The forced movement of the coolant in the water heating system is provided by a circulation pump capable of pumping liquid at a temperature of 110 ... 115 ° C. In private houses and apartments with individual heat sources, low-noise devices of the household series with clutch connection are used, equipped with a “wet” rotor (the engine armature is washed and cooled by flowing water).
If you decide to independently choose a pump for heating, consider 3 main criteria:
- Specifications - performance, working pressure.
- Connecting and overall dimensions.
- Product price, brand popularity.
Consider the points on how to choose the right circulation pump for the radiator system, underfloor heating and the primary boiler circuit.
The most "running" models of pumping units
Manufacturers offer a wide selection of equipment of different capacities, designed for pumping liquid media with various parameters. But we are only interested in flowing models working in home heating and hot water supply networks.
How to distinguish circulating units from centrifugal and other types of pumps:
- in shape - the electric motor and the impeller are installed in one housing, the nozzles exit on the sides of the lower part (not in the middle);
- by the presence of a "wet" rotor, significantly reducing the noise of rotation of the impeller;
- 2 sizes with mounting lengths of 130 and 180 mm;
- nominal passage of nozzles - 15, 20, 25 and 32 mm, connection - coupling (threaded);
- passport pressure - 0.4, 0.6 and 0.8 Bar.
The indicated parameters are easily ascertained from the product labeling. Example: the numbers in the name Wilo Star-RS 15/4 indicate the internal diameter of the connecting pipes 15 mm (DN 15) and the pressure of 4 m water column (0.4 Bar). An example of the second: the Grundfos ALPHA2 25-60 apparatus is connected to the Du 25 pipes and develops a pressure of 0.6 Bar (6 meters).
Reference. Typically, manufacturers produce extended product lines. The German brand Wilo offers circulation superchargers with a pressure of 2, 4, 6, 7 and 8 m. Of water. Art. But the "four" and "six" are still the "running" models, less often the "eight".
Of course, there are more powerful pumps, whose pressure reaches 1 ... 10 Bar, but in private homes they are not used. Small units with a length of 130 mm with pipes ½ and ¾ inches are usually placed inside the boilers, large (18 cm, 1 and 1 ¼ ") - cut into the heating mains.
Pump selection methods
The most correct way is to make a full hydraulic calculation and accurately determine the main parameters of the pump - the developed head and capacity. This is how the centralized heat supply of apartment buildings and industrial buildings is designed.
Not all masters involved in the installation of autonomous water systems possess engineering calculation methods, let alone ordinary homeowners. How can I choose a circulation pump for heating in a simpler way:
- In case of replacement of the old worn-out unit, a new one with the same parameters is purchased. The price and quality of the product come to the fore.
- Order a home heating system project to a heating engineer. Below we will explain the advantages of this option.
- Calculate the required pump head by a simplified method.
- Believe the long-term practice of our experts and buy the device, guided by their advice.
Expert advice. In country houses and apartments with an area of up to 250 m² a domestic pump is enough, developing a pressure of 4 m water column or 0.4 Bar. For a square of 250 ... 500 m², it is better to buy a more powerful unit with a pressure of 6 m (0.6 Bar), over 500 m² - 8 m.
The order of engineering calculations and development of the scheme costs money, but will pay off with interest. When you install heating yourself or hire workers, components and equipment are purchased with a decent margin - just in case. An intelligent designer will clearly substantiate why it is necessary to supply a small power pump and a pipe of a smaller diameter. The result will be savings on materials, and in the future - the cost of electricity.
If you trust only numbers or want to check the installers, choose a heating pump according to your own calculations, using the method below. Do not forget to compare the calculated characteristics of the unit with the recommendations of experts - the result will certainly come out similar.
Calculation of pump characteristics
Heating works efficiently when all the batteries or floor heating circuits get the right amount of heat. That is, the pump unit must provide the required flow rate of the coolant in each section of the system, overcoming the hydraulic resistance of pipes, fittings and valves.
Before choosing a pump, you need to calculate its performance according to the formula:
- G is the mass flow rate of the coolant, kg / h;
- Q - total heating load, W;
- Δt is the difference between the temperature of the water in the supply and return lines, in the calculations it is usually taken equal to 20 ° C.
