RU2566640C2 - Method of measurement of surface heat exchange resistance of heating device - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: invention relates to the field of thermophysical measurements and can be used for determination of thermal performance of heating devices. According to the offered method thermal conditions of the room, where a heating device is located, are put into time non-stationary state, the behaviour time of average temperature of the heating device is measured, the average air temperature indoors, the average temperature of internal barriers and ambient temperature. Non-stationary state is provided with switching off of the heating device. The non-stationary heat balance equation for the heating device itself is used.

EFFECT: higher measurement accuracy.

Description

Title of invention

A method of measuring the heat transfer resistance of a heating device.

FIELD OF THE INVENTION

The invention relates to the field of thermophysical measurements, in particular for determining the thermal characteristics of heating devices.

State of the art

Description of the invention

Heat transfer resistance is one of the important characteristics of heating appliances. It allows you to:

- evaluate the efficiency of the heat transfer process;

- calculate the heat output given by the heater.

The heat transfer resistance can be determined from the Newton-Richmann law, according to which the thermal power P is _warm. given by the heater is proportional to the difference between the average temperature of the heater T _East and the average room temperature T _in :

$$P_{tePl}=G_{\mathrm{and}\mathrm{from}t}\cdot \left(T_{\mathrm{and}\mathrm{from}t}-T_{\mathrm{at}}\right),\left(\mathrm{one}\right)$$

where G _East - heat transfer coefficient of the heater [W / ° C].

The reciprocal of the heat transfer coefficient is called the heat transfer resistance (thermal resistance) R _source :

$$R_{\mathrm{and}\mathrm{from}t}=\frac{\mathrm{one}}{G_{\mathrm{and}\mathrm{from}t}}.\left(2\right)$$

In stationary mode, when the heat balance is fulfilled, P heat ₌ P _in , where P _in is the thermal power supplied to the heater:

$$P_{tePl.}=P_{\mathrm{at}x.}=G_{\mathrm{and}\mathrm{from}t}\cdot \left(T_{\mathrm{and}\mathrm{from}t}-T_{\mathrm{at}}\right).\left(3\right)$$

There is a method of determining the values of radiator coefficients for cast iron radiators experimentally from bench tests by measuring water temperatures at the inlet and outlet of the radiator, water flow rate, time and amount of heat that the heat carrier gives off in a heating device using a heat meter installed on the heat carrier pipeline, surface temperature measurements the radiator and the air temperature near the radiator using a heat flow recorder and finding the average surface temperature of the radiator with by the power of a copper-constantan thermocouple, the balance equation is used: Q / S = K · ∑, where Q is the amount of heat given off by the radiator; S is the surface area of the radiator;

∑ - testimony of the registrar; K is the coefficient that was determined from the experiment, it is convenient to present it in the form K = k · k _H , where k is the radiator coefficient and k _n is the nominal conditional coefficient of heat transfer of the heating device (Nizovtsev M.I., Terekhov V.I., Chepurnaya ZP Effect of physical parameters on the radiator coefficients of heat flow recorders for heating appliances // Ventilation, heating, air conditioning, heat supply and building thermal physics. - 2005. - No. 5. - P.36-40).

This method is based on experimental studies in laboratory conditions, does not take into account the individual characteristics of each heating device and the change in its characteristics during operation. The use of a heat meter in measurements requires insertion into the pipeline and introduces significant errors.

A known metering device for the consumption of thermal energy of a heating device, comprising a unit for calculating the heat transfer coefficient calculated by a straightforward dependence on the temperature difference according to the formula (1) (RU No. 2095769, IPC G01K 17/20, 10.11.1997).

However, all attempts led to the complication of determining the heat transfer coefficient or lowering the accuracy of its determination.

A device is known for determining the heat transfer coefficient in an unsteady process, comprising sensitive surface temperature sensors and an electronic coefficient measurement circuit, according to the following relationship: α = N / FΔt; where Q = N = αF (t _p -t _v ) = αFΔt; α is the heat transfer coefficient; N is thermal energy; F is the surface area; (t _p -t _v ) is the difference of temperature surfaces (CS No. 217269, IPC G01N 25/20, 03/26/1982).

