ASHRAE Journal - May 2009 - 48

day scheduling function that operates the HVAC system can also be used to turn on and off lights inside the buildings. In a building that uses a card access security system, data from that system could be used to turn lights on and off or adjust the amount of ventilation airflow delivered to a specific area of the building. In a theater complex, information from the ticket sales system could be used to adjust the amount of ventilation airflow delivered to a specific theater, based on known ticket sales for that show. Sustaining Performance Occupied Expected Occupied Period (7 a.m. to 8 p.m.) Room 3003 Operating Outside Expected Schedule Unoccupied 12a 2a 4a 6a 8a 10a 12p 2p 4p 6p 8p 10p 12a 2a 4a 6a 8a 10a 12p 2p 9 January 2008 10 January 2008 Just as regularly scheduled maintenance helps equipment operate as Figure 6: Sample trend data of time-of-day schedules. intended, regular checkups (or periodic 75 commissioning) help to maintain the energy savings expected through proper Expected Temperature Range 74 During Occupied Period time-of-day scheduling. As mentioned previously, most building 73 managers or operators want to avoid com72 plaints from the occupants and the time needed to respond to those complaints. In 71 response to a complaint, it is often easier Room 3003 and quicker to override a schedule or setOperating 70 Expected Occupied Period point and attempt to determine the actual Cooler Than (7 a.m. to 8 p.m.) Expected cause later. During the busy schedule of 69 a building operator, however, these tem68 porary changes or overrides often become 12a 2a 4a 6a 8a 10a 12p 2p 4p 6p 8p 10p 12a 2a 4a 6a 8a 10a 12p 2p permanent, wasting energy. Room 2002 Room 3003 Room 4002 Figures 6 and 7 show example charts generated from trend data provided by a Figure 7: Sample trend data of zone temperatures. building automation system. This type of data helps the operator or remote service provider identify Zones with predictable occupancy patterns are good candichanges or overrides to the time-of-day schedules or temperature dates for using time-of-day scheduling for DCV. Combine setpoints for various areas in the building. Some of these changes an occupancy sensor with a time-of-day schedule to enable may need to remain permanent, but many can be returned to their an occupied standby mode for saving energy throughout the intended state, restoring energy-efficient operation. day. With the BAS in place, use it to optimize the operating schedules of the HVAC systems to reduce energy use, Summary and monitor system operation to sustain energy-efficient Time-of-day scheduling for night setback is well understood. performance. However, the programming of a building automation system is typically changed after initial installation, often taking a References 1. ANSI/ASHRAE/IESNA Standard 90.1-2007, Energy Standard conservative approach to minimize occupant complaints. This for Buildings Except Low-Rise Residential Buildings. can be costly from an energy perspective. 2. Murphy, J. 2007. “Energy-saving control strategies for waterAvoid overly conservative scheduling by using timed oversource heat pump systems.” Engineers Newsletter 36-2. La Crosse, ride buttons, use separate time-of-day schedules for areas with Wis.: Trane. differing usage patterns, and use zone temperature sensors with 3. Murphy, J. 2005. “CO2-based demand-controlled ventilation with a BAS rather than programmable thermostats. These simple ASHRAE Standard 62.1-2004.” Engineers Newsletter (34)5. strategies help improve this low tech idea to save energy without 4. ANSI/ASHRAE Standard 62.1-2007, Ventilation for Acceptable sacrificing occupant comfort. Indoor Air Quality. In addition, there are other overlooked opportunities for 5. Murphy, J. 2007. Rooftop VAV Systems applications engineering using time-of-day scheduling to save energy in buildings. manual SYS-APM007-EN. La Crosse, Wis.: Trane. 48 ASHRAE Journal Zone Temperature (°F) Room 2002 Room 3003 Room 4002 ashrae.org May 2009

ASHRAE Journal - May 2009

Table of Contents for the Digital Edition of ASHRAE Journal - May 2009