Heating systems are divided into systems with natural (gravity) and forced circulation. In systems with forced circulation, the installation of a circulation pump is required. Its task is to ensure the movement of coolant through the system at a given speed. And in order for it to cope with its task, you must choose the right circulation pump.
Purpose and types
As already mentioned, the main task of the circulation pump is to provide the required speed of coolant movement through the pipes. For systems with forced circulation, only under such conditions will the design capacity be achieved. During operation of the circulation system, the pressure in the system increases slightly, but this is not its task. It's more of a side effect. There are special ones to increase the pressure in the system.
There are two types of circulation pumps: dry and wet rotor. They differ in design, but perform the same tasks. To choose what type of circulation pump you want to install, you need to know their advantages and disadvantages.
With dry rotor
It got its name due to its design features. Only the impeller is immersed in the coolant; the rotor is in a sealed housing, separated from the liquid by several sealing rings.
The design of a circulation pump with a dry rotor - only the impeller is in the water
These devices have the following properties:
- They have high efficiency - about 80%. And this is their main advantage.
- Requires regular maintenance. During operation, solid particles contained in the coolant fall on the sealing rings, breaking the tightness. Maintenance is required to prevent depressurization.
- Service life is about 3 years.
- During operation they produce a high level of noise.
This set of characteristics is not very suitable for installation in heating systems of private houses. Their main advantage is high efficiency, which means lower energy consumption. Therefore, in large networks, circulation pumps with a dry rotor are more economical, and are mainly used there.
With wet rotor
As the name implies, in equipment of this type, both the impeller and the rotor are located in the liquid. The electrical part, including the starter, is enclosed in a sealed metal cup.
Wet rotor pump design - only the electrical part is dry
This type of equipment has the following properties:
- Efficiency is about 50%. Not the best indicator, but for small private heating systems this is not critical.
- No maintenance required.
- Service life is 5-10 years depending on the brand, operating mode and condition of the coolant.
- During operation they are almost inaudible.
Based on the above properties, choosing a circulation pump by type is not difficult: most people choose devices with a wet rotor, since they are more suitable for working in an apartment or private house.
How to choose a circulation pump
Each circulation pump has a set of technical characteristics. They are selected individually for the parameters of each system.
Selecting technical specifications
Let's start with the selection of technical characteristics. There are a lot of formulas for professional calculations, but to select a pump for the heating system of a private house or apartment, you can get by with average standards:
Selecting a circulation pump for heating following these rules is not difficult. Elementary calculations. But it must be said that these figures are statistical averages. If your house at some point differs greatly from the “average” indicators, you need to make adjustments either towards increasing or decreasing technical characteristics. For example, you have insulated your house well, but the power of the previously purchased boiler turned out to be excessive. In this case, it makes sense to choose a pump with a lower capacity. In the opposite situation - the house is chilly in extreme cold - you can install a more efficient circulator. It will temporarily solve the problem (in the future you will need to either insulate or change the boiler).
Model selection
When choosing a specific model, pay attention to the graph with the pressure characteristics of the pump. On the graph you need to find the point where the pressure and productivity values intersect. It should be located in the middle third of the curve. If it does not fall on one of the curves (there are usually several of them, characterizing different models), take the model whose graph is closer. If the point is in the middle, take the less productive one (the one located below).
What else to pay attention to
In the technical characteristics of circulation pumps there are several more items that are worth paying attention to. The first is the permissible temperature of the pumped medium. That is, the temperature of the coolant. In high-quality products this indicator ranges from +110°C to +130°C. In cheap ones it can be lower - up to 90°C (but in fact 70-80°C). If your system is designed as a low-temperature system, this is not a big deal, but if you have a solid fuel boiler, the temperature to which the coolant can be heated is very important.
It is also worth paying attention to the maximum pressure at which the pump can operate. In the heating system of a private house, it is rarely higher than 3-4 atm (this is for a two-story house), but normally it is 1.5-2 atm. But still, pay attention to this indicator.
