Carrier 48HJ004---007 Units With Humidi-Mizer Adaptive, Subcooling Mode, Humidi-MiZerNormal

SSPT reading is available

S OAT ± SPT

SEconomizer Position is NOT forced

If any of the above conditions are not met, the economizer submaster reference (ECSR) is set to maximum limit and the damper moves to minimum position. The operating sequence is complete. The ECSR is recalculated every 30 seconds.

If an optional power exhaust is installed, as the outdoor-air damper opens and closes, the power exhaust fans will be energized and deenergized.

If field-installed accessory CO2 sensors are connected to the PremierLink™ control, a PID-controlled demand ventilation strategy will begin to operate. As the CO2 level in the zone increases above the CO2 set point, the minimum position of the damper will be increased proportionally. As the CO2 level decreases because of the increase in fresh air, the outdoor-air damper will be proportionally closed.

HEATING - UNIT WITH ECONOMI$ER2, PREMIER- LINK CONTROL AND A ROOM SENSOR

Every 40 seconds the controller will calculate the required heat stages (maximum of 3) to maintain Supply-Air Temperature (SAT) if the following qualifying conditions are met:

SIndoor fan has been on for at least 30 seconds. S COOL mode is not active.

SOCCUPIED, TEMP. COMPENSATED START or HEAT mode is active.

SSAT reading is available.

SFire shutdown mode is not active.

If all of the above conditions are met, the number of heat stages is calculated; otherwise the required number of heat stages will be set to 0.

If the PremierLink controller determines that heat stages are required, the economizer damper will be moved to minimum position if occupied and closed if unoccupied.

Staging should be as follows: If Heating PID STAGES=2

SHEAT STAGES=1 (50% capacity) will energize HS1 S HEAT STAGES=2 (100% capacity) will energize HS2

If Heating PID STAGES=3 and AUXOUT = HS3

SHEAT STAGES=1 (33% capacity) will energize HS1 S HEAT STAGES=2 (66% capacity) will energize HS2 S HEAT STAGES=3 (100% capacity) will energize HS3

In order to prevent short cycling, the unit is locked into the Heating mode for at least 10 minutes when HS1 is deenergized. When HS1 is energized the induced-draft motor is then energized and the burner ignition sequence begins. On units equipped for two stages of heat, when additional heat is needed, HS2 is energized and the high-fire solenoid on the main gas valve (MGV) is energized. When the space condition is satisfied and HS1 is deenergized the IFM stops after a 45-second time-off delay unless in the occupied mode. The fan will run continuously in the occupied mode as required by national energy and fresh air standards.

UNITS WITH HUMIDI-MIZER™ADAPTIVE

DEHUMIDIFICATION SYSTEM

Normal Design Operation

When the rooftop operates under the normal sequence of operation, the compressors will cycle to maintain indoor conditions. (See Fig. 53.)

The Humidi-MiZer adaptive dehumidification system includes a factory-installed Motormaster→ low ambient control to keep the

head and suction pressure high, allowing normal design cooling mode operation down to 0° F.

Subcooling Mode

When subcooling mode is initiated, this will energize (close) the liquid line solenoid valve (LLSV) forcing the hot liquid refrigerant to enter into the subcooling coil. (See Fig. 54.)

As the hot liquid refrigerant passes through the subcooling/ reheat dehumidification coil, it is exposed to the cold supply airflow coming through the evaporator coil. The liquid is further subcooled to a temperature approaching the evaporator leaving-air temperature. The liquid then enters a thermostatic expansion valve (TXV) where the liquid drops to a lower pressure. The TXV does not have a pressure drop great enough to change the liquid to a 2-phase fluid, so the liquid then enters the Acutrol™ device at the evaporator coil.

The liquid enters the evaporator coil at a temperature lower than
in standard cooling operation. This lower temperature increases
	48HE,HJ
the latent capacity of the rooftop unit. The refrigerant passes
through the evaporator and is turned into a vapor. The air passing
over the evaporator coil will become colder than during normal
operation. However, as this same air passes over the subcooling
coil, it will be slightly warmed, partially reheating the air.
Subcooling mode operates only when the outside air
temperature is warmer than 40_F. A factory-installed temperature
switch located in the condenser section will lock out subcooling
mode when the outside temperature is cooler than 40_F.
The scroll compressors are equipped with crankcase heaters to
provide protection for the compressors due to the additional
refrigerant charge required by the subcooling/reheat coil.
When in subcooling mode, there is a slight decrease in system
total gross capacity (5% less), a lower gross sensible capacity
(20% less), and a greatly increased latent capacity (up to 40%
more).

C06135

Fig. 53 ---Humidi-MiZer Normal

Design Cooling Operation

49