RU2022235C1 - Method of finding of heat removal in heating system - Google Patents

Abstract

FIELD: instrumentation engineering. SUBSTANCE: active power consumed with electric motor of pump drive, intake and discharge pressures of pump, temperature of heat-transfer agent in feed and return pipe-lines of heating system are measured simultaneously. Power on shaft of pump and discharge pressure delivered by pump proper are calculated. Calculation coefficient of feed is found by division by power and result is subtracted from constant number equal to relation of pressure to power at zero feed. Characteristic reflecting dependence of calculation coefficient on feed is plotted. Productivity of pump is determined by it and is multiplied by difference of temperatures in feed and return pipe-lines. EFFECT: increased accuracy and simplified measurement of heat removal. 5 dwg

Description

 The invention relates to instrumentation and can be used to measure heat consumption in heating networks containing centrifugal electric pumps.

 Known methods of measuring heat consumption using mechanical and electrical heat meters containing liquid counters and thermometers in the supply and return pipelines of a heating network (see Skritsky LG Fundamentals of automation and automation of heat and gas supply and ventilation systems. M.: 1968, p. 43 -44 and Automatic Devices, Regulators, and Computing Systems, Reference Manual, 3rd ed., Revised and supplemented by BD Kasharsky, Leningrad: Mechanical Engineering, 1976, p. 61).

However, this method of measuring heat consumption requires the installation of flow meters, the sensitive elements of which are in the measured flow and rotate continuously. The maximum flow measurement limit is up to 300 m ³ / h, which does not always satisfy production requirements. The reliability of such heat meters is insufficient.

 There is also a method of calculating heat consumption by imperial formulas.

 The disadvantage of this method is the low accuracy due to the availability of source data obtained in an approximate way.

 The purpose of the invention is to increase the accuracy of measuring heat consumption, instrumentation of the accumulated heat consumption, the elimination of existing bulky and complex devices for measuring heat consumption, reducing operating costs.

 The goal is achieved by the fact that in a heating network containing a centrifugal electric pump, the active power consumed by the pump drive electric motor, the pressure on the discharge and intake of the pump, the temperature of the coolant on the supply and return pipes of the heating network are measured at the same time, the power acting on the pump shaft and pressure are calculated on the outflow developed by the pump itself, the calculated feed rate is determined by dividing the pressure by power and subtracting the result from a constant number equal to the ratio of pressure to power STI at zero flow, build characteristic relationship reflects the estimated flow rate, and it is determined by the pump capacity and multiplying it by the difference in temperature flow and return pipe heat network.

 In FIG. 1 is a structural diagram of a portion of a heating network; in FIG. 2 shows the characteristic of the centrifugal pump SE 800-100, where instead of the pressure in meters the pressure is accepted, as well as the proposed new characteristic of the pump; in FIG. 3 - characteristics of a centrifugal pump type SE 1250-140 with different values of the diameter of the impellers, as well as a new energy characteristic; in FIG. 4 - characteristics of another type of pump TsNS-180 with different impeller diameters and a new energy characteristic; in FIG. 5 is a structural diagram explaining the principle of measuring heat consumption in a heating network.

 The heat network (Fig. 1) consists of a heat source 1, a supply pipe 2, a heat consumer 3, a return pipe 4, in which a centrifugal pump 5 with an electric motor 6 is installed. To measure the amount of heat consumed by a consumer, the temperature difference between the forward and reverse is measured pipelines with manometers 7, 8, the pressure difference at the outlet and intake of the pump with manometers 9, 10, as well as the active power consumed by the pump drive motor. The difference in pressure and power calculate the flow rate of the coolant and multiply it by the temperature difference by the device 11.

Qdt , где G - количество тепла;
С - теплоемкость воды;
Q - расход теплоносителя на обратном трубопроводе;
Θ - разность температур в прямом и обратном трубопроводах тепловой сети;
t₁-t₂ - промежуток времени, в течение которого измерялся расход тепла.Then the amount of heat released by the consumer will be equal
G = c

Qdt, where G is the amount of heat;
C is the heat capacity of water;
Q is the flow rate of the coolant in the return pipe;
Θ - temperature difference in the forward and reverse pipelines of the heating network;
t ₁ -t ₂ is the period of time during which the heat consumption was measured.

 The most difficult is to measure the flow of coolant, especially with large diameters of pipelines and large flows. According to the proposed method, the fluid flow is made without installing special devices in the fluid flow, but directly by analyzing the parameters of the pumping station itself.

Pump 5 serves to supply fluid. The main parameters of centrifugal electric pumps are: feed and developed head N in mm water column The head is equal to the maximum height that liquid (water) can rise. Head and supply are interrelated values: the higher the head developed by a given pump, the lower its productivity. Since all the typical characteristics of the pump were taken on water with a density of 100 kg / m ³ , instead of pressure in meters we will continue to use pressure in MPa, at the rate of 1 MPa it is 100 m of pressure. A typical dependence of the developed pressure on the supply is shown in FIG. 2.

K , где N - мощность на валу насоса;
Р - разность давлений на приеме и выкиде насоса.To measure the flow rate by this method, it is proposed to introduce a new characteristic M - Q among the passport characteristics of the pump (Fig. 2-4). This characteristic reflects the change in the value of power consumption to create a pressure unit, which we denote by M, and the corresponding characteristic through M - Q, which for this value is
M = A -

K, where N is the power on the pump shaft;
P is the pressure difference at the inlet and outlet of the pump.

 The value of the M - Q characteristics for this type of pump, regardless of the flow rate, remains unchanged. Therefore, if you know the nature of the change in power on the pump shaft at a certain pressure, then you can judge the performance of the pump.