Something else to pay attention to is the material from which the case is made. The optimal one is cast iron, the cheaper one is made of special heat-resistant plastic.
Connection type and size. The circulation pump can have threaded or flanged connections. The thread can be external or internal - appropriate adapters are selected for it. Connection sizes can be: G1, G2, G3/4.
It is also worth paying attention to the presence of protection. There may be dry-running protection. In circulation pumps with a wet rotor, it is very desirable, since the cooling of the motor occurs due to the moving medium. If there is no water, the motor overheats and fails.
Another type of protection is overheating protection. If the motor heats up to a critical value, the thermal relay turns off the power and the pump stops. These two features will extend the life of the equipment.
Manufacturers and prices
| Name | Performance | Pressure | Number of speeds | Connection dimensions | Maximum working pressure | Power | Housing material | Price |
|---|---|---|---|---|---|---|---|---|
| Grundfos UPS 25-80 | 130 l/min | 8 m | 3 | G 1 1/2" | 10 bar | 170 W | Cast iron | 15476 RUR |
| Caliber NTs-15/6 | 40 l/min | 6 m | 3 | external thread G1 | 6 atm | 90 W | Cast iron | 2350 rub. |
| BELAMOS BRS25/4G | 48 l/min | 4.5 m | 3 | external thread G1 | 10 atm | 72 W | Cast iron | 2809 RUR |
| Gilex Compass 25/80 280 | 133.3 l/min | 8.5 m | 3 | external thread G1 | 6 atm | 220 W | Cast iron | 6300 rub. |
| Elitech NP 1216/9E | 23 l/min | 9 m | 1 | external thread G 3/4 | 10 atm | 105 W | Cast iron | 4800 rub. |
| Marina-Speroni SCR 25/40-180 S | 50 l/min | 4 m | 1 | external thread G1 | 10 atm | 60 W | Cast iron | 5223 RUR |
| Grundfos UPA 15-90 | 25 l/min | 8 m | 1 | external thread G 3/4 | 6 atm | 120 W | Cast iron | 6950 rub. |
| Wilo Star-RS 15/2-130 | 41.6 l/min | 2.6 m | 3 | internal thread G1 | 45 W | Cast iron | 5386 RUR |
Please note that all specifications are based on water movement. If the coolant in the system is a non-freezing liquid, adjustments must be made. You will have to contact the manufacturer for relevant data for this type of coolant. It was not possible to find similar characteristics in other sources.
In order to install a water heating system with forced circulation, it is necessary to correctly select and install a circulation pump in it, which will provide it. Currently, there is a wide variety of models of different designs and with different characteristics. Which one and how to choose? In this article we will look at how to select a circulation pump for a heating system yourself.
Main selection criteria
In order to select a circulation pump for a heating system, it is necessary to determine its main characteristics that will be required during its operation: the operating pressure (pressure) and flow rate (supply) that it must provide. And in order to determine them, it is necessary to know both the power of the heating system itself and its hydraulic resistance. Both of these indicators can be calculated more accurately, using complex calculations, or simplified, using a calculation that almost anyone can do. We will consider it.
Heating system power and required flow
As we have already said, when selecting a circulation pump for a heating system, first of all, you need to determine its thermal power. It must correspond to the amount of heat required to heat the building, which, in turn, is determined by its area and the level of thermal insulation of external structures (walls, floors, ceilings, windows, doors). To calculate this indicator accurately, it is necessary to take into account their thickness, material, design and other factors.
In order to simplify the calculation, you can take an average of 100-150 W of thermal energy for every 1 m2 of room, with a ceiling height of up to 3 m. If the building is insulated well enough, you can take a lower value. So, for example, a well-insulated house with an area of 100 m2 will require heating with a thermal power of 10 kW. If the circulation pump is installed in an existing system with natural circulation, then its power can be found out from the technical characteristics of the boiler that is installed.
