Bryant 581C024--060 Heating Units With Economi$er, Subcooling Mode, Hot Gas Reheat Mode

581B,C

Heating - Units With Economi$er IV

When the room temperature calls for heat, the heating controls are energized as described in the Heating, Units Without Economizer section. During the occupied mode, whenever the indoor fan contactor is energized, the economizer damper moves to the minimum position.

Units With Perfect Humidity™ 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. 44.)

The Perfect Humidity 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. 45.)

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 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).

Hot Gas Reheat Mode

When the humidity levels in the space require humidity control, a hot gas solenoid valve (specific to hot gas reheat mode only) will open to bypass a portion of hot gas refrigerant around the condenser coil. (See Fig. 46.)

This hot gas will mix with liquid refrigerant leaving the condenser coil and flow to the subcooling/reheat dehumidification coil. Now the conditioned air coming off the evaporator will be cooled and dehumidified, but will be warmed to neutral conditions (72_F to 75_F) by the subcooling/reheat dehumidification coil.

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Fig. 44 ---Perfect Humidityt Normal

Design Cooling Operation

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Fig. 45 ---Perfect Humidity Subcooling

Mode Operation

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Fig. 46 ---Perfect Humidity Hot Gas

Reheat Mode Operation

See Table 37 for the Perfect Humidity adaptive dehumidification system sequence of operation.

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