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Engineering Systems

August 12, 2017 18:08

Circulation pump for heating : characteristics and selection

Main features of the circulation pump

Main features of the circulation pump
Main features of the circulation pump
When selecting a pump is necessary to consider following its characteristics:

  1. circulation pump is used for the heating system must withstand high temperatures (100 ° C).
  2. Head;
  3. power;
  4. Work flow.

and identify with the amount of heat required for heating.

calculation of the required power for the premises

In order to determine the required amount of heat necessary to know the area of ​​heated space.Knowing this figure, you can refer to the standards applied in the area of ​​residence.In European countries, calculation is performed at the rate of 100 watts per 1m2 at home if it 1-2 apartments, and 70 watts, if an apartment building.If damp indoor conditions, the rate was reduced to 30-50 watts.

In the CIS countries, according to the SNIP 2.04.07-86 *, should adhere to these indicators:

  1. for buildings less than 3 floors - 173 watts per square meter at temperatures down to -25 ° C and 177 watts per square meter at-30 ° C.
  2. For buildings with more than with 3 floors - 97 and 101 watts per square meter, respectively.

pump capacity calculation

To calculate the performance of the pump is necessary to calculate its filing.There are two formulas for this.The first is used for the design in Europe and the second in the CIS countries and is registered in the SNIP 2.04.05-91.

P = Q / (1,16 x ΔT) (kg / h),

where ΔT - the difference between the flow and return (for two-pipe spreading room, if the wiring is a single pipe, the rate is taken 20 ° C)

116 - the value of the specific heat of water, if the system is used as a coolant is not water, then the value of 1.16 is replaced by the corresponding indicator.

P = 3.6 x Q / (c x ΔT) (kg / h),

where c - is the specific heat of the substance (if water is used, then we take 4.2 kJ / Kg * ° C)

pressure calculation

to effectively circulate the coolant in the system is necessary to ensure the pressure that can deal with hydraulic resistance.

To calculate this figure, it is necessary to choose the most distant point from the pump in the system (far cooler).

for designing the network, you can use this formula:

J = (F + R x L) / p × g (m)

where:

L - the length of the site (m),

R - hydraulic resistance on the straight sectionpipe (Pa / m),

p - the working fluid density (kg / m3),

F - resistance sewer valves (Pa),

g - acceleration of free fall (m / s2).

These indicators can be found in catalogs and accompanying technical literature.

You can use a simplified procedure, about assessing resistance.

During the experiments, these data were obtained:

  1. resistance on the straight sections of the pipeline 105-150 Pa / m;
  2. each fitting an additional 30% of the loss in a straight pipe;
  3. thermostatic valve - 70% of losses;
  4. mixer - 20%.

easiest way computing was offered by E. Bucher, and K. Walter.

J = R x L x k

where k - factor responsible for the increased load.

accepted that systems without complex structures and fittings k = 1,3.If there are valves, k = 2,2.In the presence of fittings and valves at the same time - k = 2,6.

Selection of pump models on the results of calculations carried out

In order to choose the right pump to do a chart with coordinates P and J, note obtained by computing performance and find their point of intersection.

then the catalogs and the accompanying technical literature to choose the most satisfying of the pump model.

This view is wrong-chosen model:

Selection of pump models on the basis of calculations carried out

But it should be:

Selection of pump models on the basis of calculations carried out

indicators that have been calculated should be as accurate as possible coincide with the characteristics of the pump.If the characteristics of the pump higher, then it will work in the idle, consuming unnecessary electricity.

pump performance computing Checking for home heating: Example

To understand how to check the calculations, try to understand the example taken along all the requirements of SNIP.

In the example calculation is carried out for two-pipe heating systems with forced circulation.

was calculated the required amount of heat - 45.6 kW.and coolant flow rate - 2.02 m3 / h.

also on the conditions we have teploreguliruyuschy valve and 4 sites with the trumpets.

All losses we complement factor unaccounted losses (10%)..

H = (0,141 + 0,29 + 0,63 + 0,11) * 1,1 = 1,295 m

Proceeding from the above calculation shows that the pump is suitable for a given heating system should have the following characteristics:

consumption - 2.02 m3 / h;

Head -. 1,295 m

continue to build the schedule and select the most suitable model.

When selecting a model it should be noted that the calculation laid margin of 1-5%.