Now, knowing the required heating power, you can determine the required performance (flow) of the circulation pump using one of the following formulas:
P = Q/(1.16 x ΔT),(kg/h)
- Q– thermal power of the heating system (W);
- ΔT– the temperature difference between the supply and return pipes (for two-pipe systems is usually taken within 20°C, and for heated floors – about 5°C);
- 1,16 – coefficient of specific heat capacity of water, W× h/kg× °C(for other types of coolants this indicator will be slightly different and can be found in reference books or on the Internet).
Another formula that can be used to calculate the required performance:
P = 3.6 x Q/(c × ΔT),(kg/h)
Where: With– specific heat capacity of the coolant (for water it is 4,2 kJ/kg×°С).
For example, for the thermal energy power of 10 kW discussed above and a two-pipe water heating system, using the first formula we obtain:
P = 10000/(1.16×20) = 431 kg/h or 0.43 m 3 /h(for coolant water 1kg=1l).
Hydraulic resistance and required pressure
In order to select a pump for a heating system based on this parameter, it is necessary to calculate the hydraulic resistance that it will need to overcome to ensure normal circulation of the coolant (water). To calculate, you can use the following formula:
J = (F+R×L)/p×g(m)
- L– length of the system to the most distant radiator (m);
- R– hydraulic resistance of a straight pipe section (Pa/m);
- p– coolant density (for water – 1000 kg/m3);
- F– resistance of connecting and shut-off valves (Pa);
- g– 9.8 m/s2 (gravitational acceleration).
To accurately calculate the value R And F can be found in the reference literature. For simplicity, we can accept the averaged data obtained experimentally:
R— within 100-150 Pa/m;
F– depending on the type:
- in each connecting fitting, about 30% is lost additionally to the losses in a straight pipe in this section;
- in a three-way mixer or similar devices – additionally up to 20%;
- in thermostats – up to 70% of losses in a straight pipe.
In addition to the above, you can use another formula proposed by specialists from the famous German company Wilo:
J = R× L × k, m
Where: k– coefficient taking into account the resistance in shut-off and control valves and which has the following values:
- 1.3 – for simple systems without complex fittings;
- 2.2 – with control valves;
- 2.6 – for more complex ones.
If one pump will provide circulation in a heating system with several circuits (branches), then to select it it is necessary to take into account their total resistance. If it is planned to install a separate pump for each circuit, then each such branch of the line must be calculated separately, both in terms of thermal power and hydraulic resistance. At the same time, the number of storeys of the building does not play a big role when calculating the pressure. Since in a closed system the liquid columns of the supply and return lines are balanced.
How to choose a circulation pump based on the data received
Having calculated and now knowing the main required characteristics of the circulation pump, you can easily select the required option using the characteristics graphs that are in the operating instructions or data sheet of any model. As a rule, such graphs have two axes: pressure (pressure) and flow (feed).
Rice. 1 Example of a graph of the characteristics of a circulation pump
We can plot the previously obtained results on the existing graph, plotting their values along the corresponding axes, and at their intersection we can obtain a working point, which should be slightly below the line IN a graph displaying the characteristics of a given pump (the best option is A2). If the point is above ( A3) – such a pump is not suitable, it will not be able to provide the necessary circulation. If the operating point is significantly below the schedule ( A1), this is also not very good, since it will provide circulation, but having too large a reserve, it will consume more electricity, and its cost will also be higher than a pump with more modest characteristics.
Rice. 2 Selection of a pump according to its characteristics graph
If the model has not one, but 2 or 3 speeds, then the lines on the characteristics graph will be, respectively, 2 or 3. In this case, it is necessary to select a pump for the heating system according to the schedule of the speed at which it is supposed to be operated.
Other factors influencing choice
In addition to the main characteristics discussed above, the selection of a circulation pump for a heating system is influenced by other factors, such as: reliability, workmanship, operating temperature, cost, connection method, etc.
Workmanship, reliability and durability are usually directly related to cost. Manufacturers that offer reliable and high-quality models, for example: Grundfos (Denmark), Wilo (Germany), DAB, Lowara, Ebara and Pedrollo (Italy), evaluate their products accordingly.
wilo circulation pump in a heating system
Domestic or Chinese models are cheaper, but the guarantee of their quality is correspondingly lower. Here everyone must make a choice themselves, choose a quality product at a higher price or buy a cheaper circulation pump, with the knowledge that it may have to be changed soon.
