How a heat meter works

Operation principle of a heat meter

The operation principle of a heat meter is based on measuring the amount of heat using data obtained from the heat carrier flow sensor and two temperature sensors. The meter measures the amount of water that enters the heating system, as well as the temperature of the water at the inlet and outlet of the heating system.

The amount of heat is determined as the product of the heat carrier flow rate that passed through the heating system and the temperature difference at the inlet and outlet.

Q = 1.163 · G · (t1 - t2), MW

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

Data on the flow rate are transmitted to the computational system from the flow sensor, and data on temperature are transmitted from two temperature sensors, one of which is installed in the supply pipe of the heating system, and the other - in the return pipe.

The computational system of the heat meter determines the amount of consumed heat based on the collected data and records this data in the archive. Data on the consumed thermal energy are displayed on a liquid crystal display or can be retrieved using a standard optical interface.

Factors affecting the accuracy of a heat meter

The meter error in calculating the amount of consumed heat depends on the errors of the flow meter, temperature sensors, and the processor that processes the collected data.

For accounting in apartments, meters with an allowable error in calculating the amount of heat in the range from +/-6 to +/-10% are used. More information on accuracy classes and instrument errors can be found in the section on Technical Characteristics of Heat Meters.

The actual error may be higher than the base error determined by the technical characteristics of the components. The instrument error increases if:

The temperature difference between the inlet and outlet of the system is less than 3°C.
The heat carrier flow rate is lower than the minimum value specified in the instrument's technical specifications.
The installation is carried out in violation of the manufacturer's requirements (most manufacturers waive their warranty obligations if the meter is installed by an unlicensed organization).

And here's an unpleasant moment for fans of magnetic braking of the device - modern heat meters are protected from magnetic fields.

Measurement of consumed thermal energy

When calculating the tariff, the unit of measurement for thermal energy is a gigacalorie (Gcal) or MWh (megawatt-hours). A gigacalorie is a non-SI unit of measurement that was widely used since the Soviet era and has been inherited by post-Soviet countries.

Most heat meters are manufactured in Europe and use the international unit of measurement, introduced into the International System of Units (SI) - gigajoules (GJ) or the widely accepted non-SI unit - kilowatt-hour (kWh) to measure the consumed thermal energy.

This difference does not pose an obstacle in calculations with the heat supply organization, as both gigajoules and kilowatt-hours can be converted to gigacalories by a simple multiplication coefficient.

Reading data from a heat meter

LCD display - all heat meters have a screen for visual reading of readings by simply switching between menu sections with one button.

OPTO transmitter is included in the basic equipment of most European-made devices and is designed to read readings using an OPTO head and output them to a PC. Typically, the OPTO sensor is used to obtain and print extended data on the operation of the heat meter.

M-Bus module can be included in the meter's delivery set and is designed to connect the device to the wired network of the centralized collection of readings by the heat supply organization. Several devices are connected to a low-voltage (39V) network using twisted pair and connected to a concentrator, which polls them with a certain periodicity, generates a report, and outputs it to a PC or transmits it to the heat supply organization.

Radio module can also be included in the heat meter's delivery set and is designed for wireless data transmission over a distance of several hundred meters. An inspector with a receiver tuned to the appropriate frequency, upon entering the device's range of action, records the readings obtained and transmits them to the heat supply organization.

In some European countries, the collection of readings from accounting devices is entrusted to the household waste collection service. The receiver is attached to a garbage truck that moves along a fixed route and polls accounting devices installed in this area.

Registration of errors

All heat meters are equipped with a self-check system for errors. The calculator periodically polls the connected sensors and in case of their damage registers an error, displays the error code on the display, and records data about its occurrence in the archive.

Below are some of the possible errors that the heat meter records:

Damage to the temperature sensor
Damage to the flow sensor
Incorrect installation of temperature sensors
Incorrect installation of the flow sensor
Air in the flow part
Weak battery charge
Positive temperature difference in the absence of flow for more than 1 hour.

Archiving of readings

All heat meters store data in the archive about accumulated values of thermal energy, volume, and operating time with an error on a specified day of the month.

Some heat meters allow you to set the date for recording the readings, and some also the frequency.