Economizer Actuator Communication; Minimum Ventilation; Free Cooling - Carrier 48HC 04-28 Controls, Start-Up, Operation And Troubleshooting

ECONOMIZER ACTUATOR COMMUNICATION

The economizer actuator used with the 48/50HC units is a
Multi-Function Technology (MFT) actuator. This allows the
ComfortLink system to communicate with the actuator digital-
ly using Belimo MP protocol. The configuration Economizer
Control Type (Configuration
the communication method, either digital or analog, used to
communicate between the Economizer Control Board and the
economizer actuator.
NOTE: The power to the unit must be cycled after the Econo-
mizer Control Type (Configuration
figuration parameter is changed.
E.CTL = 1 or 2 (Digital/Position or Digital/Command)
When Economizer
 
tion ECON E.CTL) is set to 1, the Economizer Control
Board will communicate with the economizer actuator using
the digital protocol, from Economizer Control Board plug J7-1
to actuator pin 5. The commanded position and the actuators
actual position are communicated back and forth between the
actuator and the Economizer Control Board. When the Econo-
mizer Control Board and actuator first initiate communication,
a Control Angle (Operating Modes
vided to the Economizer Control Board and defines the actua-
tor's range of motion. The control angle must be greater than
the Min Actuator
 
tion ECON M.ANG). During this digital control, the Econ-
omizer Control Board analog 4 to 20 mA output will represent
the actuator's actual position when E.CTL = 1 or commanded
position when E.CTL = 2. Because the wiring has a built-in
500-ohm resistor, the 4 to 20mA signal is converted to a 2 to
10VDC signal at the actuator.
E.CTL = 3 (Analog Control)
When E.CTL is set to 3, the Economizer Control Board will
NOT communicate with the actuator using digital MFT. It will
instead control the economizer actuator directly with the 4 to
20mA analog signal wired with the 500-ohm resistor produc-
ing a 2 to 10VDC signal for the actuator. While in this mode,
the actuator's built-in 2 to 10VDC feedback signal can be read
as actual position any time because it is not used by the Econo-
mizer Control Board.

MINIMUM VENTILATION

The economizer will open to allow ventilation when the indoor
fan is turned on and the unit is in the occupied state. The econ-
omizer damper position at any given time for ventilation is dis-
played as the Min Position
 
tus ECON EC.MP). This minimum position can be effect-
ed by the indoor fan speed (F.SPD) and indoor air quality. On
single speed units, the economizer minimum position will be
equal to the ECON MIN at MAX Fan Speed (Configura-
 
tion ECON MP.MX) unless Indoor air quality requests
something different.
On Staged Air Volume (SAV) units, to maintain a constant air-
flow through the economizer, as the indoor fan speed decreases
or increases, the damper minimum position will increase or de-
crease, respectively. This relationship curve is shown in Fig. 7.
Units can also be equipped with optional CO
tional indoor air quality control. When unit is equipped with a re-
turn duct CO sensor or return duct CO
2
CO sensor the Economizer minimum position will be recalculat-
2
ed based on the CO level of the return and/or outside air. On
2
SAV units the fan speed will also be used in recalculating mini-
mum position, as shown in Fig. 7. When the Commanded Fan
Speed (F.SPD) is less than the Supply Fan Maximum Speed
(FS.MX) the damper will operate in the shaded area of Fig. 7
based on the IAQ Level (IAQ). See the Indoor Air Quality (IAQ)
section for more details on Demand Controlled Ventilation
(DCV).
 
ECON E.CTL) determines
 
ECON E.CTL) con-
Control Type (Configura-
 
ECON C.ANG) is pro-
Ctrl Angle (Configura-
in Effect (Run
sensors for addi-
2
sensor and outside air
2
Economizer Position %
100
75
MP.25
50
25
0
0 2 0 2 5
Minimum
Fan Speed
Fig. 7 — Minimum Damper Position Curve (on SAV
The shape of the Economizer Minimum Position vs. Fan Speed
curve is determined by the configuration parameters: Econ Min
at 25% Fan speed (Configuration
Min at 50% Fan speed (Configuration
Econ Min
 
tion ECON MP.75) and Econ Min at Max Fan speed (Con-

figuration ECON
set at the factory for default purposes. The Econ Min at Max
Fan Speed (MP.MX) should be changed based on the air bal-
ance of the unit for proper ventilation. The Econ Min at 25%
Fan speed (MP.25), Econ Min at 50% Fan speed (MP.50) and
Econ Min at 75% Fan speed (MP.75) damper positions will be
calculated and changed automatically after changing the Econ
Min at Max Fan Speed (MP.MX) and Supply Fan Maximum
Speed (Configuration
The damper position curve can be field adjusted per application,
if needed. The Econ Min at 25% Fan speed (Configura-
 
tion ECON MP.25), Econ Min at 50% Fan speed (Configu-
 
ration ECON

(Configuration
Sta-
configurable and can be determined by setting the fan speed at
25, 50 and 75% and determining the damper position required to
maintain the Econ Min at Max Fan Speed (Configura-
 
tion ECON MP.MX) outside air CFM through the econo-
mizer outside air dampers. The default calculations programmed
into the HC controls are based on a side shot economizer at 400
CFM/TON Supply Air flow with negative 0.25 in.wg H
sure in the return duct. Econ Min at Max Fan Speed (FS.MN) is
set by user based on minimum required outside air ventilation
CFM required for the application. This procedure would be the
same as if this were a CV unit with the unit running at the design
point CFM. This determines the minimum position amount of
outside air CFM required when the fan is running at maximum
speed.

FREE COOLING

The economizer will be allowed to help with cooling (Run Sta-
 
tus MODE OK.EC = Yes) if the supply air temperature sen-
sor reading is valid, there are no applied lockouts, and there is
not a dehumidification demand. There are four economizer lock-
outs that can be applied at any time. Econo Cool OAT Lockout
(Operating Modes
Air Temperature (OAT) is greater than the configured Econo
Cool Hi Temp Limit (Configuration
25
MP.50
MP.25 DCV
MP.75
MP.50 DCV
MP.75 DCV
50 75 1
units)

ECON

at 75% Fan speed

MP.MX). These configurations are pre-
 
I.FAN FS.MX).
MP.50) and Econ Min at 75% Fan speed

ECON MP.75) damper position are user
 
ECON E.LOC) occurs when the Outdoor

ECON
EC.MX
MP.MX
AQ.MN for DCV
Fan
0 0
Speed %

MP.25), Econ

ECON MP.50),
(Configura-
O pres-
2

EH.LO) or less