A water meter (also popularly known as a water meter ) is a measuring device that shows the volume of water that has flowed through . Mostly, water meters are used in business transactions, e.g. B. between utility companies (municipal utilities) and consumers. In this case, the water meters must be calibrated (in Germany in accordance with the measurement and calibration law ).
It should be possible to isolate water meters from the rest of the water network by isolating them for the first time so that the measuring device can be exchanged without any problems.
During the industrialization at the beginning of the second half of the 19th century, the first private houses also received their own water connections. Carl Wilhelm Siemens developed a water meter in England in 1851 which, in contrast to earlier designs, displayed the amount of water consumed directly. An impeller was used in the supply line, the speed of which is proportional to the flow. A gear transmission transmitted the number of revolutions to a counter. The device was a great success and was also sold in Germany from 1858 (by Siemens until the mid-1950s).
Impeller water meter
Vane flow meters are used to measure small to medium water volumes for nominal flows of up to 15 m³ / h . A distinction is also made here with regard to the single-beam and multi-beam measuring principles .
- Apartment water meters are usually single-jet meters: the flow to the impeller is tangential .
- The domestic water meters are usually multi-jet meters: the flow onto the impeller is symmetrical from the outer surface of the measuring chamber. As a result, the amount of water acts evenly on the impeller, which ensures increased measurement stability and measurement accuracy .
Volume counters are available with fixed or movable measuring chamber partitions, e.g. B. disc counters or rotary piston counters .
Volume counter with turbines
Used as bulk water meter ( Woltmann meter ) for nominal flow rates from 15 m³ / h.
Compound water meter
Compound water meters are a combination of large water meters as the main meter and a secondary meter for smaller flows. A spring switch valve automatically switches on the bulk water meter at high flow rates so that both meters then run in parallel. On the other hand, only the secondary meter runs at low flow rates. This type of construction is used where both small to medium flows, but occasionally also large flows occur (industry, swimming pools, buildings with fire extinguishing systems).
Measuring capsule counter
A meter with a measuring capsule consists of the actual counter in the measuring capsule and the measuring capsule holder with the pipe connections. As a result, the counter can be exchanged without having to loosen the screw connections of the meter housing (the measuring capsule holder) with the pipelines, as was previously the case, in order to remove the meter as a whole.
Flush-mounted meters are usually designed as measuring capsule meters.
The display is carried out by means of number rollers and, for the low-order digits, also by small pointers with a decimal scale. According to the regulation, the measured value must be displayed in cubic meters (black digits), the fractions of a cubic meter are displayed by red digits or pointers. Water meters can be equipped with contactors that e.g. B. at each 1, 10 or 100 liters a pulse to an additional electronic counter for further processing. This technology is used to record consumption data in building automation or to dose additives. Some water meters have a digital counter with LCD and long-life battery.
Sizes and dimensions
According to DIN ISO 4046-1, water meters are divided into sizes according to the nominal load Q 3 (or earlier the nominal flow rate Q n ) and marked. The nominal load corresponds to half the value of the maximum load Q 4 or earlier Q max .
The load (flow rate per hour) is divided into a lower range (Q 1 = Q min to Q 2 = Q trenn ) and an upper range (Q 2 = Q trenn to Q 4 = Q max ).
The smallest size, which is used in single-family houses and multi-family houses with up to 30 residential units, is labeled with Q 3 = 4 or earlier Q n 2.5 m³ / h. These meters have a minimum load Q min of 50 l / h, a separation limit Q separ of 200 l / h and a maximum load Q max of 5000 l / h. The short-term possible flow of 5 m 3 is also sufficient to operate pressure washers . It should be noted that many water suppliers charge twice to ten times the monthly basic fee for a meter of the next larger size.
In the lower load range, the meter must show an error of less than ± 5% during calibration , in the upper range a maximum of ± 2%. During operation, the error can occur e.g. B. increase through wear and tear or deposition. The permissible traffic error limit is twice the calibration error limit .
According to DVGW (Deutsche Vereinigung des Gas- und Wasserfach eV) worksheet W 406, meters with Qn 2.5 for 1 to 30 (1 to 15) residential units, with Qn 6 for 31 to 200 (15 to 85) residential units and with Qn 10 is suitable for 200 to 600 (86 to 200) residential units. The information in brackets in the worksheet from 2003 applies to apartments whose toilets are equipped with flush valves, as flush valves require a greater water flow.
