61
When a condenser fan output is common to both refrigera-
tion circuits, in other words when the fan(s) will affect both cir-
cuit A and circuit B, the following logic is used: in order to add
a fan stage, the SCT of either circuit must be above SCT.H for
30 seconds and in order to subtract a stage, the SCT of both cir-
cuits must be below SCT.L for 30 seconds.
Whenever the outdoor ambient temperature (OAT), is
above 70 F, the maximum stage will always be on when the
compressors are on.
On the initial start-up of a circuit, the condenser fans will
start 5 seconds prior to the compressor starting in order to en-
sure proper head pressure of the compressor immediately at
start-up. After the compressor starts, the normal head pressure
routine will begin 30 seconds after the condenser fan pre-start.
What stage fans starts depends on the outdoor ambient temper-
ature. The three situations are:
OAT <
50 F
50 F < OAT < 70 F
OAT >
70 F
See Fig. 10-13 for what stage of fans starts for each
scenario.
ECONOMIZER INTEGRATION WITH MECHANICAL
COOLING — When the economizer is able to provide free
cooling (Run Status
ECON
ACTV = YES), mechanical
cooling may be delayed or even held off indefinitely.
NOTE: Once mechanical cooling has started, this delay logic
is no longer relevant.
Multi-Stage Cooling Economizer Mechanical Cooling
Delay — This type of mechanical cooling delay is relevant to
the following machine control types:
C.TYP = 1 VAV-RAT
C.TYP = 2 VAV-SPT
C.TYP = 3 TSTAT-MULTI
C.TYP = 4 SPT-MULTI
If the economizer is able to provide free cooling at the start
of a cooling session, the mechanical cooling algorithm
(SumZ), checks the economizer’s current position (Run Status
ECON
ECn.P) and compares it to the economizer’s
maximum position (Configuration
ECON
EC.MX) – 5%.
Once the economizer has opened beyond this point a 150 sec-
ond timer starts. If the economizer stays beyond this point for
2.5 minutes continuously, the mechanical cooling algorithm is
allowed to start computing demand and stage compressors and
unloaders.
Heating Control — The N Series ComfortLink controls
offers control for six different types of heating systems to satisfy
general space heating requirements: 2-stage gas heat, 2-stage
electric heat, SCR (modulating) electric heat, steam heat, modu-
lating gas heat, and hydronic heat. Heating control also provides
tempering and reheat functions. These functions are discussed in
separate sections. Reheat is discussed under Dehumidification
function on page 87.
Variable air volume (VAV) type applications (C.TYP = 1 or
2) require that the space terminal positions be commanded to
open to minimum heating positions when gas or electric heat
systems are active, to provide for the unit heating system’s
Minimum Heating Airflow rate.
Also, for VAV applications, the heat interlock relay (HIR)
function provides the switching of a control signal intended for
use by the VAV terminals. This signal must be used to
command the terminals to open to their Heating Open posi-
tions. The HIR is energized whenever the Heating mode is ac-
tive, an IAQ pre-occupied force is active, or if fire smoke
modes, pressurization, or smoke purge modes are active.
Hydronic and steam heating applications that use the unit’s
control require the installation of a communicating actuator on
the hydronic heating coil’s control valve. This actuator (with or
without matching control valve) may be separately shipped for
field installation.
All heating systems are available as factory-installed
options. The hydronic or steam heating coil may also be field-
supplied and field-installed; the actuator is still required if unit
control will be used to manage this heating sequence.
POST FILTER APPLICATION — Gas heat controls also use
an airflow switch when post filter option is installed in unit.
Lack of airflow will prevent gas heat from operating.
Electric heat controls add filter temperature switches at the
post filters. The filter temperature switches will prevent electric
heat from operating when high temperatures are experienced.
SETTING UP THE SYSTEM — The essential heating con-
figurations located at the local display under Configuration
HEAT. See Table 34.
Heating Control Type (
HT.CF) — The heating control types
available are selected/configured with this variable.
0 = No Heat
1 = 2 Stage Electric Heat
2 = 2 Stage Gas Heat
3 = Staged Gas Heat or Modulating Gas Heat
4 = Hydronic Heat (Hot Water or Steam)
5 = SCR Electric Heat
Heating Supply Air Set Point (
HT.SP) — In a low heat mode
for either modulating gas, SCR electric, or hydronic heat, this
is the supply air set point for heating.
Occupied Heating Enable (
OC.EN) — This configuration
only applies when the unit’s control type (Configuration
UNIT
C.TYP) is configured for 1 (VAV-RAT) or 2 (VAV-
SPT). If the user wants to have the capability of performing
heating throughout the entire occupied period, then this
configuration needs to be set to “YES.” Most installations do
not require this capability, and if heating is installed, it is used
to heat the building up in the morning. In this case set OC.EN
to “NO.”
NOTE: This unit des not support simultaneous heating and
cooling. If significant simultaneous heating and cooling
demand is expected, it may be necessary to provide additional
heating or cooling equipment and a control system to provide
occupants with proper comfort.
MBB Sensor Heat Relocate (
LAT.M) — This option allows
the user additional performance benefit when under CCN
Linkage for the 2-stage electric and gas heating types. As two-
stage heating types do not “modulate” to a supply air set point,
no leaving air thermistor is required and none is provided. The
evaporator discharge thermistor, which is initially installed up-
stream of the heater, can be repositioned downstream and the
control can expect to sense this heat. While the control does not
need this to energize stages of heat, the control can wait for a
sufficient temperature rise before announcing a heating mode
to a CCN Linkage system (ComfortID™).
If the sensor is relocated, the user will now have the
capability to view the leaving-air temperature at all times at
Tempe ratur es
AIR.T
CTRL
LAT.
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