Single Stage Electric Auxiliary Heat; Automatic Fan Speed Control; Fan Speed Control - During Heating; Fan Speed Control - During Cooling - Carrier Aquazone 50HQP Series Installation, Start-Up And Service Instructions Manual

SINGLE STAGE ELECTRIC AUXILIARY HEAT

The control can operate a single stage of electric heat connected to
a coil on the discharge side of the unit in order to maintain the de-
sired heating setpoint should the compressor capacity be insuffi-
cient or a compressor failure occurs. Unless the compressor fails,
the heat stage will only operate to supplement the heat provided by
the compressor if the space temperature falls two degrees or more
below the desired heating setpoint. The heat stage will be con-
trolled so the SAT will not exceed the Maximum Heating SAT
limit and subject to a two minute minimum OFF time to prevent
excessive cycling.

AUTOMATIC FAN SPEED CONTROL

The control is capable of controlling up to 3 fan speeds. The motor
will operate at the lowest speed possible to provide quiet and effi-
cient fan operation. The motor will increase speed if additional
cooling or heating is required to maintain the desired space tem-
perature setpoint. The control increases the motor's speed by one
step for each 2°F above the cooling or below the heating setpoint.
Also, the control will increase the fan speed as the Supply Air
Temperature approaches the configured minimum or maximum
limits. Fan speed for PSC motors is controlled by energizing and
de-energizing low, medium and high speed relays. Fan speed for
ECMs is controlled by first energizing the low speed tap. If a high-
er speed is required, the low speed tap remains energized while the
medium speed tap is also energized. If high motor speed is re-
quired, all 3 speed taps are energized. If more than one speed tap is
energized for an ECM, the ECM will default to the higher speed.

FAN SPEED CONTROL - DURING HEATING

Whenever heat is required and active, the control continuously
monitors the supply air temperature to verify it does not rise above
the configured Maximum Heating SAT Limit (110°F Default). As
the SAT approaches this value, the control will increase the fan
speed as required to insure the SAT will remain within the limit.
This feature provides the most quiet and efficient operation by op-
erating the fan at the lowest speed possible.

FAN SPEED CONTROL - DURING COOLING

Whenever mechanical cooling is required and active, the control
continuously monitors the supply air temperature to verify it does
not fall below the configured Minimum Cooling SAT Limit (50°F
Default). As the SAT approaches this value, the control will in-
crease the fan speed as required to insure the SAT will remain
within the limit.

MODULATING WATER ECONOMIZER CONTROL

The control has the capability to modulate a water valve to control
condenser water flowing through a coil on the entering air side of
the unit.
COOLING
The purpose is to provide an economizer cooling function by us-
ing the water loop when the entering water loop temperature is
suitable (at least 5°F below space temperature). If the water loop
conditions are suitable, then the valve will modulate open as re-
quired to maintain a Supply Air Temperature that meets the load
conditions. Should the economizer coil capacity be insufficient for
a period greater than 5 minutes, or should a high humidity condi-
tion occur, then the compressor will be started to satisfy the load.
As the SAT approaches the Minimum Cooling SAT limit, the
economizer valve will modulate closed during compressor
operation.
HEATING
Additionally, the control will modulate the water valve should the
entering water loop temperature be suitable for heating (at least
5°F above space temperature) and heat is required. The valve will
be controlled in a similar manner except to satisfy the heating re-
quirement. Should the coil capacity be insufficient to satisfy the
space load conditions for more than 5 minutes, then the compres-
sor will be started to satisfy the load. As the SAT approaches the
Maximum Heating SAT limit, the economizer valve will modulate
closed during compressor operation.

TWO-POSITION WATER ECONOMIZER CONTROL

The control has the capability to open a NO or NC, two-position,
water valve to control condenser water flow through a coil on the
entering air side of the unit.
COOLING
The purpose is to provide a cooling economizer function directly
from the condenser water loop when the entering water loop tem-
perature is suitable (at least 5°F below space temperature). If the
optional coil is provided and the water loop conditions are suit-
able, then the valve will open to provide cooling to the space when
required. Should the capacity be insufficient for a period greater
than 5 minutes, or should a high humidity condition occur, then
the compressor will be started to satisfy the load. Should the SAT
reach the Minimum Cooling SAT limit, the economizer valve will
close during compressor operation.
HEATING
Additionally, the economizer control will open the water valve
should the entering water loop temperature be suitable for heating
(at least 5°F above space temperature) and heat is required. The
valve will be controlled in a similar manner except to satisfy the
heating requirement. Should the coil capacity be insufficient to
satisfy the space load for more than 5 minutes, then the compres-
sor will be started to satisfy the load. Should the SAT reach the
Maximum Heating SAT limit, the economizer valve will close
during compressor operation.

POWER FAIL RESTART DELAY

The control provides a delay when recovering from a power fail-
ure in order to insure stable utility power and to prevent excessive
demand when many units start simultaneously. Each unit can be
user configured for a unique delay between 0 and 600 seconds.
The factory programmed default delay is 60 seconds. (Note that
the onboard control will not start the compressor on any call for
heating, cooling or dehumidification until 5 minutes has elapsed
from the power restoration. If a lower restart time delay is config-
ured, only the fan start will be affected as the internal logic boards
will prevent compressor operation for more than 300 seconds).
SUPPLY AIR TEMPERATURE MONITORING/CONTROL/
ALARM
The control has 2 configurable control limits for supply air tem-
perature. The control will monitor the supply air temperature
(SAT) and verify it is within limits. During cooling, the control
will increase fan speed and reduce compressor stages should the
SAT approach the Maximum Cooling SAT limit. Likewise, during
heating, should the SAT approach the Maximum Heating SAT
limit, the fan speed will be increased, followed by reducing com-
pressor stages. Auxiliary heating coils are controlled so as not to
exceed the Maximum Heating SAT limit. Additionally, a separate
High SAT Alarm Limit and Low SAT Alarm Limit are provided
so that an alarm can be generated to indicate an abnormal SAT
condition should the SAT exceeds the alarm limit for more than
1 minute.
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