What power is needed for a heating pump. Features of the selection of a circulation pump for a heating system
In order to mount 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 circulation pump for the heating system itself.
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 working head (pressure) and the flow (flow) 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, it is required 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 m 2 of a 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 m 2 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 from technical specifications 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 \u003d Q / (1.16 x ΔT),(kg/h)
- Q – thermal power heating systems (W);
- ∆T- the temperature difference between the supply and return pipes (for two-pipe systems it is usually taken within 20 ° C, and for a warm floor - about 5 ° C);
- 1,16 is the coefficient of specific heat capacity of water, Tue× h/kg× °С(for other types of coolants, this indicator will be somewhat different and can be found in reference literature or on the Internet).
Another formula by which you can calculate the required performance:
P \u003d 3.6 x Q / (c × ΔT),(kg/h)
where: With– specific heat capacity of the coolant (for water is 4,2 kJ/kg×°C).
For example, for the heat power of 10 kW discussed above and two-pipe system water heating according to the first formula we get:
P \u003d 10000 / (1.16 × 20) \u003d 431 kg / h or 0.43 m3/h(for heat carrier-water 1kg=1l).
Hydraulic resistance and required head
In order to make the selection of a pump for a heating system according to this parameter, it is necessary to calculate the hydraulic resistance that it will need to overcome in order to ensure the normal circulation of the coolant (water). You can use the following formula to calculate:
J = (F+R× L)/p× g(m)
- L– length of the system to the most distant radiator (m);
- R- hydraulic resistance of the straight section of the pipe (Pa / m);
- p- heat carrier density (for water - 1000 kg / m 3);
- F is the resistance of the connecting and stop valves(Pa);
- g– 9.8 m/s2 (gravitational acceleration).
For accurate calculation values R and F can be found in the reference literature. For a simplified one, you can take the averaged data obtained experimentally:
R— within 100-150 Pa/m;
F- depending on the type:
- in each connecting fitting, an additional 30% is lost to the losses in the straight pipe in this section;
- in a three-way mixer or similar devices - additionally up to 20%;
- in thermostats - up to 70% of the losses in a straight pipe.
In addition to the above, you can use another formula proposed by experts from the well-known 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 circulate in a heating system with several circuits (branches), then for its selection 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 main must be calculated separately, both in terms of thermal power and in terms of hydraulic resistance. At the same time, the number of storeys of the building, when calculating the pressure, does not play a big role. Since in a closed system the liquid columns of the supply and return lines are balanced.
How to choose a circulation pump according to the data received
Having now calculated and knowing the main required parameters of the characteristics of the circulation pump, you can easily select the required option using the performance graphs that are in the instruction manual or passport of any model. As a rule, such graphs have two axes: head (pressure) and flow (flow).
Rice. 1 Example of a circulation pump curve
We can plot the results obtained earlier on the existing chart, plotting their values along the corresponding axes, and at their intersection get a working point, which should be slightly below the line AT graph showing 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 graph ( A1), this is also not very good, since it will provide circulation, but having too much supply, it will consume more electricity, and its cost will also be higher than a pump with more modest characteristics.
Rice. 2 Selection of the pump according to the graph of its characteristics
If the model has not one, but 2 or 3 speeds, then there will be 2 or 3 lines on the performance graph, respectively. 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 operate.
Other factors influencing the choice
The selection of a circulation pump for a heating system, in addition to those discussed above, its main characteristics are also influenced by other factors, such as: reliability, workmanship, temperature regime operation, cost, method of connection, etc.
Workmanship, reliability, and durability tend to be directly related to cost. Manufacturers that offer reliable and high-quality models, such as 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, respectively, is lower. Here, everyone must make a choice himself, choose a quality product at a higher price or buy a cheaper circulation pump, with the knowledge that it may soon have to be changed.
If you want to save money, you can also buy used Grundfos or Wilo, they can often work normally longer than new Chinese ones, but it’s better to buy them from familiar, trusted specialists who give a certain guarantee.
In addition, when choosing, it is necessary to pay attention to the type and diameter of the connection between the pump and the pipes of the system. Some models are equipped with connecting elements such as "American", and some will have to be selected independently.
