Powerful circulation pump. How to choose the right pump for the heating system
Firstly
The starting point for the selection of the circulation pump for the heating system is the heat demand of the building, calculated for the coldest season. In professional design, this indicator is determined on a computer. Approximately it can be calculated by the area of the heated room.
According to European standards, 100 W is required for heating 1 sq.m in a house with 1-2 apartments, and 70 W for apartment buildings. If the condition of the building does not meet the standards, the designer takes into account the higher specific heat consumption. For residential buildings with improved thermal insulation and industrial premises, 30-50 W / sq.m.
In Russia, similar standards for houses with 1-2 apartments have not yet been defined. SNiP 2.04.07-86* " Heating network” recommends calculating the maximum heat flow for heating 1 sq.m of the total area of residential buildings built since 1985 according to new standard projects, according to the following aggregated indicators:
- for 1-2-storey buildings - 173 W/sq.m at an estimated outdoor air temperature of -25 degrees C and 177 W/sq.m at -30 degrees C;
- for 3-4-storey buildings - respectively 97 and 101 W/sq.m.
According to SNiP 2.04.05-91* “Heating, ventilation and air conditioning”, the estimated outdoor temperature in Moscow is -26 degrees C. By interpolation, we get that in the capital, the specific heat demand of 1-2-storey residential buildings is 173.8 W / sq.m, and 3-4-storey - 97.8 W / sq.m.
Secondly
Having determined the heat consumption (Q, W), you should proceed to the calculation of the required pump performance (delivery) using the formula:
G = Q / 1.16 x DT (kg / h), where:
DT - temperature difference in the supply and return pipeline heating schemes (in standard two-pipe systems it is 20 degrees C; in low-temperature systems 10 degrees C; for warm floors 5 degrees C);
1.16 - specific heat capacity of water (W * h / kg * deg C). If another coolant is used, appropriate adjustments must be made to the formula.
This calculation method is offered by foreign designers. The mandatory annex to SNiP 2.04.05-91* contains the following formula:
G = 3.6 x *Q / (c x DT) (kg / h), where:
c - specific heat capacity of water, equal to 4.2 kJ / kg * deg C. To recalculate the obtained value in cubic meters per hour (as a rule, it is this unit of measurement of pump performance that is used in the technical documentation) it is necessary to divide it by the density of water at the design temperature; at 80 degrees C it is 971.8 kg/cu.m.
Thirdly
In addition to the necessary supply, the pump must provide enough pressure (pressure) in the heating system to overcome the resistance of the pipeline network. For right choice you need to determine the losses in the longest line of the circuit (to the farthest radiator).
When designing new system accurate calculations are possible, taking into account the resistance of all elements of the thread (pipes, fittings, fittings and devices); usually the necessary information is given in the passports for the equipment. Here you can use the formula:
H \u003d (R x l + * Z) / p x g (m), where:
R - resistance in a straight pipe (Pa / m);
l - pipeline length (m);
*Z - resistance of fittings, etc. (Pa);
p is the density of the pumped medium (kg/m3);
g - free fall acceleration (m/sq.s).
In cases with operating heat pipelines, such calculations are usually impossible. In such situations, rough estimates are most often used.
Empirically obtained data indicate that the resistance of straight pipe sections (R) is about 100-150 Pa/m. This corresponds to the required pump head of 0.01-0.015 m per 1 m of pipeline. In the calculations, you need to take into account the length of both the supply and return lines.
It has also been experimentally determined that about 30% of the losses in a straight pipe are lost in fittings and fittings. If the system has a thermostatic expansion valve, about 70% more is added. On a three-way mixer in the control unit of the entire heating system or a device that prevents natural circulation accounts for 20%.
Wilo specialists E. Buscher and K. Walter recommend the following formula for an approximate calculation of the head (in meters):
H = R x l x ZF, where
ZF - safety factor.
If the installation is not equipped with either a thermostatic expansion valve or a mixer, ZF = 1.3; for a circuit with a thermostatic expansion valve ZF = 1.3 x 1.7 = 2.2; when the system includes both devices ZF = 1.3 x 1.7 x 1.2 = 2.6.
