Define thermostat setpoints

A thermostat (t-stat) is a device that senses the temperature of a room and controls the HVAC systems so that the room's temperature is maintained near a desired setpoint. The setpoint is the desired temperature for the HVAC system to maintain in a room where the thermostat is located. Buildings with both heating and cooling systems will often have different setpoints for heating and cooling modes of operation, and the setpoints may be raised or lowered during unoccupied periods as an energy efficiency measure.

Gather project information

Setpoints are often included in the HVAC specifications or basis-of-design documents. They may also be listed on HVAC drawings such as terminal unit schedules, or zone HVAC system schedules. The specification should also include setback (or setup) temperature setpoints and schedules for periods when the building is not occupied.

Setback temperatures (heating) indicate that the thermostat setpoint should be lowered during unoccupied periods so that the heat will not run when there are no occupants. In some cases, it is acceptable to turn the heating off entirely during setback mode, however in colder climates this may lead to pipe damage (from freezing), and it may also result in taking too long to warm up the building in the morning if the temperature drops too much at night.

Setup temperatures (cooling) indicate that the t-stat setpoint should be raised during unoccupied periods so that the cooling will not run when there are no occupants.

Note that weekend and holiday schedules may vary from weekday schedules for certain building types. For example, an unoccupied office or school may likely have the setback and setup temperature setpoints throughout the whole weekend when unoccupied.

Additionally, buildings that are used seasonally may have reduced system use during unoccupied seasons. For example, a school may reduce HVAC system operation during the summer or other vacation weeks during the year. However, be careful using default schedules - some schools offer summer programs and camps and may operate during the summers.

Enter zone-level inputs

Example weekday t-stat schedule for office building (Source: PNNL small office prototype model)

Inputs for thermostat set-points may vary between different software tools, but they are generally defined in terms of a schedule that is then applied either to the thermal zone inputs, or to terminal unit inputs.

In building types that are uniform in their usage (e.g. office buildings are primarily office spaces), there will likely be similar setpoints in all similar space types. In this case, you would assign the same thermostat schedule to all of the spaces. Many tools will allow for a bulk assignment of schedules to multiple zones.

Setpoint assumptions for early-stage modeling

Thermostat setpoints for cooling and heating are not set by code, but there are several reference sources that provide guidance on typical values. COMNET cooling setpoint schedules use values of 75F during operating hours and 80F setup at night. The heating setpoints are 70F with setback to 60F.