Economizer Cycle Decision-Outdoor Air Enthalpy Control - Honeywell AUTOMATIC CONTROL Engineering Manual

AIR HANDLING SYSTEM CONTROL APPLICATIONS
CONDITIONS FOR SUCCESSFUL OPERATION
Local weather data analysis needed to determine the optimum
changeover setpoint. The analysis need only consider data when the
OA is between approximately 60°F and 78°F, and during the occupancy
period.
NOTE: The dry bulb economizer decision is best on small systems
(where the cost of a good humidity sensor cannot be
justified), where maintenance cannot be relied upon, or
where there are not frequent wide variations in OA RH
during the decision window (when the OA is between
approximately 60°F and 78°F).
ECONOMIZER CYCLE DECISION—OUTDOOR AIR ENTHALPY CONTROL
Functional Description
OA
1 2
49
52
16.8
ENTHALPY
BTU PER POUND
4
Item
No. Function
1 Sensor senses OA temperature.
2 Sensor senses OA humidity.
3 OA enthalpy calculated from OA temperature
and humidity.
4 Economizer mode decision selector, including
OA enthalpy setpoint below which the
economizer decision is invoked, and command
schedule.
ENGINEERING CMANUAL OF AUTOMATION CONTROL
EA
8
83
7
83
CONTROL
3
PROGRAM
ECONOMIZER
STATUS
ECONOMIZER MODE SELECTOR
1
1 = AUTO BASED UPON OA
27.0
ENTHALPY BELOW
2 = AUTO BASED UPON OA DB
TEMPERATURE BELOW
3 = MANUAL, ECONOMIZER ON.
4 = MANUAL, ECONOMIZER OFF.
SPECIFICATIONS
A global economizer function shall be provided to switch all AHUs
from OA cooling to minimum OA based upon an OA temperature
setpoint. Software shall also be provided to allow the user to override
the decision from being based upon OA dry bulb (with an appropriate
commandable setpoint), to manually lock the system into or out of the
economizer mode.
RA
MA
OTHER INPUTS
AND OUTPUTS
22
9
OA MINIMUM SETPOINT
ON (NOTE: THE TEST AND BALANCE INITIAL
5
BTU PER POUND
72.0
DEGREES NOTE: THE SYSTEM IS LOCKED OUT OF
5 Economizer decision status (operator
information).
6 Setpoint for minimum OA damper position.
7 Actuator positions OA and RA dampers.
8 Actuator positions EA dampers.
9 Control program coordinates occupancy,
temperature, smoke, and ventilation controls.
216
6
VALUE FOR PROPER VENTILATION IS 22)
THE ECONOMIZER MODE ANYTIME
THE OA DRY BULB IS
81.0
ABOVE DEGREES.
M10455