Heat meter performance downstream of bends and the asymmetric swirl generator

Abstract Heat meters are sensitive to non-ideal flow conditions and are therefore tested during type approval using standardized disturbances. EN 1434 employs the asymmetric swirl generator (ASG) installed 7 pipe diameters (7 D ) upstream of the meter as a substitute for real bends, assuming it approximates bend-induced flow conditions even at short installation lengths such as 0 D . This study investigates the validity of this assumption through measurements with 14 commercially available heat meters in DN 15 and DN 25. It is found that while the ASG at 7 D reproduces the double bend at 5 D , both single and double bends at 0 D cause substantially larger faults. Four meters exceeded the maximum permissible error (MPE) downstream of a bend configuration, yet only two were detected by the ASG. Four additional meters operated close to the MPE and, considering angular sensitivity, would likely exceed it at other orientations, yielding up to 6 of 14 potential false negatives. Furthermore, the ASG at 0 D caused the largest meter faults, indicating that disturbances involving flow recirculation may be even more severe than bends. Implications for future revisions of EN 1434 include adding a second disturbance generator or using real bends, and evaluating whether disturbances that induce recirculation should be included.