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178113-BIM-D-0906
Supply Air Drive Adjustment
The RPM of the supply air blower will depend on the required
CFM, the unit accessories or options and the static resistances
of both the supply and the return air duct systems. With this
information, the RPM for the supply air blower and the motor
pulley adjustment (turns open) can be determined from the
Blower Performance Data Tables.
High speed drive accessories (containing a smaller blower
pulley and a shorter belt) are available for applications requiring
the supply air blower to produce higher CFM's and/or higher
static pressures. Use Model 1LD0460 for 15 ton units, Model
1LD0417 for 17.5 and 20 ton units, and Model 1LD0435 for 25
ton units. Refer to the Blower Motor and Drive Data Table 16.
Note the following:
1.
The supply air CFM must be within the limitations shown in
the Blower Performance Tables 14 and 15.
2.
Pulleys can be adjusted in half turn increments.
Table 18: Additional Static Resistance
Size
CFM
Economizer
(Tons)
4500
0.10
-15
6000
0.10
(15)
7200
0.10
6000
0.10
-18
7500
0.10
(17.5)
9000
0.10
6000
0.10
-20
8000
0.10
(20)
9400
0.10
7500
0.06
-25
10000
0.11
(25)
12500
0.18
1. Deduct these values from the available external static pressure
shown in the respective Blower Performance Tables.
2. The pressure drop through the economizer is greater for
100% outdoor air than for 100% return air. If the resistance of
the return air duct is less than 0.25 IWG, the unit will deliver
less CFM during full economizer operation.
Operation
Cooling Sequence Of Operation
For ZW units, the thermostat makes a circuit between "R" and
"Y1" for the first stage of cooling.
The call is passed to the Unit Control Board (UCB), which
then determines whether the requested operation is available
and, if so, which components to energize.
For gas heating, the UCB monitors the "W1" call but does not
handle the operation of the gas furnace. An ignition control
board controls the gas heater operation. For electric heat units,
the UCB passes the call to the electric heater. In both cases,
when the "W1" call is sensed, the indoor air blower is energized
following a specified heating delay.
Unitary Products Group
Electric Heat kW
1 2
18
36
54
0.10
0.10
0.20
0.10
0.20
0.30
0.10
0.30
0.40
0.10
0.10
0.20
0.10
0.20
0.30
0.10
0.30
0.40
0.10
0.10
0.20
0.10
0.20
0.30
0.10
0.30
0.40
0.31
0.38
0.62
0.56
0.68
1.10
0.87
1.07
1.72
If at any time a call for both heating and cooling are present, the
heating operation will be performed. If operating, the cooling
system is halted as with a completion of a call for cooling.
Heating always takes priority.
Continuous Blower
By setting the room thermostat fan switch to "ON," the supply
air blower will operate continuously.
Intermittent Blower
With the room thermostat fan switch set to "AUTO" and the
system switch set to either the "AUTO" or "HEAT" settings, the
blower is energized whenever a cooling or heating operation is
requested. The blower is energized after any specified delay
associated with the operation.
When energized, the indoor blower has a minimum run time of
30 seconds. Additionally, the indoor blower has a delay of 10
seconds between operations.
No Outdoor Air Options
When the thermostat calls for the first stage of cooling, the low-
1
voltage control circuit from "R" to "Y1" and "G" is completed.
72
The UCB energizes the economizer (if installed and free cooling
0.20
is available) or the first available compressor
0.40
condenser fans. For first stage cooling, compressor #1 is
0.60
energized. If compressor #1 is unavailable, compressor #2 is
0.20
energized. After completing the specified fan on delay for
0.40
cooling, the UCB will energize the blower motor.
0.60
0.20
When the thermostat calls for the second stage of cooling, the
0.40
low-voltage control circuit from "R" to "Y2" is completed.
0.60
Compressor #2 is energized, provided it has not been locked
0.68
out, and condenser fan motor #1, and condenser fan motor #2
1.21
remain energized. (If the ambient temperature is above 60ºF.)
1.90
If there is an initial call for more than one stage of cooling, the
UCB will delay energizing compressors #2, #3 & #4 by 30
seconds each, depending on how many stages are called for, in
order to avoid a power in-rush.
Once the thermostat has been satisfied, it will de-energize Y1,
Y2, Y3 and Y4. If the compressors have satisfied their minimum
run times, the compressors and condenser fans are de-
energized. Otherwise, the unit operates each cooling system
until the minimum run times for the compressors have been
completed. Upon the final compressor de-energizing, the
blower is stopped following the elapse of the fan off delay for
cooling.
To be available, a compressor must not be locked-out due to a
high or low-pressure switch or freezestat trip and the Anti-
Short Cycle Delay (ASCD) must have elapsed.
These units utilize a lead-lag feature that results in an equal
amount of run hours on all compressors, thereby extending the
life of the compressors. This feature works as follows: If the
thermostat requires for more than one stage of cooling, the
currently off compressor with the least number of run hours will
be the next to be energized. When the thermostat requires
fewer stages of cooling, the currently running compressor with
the most run hours will be the first to be de-energized.
*
and the
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