Knowledge · basics
Water meter or heat meter?
Both are installed in a water pipe and both can measure ultrasonically, but they answer different questions.
What does a water meter measure?
A water meter such as the H2O measures the volume flowing through the pipe in cubic metres. Whether the water is cold or hot does not change the measured quantity; the temperature class only defines the maximum water temperature at which the meter may be used. The relevant regulations are the Measuring Instruments Directive (MID), OIML R 49 and ISO 4064, plus EN 14154 for ultrasonic meters.
What does a heat meter measure?
A heat meter such as the DELTA III measures energy, in kWh, MWh or GJ. It needs three components: a flow sensor, two temperature sensors and a calculator. Energy is derived from the volume, the temperature difference between flow and return, and a heat coefficient. The MID and the EN 1434 standard apply.
And a cooling meter?
Technically, a cooling meter works like a heat meter, except that the temperature difference is reversed: the return is warmer than the flow. The DELTA III records heating and cooling in separate registers, which makes it suitable for plants that supply both and for district cooling. In the Middle East such meters are often called BTU meters.
Side by side
| Question | H2O water meter | DELTA III heat meter |
|---|---|---|
| Measured quantity | Volume in m³ | Energy in kWh, MWh, GJ, Gcal |
| Components | Measuring tube with electronics | Flow sensor, sensor pair, calculator |
| Temperatures | maximum and minimum recorded, if used | flow and return, continuously |
| Standards | MID, OIML R 49, ISO 4064, EN 14154 | MID, EN 1434 |
| Typical billing | Cold and hot water | Heating, cooling, district heating, district cooling |
Hot water: water meter or heat meter?
To bill hot water by volume, a water meter with a suitable temperature class is sufficient; for the H2O, T50 is standard, with T70 and T90 on request. If you want to bill the energy used for hot-water production, you need a heat meter in the charging circuit of the hot-water cylinder.