The disadvantage of this technical solution is the need to measure thermal energy, which complicates the measuring system (requires the use of a flow meter and two temperature sensors, requires insertion into pipelines), which in turn does not allow to obtain sufficient measurement accuracy.

A device for measuring thermal resistance is also known, comprising a source of thermal energy, a temperature meter, an electronic processing unit, wherein the output of the temperature meter is connected to the input of the electronic processing unit, further comprising an external heat exchanger, an internal heat exchanger, an inlet pipe, a first connecting pipe, and a second connecting one pipeline, third connecting pipeline, outlet pipeline, device for pumping coolant, second, third, four the fifth, sixth and sixth temperature meters, wherein the output of the inlet pipe is connected to the input of the external heat exchanger, the output of the external heat exchanger is connected to the input of the first connecting pipe, the output of the first connecting pipe is connected to the input of the device for pumping the coolant, the output of the device for pumping the coolant is connected to the input of the second connecting pipe, the output of the second connecting pipe is connected to the input of the heat energy source, the output of the heat source energy is connected to the input of the third connecting pipe, the output of the third connecting pipe is connected to the input of the internal heat exchanger, the output of the internal heat exchanger is connected to the input of the output pipe, the external surface of the external heat exchanger is provided with thermal insulation, except for the external surface of the external heat exchanger adjacent to the external surface of the object under study, the external surface of the internal the heat exchanger is provided with thermal insulation, except adjacent to the inner surface On the external surface of the internal heat exchanger, the temperature meter is located inside the inlet pipe, the second temperature meter is located on the outer surface of the external heat exchanger not equipped with thermal insulation, the third temperature meter is located inside the first connecting pipe, the fourth temperature meter is located inside the third connecting pipe, the fifth temperature meter placed on the external surface not provided with thermal insulation heat exchanger, a sixth temperature meter is located inside the outlet pipe, the output of the second temperature meter is connected to the second input of the electronic processing unit, the output of the third temperature meter is connected to the third input of the electronic processing unit, the output of the fourth temperature meter is connected to the fourth input of the electronic processing unit, the output of the fifth meter temperature is connected to the fifth input of the electronic processing unit, and the output of the sixth temperature meter is connected to the sixth input of the electronic processing unit, in addition, the internal heat exchanger contains a connected coil and a plate, or the internal heat exchanger contains N parallel connected heat exchangers, where N is a natural number, with 0 <N <∞, or that the external heat exchanger contains a connected coil and plate, or an external heat exchanger contains N parallel connected heat exchangers, where N is a natural number, with 0 <N <∞ (RU No. 52186, IPC G01N 25/18, 03/10/2006).

The disadvantage of this solution is its complexity, the inability to use in the conditions of operation of buildings and structures. This device cannot take into account the individual characteristics of each thermal device and the change in its characteristics during operation. In this regard, the value of thermal resistance for each individual device will have a large scatter in relation to measurements made in laboratory conditions for a reference sample. From the practice of operating thermal devices it is known that this scatter is quite high.

A device for measuring the thermal resistance of a heating system of a separate room, containing m sensors for measuring the average temperature of the room air and n sensors for measuring the average temperature of the internal enclosure of the room, as well as an ambient temperature sensor and a temperature source of the heat source, the outputs of which are connected to the inputs of the microprocessor controller for collecting and transmitting information, the communication bus of which is connected to the input bus of the data processing device (RU No. 115472, IPC G01K 17/00, 05/04/2011) ( rototip). In total, the values of four temperatures are measured in this device.

The basis of this invention is a method for dynamically changing the thermal regime of a room over time, when the temperatures of the air and internal fences of the room are forced to change in time, for example, by cooling the room. In this method of measuring thermal resistance, individual characteristics of the heating device are taken into account, but there are disadvantages: the presence of excessive temperature measurements (four measurements instead of two), which reduces the accuracy of calculating thermal resistance; the occurrence of errors due to the low temperature difference and the internal fencing of the room; To measure thermal resistance, it is necessary to conduct a complex experiment related to the cooling of the room.

