Dimensioning district heating protection systems

Design Target:

DanTaet determines the size of leakage protection systems for district heating installations from Qmax (peak flow on the coldest day of the year) and the following criteria:

  • Lifespan: No component may suffer overload at Qmax
  • Comfort: Aggregate head loss of system components not to exceed 1mWc (10kPa)

From these criteria, the maximum load for the various types of protection system at ΔT=30°C becomes:

Mechanical meters Ultrasonic meters
Dim. System Max kW  Max Q m³/h System Max kW  Max Q m³/h
½" FB 20 0,57 FBU 21 0,96
¾" FX 35 1,00 FXU 64 1,83
¾" WLP-2-F2,5 35 1,00 KMP-F2,5-M2 64 1,83
1" WLP-2-F3,5 50 1,43 KMP-F3,5-M2 81 2,32
1¼" WLP-2-F6 88 2,52 KMP-F6-M2 97 2,78
1½" WLP-2-F10 142 4,07 KMP-F10-M2 225 6,45
2"/DN50 WLP-2-F15 213 6,10 KMP-F15-M2 267 7,65
DN65 WLP-2-F25 525 15,1 KMP-F25-M2 560 16,1
DN80 WLP-2-F40 770 22,1 KMP-F40-M2 970 27,8
DN100 WLP-2-F60 1215 34,8 KMP-F60-M2 1860 53,3
DN150 WLP-2-F150 2810 80,5 KMP-F150-M2 5740 165

 

KMP-F: use of existing heat meter

If the Utility has installed a Kamstrup heat meter MULTICAL®601/602 or MULTICAL®801 it may be possible to employ this as part of the protection system (KMP-Fxx-M1), always providing the Utility permits.

As the above table reveals, the Design Target causes the load on the flow meters of the protection system to be in the range approx. 40% (small systems) to 55% (large systems) of the meter's qp. If the heat meter is laid out so that this is the case for its flow sensor, it may be employed straightaway.

If at Qmax the flow sensor of the heat meter is loaded to a higher proportion of qp, and it is nevertheless used as a component of the KMP-F system, it is up to the consultant, designer or Utility to demonstrate that the heat requirement of the installation may still be met on the coldest day of the year, under the then prevailing operating comditions.

Note that the Utility quotes differential pressure in the street, or possibly in the branch pipes (always outboard of the heat meter), and that the head loss in the flow sensor(s) of the heat meter - if used - must be attributed to the protection system.

Where use of the heat meter is impossible, the protection system is laid out solely with regard to the design target (KMP-Fxx-M2). In extreme cases this may result in a protection system several sizes larger than the heat meter.

Where the Utility has installed a heat meter with an extra flow sensor, the type KMP-Fxx-M0 protection system is used. The load on the flow sensors at Qmax must be checked - if the load exceeds 40-55% qp, the protection system is chosen one or two sizes larger to ensure the flow sensor head loss dominates, whereby the responsibility for any discomfort lies unequivocally with the Utility. This has no adverse influence on the sensitivity of the protection system, which basically derives from the MULTICAL® heat meter.

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