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Table 79 — Economizer Configuration Table
Custom Psychrometric Curves
— Refer to the psychrometric
chart and the standard Honeywell A-D curves in Fig. 10. The
curves start from the bottom and rise vertically, angle to the left
and then fold over. This corresponds to the limits imposed by
dry bulb changeover, outdoor enthalpy changeover and
outdoor dewpoint limiting respectively. Therefore, it is now
possible to create any curve desired with the addition of one
outdoor relative humidity sensor and the options for change-
over now available. See Fig. 11 for an example of a custom
curve constructed on a psychrometric chart.
UNOCCUPIED ECONOMIZER FREE COOLING — This
Free Cooling function is used to start the supply fan and use
the economizer to bring in outside air when the outside
temperature is cool enough to pre-cool the space. This is done
to delay the need for mechanical cooling when the system
enters the occupied period. This function requires the use of a
space temperature sensor.
When configured, the economizer will modulate during an
unoccupied period and attempt to maintain space temperature
to the occupied cooling set point. Once the need for cooling has
been satisfied during this cycle, the fan will be stopped.
Configuring the economizer for Unoccupied Economizer
Free Cooling is done in the UEFC group. There are three
configuration options, FC.CF, FC.TM and FC.LO.
Unoccupied Economizer Free Cooling Configuration
(FC.CF) — This option is used to configure the type of unoc-
cupied economizer free cooling control that is desired.
0 = disable unoccupied economizer free cooling
1 = perform unoccupied economizer free cooling as available
during the entire unoccupied period.
2 = perform unoccupied economizer free cooling as available,
FC.TM minutes before the next occupied period.
Unoccupied Economizer Free Cooling Time Configuration
(FC.TM) — This option is a configurable time period, prior to
the next occupied period, that the control will allow unoccu-
pied economizer free cooling to operate. This option is only
applicable when FC.CF = 2.
ITEM EXPANSION RANGE UNITS CCN POINT DEFAULT
EC.EN Economizer Installed? Yes/No ECON_ENA Yes
EC.MN Economizer Min.Position 0 - 100 % ECONOMIN 5
EC.MX Economizer Max.Position 0 - 100 % ECONOMAX 98
E.TRM Economzr Trim For SumZ ? Yes/No ECONTRIM Yes
E.SEL Econ ChangeOver Select 0 - 3 ECON_SEL 0
OA.E.C OA Enthalpy ChgOvr Selct 1 - 5 OAEC_SEL 4
OA.EN Outdr.Enth Compare Value 18 - 28 OAEN_CFG 24
OAT.L High OAT Lockout Temp -40 - 120 dF OAT_LOCK 60
O.DEW OA Dewpoint Temp Limit 50 - 62 dF OADEWCFG 55
ORH.S Outside Air RH Sensor Enable/Disable OARHSENS Disable
E.TYP Economizer Control Type 1 - 3 ECON_CTL 1
EC.SW Economizer Switch Config 0 - 2 ECOSWCFG 0
E.CFG ECON.OPERATION CONFIGS
E.P.GN Economizer Prop.Gain 0.7 - 3.0 EC_PGAIN 1
E.RNG Economizer Range Adjust 0.5 - 5 ^F EC_RANGE 2.5
E.SPD Economizer Speed Adjust 0.1 - 10 EC_SPEED 0.75
E.DBD Economizer Deadband 0.1 - 2 ^F EC_DBAND 0.5
UEFC UNOCC.ECON.FREE COOLING
FC.CF Unoc Econ Free Cool Cfg 0-2 UEFC_CFG 0
FC.TM Unoc Econ Free Cool Time 0 - 720 min UEFCTIME 120
FC.L.O Un.Ec.Free Cool OAT Lock 40 - 70 dF UEFCNTLO 50
Fig. 11 — Custom Changeover Curve Example
A48-7731