Communal Heating Design

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

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.

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).

Converted from the Heatweb wiki article “Communal Heating Design”, last edited 2019-02-15. Under review for the new site.