Commercial & tower controls

How does Commercial & tower controls work, step by step?

1. 1

   Step 1: Fix the control philosophy and the points schedule

   The services engineer produces a control philosophy describing what every system does, in what sequence, under what conditions and with what interlocks, together with a points schedule listing every input and output the system needs. Those two documents are the specification for the whole controls package, and everything downstream - panel sizing, network design, software, commissioning - is derived from them. Ambiguity at this stage becomes a variation later, so the philosophy is reviewed and agreed by the client team and the specialist controls contractor before any equipment is ordered.

2. 2

   Step 2: Agree the trade split and the equipment responsibility

   Controls equipment is bought by one party, installed by another, wired by a third and commissioned by a fourth more often than not. Who supplies each valve, who fits the sensor pockets, who pulls the control cabling, who terminates it and who owns the network are all confirmed in a responsibility matrix at the outset. Free-issued equipment needs an agreed delivery and storage arrangement. This is unglamorous and it is the single biggest source of delay on a controls package when it is left vague.

3. 3

   Step 3: Coordinate risers, plantrooms and panel positions early

   Sensor pockets, control valve sets, isolation and strainers all need physical space and access, and in a riser or a busy plantroom that space is contested. The controls layout is coordinated with the mechanical and electrical models before the shafts and plantrooms are built, with panel positions, containment routes and maintenance access agreed and access panels shown on the architect's drawings. A valve set that has to be reached from a ladder over a pump is a valve that will not be maintained.

4. 4

   Step 4: Install the field devices and the containment

   Sensors go into their pockets in the positions the design gives, in the flow rather than in a dead leg, with immersion depths and straight lengths as specified. Control valves and actuators are installed the right way round with clearance to remove the actuator, and dampers, meters and switches follow the same rules. Control cabling is run on its own containment, segregated as the electrical design requires, and every core is labelled at both ends against the points schedule. Devices are labelled to match the schedule as they are fitted, because retrospective identification of an unlabelled riser is slow and expensive work.

5. 5

   Step 5: Build and energise the panels under qualified supervision

   Control panels are built and tested off site where the project allows, delivered, positioned and terminated, and energised by a competent qualified electrician. All power connections, interlocks with the heat source and any interface with life safety systems are the province of the qualified people entitled to work on them. Where the heat source is a gas appliance the appliance commissioning belongs to a suitably qualified and registered engineer, and the controls commissioning is sequenced around it rather than in parallel with it.

6. 6

   Step 6: Complete static checks and point-to-point testing

   Before anything is run, static checks confirm that every device on the points schedule exists, is in the right place, is the right type and is correctly wired. Point-to-point testing then proves each signal end to end: the sensor is disturbed and the value is watched changing on the head-end, the output is driven and the actuator is watched moving on the plant. Every point is signed off individually on a schedule. This is slow, methodical work and skipping it simply moves the same problems into functional testing, where they cost far more to find.

7. 7

   Step 7: Load the software and run functional testing

   The control logic, graphics, schedules, alarms and trend logs are loaded and each sequence in the control philosophy is then tested as a sequence: enabling and disabling plant, proving the interlocks, forcing failure conditions to confirm the alarms and the standby arrangements, and confirming that a plant item does what the philosophy says under every stated condition. Metering and billing data paths are proved at this stage too, which on a communal heat network matters as much to residents as the heating itself. Results are recorded against the philosophy clause by clause.

8. 8

   Step 8: Witness, hand over and tune through the seasons

   The client team or an independent commissioning specialist witnesses a demonstration of the system, and the record of that demonstration forms part of the handover. Training is given to the people who will actually operate the building, head-end accounts are set up in the client's name and the specialist contractor's access is agreed. Then the fine-tuning period runs: schedules, setpoints and sequences adjusted as the building is occupied and as the weather turns, typically covering at least one heating season and one cooling season. The best-commissioned building in the country still needs that period, because no test rig reproduces the day the building fills up on a cold morning.