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How to correctly select the method of circulating DC water pump

Published:2021-08-06

circulating DC pump


1.Selection method of circulating DC pump


The general method of circulating DC water pump selection is to obtain the water flow required by the floor heating system and the head required to overcome the resistance of the floor heating system pipe network and the wall-hung boiler itself based on the results of hydraulic calculations. Comprehensive consideration of the circulating DC water pump in the floor heating system For work efficiency, choose a suitable circulating DC water pump.


1.1 System flow

Formula 1)

G=3.6Q/C(Tg-Th)

G—Required flow of heating pipe network, m3/h

Q—The heating load required by the house, kW

C—Specific heat of water, kJ/(kg•℃)

Tg—heating water temperature, K

Th—heating return water temperature, K


Formula (2)

Q=K1K2qA

Q—The heat load required for heating of the house, kcal/h;

K1—Considering the safety factor of neighbor heating asynchronous, take 1.2 here;

K2—Considering the safety factor of intermittent heating, take 1.2 here;

q—The estimated value of standard residential heat index, kcal/m2;

A—standard residential building area, m2;

 

1.2 System resistance


The system resistance is divided into pressure loss along the way, local pressure loss and internal resistance of the machine. The pressure loss along the way refers to the continuous and consistent pressure loss in the pipeline; the local pressure loss refers to the special parts in the pipeline system, due to its changes. The direction of the water flow or the discontinuous pressure loss caused by the narrowing of the local water flow channels (such as reduced diameters, tees, valves, joints, filters, etc.); the internal resistance of the machine is the resistance of the machine itself.


1.2.1 Pressure loss along the way

The floor heating pipe is a round pipe with a relatively smooth inner wall, which is of low roughness. The calculation formula for selecting the pressure loss along the way is as follows:


Formula (3)

Hf=λ•L/D•V2/2g

Hf—pressure loss along the way, mm/m

λ—Friction resistance coefficient (not a fixed value)

L—Length of loop water pipe, m

D—pipe inner diameter, m

V—average water velocity m/s

Re<2300 is laminar flow:

Formula (4)

λ=64/Re

Re>2300 is turbulent flow:


Formula (5)

λ=0.316Re-0.25

Formula (6) is used to judge the water flow mode: laminar flow or turbulent flow

 Table 2 Water temperature and fluid viscosity

Re=VD/γ

γ: dynamic viscosity coefficient, m2/s


1.2.2 Local pressure loss

The local pressure loss is mainly limited by the flow capacity of some valves and filters. The calculation formula for selection is as follows:


Formula (7)

ΔP=102(G/KV0.01)2        

ΔP; local pressure loss, mmh2o

G—Water flow required for heating pipe network, l/h

KV0.01—Flow capacity (pressure difference equal to 0.01bar), l/h

1.2.3 The internal resistance of the machine itself is an actual measured value. Because the wall-hung boiler industry has a relatively high start and the degree of standardization is better, the internal resistance of the same type of products from different manufacturers is not much different.


1.3 Circulating DC pump efficiency curve


At present, most of the water pumps used in gas heating water heaters are backward impeller centrifugal pumps. This type of water pump has low efficiency. According to the information provided by a certain water pump manufacturer, the efficiency and flow curve are as follows


Dongguan Shenpeng Electronics Co., Ltd. was founded in 2004. It is the first domestic manufacturer to develop brushless DC pumps and professionally design and produce high-end micro DC brushless pumps in various industries. It is the first in research and development with the "Beijing Fuwai Hospital" directly under the Chinese Academy of Medical Sciences Taiwan-made artificial heart pump and control system to replace artificial heart. Won the national "high-tech enterprise", the national "multiplier enterprise" and other honors. Has passed ISO9001 and IATF16949, OHSAS18001, ISO14001 and other management system certifications. All products have passed CE, ROHS, SGS certification, and some have passed FDA, REACH certification. The company adopts "Six Sigma" quality management and pursues "zero defect" of products. We follow the business philosophy of "powered by science and technology, survive by quality" and serve our customers wholeheartedly!


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