Finally
Having determined the so-called operating point of the “circulator” (pressure and flow), it remains to select a pump with a similar characteristic in the catalogs. In terms of performance (Q), the operating point should fall in the middle third of the diagram (Fig. 1).
We must not forget that the calculated parameters are necessary for the operation of the system when maximum load. Such conditions are extremely rare, most heating season the need for heat is not so great. Therefore, if in doubt, a smaller pump should always be selected. This allows not only to save money when buying it, but also to reduce the cost of electricity in the future.
An example as a test
The correctness of the calculations according to the presented method can be verified by comparing their results with the results of exact calculations in a real project, performed in accordance with SNiP.
The task was to calculate circulation pump for two-pipe system heating with floor-by-floor piping from the collector. It was preliminary determined that the building's demand for heat is 45.6 kW, the coolant consumption required for heating is 2.02 cubic meters per hour. The piping scheme to the most distant radiator includes four sections and a heat control valve.
The total pressure loss in them is equal to:
DP = 0.63 + 0.111 + 0.142 + 0.289 = 1.178 m
According to SNiP 2.04.05-91*, 10% should be added to this value for unaccounted for pressure losses:
DP = 1.178 x 1.1 = 1.296 m
Thus, the “circulator” for this system must provide a supply of 2.02 cubic meters per hour of coolant and a head of 1.3 m. The HZ 401 (Deutsche Vortex) or UPS 25-40 (Grundfos) pump meets these conditions.
When calculating according to the method described in the article, we get:
H \u003d 0.015 x (3.2 + 4.4 + 8.9 + 21.7) x 1.3 x 1.7 \u003d 1.266 m,
In addition
Based on this technique, some pump manufacturers are developing more convenient and accurate ways to select equipment for heating systems. In particular, we can recommend readers the diagrams presented in the Grundfos Sealless Circulation Pumps catalog.
Material from the site:http://www.teplograd.ru
The pump must match the parameters of the heating system
Modern heating systems, especially in large buildings, require constant movement of the coolant through pipes and radiators. This is necessary so that the heat is evenly distributed throughout the system. This increases the heat transfer and the rate of heating of the premises. Therefore, the correct selection of the circulation can provide a comfortable temperature level in any home. It is this device that is designed to promote the flow of coolant through pipes and batteries.
Let's discuss how to choose the most efficient type of pump for heating system, regardless of the source of energy - be it gas, electricity, liquid or solid fuel.
Types of circulation pumps
The industry produces a lot of varieties of pumps for the heating system. You can't list them all, and you don't have to. Let's focus on two main types - pumps with a wet rotor and dry.
Heating system parameters
But first you need to understand some of the characteristics that determine the choice of a particular pump:
- Area of premises to be heated.
- The temperature level in the building - it may differ depending on its purpose. For example, in a residential building, in medical, school and preschool institutions, the temperature should always be higher than in industrial premises.
- The temperature of the coolant at the inlet and outlet of the heating system.
- Type of heating boiler, its equipment with various functional devices and automatic systems control and blocking.
- The pressure of the coolant is its pressure in pipes and radiators.
- Floors of the building.
- Heat carrier type.
Important! The coolant circulation pump is a conventional electric motor, which consists of a fixed part - the stator and a movable part - the rotor. An impeller is installed on one part of the rotating rotor, which includes blades. When they rotate, a rarefaction of water is created, as a result of which its movement occurs.
There is heating boilers the old model, in which there is no pump, and the circulation of the coolant occurs under the action of gravity. It is determined by the slight slope of the pipes and the difference in the density of cold and hot water. Because the hot water lighter than cold, it rises according to the laws of physics, passing by gravity into pipes and radiators. Having given off heat through the surface of these devices, the cooled water returns to the heating boiler for subsequent heating. At the same time, at the outlet of the boiler, the temperature of the liquid is always higher than at the inlet - the temperature difference also contributes to the movement of water.
If the owner wants to make the heating system more efficient, he will have to weld the circulation pump into the pipeline in front of the heating device. It is expensive, and the quality of such installation does not give a 100% guarantee that the system will work successfully.
In modern heating devices, pumps are already part of them, and this is a clear advantage of heating boilers with forced circulation. However, a sufficient number of old products are still in operation. Therefore, the selection of a circulation pump for a heating system is an urgent task for many owners of private houses.