If you want to save money, you can also buy used “Grundfos” or “Wilo”; often they can work normally longer than new Chinese ones, but it is better to purchase them from familiar, trusted specialists who give a certain guarantee.
In addition, when choosing, you need to pay attention to the type and diameter of the connection between the pump and the system pipes. Some models are equipped with “American” type connecting elements, while for some you will have to select them yourself.
Another parameter that you need to pay attention to is the operating temperature of the circulation pump, which should be in the passport. This is especially important if it is installed on the supply pipe in a system with a solid fuel boiler. In this case, the maximum permissible temperature must be at least 110°C. If the pump is installed on the “return”, then this is not so important, since the temperature at the boiler inlet rarely exceeds 80°C.
First of all, of course, the circulation pump must correspond to the characteristics of the boiler, which, in turn, are selected based on their heated area. Otherwise, if there is insufficient flow, the “extreme” batteries will be too cold.
The approximate formula for calculating the required performance is simple: Q = 0.86 x P/dt. Here P is the thermal power of the system, and dt is the temperature delta at the boiler outlet and return. That is, if we use a 40-kilowatt boiler and want to provide a delta of 20 degrees (usually this value is taken for normal operation), then in theory it will be enough for us to have a productivity of 1.72 cubic meters per minute. Then why did we list much more efficient pumps in the rating? Wait, that's not all.
During operation, the circulation pump must overcome the hydraulic resistance of the heating system. Please note that it is this that is important, and not the height of the system: the return balances the supply, that is, if the resistance was equal to zero, the pump would not actually be loaded with pumping. But in reality, pipes and radiators will always have resistance. A rough calculation for a two-pipe system gives the required lift height equal to the number of floors multiplied by a factor from 0.7 to 1.1; for a collector-beam system it increases to 1.16-1.85. That is, if we heat two floors with a “two-pipe”, and the boiler is in the basement, then the pump requires a lift height of about 3.3 m. Again, less than the pumps in the rating.
The fact is that volume height and pump performance are antagonists: increasing resistance inevitably limits performance. Therefore, each pump’s documentation contains a “height-performance” graph for each speed. So, the pump that suits us should have a graph such that the points of the required performance and lift height intersect approximately in the middle - such a “middle point” guarantees us that the pump will not be overloaded. This is especially important at the time of start-up, because the motor has to spin up immediately under load. Accordingly, the maximum performance and lift height figures for a properly selected pump will be higher than those obtained from the calculation.
Also keep in mind that glycol coolants have a higher viscosity compared to water, and the graphs are given specifically for water: you also need to make a reserve for this. In this case, the manufacturer must directly indicate in the pump characteristics the maximum concentration of propylene glycol in the coolant.
Finally, the pump itself must match the installation method(not everyone can work both horizontally and vertically), installation dimensions. Otherwise, the already assembled heating will have to be redone.
The use of a circulation pump for heating systems significantly improves their performance characteristics. In addition, such pumps, thanks to which the water heated by the boiler enters all elements of the heating systems much faster and less cold, allow you to save on energy resources (electricity, fuel for the boiler). The effectiveness of using circulation pumps as part of heating systems largely depends on the correct choice of such equipment, made on the basis of its technical characteristics.
Types and main characteristics
Before understanding the technical characteristics of circulation pumps for heating systems, you should become familiar with the different types of such equipment. According to their design, circulation pumps are divided into:
- with a “wet” rotor;
- with a “dry” rotor.
The design feature of devices of the first type is that the moving elements of their rotor assembly are constantly in contact with the pumped medium, which ensures not only their lubrication, but also effective cooling. In addition, the operation of such equipment, the rotor of which is constantly located in a liquid medium that perfectly absorbs all vibrations, is characterized by a minimal noise level. The advantages of circulation pumps with a “wet” rotor are also their compact size, ease of installation and maintenance. If we talk about the disadvantages of such hydraulic machines, the most significant of them is low efficiency.
