People don’t leave their car idling in the garage nor the shower running while they’re away, so why would anybody leave their air handling equipment on full-bore during unoccupied periods? Going even further, should the printer/copier, air compressor, boiler, pumps, computers, etc. be on either? The answer is – it depends. Some equipment shouldn’t be turned off during unoccupied periods, but can be turned down instead. Furthermore, those unoccupied periods can be day, night, mid-morning – whenever! The goal is to make a business more efficient during any unoccupied period by relaxing temperature set points, ventilation, and other equipment when the business is closed.
Too Much of a Good Thing
Being too aggressive with the controls can also be an issue. For example, if the thermostat is set back too aggressively resulting in chilly conditions early in the day, occupants may unwisely overcompensate and set the occupied temperature higher to warm up faster. Generally, a 10F (5.6C) setback is recommended but can vary depending on several factors (e.g. the amount of time the space is unoccupied). For instance, a building with an unoccupied period of only a couple hours might be recommended to adopt a 5F (2.8C) setback instead.
Autonomous Programming – Not Happening
While there is much more computational power in today’s air handling unit (AHU) controllers than Apollo 11 had to navigate to the moon, they are not able to program themselves. Many times, after purchasing and installing high-tech equipment, personnel forget to program or calibrate the equipment properly. For AHU’s, the night setback temperatures still need to be entered along with the time at which the space will be unoccupied. If a contractor says it’s ready and will need no adjustments – trust, but verify!
Another thing to remember is that the unoccupied set points shouldn’t only be when the doors open and close for a business. Example: A business operates from 8 am to 6 pm. However, the first employee shows up at 6:30 am, and the last employee leaves at 7 pm. The temperature is kept at a comfortable 72F, and the night setback is 62F. If the unoccupied period is set from 7 pm to 6:30 am the next morning, that first employee is going to be unpleasantly cold and uncomfortable because the heater just kicks on as they walk through the door. It’s important to give the AHU’s enough time to heat the space to occupant-desired temperature so when the first employee walks through the door, it’s already comfortable.