculation of the circulation pump and the choice of a reliable model are a guarantee of stable operation of the system. Without forced water injection, such a structure simply cannot work. Pump installation principle next:
- hot water from the boiler is supplied to the inlet pipe, which is mixed through the mixer block with the return flow of the underfloor heating;
- the supply manifold for underfloor heating is connected to the pump outlet.
The distribution and control unit of the underfloor heating is as follows:
The system works according to the following principle.
- Installed at the pump inlet main thermostat, which controls the mixing unit. It can receive data from an external source, such as remote sensors in the room.
- Hot water of the set temperature enters the supply manifold and diverges through the floor heating network.
- The incoming return has a lower temperature than the supply from the boiler.
- The temperature regulator with the help of the mixer unit changes the proportions of the hot flow of the boiler and the cooled return.
- Water of the set temperature is supplied through the pump to the inlet distribution manifold of the underfloor heating.
Important! In such a structure, there is no gravitational component of circulation. Therefore, when the power and pump are turned off, the warm floor simply does not work.
Calculation of the circulation pump
The circulation pump in the heating system of the house must solve the main task: to ensure sufficient pumping of the working fluid to return the normalized amount. That is, to pump through the pipes such a volume of coolant that, when cooled in one cycle, will transfer the energy specified in the SNiP to the air of the rooms (at least).
The calculation uses standards for the coldest time of the year. Namely, with the requirements of heat transfer at the level of 173-177 W / sq.m in the conditions of air temperature outside from -25 to -35 degrees. This standard is valid for one- and two-story buildings. In houses of greater height, a return of 100 W / sq.m is accepted.
According to these indicators, first of all, the power of the main heater, electric, gas, liquid or solid fuel boiler is calculated. The main parameter of the circulation pump, flow or performance, is quickly and conveniently calculated based on the characteristics of the heater. To do this, it is enough to divide the boiler power in Watts by the temperature delta, the indicator of water cooling in one operating cycle. This is the difference between supply and return. In practice, it is taken equal to 20-25, since the coolant has 80-95% at the boiler outlet, and after passing through the batteries from 60 to 70 degrees Celsius.
However, calculating pump performance is only half the battle. Its characteristics should be sufficient to overcome the hydraulic resistance of the entire network of pipes inside the house. It is reduced to the pump head parameter in the following ratio: 100 Pa / m corresponds to 0.01 m.
For hydraulic resistance calculation pipe network inside the house ignore its number of storeys. The reason is simple: the length of the pipes for lifting water from the boiler is almost always equal to the length of the return. To calculate the hydraulic resistance, special formulas are usually used that take into account all the features of the distribution network.
There are also simplified version of the calculation. The following assumptions are used in the calculation:
- one meter of straight pipe creates a resistance of 100 to 150 Pa per meter, depending on the material;
- the use of fittings increases the resistance of the network by 30%;
- when using three-way mixers, you need to add another 20% of the direct resistance to the final result.
The calculation procedure is as follows: first measure the total length of the pipes. Multiplying it by the normalized resistance, you get the basic result. Then losses are added to it. That is, they add percentages for fittings, mixers, turns. If the network is built according to a single-pipe scheme and thermostatic valves are used in the radiators, 70% of the base resistance value is added to the final result.
There is an opinion that the target parameters of the circulation pump obtained as a result of the calculations describe the technical maximum. But in practice, you can take a device with low performance. However, a simplified calculation means a rather serious backlash in the final results. Many factors remain unaccounted for.
At the same time, advice can be given quite simple: buy a circulation pump with a speed controller. It will allow you to empirically select the parameters if the device is operating in a constant mode.
Other options for pump selection
In addition to the key parameters, when choosing a particular model, you need to pay attention to a number of its important characteristics.
The documentation for the pump indicates what temperature of the coolant it can work with. Most manufacturers, especially budget segment models, this figure is too high. So, if 90% is declared on an inexpensive device, in practice it will be able to work trouble-free with a coolant of 70-80 degrees Celsius.
Here the key requirement is to comply with the parameters of the heater and the heating network as a whole.. In the system of warm floors, the water temperature is quite low. As well as in several other schemes. But when using a heating boiler, you will either need to buy a fairly expensive pump, or regulate the temperature of the water at the inlet of the pipe network.
High-quality and reliable circulators have permissible working fluid parameters of 110-130 degrees. The price of such solutions is high. However, users have a minimum of complaints about their reliability.
In one and two-story houses, the pressure in the heating network usually does not exceed 2 atm. Very rarely, this parameter is from 3 to 4 atm. A pump that is correctly sized according to the pressure characteristic will cope with the task assigned to it. However, if you need to choose an inexpensive circulator, you should pay close attention to its operating pressure indicator.
Automatic protection is an extremely useful option for a circulation pump. It significantly extends the life of the device or blocks the occurrence of emergencies. Today, two types of protection are common.
- From overheating. The thermocouple, which controls the temperature of the electric motor, will automatically turn off the pump when it overheats.
- From dry run. Especially important in models with a wet rotor. It won’t let the engine overheat.
In addition to taking care of the engine, dry-running protection plays another role. It stops the pump, thereby preventing the impeller and seals from failing. Jamming and damage are excluded.
Number of speeds
With the correct calculation, it does not matter how many speeds the circulator has. But if you want to optimize system performance, achieve lower noise levels and save energy, you should pay attention to three-mode models. This is an affordable home option.
More complex pumps can have more speeds or be electronically controlled by an external signal, providing smooth power output and fully controlled flow.
Speaking about the structural design, we mean the dimensions of the fittings, the dimensions and the material of the body. Regarding the latter, everything is simple. Cast iron housings strong, durable, contribute to better heat dissipation from the engine. Inexpensive plastic practical and acceptable for pumps installed in places where they are not threatened by temperature changes or mechanical damage.
Fittings ideally should match the network parameters. That is, for a 25 mm plastic pipe, a pump with the same characteristic is selected. Larger nozzle diameter is allowed. The pump can be connected using adapters of various kinds. But a smaller diameter is not allowed.
Dimensions standard pump are normalized. This is 180 mm between the connection points on the fittings. All bypasses and spurs that are offered in stores are designed for this particular size. There are more compact solutions to fit inside equipment or where space is limited. The length of such a pump is 130 mm.
All data required by the user is contained markings on the front. The numbers on the circulation pump mean:
- type of device (most often it is UP — circulation);
- type of speed control (not specified — single-speed, S — step switching, E — smooth frequency control);
- nozzle diameter (indicated in millimeters, means the internal dimension of the pipe);
- head in decimeters or meters (may vary from manufacturer to manufacturer);
- mounting dimension.
The marking of the pump contains information about the types of connections of the inlet and outlet pipes. The complete coding scheme and word order looks like this:
Responsible manufacturers always follow standard labeling rules. However, individual companies may not indicate some of the data, for example, the installation dimension. You need to learn it directly from the documentation for the device.
Choose a pump only from trusted brands. Reliable devices are also presented in the middle price category. And if you need the highest quality and there is an opportunity to pay one and a half to two times more, you should pay attention to the products of the brands GRUNDOFS, WILO.
Today on the market you can buy any circulation pump. For the user, the main thing is to correctly calculate the required performance of the supercharger. And then, if you do not buy frankly junk products from the Chinese garage industry, the heating system with a high-quality pump will function for a long time, without fail and stably.
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