22
Table 20 — Unoccupied Free Cooling Definitions
When Nighttime Free Cooling is initiated, the economizer
dampers drive full open. The supply fan runs until the space
temperature drops below NTSP or space temperature drops be-
low (OAT + 3 F). When the conditions are met, the economizer
dampers close and the fan shuts off.
Configuration — To enable Nighttime Free Cooling, press
to enter into the Service function. Enter the password.
Press
to enter into the User Configuration sub-
function. Scroll down to NTEN. The current configuration will
be shown. The default is 0 (disabled). Press
to enable
the Nighttime Free Cooling. The acceptable range of values is
0 and 1, where 0 is disabled and 1 is enabled.
To set the Lockout Temperature, press
to enter
into the Service function. Enter the password. Press
to enter into the NTFC (Nighttime Free Cooling)
subfunction. Scroll down to NTLO. The current lockout tem-
perature will be shown. The default is 50 F. The acceptable
range of values is 40 to 70 F. To change the set point, enter the
new number (example:
) and press
. See Table 21.
MODULATING POWER EXHAUST — Building pressure
control is used to modulate the Power Exhaust function to
maintain a building static pressure set point. The factory-
installed economizer option, factory-installed modulating pow-
er exhaust option, and field-provided and installed tubing and
space pressure pickup are required.
The supply fan must be on for the power exhaust fan routine
to operate. See Table 22 for fan operation definitions.
Sequence of Operation — If the PWRX is set at ‘modulating,’
the following logic applies when the supply fan is turned on:
Fan no. 1 is equipped with a variable position discharge
damper located in the outlet of the fan housing. This damper is
controlled by an actuator (PEDM), based on signals from the
Building Pressure Differential Pressure Submaster Loop
(PSIO-1, Channel 15). Building pressure is sensed by a pick up
(field-supplied and -installed) located in the occupied space.
Operation of the Modulating Power Exhaust is a combina-
tion modulating/staged control, with fan no. 1 providing modu-
lating control from 0 to 100%, and fan no. 2 being staged On/
Off according to damper position on fan no. 1.
If building pressure is greater than BPSP, PSIO-1,
Channel 28 energizes fan contactor PEC1. Fan motor no. 1
starts and runs.
Capacity of fan no. 1 is controlled by the position of the out-
let damper. As building pressure increases above set point, the
control output from PSIO-1, Channel 15 drives the power ex-
haust damper motor (PEDM) open until set point is achieved.
When space demand moves PEDM to 90% of full-open
position, auxiliary switch PEDM2 closes, energizing fan con-
tactor PEC2 and auxiliary control relay PER. Fan motor no. 2
starts and runs. Increased exhaust airflow will lower space
pressure, causing DPS to drive PEDM back toward its closed
position, until the set point is achieved.
Table 21 — Configuring Nighttime Free Cooling (NTFC)
ITEM
DEFINITION
NTEN
Nighttime Free Cooling Enable/Disable
NTLO
Nighttime Free Cooling Lockout Temperature
NTSP
Nighttime Free Cooling Set Point
OAT
Outdoor-Air Temperature
OCSP
Occupied Cooling Set Point
OHSP
Occupied Heating Set Point
ENTER
ENTER
DESCRIPTION
HOW TO CONFIGURE AT HSIO
SET POINT
RANGE
Enable NTFC
NTEN
Enable = 1; Disable = 0
Select Lockout Temperature
NTOL
40 to 70 F (4 to 21 C)
O
ENTHALPY
SETTING
DIAL
ENTHALPY
CONTROLLER
LED
A
B
C
D
TR
TR1
SO
SR
2
3
1
+
+
S
+
(HH57AC078
SENSOR)
24 VAC SUPPLY FROM
ECONOMIZER CONTROL
SECTION (RED TO TR,
BRN TO TR1)
TO SENSOR MOUNTED
ON BACK OF CONTROL
GRAY WIRE FROM
ECONOMIZER HARNESS
RED WIRE FROM
ECONOMIZER SWITCH 3
(NORMALLY CLOSED)
Fig. 11 — Enthalpy Controller
NOTES:
1. Remove factory-installed jumper across SR and + before con-
necting wires from HH57AC078 sensor.
2. Switches shown in high outdoor air enthalpy state. Terminals 2
and 3 close on low outdoor air enthalpy relative to indoor air
enthalpy.
Fig. 12 — Wiring Connections for Differential
Enthalpy Control (HH57AC077 and HH57AC078)