Knowledge · sizing
Choosing the right nominal size
A meter that is too large barely registers small flows; one that is too small causes pressure loss and runs at its limit. Here is how to size the H2O and DELTA III correctly.
Basic rule: size by flow rate
The nominal size of the meter does not have to match that of the pipe. What matters is the flow rates that occur in operation: normal continuous operation, peaks and the smallest flows, for example at night. Reducers upstream and downstream of the meter are common.
Key values of the H2O water meter
- Q3, permanent flow rate
- The flow rate at which the meter may be operated continuously. It defines the meter’s rating, for example Q3 = 4.0 m³/h for DN20.
- Q4, overload flow rate
- Permitted for short periods; for the H2O, 1.25 × Q3.
- Q1, minimum flow rate
- From this flow rate upwards, the meter measures within the maximum permissible errors. Q3/Q1 is the dynamic range: for the H2O, R250 to R500 threaded and R400 or R800 flanged.
Example: an H2O DN20 with R250 has Q3 = 4.0 m³/h and Q1 = 0.016 m³/h, i.e. 16 litres per hour. In the R400 version, Q1 drops to 10 l/h. If you want to detect dripping taps and leaks, the wider range is an advantage.
Key values of the DELTA III heat meter
- qp, nominal flow rate
- Continuous operation, for example 2.5 m³/h for DN20.
- qs, maximum flow rate
- Permitted for short periods; for the DELTA III, 2 × qp.
- qi, minimum flow rate
- qp/qi = R100 as standard, R50 or R250 as an option.
With a heat meter, the temperature difference also comes into play. The design flow rate is the heating or cooling capacity divided by Δθ and the heat capacity of water. Chilled-water plants operate with small temperature differences and therefore need considerably more flow than heating systems for the same capacity.
Check the pressure loss
The meter slightly restricts the flow. For the DELTA III, the pressure loss at qp is 110 to 180 mbar for the threaded versions and 2 to 11 kPa for the flanged versions. Include this value in the pump sizing.
Thread or flange?
For both products: DN15, DN20, DN25, DN32 and DN40 have threaded connections from G 3/4 B to G 2 B. From DN50 the meters are flanged. The length increases with the nominal size; it is shown for every size in the nominal size selector on the product pages.
Step by step
- Determine the flow rates: continuous, peak, minimum.
- Choose the smallest nominal size whose Q3 or qp covers continuous operation.
- Check that the peak stays below Q4 or qs and the minimum stays above Q1 or qi.
- Include the pressure loss in the pump sizing.
- Specify the connection, temperature class and interface.
H2O nominal sizes DELTA III nominal sizes
We are happy to advise you on final sizing.