A setpoint tells the control system what value to maintain. It might specify an airflow or a supply air temperature. The system then adjusts fans, valves and other equipment to reach that value.
Equipment can therefore vary its output even when the setpoint is fixed. A fan can change speed to maintain a specified pressure. When optimising energy use, the question is whether the target matches what the building needs at that moment.
What do the premises need throughout the day?
In an office, for example, conditions vary between rooms and over time. Meeting rooms fill and empty, the sun warms parts of the building, and equipment gives off heat. This affects the need for both ventilation and temperature control.
Existing systems may already use time schedules, temperature control and demand control. The starting point is therefore to understand how they work in the particular building and where operation could be improved. Demand-controlled ventilation is an established approach, but these systems also need functioning sensors, suitable settings and follow-up. Belok’s review of demand-controlled ventilation systems (in Swedish).
Airflow and temperature need to be considered together
Reducing an unnecessarily high airflow will normally reduce the fan’s electricity use. It can also reduce the energy needed to heat or cool the ventilation air. At the same time, ventilation must meet the premises’ requirements for air quality and indoor conditions.
Supply air temperature also affects how much heating or cooling other parts of the installation need to provide. A change therefore needs to be assessed across the building as a whole. Otherwise, a saving at the air-handling unit could be accompanied by increased energy use elsewhere. The Swedish Energy Agency highlights this interaction between systems when improving energy efficiency in non-residential buildings. Guidance from the Swedish Energy Agency (in Swedish).
How Sally R works with setpoints
Sally R uses measurements from the building to continually adjust airflow and temperature setpoints. The new setpoints are sent to the existing control system, which continues to control the equipment.
This allows settings to follow changes in the building’s needs. Airflow can be adjusted as ventilation demand changes, while temperatures are adjusted with regard to indoor conditions and how the systems interact.
For a property manager, the work begins with reviewing the available measurements, which setpoints can be adjusted and the requirements the premises must meet. Energy use and indoor conditions then need to be monitored together. This makes it possible to assess whether the changes to the controls are delivering the intended improvement.
