Set point

In the construction industry, the term ‘set point’ (or sometimes set-point or setpoint) typically refers to the point at which a building system is set to activate or deactivate.

For example, a heating system might be set to switch on if the internal temperature falls below 20°C, an extract fan might be set to switch on if the relative humidity in a room exceeds 65% and so on.

Set points can be fixed, adjustable or variable. An adjustable set point might be controlled for example by a manually-operated thermostat. A variable set point might be controlled by some form of calculation, for example, set points for air conditioning systems may be programmed to be higher when outdoor temperatures are higher as people are more conditioned to, and dressed for those higher temperatures. Alternatively, if a building is unoccupied, the set point for the heating might be programmed to reduce to just 5°C to prevent pipework from freezing.

The set point at which something is activated may be different from the set point at which it is de-activated. This prevents continually switching on and off if the conditions are very close to the set point.

Set points may be fine-tuned during the commissioning process, and building occupants may be given control of some set points, perhaps within prescribed parameters.

Set points should be monitored, and checked regularly to ensure that they are correctly set and that they are delivering the required result. Seemingly small changes in set points can have a significant impact on performance and energy use. In addition, some building spaces may house critical operations requiring very specific, closely-controlled set points.

It is important therefore that building operators and occupants are provided with an explanation of set points, their operating ranges, and the impact of adjustments on performance and energy use.

NB Guide to Controls (BG 83/2023) written by John Marrow and published by BSRIA in June 2023, defines setpoint as: ‘An adjustable level of a parameter, such as temperature, humidity or pressure, which a control system aims to achieve.’

[edit] Related articles on Designing Buildings

• Building services.
• Thermal comfort.
• Building management system.
• Building Automation and Control System BACS.
• Building energy management systems.
• Electrical control systems.
• Energy management and building controls.
• Intelligent building management systems IBMS.
• Smart buildings.
• Thermostat.