Page 224 - Alternative Energy Systems in Building Design

200 ENERGY CONSERVATION

subgroup number, a unit number, and a command with both time and temperature
instructions to the master control unit. This command structure allows up to 999 area
groups with up to 99,999 subgroups in each area group and up to 9999 master control
units in each subgroup.

Sender identification The sender identification number prevents unauthorized or
accidental accessing of the systems. There are three access codes available for enter-
ing commands into the energy-management control system, each associated with
access restriction codes. The utility service provider using the code is allowed to have
control of the heating and cooling setpoint temperatures remotely. The users also have
an access code that allows them to completely program and control the master control
unit remotely.

COMPARISON OF A CONVENTIONAL ENERGY-MANAGEMENT
SYSTEM WITH DEMAND-SIDE MANAGEMENT (DSM) CONTROL
USED BY UTILITIES

Earlier approaches to demand-side management by utilities used an external control,
referred to as a duty cycler, that was installed at the HVAC system and was activated by
an ac carrier signal imposed on the ac power lines. The control normally was wired to
open the control wired from the thermostat to the contactor controlling the compressor.
This turned the compressor off for varying periods of time to reduce energy consump-
tion. Each facility would respond differently to the loss of compressor cooling, and there
was no control over the indoor temperature. Typically, the user had no idea the utility
had turned the air-conditioning off. This resulted in confusion and sometimes caused the
user to call his or her HVAC service contractor because he or she believed that the HVAC
system had failed or malfunctioned.
Advanced energy-management systems solve these problems by providing the service
utility provider with proportional and continuous control over the cooling and heating
setpoints. This allows the setpoints to be changed as demand arises. By using a smaller
change in the setpoint over a larger number of customers, the impact on any one cus-
tomer’s comfort is minimized, and demand is still reduced. In addition, the customer can
see from the LCD on the thermostat that the utility has modified the setpoint and is in
control of the thermostat.

Consumer peak-power electrical demand savings Consumer electrical
demand savings are produced even without the intervention or control of the DMS sys-
tem by a utility. This is accomplished by programming the energy-management system to
sequence the different air-conditioning systems to minimize the number of compressors
operating at any one time on a local basis. For example, each 5-ton air conditioner that
can be kept offline can reduce demand by 6–7.5 kW. This is accomplished during the
utility peak-demand period by programming a starting date, ending date, and the start
and stop times each day.