Energy Management Software; Optimum Start; Optimum Stop - Honeywell AUTOMATIC CONTROL Engineering Manual

MICROPROCESSOR-BASED/DDC FUNDAMENTALS
Table 1. Typical DDC Operators.
Operator
Sequence Allows several controller outputs to be
sequenced, each one operating over a full
output range.
Reversing Allows the control output to be reversed to
accommodate the action of a control valve
or damper actuator.
Ratio Translates an analog output on one scale
to a proportional analog output on a
different scale.
Analog Allows a digital output to change when an
controlled analog input reaches an assigned value.
digital output Also has an assignable dead band feature.
Digital Functionally similar to a signal switching
controlled relay. One state of the digital input selects
analog output one analog input as its analog output; the
other state selects a second analog input
as the analog output.
Analog Similar to the digital controlled analog
controlled output except that the value and direction of
analog output the analog input selects one of the two
analog signals for output.
Maximum Selects the highest of several analog input
input values as the analog output.
Minimum input Selects the lowest of several analog input
values as the analog output.
Delay Provides a programmable time delay
between execution of sections of
program code.
Ramp Converts fast analog step value changes
into a gradual change.

ENERGY MANAGEMENT SOFTWARE

Microprocessor-based controllers can combine control and
energy management functions in the controller to allow sensor
and data file sharing and program coordination. Energy
management functions can be developed via the above DDC
operators, math functions, and time clock values, or they can
be separate program subroutines.
A summary of energy management programs possible for
integration into microprocessor-based controllers follows:

Optimum Start

Based on measurements of indoor and outdoor temperatures
and a historical multiplier adjusted by startup data from the
previous day, the optimum start program (Fig. 5) calculates a
lead time to turn on heating or cooling equipment at the
optimum time to bring temperatures to proper level at the time
of occupancy. To achieve these results the constant volume
AHU optimum start program delays AHU start as long as
possible, while the VAV optimum start program often runs the
ENGINEERING MANUAL OF AUTOMATIC CONTROL
Description
VAV AHU at reduced capacity. Unless required by IAQ,
outdoor air dampers and ventilation fans should be inactive
during preoccupancy warmup periods. For weekend shutdown
periods, the program automatically adjusts to provide longer
lead times. This program adapts itself to seasonal and
building changes.
AHU ON
AHU OFF
6:00 AM
ADAPTIVELY
ADJUSTED
LEAD TIME
80
75
70
65
6:00 AM
Fig. 5. Optimum Start.

Optimum Stop

The optimum stop program (Fig. 6) uses stored energy to
handle the building load to the end of the occupancy period.
Based on the zone temperatures that have the greatest heating
and greatest cooling loads, and the measured heating and
cooling drift rates, the program adjusts equipment stop time
to allow stored energy to maintain the comfort level to the
end of the occupancy period. This program adapts itself to
changing conditions.
AHU ON
AHU OFF
4:00 PM
3:00 PM
76
SUMMER
74
WINTER
72
70
3:00 PM 4:00 PM
Fig. 6. Optimum Stop.
138
12:00 NOON
8:00 AM 10:00 AM
NORMAL
OCCUPANCY
COOLING
COMFORT
LEVEL
HEATING
8:00 AM 10:00 AM 12:00 NOON
TIME
C2436
LEAD TIME
OF SHUTDOWN
OPTIMUM STOP
PERIOD
6:00 PM
5:00 PM
END OF
OCCUPANCY
NORMAL
CONTROL
RANGE
5:00 PM 6:00 PM
TIME
COMFORT
LIMITS
C2437