Communal Heating Design
From Heatweb Wiki
- 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
- 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.
- 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