Glandless pump
Grundfos pump
The name speaks for itself - the rotor of the engine with the impeller is located in water or another type of coolant that lubricates and cools the design of the device from overheating. The rotor is in a separate housing, which is made of non-corrosive metals - stainless steel, bronze or brass.
Advantages of this product:
- Little noise during operation.
- Does not require frequent maintenance and repair.
- Low price.
The disadvantage is the low level of efficiency. Therefore, such devices are designed for heating systems in houses with a small area. Here, significant pump power is not required, and a small volume of coolant is used.
Dry circulation pump
In this product, the rotor is separated from the liquid by small sealing parts, and the impeller is directly involved in the movement of the coolant.
Advantages:
- the possibility of creating powerful pumps capable of moving a large amount of water
- high efficiency
Flaws:
- frequent maintenance, as they wear out quickly sealing connections so they need to be lubricated.
- loud noise during operation requires a separate room for such a pump
Dry pumps are most often used in multi-storey buildings with an area of more than 300 square meters.
How to choose the right circulation pump
They differ in their characteristics
For the right choice, there are many different formulas. However, it is very difficult for an ordinary consumer to understand them. Therefore, there is an easier way. Its essence is this:
- To determine the amount of water, you need to equate one unit of boiler power of 1 kilowatt to 1 liter of coolant per minute. That is, if heating device has a power of 20 kW, then in one minute 20 liters of liquid pass through its heat exchanger. This parameter is approximate, but verified by practice.
- The speed of movement of fluid in pipes is usually determined by the value of 1.5 meters per second.
- For 10 meters of the heating system, a pump head of 0.6 meters is required. If the length of the pipes and batteries is 80 meters, then the pressure of the circulation pump should be 4.8 meters.
- The dependence of fluid flow on the dimensions of the heating pipes can be easily determined from the table:
If the diameter of the pipes is small, then the pump power increases. The wider the pipe, the less power the circulation device will require.
All calculations are approximate, therefore, with a large length and complex design of pipes and radiators, the selection of a pump for a heating system should be entrusted to specialists. The pump power should be 10 percent higher than the calculated parameters. This is necessary for the stable and efficient operation of the entire heating system.
Where is the best place to put the circulation pump
Pump installation
It is considered traditional to install a pump on the return, that is, at the inlet of the liquid that has passed through the heating system and has more low temperature. Modern devices can be installed in any convenient place, especially with a wet rotor.
In this case, you should follow simple rules:
- The expansion tank with water must be located at least 1 meter above the highest point of the pipeline. With the natural movement of the coolant, this device was usually installed in the attic, which threatened to freeze the water in the coldest winter months. And this could turn into an accident of the entire heating system. To eliminate such a risk, the owner had to carefully insulate the expansion tank, as well as constantly monitor the condition and level of the coolant.
- The expansion tank can be cut into highest place location of pipes and batteries.
- Install a bypass at a convenient location to bypass the forced circulation system. This is true if the pump is damaged or there are interruptions in the electrical network.
- To prevent the accumulation of air in the heating system, it is necessary to insert a Mayevsky valve or an automatic air vent element into the bypass or the highest points of the pipes.
Conclusion
Designed for forced movement of the coolant. Its installation provides rapid heating of the premises and creates a more comfortable temperature.
And the correct selection of this device will increase the efficiency of the heating boiler and reduce the cost of paying for energy.
Before choosing a pump for heating, you need to understand one important point, consisting in the following - the choice depends on a number of indicators that determine the capabilities of the device.
How to choose a pump?
Currently used heating systems designed for battery life, in most cases are equipped with circulation pumps. Such devices significantly increase the efficiency of work and increase the reliability of the equipment. As a result, this has a positive effect on their operational life.
The selection of the pump must be carried out according to certain parameters. What are these parameters? Flow, pressure and amount of heat required for heating. The value of each parameter can be found in the passport of any pump or calculated by yourself.