10³
Для характеристики, показанной на фиг. 3, это выражение равно
M = 9,64 - 2

10² а для характеристики, показанной на фиг. 4, M = 27 -

10³
Для вычисления мощности, действующей на валу насоса, измеренное значение активной мощности умножается на КПД электродвигателя η_э, которое находится из рабочей характеристики электродвигателя по известному рабочему току I.To measure heat consumption by the proposed method (Fig. 5), it is necessary to carry out the following measurements and calculations. For this, on a section of a heating network with an electric centrifugal pump, the following are measured: active power consumed by the pump drive motor P, kW; current in the supply network of the pump drive electric motor I, A; pressure on the pump discharge R _in , MPa; pressure at the pump intake R _p , MPa; temperature in the supply pipe of the network T _p , ^about C; the temperature in the return pipe of the heating network T _o , ^o C. On the typical characteristic of the pump (Fig. 2), the ratio of the supply value for a certain pressure to the power on the pump shaft is taken and the corresponding dependence M - Q is built. For convenience of calculations, this dependence is brought to the origin as shown in FIG. 2 -4. So, for the characteristic shown in FIG. 2, point M for a certain value of power and pressure is determined by the expression
M = 9.3 -

10 ³
For the characteristic shown in FIG. 3, this expression is equal
M = 9.64 - 2

10 ² a for the characteristic shown in FIG. 4, M = 27 -

10 ³
To calculate the power acting on the pump shaft, the measured value of the active power is multiplied by the efficiency of the electric motor η _e , which is found from the operating characteristics of the electric motor according to the known operating current I.

In the absence of a wattmeter, the power on the pump shaft can be determined by calculation using the formula
N = 1.73U ^. Icos φ η _e . Here η _e , ssφ is also found from the operating characteristics of the electric motor depending on the value of the operating current. The pressure at the pump side, which is directly generated by the pump, is determined in the general case by subtracting from the effective pressure P _in the pump side that part of the pressure at the pump inlet that exceeds the nominal passport pressure at the pump inlet:
P = P _in - (P _p - R _n ), where P is the resulting pressure;
P _in - pressure on the pump out;
R _p - pressure at the pump intake;
R _n - nominal pressure at the pump intake.

K , где А - постоянный коэффициент для данной характеристики;
К - масштабный коэффициент;
N - мощность на валу насоса, кВт;
Р - результирующее давление на выкиде насоса, МПа. Далее определяют разность температур на подающем и обратном трубопроводах тепловой сети
Θ = Т_п - Т_о
Обозначим теплоемкость перекачиваемой жидкости через С, тогда расход тепла будет равен
G = C Θ Q. Расход тепла за промежуток времени от t₁ до t₂ равен
G = C

Qdt Рассмотрим пример определения расхода тепла для сети с насосом СЭ-800-100, характеристика которого показана на фиг. 2.Based on the obtained power and pressure values, the energy coefficient M is calculated
M = A -

K, where A is a constant coefficient for a given characteristic;
K is a scale factor;
N is the power on the pump shaft, kW;
P is the resulting pressure on the pump outflow, MPa. Next, determine the temperature difference on the supply and return pipelines of the heating network
Θ = T _p - T _about
Denote the heat capacity of the pumped liquid through C, then the heat consumption will be equal to
G = C Θ Q. Heat consumption over a period of time from t ₁ to t ₂ is
G = c

Qdt Consider an example of determining the heat consumption for a network with an SE-800-100 pump, the characteristic of which is shown in FIG. 2.

Initial data: active power consumed by the pump drive electric motor, P = 240 kW; operating current of the electric motor I = 445 A; from the characteristics we find that the efficiency of the electric motor is η _e = 0.82; the pressure on the pump discharge P _in = 1.6 MPa; pressure at the pump intake P _p = 0.45 MPa; the temperature at the feed pipe T _p = 176 ^about ; return temperature Т _о = 78 ^о С; nominal pressure at the pump inlet P _n = 0.1 MPa.

1000 = 2,93
По характеристике М - Q (фиг. 2) находим: точку А = 2,93; точку В = пересечение характеристики М; точку С = 815 м³/ч = 815^.с= = 1^.815 = 815 кг/ч.Calculation: we find the power acting on the pump shaft
N = P η _e = 240 x 0.82 = 196 kW; we find the pressure that the pump creates at the outlet
P = P _in - (P _p - P _n ) = 1.6 - (0.45 - 0.1) =
= 1.6 - 0.35 = 1.25 MPa; determine the energy coefficient
M = 9.3 -

1000 = 2.93
According to the characteristic M - Q (Fig. 2) we find: point A = 2.93; point B = intersection of characteristic M; point C = 815 m ³ / h = 815 ^. c = 1 ^. 815 = 815 kg / h.

We find the temperature difference in the supply and return pipelines Θ = Т _p - Т _о = = 176 - 78 = 98 ^о С; we take the heat capacity of water equal to unity C = 1, we find the heat consumption for 1 h
G = c ^. Θ Q = 1 ^. 98 ^. 815 = 79870 kcal / h or 79870 ^. 4.19 ^. 10 ³ = 33.465 kJ / h.

Claims (1)

 METHOD FOR DETERMINING HEAT CONSUMPTION IN A HEAT NETWORK, which consists in measuring the pressure on the discharge of a centrifugal electric pump, the temperature difference in the direct and return pipelines of the heating network, characterized in that, in order to improve accuracy, at the same time measure the active power consumed by the electric pump and the pressure on the suction of the centrifugal pump pump, in this case, determine the calculated feed coefficient of the centrifugal pump and build a calibration characteristic, which determines the performance of the centrifugal pump with There is a difference in temperature in the forward and reverse pipelines of the heating network.

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