University of Arizona
Tier2-5: Energy Management System

The UA's energy management system (EMS) saves energy through time schedules, reset schedules, economizing, and fan speed control.

The biggest savings in energy occurs with the use of time of day schedules that only run the building HVAC systems during scheduled occupancy times. There are two adjuncts to the scheduling system temperature sensor override and occupancy sensors. In some buildings, special temperature sensors monitor the building core temperature and will automatically start the HVAC system to prevent the interior temperature from going over a critical temperature, usually 85-90 degrees. Many of the larger classrooms and auditoriums now have occupancy sensors that control their temperatures. These spaces are allowed to get up to 82 degrees when empty, but return to their normal occupied temperature soon after they detect a person in the room.
EMS uses reset schedules to modulate the discharge temperature of the air handlers according to the outside air temperature. During the summer, the discharge air temperature is lower than it is in the winter. This allows the air handler fan motor to run more slowly. Due to fan power curves, it only takes a small reduction in fan speed to result in a significant reduction in electrical power used by the fan. The energy saved at the fan is much greater than the extra energy used in chilled water or steam.

In some buildings, the EMS is capable of monitoring the outside and inside temperature and humidity. When the outside conditions are correct, the EMS opens economizer dampers which use outside air to cool the building instead of chilled water or refrigeration. Because of our weather patterns, this method of energy conservation only is viable for a couple of months every year.

The last major energy saving protocol in the EMS is fan speed control. In buildings with full digital controls, the EMS is capable of adjusting the fan speed to provide just the amount of air pressure needed to keep any one room controller from having to be open 100%.

UA specific EMS controls

EMS controls were first installed on campus in the 1980’s. Many of those original systems are still in service today. The original systems were a hybrid of digital controls and pneumatic controls. The digital controllers typically operated the air handlers while the room controls were operated with older pneumatic controls. Over the years, EMS controls from different vendors were installed in new buildings and during retrofits of existing buildings. Several years ago, Facilities Management and Planning, Design, and Construction decided to limit EMS systems to the LON LNS standard. In theory, any LON LNS controller, regardless of manufacturer, can be installed in any existing LON LNS EMS. The idea was to avoid having proprietary systems where service was available from only the installing vendor.

While we would like to go back and retrofit every EMS system to meet the LON LNS specification, it cannot be cost justified. Therefore, there is not a homogenous EMS system on campus, but rather a heterogeneous network. Monitoring of building EMS is currently done with three computer systems; Metasys, Invensys, and Tridium AX. The Metasys system is not Web enabled but has supervisory PCs in several shops on campus. The Tridium AX system is a Web based system with drivers for LON LNS and several of the older, proprietary system on campus. The Invensys system also has a web server that monitors/controls several generations of Invensys EMS on campus. Links from the Tridium AX system to the Invensys system provide for a single web server used to monitor/control the majority of EMS on campus. We are investigating drivers that would allow the Tridium AX system to access data from the Metasys network which would then allow at monitoring, but not control, of all but a few buildings from a single Web server.