Another parameter that you need to pay attention to is the temperature regime for the operation of the circulation pump, which should be in the passport. This is especially important if it will be installed on the supply pipe in a system with solid fuel boiler. In this case, the maximum allowable temperature must be at least 110°C. If, however, the pump will be installed on the "return", then this is not so important, since the temperature at the boiler inlet rarely exceeds 80 ° C.
Related videos
Water heating with the presence of a special pump necessary for pumping the coolant is in many ways superior to similar systems with natural circulation of the working medium. Efficiency with the installation of such a device increases significantly. In addition, there are additional features in terms of adjustment. With regard to the pipelines used, it is possible to choose products with a smaller diameter, and this allows you to create very economical heating networks.
The forced circulation heating system will work properly, provided that the performance and some other pump parameters are correctly selected. First of all, it should be clarified how much coolant the product can pump over a specific period of time.
Initially purchase a pump model with a large margin performance characteristics impractical. Firstly, the cost of the device will be too high, so you will have to spend a significant part of the budget. Secondly, the device will consume excess energy, since with an increase in power, its consumption also increases.
Last but not least, the choice should take into account the factors of comfort and quality characteristics. For a quiet stay, it is better, of course, to purchase a device that does not create much noise and is durable. Such requirements are usually met by products of trusted manufacturers that have been on the market for a long time.
Calculator for calculating the performance of the circulation pump
Instrument Performance Calculation
Calculate the throughput of the pump for a certain time will help the calculator, which has only two fields for entering information. The peculiarity of the computational process lies in the fact that it is not ordinary water that is pumped, but a carrier of thermal energy. From the boiler working fluid distributed through pipelines.
The simplified formula for calculations is as follows:
G = W/(∆t x Kt) , where
G – throughput in kilograms per hour;
W – power of the boiler used for heating system;
∆t - the temperature difference between the supply and return pipelines (taken thermal energy heaters);
Kt - coefficient denoting the thermal capacity of the working fluid.
The power of the heating boiler must be known. If the system is arranged from scratch, then this parameter is calculated using a special formula. For the temperature difference, you can take the average value. For water-type underfloor heating circuits, it is 5 degrees, for heating radiators - 20 degrees, and for - 15 degrees. The coefficient indicated in the formula can be taken as 1.16.
How to choose a pump for heating?
Often, "classical" heating systems based on natural circulation coolant, there is not enough coolant in the system, because. pressure in such systems does not exceed 0.6 MPa. To increase the pressure and improve the circulation of the coolant, it is necessary to install a circulation pump.
The main task of the work circulation pump- help the coolant overcome the resistance that occurs in certain sections of the heating system. The principle of operation of such a pump is simple, the pump sucks in the coolant from one side and, due to centrifugal force, pumps it into the pipeline on the other, which arises from the rotation of the impeller, as a result of which a vacuum occurs in the inlet pipe, and compression occurs at the outlet.
Circulation pumps are divided into two types: with a "dry" rotor and with a "wet" one. In the design with a "dry" rotor, the rotor does not come into contact with the coolant, its working part is separated from the electric motor by sealing rings. Such pumps have a high efficiency (80%), but, unfortunately, they emit a loud noise during operation. In wet rotor pumps, the impeller is immersed in the coolant along with the rotor. The coolant in this case acts as a lubricant and cools the engine. Much less noisy, do not require maintenance for years, but have a lower efficiency (50%). It is because of this that "wet" type pumps are mostly used for circulation in domestic heating systems.
How to choose a circulation pump?
To select a pump, you need to know several parameters. 1. Pump connection diameter. 2. The volume of the pumped coolant (pump performance). 3. Lifting height of the system (maximum head). 4. Manufacturer.
Therefore, if you decide to buy a circulation pump, be sure to consult with the person who will install it or with the specialists of our store + 7 499 272-2229
How to choose on our website
If you have all the parameters of the required pump, go to the circulation pumps section. Open the feature filter, enter the required parameters, for convenience, each product card has a "Compare" button
Remember that pumps are mass-produced with average parameters, and each heating system is individual. Excessive power will cause noise in the pipes during operation. The right decision would be to choose a pump with several operating modes, the power of which exceeds the calculated one by 5-10%.
Be sure to check out our special offers for circulation pumps!