Is there a typical rule-of-thumb for how much energy can be saved in a commercial building by raising the cooling setpoint in the summer and lowering the heating setpoint in the winter?
As a rule of thumb, energy savings are 2% to 4% for every 1 degree difference in thermostat setting—either raising the cooling setpoint or lowering the heating setpoint—for a 24 hour period. To estimate the savings from changing the setpoint during unoccupied periods, prorate the percentage based on the number of hours of setback/setup. For example, if you are raising the cooling setpoint by 10 degrees for a 12 -hour period, estimated savings are 10% to 20%, calculated as:
2% to 4% per degree * 10 degrees * (12 hours/24 hours) = 10% to 20% savings
Note these estimates are percentages of your electrical use for heating and cooling—not a percentage of your total electric bill.
Keep in mind that actual savings depend on your climate zone. Savings as a percentage of your heating and cooling bill will be greater in mild climates than in more severe climates. You may see minor variations of this rule-of-thumb in the literature. For example, one reference may report 3% to 4% and another 2% to 3% per degree over 24 hours. Another may report 1% savings per degree for a setback or setup lasting 8 hours. These are all in the same range. Variation within this range is largely due to differences in climate zone.
More information on the energy savings due to adjusting thermostat setpoints is available at "Thermostats and Control Systems," U.S. Department of Energy.