Page 225 - Alternative Energy Systems in Building Design

DEMAND-SIDE ENERGY MANAGEMENT AND CONTROL 201

Intelligent control During the peak utility demand periods, the energy-management
system periodically turns air-conditioning compressors off to control the number of
compressors operating at any one time. Before turning a compressor off, the system
looks at the setpoint temperature and the room temperature and selects the systems
that have been running the longest and closest to the setpoint or satisfying the call for
cooling. The software within the energy-management system also considers the priority
of each system, the amount of temperature rise allowed for each system, and the number
of systems that are allowed to operate at any one time.

Energy conservation The energy-management systems conserve energy by mini-
mizing the amount of time the HVAC systems operate and by monitoring the perform-
ance of the HVAC systems to ensure that all components are operating efficiently and
together in the most efficient mode for the application.

Time/temperature programming Energy-management systems in general can
be programmed so that each day may have a different time and temperature schedule
with up to four temperature changes per day for cooling and heating. Each program or
schedule can use different temperatures for cooling and heating.
The energy savings achieved by raising the cooling setpoint 5°F for an 8-hour period
are widely stated as 15–30 percent depending on the geographic location. Similarly, a
10°F setback in heating for an 8-hour period can reduce energy consumption by another
7–15 percent depending on geographic location.

Just-in-time temperature programming The energy-management system
monitors the outdoor temperatures and computes when it should turn on the heating
or cooling to ensure that the temperature programmed will be reached at the proper
time and not too early. Starting a heating or cooling call 30 minutes early can increase
the energy consumption by 6 percent in 8 hours of call time.

Vacation/holiday programming The energy-management system can be pro-
grammed at the beginning of the year for up to 12 vacation or holiday periods. These
days are entered by date to program holiday temperature settings for both heating and
cooling. In a commercial application, this results in significant energy savings.

Alarm reporting The energy-management system can be programmed to report
alarm conditions of peak demand or energy consumption. The alarms will be reported
locally on the master control unit or PC and dialed out to report the alarms to an offsite
PC for notification and action.

Energy conservation by improved system efficiency The energy-management
system conserve energy by operating the HVAC system in its most efficient mode by
monitoring output or supply-air temperature, return-air temperature, room temperature,