Reference. Since the density of water changes little during heating within 100 degrees, in simplified calculations, the mass flow rate is assumed to be equal to the volumetric one. Example: G = 300 kg / h = 300 liters per hour.
The thermal load can be calculated scrupulously using the SNiP method. Here we will not complicate the task and just take the amount of heat over the area.
For example, for heating a two-story house with a square of 200 m², located in the middle lane, 22 kW of heat will be needed. From here it is easy to calculate the coolant flow rate and the required pump capacity: G = 0.86 x 22000/20 = 946 kg / h = 0.95 t / h = 0.95 m³ / h.
It is immediately proposed to find out the cross-section and diameter of the main line going from the boiler, where it is planned to install the pump:
- F - pipe cross-sectional area, m²;
- ʋ - water velocity, 0.5 ... 1 m / s is assumed.
The lower the water flow rate, the lower the resistance to friction against the walls of pipes, fittings and fittings.
We take the value 0.6 m / s and determine the cross-section of the highway: F = 0.95 / 3600 x 0.6 = 0.00044 m². Further, through the circle area formula, we calculate the diameter of the passage - 0.024 m or 24 mm. Accordingly, the internal size of the pipe and connecting fittings of the pump is 25 mm.
Having found out the necessary productivity of the pumping device, we proceed to the calculation of the available pressure. Calculations will be carried out separately for the radiator network, floor heating and boiler piping loop.
Heating circuit with batteries
The task of the pump is to push the desired volume of coolant through pipes from the first to the last radiator. It is hindered by the force of friction of the fluid against the walls, the resistance from the narrowing of the duct in the control valves and turns on the fittings.
To find out the amount of resistance that the circulation unit must overcome, we suggest using the simplified formula:
- H is the desired pressure drop in meters of water;
- R is the specific friction resistance, it is considered in meters per 1 meter of running pipeline;
- L is the length of the longest heating branch, measured from the heat source to the last radiator;
- Z is the coefficient of local resistance.
Comment. The formula is greatly simplified, the engineering calculation of hydraulics is much more complicated. But it allows you to choose the right heating pump for domestic conditions. We checked an alternative - online calculators located on various Internet resources. Having received the difference between the results of 30%, we conclude: it is better to calculate the pressure manually.
How are the calculations made:
- Since the pump creates the same pressure at the inlet to each heating branch, we select the longest line and determine its length in meters. This is the exponent L in the formula. With a two-pipe system, both lines are taken into account - the return and supply lines.
- The resistivity R is taken equal to 150 Pa / m or 0.015 m water column per 1 m. Of the main line (for plastic pipes).
- If the flow through the batteries is regulated by thermostatic valves, we take the coefficient Z = 2.2. Option two: radiators are equipped with ball valves and balancing valves, then Z = 1.5.
- We calculate the required pressure and select the appropriate supercharger model.
Tip. The length of the line of deadlock and ring circuits is considered the same - plus the length of the feed and return. For a single-tube “Leningradka” we take the total length of the ring. If at the time of calculation there is no scheme, the length is determined by the internal dimensions of the house: size of the first floor + ceiling height + width of the second floor.
We calculate the pressure according to our example. The length L by the dimensions of the building is (10 + 3 + 10) x 2 = 52 m, Z = 2.2. The required pressure will be 0.015 x 52 x 2.2 = 1.716 ≈ 1.7 m. We add a margin of 1 m to the unaccounted resistance of the boiler itself and additional equipment, we get 2.7 m water column.
On the graph attached to the pump certificate, we mark the line of productivity and pressure, then we select the suitable model, in this case, the brand Wilo Star-RS 25/4.
An important point. In modern injection devices, 3–7 operating modes are often provided, and the instructions contain the same number of graphs. To calculate, select the characteristic that corresponds to the average speed (second - third).
Hinges for underfloor heating
Typically, the coolant is supplied to the floor circuits by a separate pump, coupled with a mixing valve. In this case, the maximum length of the loop does not exceed 100 meters, shaped parts are missing. Local resistance - thermostatic manifold valve and mixing three-way (or 2-way) valve.
The previous algorithm is quite suitable for calculation:
- We find out the number of circuits, the maximum length of the pipe and the total flow rate of the coolant through the comb. We calculated all the calculations for warm floors in a separate publication.
