Honeywell Design and Application User Manual

Section 1 - Ventilation
Honeywell Economizers 63-8594-02 10
Basic Economizer Control
Shown is the most basic temperature based
economizer control configuration. An
averaging element mixed air controller with
the sensing element is located in the duct
before the cooling or heating coils and
maintains the mixed air at 55°F (13°C). A two
position limit controller with sensing element in
outdoor air is used to close the outside air
dampers to a minimum position if the outdoor
air temperature is too warm to use for cooling.
There is a minimum position control on most
air handlers. The function of this control is to
ensure proper ventilation. The control provides
adjustable damper positioning between 0 and
100%. The outdoor damper position must be
set for minimum ventilation requirements
based on building occupancy as defined by
state or local code.
NOTE: A setting of 25% does not produce
25% airflow because the flow through
dampers is nonlinear.
It is important to know how much outside air is
being brought into a building through the
outdoor dampers on the air handlers. When
the return and mixed air temperatures can be
measured there is a formula used to calculate
the settings that will provide the desired
quantity of outside air.
Using the formula Vbz = Vp we know the total
ventilation and volume required. A second
formula is used to calculate the mixed air
temperature when the outside air temperature,
the return air temperature and the required
percentage of outside air are known.
DAMPER
M23916A
DAMPER
RETURN AIR
FROM ROOM
SUPPLY
AIR TO
BUILDING
H705
ENTHALPY
CONTROL
OUTSIDE
AIR
EXHAUST
AIR
DAMPER
MOTOR
PROPORTIONAL
MINIMUM POSITION
CONTROL FOR
OUTSIDE AIR
DAMPERS
DAMPER
LINKAGE
60
180
90
170
16
15
140
130
120
110
100
F
80
70
ECONOMIZER TWO-POSITION
HIGH LIMIT. CLOSES OUTSIDE
AIR DAMPERS TO MINIMUM WHEN
OUTSIDE AIR TEMPERATURE
IS HIGHER THAN 70˚F (21 C)
60
180
90
170
16
15
140
130
120
110
100
F
80
70
PROPORTIONAL MIXED
AIR CONTROLLER.
SETPOINT 55˚F (13 C)
60
100
140
120
80
40
°F
TR
TR1
A
BC
D
S
O
S
R
+
+
2
4
X
D
1
3
6
5

Honeywell Design and Application Specifications

General

Brand	Honeywell
Model	Design and Application
Category	Controller
Language	English