Communal Heating Design

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Revision as of 02:42, 15 February 2019 by Rhg (Talk | contribs) (Boilers and Buffer Sizing)

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Checklist

  • kPa per building = 150 kPa (200 kPa peak).
  • kPa per property = 50 kPa + 10 kPa for each additional bathroom.
  • kPa per riser = 100 kPa (75kPa at index DP sensors).
  • Apply diversity on all sections of pipe along index run.
  • Thermostatic bypass at 50°C fitted approximately 15m from index HIU (10s at 1.5m/s), where instantaneous DHW is used.

Flow pipe (downstream of bypass):

  • sized to smallest size where velocity at diversified peak
    • Copper/Steel < 1.5 m/s.
    • Plastic < 2 m/s.
  • 40-50mm insulation

All other flow pipes pipes

  • sized to smallest between min 0.5 m/s and 1.5 m/s.
  • 40-50mm insulation

Return pipes

  • sized to largest min 0.5 m/s.
  • sized to smallest between min 0.5 m/s and 1.5 m/s where <15m from HIU, where residual head allows on non-index branches.
  • 20-50mm insulation


  • No valves on network other than
    • full bore isolating valves where required
    • thermostatic bypasses where needed
  • Binder points external to index properties on flow and return pipes.
  • Flushing bypass (fail safe) on HIUs.
  • Building kPa controlled (via pumps) to maintain 75kPa at index risers.
  • Continuous keep warm turned off as standard, with 2 hour keep warm counter.

Controls

  • Plantroom pumps should be linked to DP sensors at index branches, typically set to 75kPa.
  • Setpoint index kPa should be linked to flow rate, increasing to a maximum of 100kPa, with rate of change limited to 5kPa/minute.
  • Network flow temperatures should be set to 60C for normal load, increasing as required to achieve higher, or exceptional (peak) loads, with rate of change limited to 3°C/minute.
  • Pumps should be capable of running to very low flow rates, and temporary periods of no flow, for a period of 12 hours - the longest time possible without significant hot water use. This will often require the use of a smaller jockey pump capable of achieving 100kPa (to keep DP sensors satisfied to 75kPa at low/no flow).

Boilers and Buffer Sizing

  • N + 1 boilers
  • N power > averaged peak load over 24 hours.
  • N + 1 power > peak instantaneous diversified load.
  • Buffer sized to meet 24 hour peak load