- We take the longest loop and count on it the required pressure of the pump unit, using the above formula. Substitute the same values for R, L and Z.
- We select a pump for floor heating loops according to the schedule presented in the product passport.
Example. Take the same two-story house with a heat load of 22 kW and a water flow rate of 0.95 m³ / h, the maximum loop length is 80 m. The value of R is taken to be 0.015, Z is 2.2, then the pressure is H = 0.015 x 80 x 2.2 = 2.64 m. The resistance of the line is not we take into account, because the boiler is equipped with its own pump. So, the final pressure of the collector unit is at least 2.64 m.
Note: increasing the length of the loops to 100 m, you raise the bar pressure of the pump, which will increase energy consumption. We check: H = 0.015 x 100 x 2.2 = 3.3 m. We draw the corresponding horizontal line on the diagram and select any model whose graph is placed above. The nearest unit is Wilo Star-RS 25/6.
Boiler circuit
As you know, in the piping diagrams of solid fuel boilers, a separate pump is provided that drives water along a small ring through a three-way valve or a buffer tank. The identical principle is applied in the primary / secondary ring system, where radiator heating lines, underfloor heating and hot water boiler are connected to the main circuit.
The pump that pumps water along the main ring has practically no resistance - the line is short, at least fittings and fittings. Therefore, the pressure of the main unit is often less than the pressure of the secondary blowers that send the coolant to the heating devices.
Size selection
You probably noticed - in the assortment of companies there are units with the same characteristics, but with different dimensions and sizes of nozzles. How to choose the external parameters of the pump:
- For installation on pipelines, bypasses and mixing units for underfloor heating, standard blowers with a length of 180 mm are used. "Shorties" 130 mm are placed inside heat generators or on highways in a very limited space.
- The diameter of the connecting pipes is selected for the cross section of the main pipeline. An increase in size is permissible, a decrease is strictly not recommended. That is, an assembly with 32 mm fittings can be installed on the Du 25 pipeline.
- Pumps with Ø32 mm nozzles are used on primary rings and boiler circuits, as well as in upgraded gravity systems.
Note. The sizes of finished bypasses sold in stores are fitted to a standard pump with an installation length of 18 cm.
The number of supercharger speeds does not play a special role. At home, 3 modes are quite enough, the optimal speed is the second. Air from the units is vented through the side screw, so you should not buy products with a separate air vent.
Manufacturers and prices
Despite the wide range of pumps in stores, it is not easy to choose a truly high-quality product. The market is flooded with Chinese goods and fakes of famous brands. To begin with, we list the manufacturers popular in the CIS:
- The highest price category is Grundfos (Denmark), Wilo (Germany). Prices for the original "Germans" start from 75 euros, "Grundfos" UPS series - 65 euros.
- The middle category is DAB, Aquario (Italy), Sprut (quality China). The cost of units of various models ranges from 40-100 euros.
- Other cheap pumps (Oasis, Neoclima, Whirlwind, Caliber, and so on to infinity). Price - from 20 euros per piece.
Comment. It is likely that we did not include some very worthy products in the highest or middle price category. The most common brands are listed here.
What distinguishes inexpensive and counterfeit pumps from high-quality blowers:
- service life - 1 ... 3 heating seasons;
- the product number is applied only to the sticker; the unit body is clean;
- pumping devices from one batch often come with the same numbers;
- the fake is noticeably different in weight from the original (it is lighter);
- a low-quality unit begins to make noise and beep, having worked for 1 season in a closed heating system, the case is very hot.
Sometimes fake heating pumps are indistinguishable from the original, only the price is half as low. The secret is in the aluminum winding, which reduces the cost of the product. How to check: find the mass of the original model on the official website of the company and compare it with a market copy. Most likely, an informed seller will refuse to weigh the counterfeit device or immediately recognize the unknown origin of the goods.
Final conclusion
When choosing a circulation pump for heating a house, it is important not to make a mistake with the characteristics and not to chase cheapness. Inadequate pressure will lead to weak heating of the distant batteries, excessive pressure will lead to noise in the radiators and rapid wear of the discharge unit. The last advice on choosing a manufacturer: if you want to save money, you better find a used original brand, it will last longer than a new cheap “Chinese”.