Consumption
Before you select a pump, you need to calculate its flow rate using a simple formula. The formula is as follows: Q = N/(t2-t1), where:
- Q is the value that determines the consumption of pumping equipment;
- N is the power of the heat source ( geyser or boiler)
- t2 - an indicator of the temperature of the liquid that comes out of the heat source and is in the supply type pipeline (most heating boilers supplied to the market operate within + 90-95 degrees);
- t1 - the temperature of the water located in the reverse type pipeline (average statistical range + 60-70 degrees).
pressure
The second value that we need to carry out the selection is pressure. The indicator depends on the type of heating system. The calculation is based on the final value of the total value, which takes into account the hydraulic resistance. If the system is of a closed type, the number of storeys of the structure can be neglected.
To calculate the pressure, you can use the simplified formula: H \u003d R * L * ZF, where:
- H is the head pressure in meters;
- R is the resistance of the straight pipe;
- L is the length of all pipes in the system;
- ZF - the multiplication factor when using ball valves is 1.3.
Proper installation of the system will provide hydraulic pressure in the form of 2-4 m of water column. This value is identical for standard heating complexes, which are used mainly in low-rise residential buildings.
The need for warmth
When choosing a pump for heating, the heat demand of the building should also be taken into account. As a rule, this indicator is indicated in the passports issued to various buildings. But sometimes it's not there. You should not worry, as the parameter is easy to calculate on your own.
Heating standards vary depending on the regulations established in the country. They are needed to calculate the amount of heat per 1 m². Let's take European requirements as an example. To heat 1 m² of a single-apartment or two-apartment residential building, 100 W of power is needed. AT apartment buildings the indicator drops to 70 watts.
The parameters of the pump are selected so that three times the total volume of the coolant is driven through it within an hour.
In our country, the necessary need for heat can be selected according to SNiP. The document regulates both heating and air conditioning together with ventilation. There is no point in listing all the values. They are different for each region. Keep in mind that when choosing a circulation pump, you must not only find the parameter for 1 m², but also multiply it by the total area.
Choosing equipment
To choose equipment, it is best to use special catalogs, which indicate specifications heating units different manufacturers. However, you should not look only at operational properties. Don't forget about installation and requirements for regular use.
Some recommend buying pumps with low flow, head and heat requirements. Why? Calculations give limit values that are rarely reached in reality. As a result, circulation pumps are not too often subjected to significant loads.
Installation requirements
Usually, the equipment is installed by specialists from the company where it was purchased. The new owner does not have to think much about how to choose and install a pump. Doing this work yourself is not an easy decision.
It is more rational to place the pump on the supply pipeline, where there is usually less hydrostatic pressure.
Place for tie-in
Installation of equipment as part of a system including radiators is carried out on a return type line next to the boiler. It is there that the lowest temperatures are observed. In houses or apartments, the area of \u200b\u200bwhich does not exceed 200 m², the above rule is considered rather arbitrary. The temperature of the heat carrier in the supply and return area differs by only a couple of degrees. Under such conditions, the location of the equipment does not play a special role.
Conditions for installation
It is best to install the pump at the stage of arranging the entire heating system. If it is already in effect, the coolant will have to be drained. If there are shut-off valves on the outgoing and incoming pipelines, this is not necessary. You just need to close access to the coolant and put the pump.
Direct connection
In some cases, it is difficult to find the necessary adapters for equipment. Therefore, it is better to choose a pump with detachable threaded connections. You also need to purchase a filter, check valve and bypass. When installing, consider the possibility of further maintenance.
When installing, consider the possibility of further maintenance.
System installation
Place the equipment, taking into account the arrow on the body. The latter indicates in which direction the coolant is moving. A cleaning filter must be installed at the inlet to the circulation pump. Plots threaded connections treated with a sealant. A gasket is required between mating elements.
Installation diagram.
The position of the unit is horizontal, otherwise there is a high probability of premature failure of the rotor. When the pump is in the right place, fill it with a heat carrier. Then open the central screw. Look for it on the top cover. Do not be alarmed when a little liquid appears from the hole. That's the way it should be. This removes excess air from the system.
On the warm floors equipment is required to be placed on the supply lines. This will prevent air from entering the pipelines of the heating system and breaking the current flow.
Network connection
Before installation, you need to make sure that there is free access to the mains or make cable wiring. to the power supply network is possible in two ways. The first is a regular fork. The second is a special electric machine.