The European Measuring Instruments Directive 2004/22 / EG ( Measurement Instrument Directive (MID)) has been in effect since November 2006, which defines better meter accuracy at low flow rates as well as the following new names:
- The minimum flow rate Q min becomes the minimum flow rate Q 1
- Separating flow Q separ becomes transition flow Q 2
- Nominal flow rate Q n (or Q nom ) is Dauerdurchfluß Q 3
- The maximum flow rate Q max becomes the overload flow rate Q 4
In contrast to the nominal flow rate Q n , which was set at half the value of the maximum flow rate Q max , the continuous flow rate Q 3 is now higher. The old counter size Q n 1.5 is now referred to as "Q 3 = 2.5". Likewise, Q n 2.5 is now identified as “Q 3 = 4”, Q n 6 as “Q 3 = 10” and Q n 10 as “Q 3 = 16”.
The permissible temperature range (or the maximum temperature of the measured water) and the installation position (H for horizontal and V for vertical) are also indicated on the dial of the domestic water meter.
With the implementation of Directive 2014/32 / EU on the harmonization of the legal provisions of the member states on the provision of measuring instruments on the market and the Directive 2014/31 / EU on the harmonization of the legal provisions of the member states on the provision of non-automatic weighing instruments on the market, the so-called EU -Water meter introduced in Germany ( Section 8 Paragraph 1 No. 1 MessEV ). EU water meters must meet the specific requirements of Annex III of Directive 2014/32 / EU.
Dirt particles, vibrations, pressure surges or air bubbles can lead to a so-called roller jump, in which a roller is set in rotation in an uncontrolled manner by its neighboring roller, whereby excessive water consumption can be simulated.
Calibration, calibration validity period, examination of findings
The year of calibration can be recognized by the so-called main stamp ( seal ). The year is stamped on one side and the identification number of the test center or the calibration office on the other . The calibration period for cold water meters is six years in Germany; for hot water meters, it is five years (ordinal number 5.5 Annex 7 MessEV), d. H. a cold water meter calibrated in 2015 may remain in the network until the end of 2021. In Austria, there is a uniform recalibration period of five years for cold, warm and hot water meters ( Section 15 no. 5. a. MEG ). The water supply company can have the calibration validity period extended by three years (i.e. several times if necessary) for a meter type (make, size) used in its area by means of a random test at a state-approved test center.
If there are doubts on the measuring accuracy of a calibrated measuring device consist, one can (in consultation with the water supply company) a request for service testing by an acknowledged service station or when Eichamt filters. There the meter is checked individually and a test certificate is issued. In practice, around 90% of the meters tested are not objectionable.
Water meter and tenancy law
If not all apartments in a house are equipped with a water meter, the fresh or cold water can be billed according to the living space ( Section 556a (1) sentence 1 BGB ). If consumption is recorded for all tenants, the water costs are to be billed according to consumption (Section 556a, Paragraph 1, Clause 2 BGB). For hot water , the consumption recording is z. B. stipulated for hot water meters in Section 4 (1) HeizkostenV . A landlord can also use the data of a non-calibrated water meter for the utility bill if he can prove that the information is correct. The installation of water meters is to be tolerated by the tenant as a modernization measure.
The building regulations of the federal states regulate whether the building owner is obliged to retrofit water meters .
- ↑ a b c d About the measuring behavior and the dimensioning of water meters , Zenner International GmbH & Co. K
↑ a b Dimensioning of the water meter , explanations on Erwin Ruff's private website:
DVGW worksheet W 406 from 2003 named lower numbers for the residential units to be connected, namely Qn 2.5 for 1 to 30 residential units, Qn 6 for 31 to 100 residential units and Qn 10 for 100 to 200 residential units. Before 2003, the information from DIN 1988 Part 3 was used, which tended to result in even lower values.
- ↑ DVGW e. V. (Hrsg.): Technical rule worksheet W 406, Volume and flow measurement of cold drinking water in pressure pipelines - selection, measurement, installation and operation of water meters . Wirtschafts- und Verlagsgesellschaft Gas und Wasser mbH, 2012, ISSN 0176-3504 .
- ↑ BGH , judgment of March 12, 2008, VIII ZR 188/07
- ↑ BGH, judgment of November 17, 2010, VIII ZR 112/10
- ↑ BGH, judgment of December 17, 2008, VIII ZR 41/08