Design of a circulation pump with a “wet” rotor
In circulation pumps with a “dry” rotor, as is clear from their name, the elements of the rotor assembly do not contact the liquid coolant, which gives such devices both advantages and disadvantages. The most significant advantages of hydraulic machines of this type are high productivity and efficiency, reaching up to 80%. Circulation pumps with a dry rotor are equipped with powerful thermal stations and heating systems for industrial use; as a rule, they are not used in domestic heating systems. Among the disadvantages of hydraulic machines with a “dry” rotor, they usually mention the rather high noise level, as well as the complexity of installation and maintenance.
Design of a circulation pump with a dry rotor
The technical capabilities and operating conditions of circulation pumps for heating systems are determined by a number of characteristics.
Performance
This parameter indicates the amount of liquid that the device is able to pump per unit of operating time. The unit of measurement for this parameter is m 3 /hour.
Pressure
Pressure is also called hydraulic resistance. The amount of pressure generated by the circulation pump is measured in meters or decimeters of water column.
Supply voltage
The type of electrical network (single- or three-phase) to which the pump can be connected depends on this parameter. Naturally, for installation in heating systems of residential buildings, you should choose hydraulic machines operating from an electrical power supply with a voltage of 220 V.
Power consumption
This characteristic depends both on the specific model of pumping equipment and on the mode in which it operates. Many models of circulation pumps designed for domestic heating systems can provide several speeds of pumping water. On the body of such pumps, as a rule, there is a special plate on which the power consumption and current strength corresponding to each operating mode are indicated. The vast majority of circulation pumps for domestic heating systems are characterized by power consumption in the range of 50–70 W.
Table 1. Main parameters and features of choosing circulation pumps for heating
Maximum coolant temperature
When choosing a circulation pump for a heating system according to this parameter, you should give preference to models designed to work with a working environment whose temperature can reach up to 110°.
Dimensions
This includes such characteristics as the diameter of the threaded part of the mounting elements of pumping equipment and the installation length of its body. Most of the circulation pumps used in domestic heating systems are simply cut into the pipeline and connected to its elements using union nuts - “American women”. Quite often, both the nuts themselves and the pipes for connecting the device to the pipeline system are already included in its factory configuration. The most common mounting diameters of circulation pumps used to equip domestic heating systems are 1 and 1.25 inches (25 and 32 mm, respectively). The installation length of household circulation pumps can be 130 or 180 mm.
Electrical protection class
Most modern models of circulation pumps for domestic heating systems according to the international classification correspond to IP44 protection class. Manufacturers provide pumping equipment of this class with protection against the entry of solid foreign particles larger than 1 mm into its interior. This is indicated by the first number 4 in the marking. The next number 4 in the designation of the protection class means that the electrical part of the equipment is insured against liquid drops and splashes flying at any angle.
Maximum fluid outlet pressure
On the housing of many models of circulation pumps you can find information about this characteristic. As a rule, for household equipment this parameter does not exceed 10 bar. From a practical point of view, it doesn’t mean anything; characteristics such as pressure and productivity are much more important.
Brand and manufacturing company
When choosing circulation pumps for heating systems (as well as any other technical devices), it is better to give preference to products from well-known manufacturers who take quality issues more seriously and provide reliable guarantees.
Technical characteristics of circulation pumps for heating systems are usually included in the designation of their models. Using such designations, in particular, you can immediately determine the following parameters: the liquid pressure created by the device, the diameters of its suction and discharge pipes, and the installation length.
Rules and features of choice
You should start choosing a specific circulation pump model only after the heating system has been designed and the total length of its closed circuit is known. In addition to the length of the heating system circuit, the choice of a circulation pump is also influenced by the number of radiators with which it will be equipped. Only after receiving all this data can it be determined with high accuracy what performance the circulation pump should have and what magnitude of coolant pressure in the system it should provide. It is very important to calculate the performance of a circulation pump for a heating system based on the lowest temperature outside, when the pumping device will operate at maximum load.
