The principle of operation of a heat meter

The principle of operation of a heat meter is based on calculating the consumed thermal energy using data obtained from a flow sensor and two temperature sensors.

The dependence of the amount of heat on the temperature difference and water flow is described by a simple formula:

Q = 1.163 · G · (t1 - t2), MW

where
G - mass flow rate of the heat carrier, t/h;
t1 and t2 - the temperatures of the heat carrier at the inlet and outlet of the system, respectively, °C.

It can be seen from the formula that to determine the amount of heat, data on the flow rate of the heat carrier and the temperature difference on which it cools down at the consumer is necessary.

The data on the flow rate of the heat carrier is determined and transmitted to the heat meter's computational unit by the flow sensor, while the temperature data is transmitted by two temperature sensors, one of which is installed at the inlet of the heating system, and the other at the outlet.

The heat meter's computational unit processes the data obtained from the connected sensors according to the formula mentioned above and records the measured values in the archive. Heat consumption data can be visually read from the liquid crystal display or transferred to a computer using a data extraction device.

Factors affecting the accuracy of a heat meter

The overall error of a heat meter in calculating the volume of consumed thermal energy depends on:

1. The error of the flow sensor in calculating the flow rate of the heat carrier. For commercial calculations, heat meters with flow meters of 2nd class accuracy with an allowable error in the range from transitional to nominal flow rates within +/- 3% are permitted. When the flow rate of the heat carrier drops below the transitional flow rate, the error may increase to +/- 5%. When the flow rate drops below the minimum, the error is not limited, although the heat meter continues to calculate thermal energy.

2. The error of the temperature sensors. Most modern heat meters fall within the range of acceptable error when the temperature difference between the supply and return pipes is more than 3 °C. When the temperature difference drops below 3 °C, the error is not limited, although the heat meter continues to calculate thermal energy.

3. The error of the computational unit in processing the received signals and calculating the volume of consumed heat. This error is associated with the processing and rounding of data by the computational unit, as well as the calculated values.

Error registration

All heat meters have a self-testing program to detect errors. The computational unit polls the sensors at a certain frequency and registers an error if they are damaged. The error code is displayed on the display, and information about its appearance is recorded in the heat meter's memory.

Possible errors detected by the heat meter:

Damage to the temperature sensor
Damage to the flow sensor
Incorrect installation of temperature sensors
Incorrect installation of the flow sensor
Air presence in the flow section
Low battery charge
The temperature difference is recorded in the absence of flow for more than 1 hour.