Disclosure of invention

The aim of the invention is to measure the heat transfer resistance of a heating device, taking into account the individual characteristics of the heating system of a separate room with increasing measurement accuracy.

This is achieved by the fact that, in contrast to the known technical solutions that use the stationary thermal mode (3), the thermal mode of the room in which the heater is located is brought into a non-stationary state in time by turning the heating device on or off. In this case, instead of the stationary equation (3), the following equation is used:

$$\frac{C_{\mathrm{and}\mathrm{from}t}\cdot d{T}_{\mathrm{and}\mathrm{from}t}}{dt}=P_{\mathrm{at}x.}-G_{\mathrm{and}\mathrm{from}t}\cdot \left(T_{\mathrm{and}\mathrm{from}t}-T_{\mathrm{at}}\right),\left(\mathrm{four}\right)$$

_ist where C - heat capacity of the heater [J / ° C];

t is the current time [sec].

In contrast to the prototype, instead of four temperature measurements, the time behavior of the average temperature of the heating device and the average temperature of the air in the room is measured, while the unsteady state is ensured by the termination of the heating process of the heating device (P _in = 0). The measured values of the temperatures T _East , T _in and the rate of change (gradient) of the source temperature dT / dt are substituted into equation (4), from which the heat transfer resistance is found:

$$R_{\mathrm{and}\mathrm{from}t}=\frac{\mathrm{one}}{G_{\mathrm{and}\mathrm{from}t}}=\frac{T_{\mathrm{and}\mathrm{from}t.}-T_{\mathrm{at}}}{C_{\mathrm{and}\mathrm{from}t}\cdot \frac{d{T}_{\mathrm{and}\mathrm{from}t}}{dt}}\left(5\right)$$

Comparison of the invention with known technical solutions shows that it has a set of new essential features (taking into account the individual characteristics of the heater in operating conditions, a simple measurement procedure, improving the accuracy of measurements), which together with the known features can successfully achieve the goal.

The implementation of the invention

Description of the measurement procedure during operation at the facility

In the room on the radiators, digital sensors are installed to measure air temperatures and the heating system. Instrument readings are automatically transmitted to the processing center, followed by statistical averaging and calculation of heat transfer resistance according to formula (5).

The proposed technical solution can be used in monitoring systems, control, accounting and management of heat consumption as a separate room, and the building as a whole.

Claims (1)

A method of measuring the heat transfer resistance of a heating device, namely, that the thermal regime of the room in which the heating device is located is brought into a non-stationary state in time, the time behavior of the average temperature of the heating device, the average air temperature in the room, the average temperature of the internal fencing and the temperature is measured environment, while the measured temperature values are substituted into the unsteady equation of the heat balance of the room for indoor air and fences, of which this heat transfer resistance is located, characterized in that, in order to simplify the measurement and calculation procedures and increase the measurement accuracy, the non-stationary state is ensured by turning the heating device on or off and the non-stationary heat balance equation is used for the heating device itself, while the heat transfer resistance turn off the heater is as follows:
$$R_{\mathrm{and}\mathrm{from}t}=\frac{T_{\mathrm{and}\mathrm{from}t.}-T_{\mathrm{at}}}{C_{\mathrm{and}\mathrm{from}t.}\cdot \frac{d{T}_{\mathrm{and}\mathrm{from}t}}{dt}}$$

,
where r_ist - heat transfer resistance of the heater [° C / W];
$$T_{\mathrm{and}\mathrm{from}t}=\frac{T_{\mathrm{at}x}+T_{\mathrm{at}sx}}{2}$$

 - the average surface temperature of the heater [° C];
T_at- the average temperature in the room [° C];
FROM_ist - heat capacity of the heater [J / ° C];
t is the current time [sec].