This unit has a bypass duct in which the electric heater is located, and utilizes face and bypass damper control.

When the room thermostat senses a drop in temperature during cooling, the face dampers close (interrupting cooling) and the bypass damper opens. In the "dead band" range of the room thermostat, neither cooling nor heating takes place.

On a further drop in room temperature, the contactor closes and the electric heater is energized.

Advantages For The Buiding Owner
• Elimination of brazed joints within the unit.
• Low maintenance (filter change only): No valves, permanently lubricated motors
• Small footprint: Smallest on the market
• Lower pumping costs: Elimination of system resistance caused by valves trains, coils and runout piping.
• Humidity Control: Face and bypass dampers
• Quiet Operation
• Aesthetics: Aluminum Grilles - No unsightly steel panels or access openings
Advantages For The Contractor
• Labor savings
• Complete piping package included.
• Risers are provided and factory installed in each unit.
• No need for labor and material for runout piping from the unit to the supply/return riser.
• No venting of individual units.
• No balancing of individual units.
• Plug-in thermostat - Surfaced mounted
• Job site distribution simplified due to precise identification and labeling of each unit.

Sequence of Operation

Two-Pipe Face and Bypass Damper Control With Auxiliary Electric Heat
This unit is basically the same as the two-pipe face and bypass damper control unit, except that a low capacity electric heater has been added to provide heat as needed during cool periods when chilled water is being circulated in the system. An aquastat is installed in the unit before shipment, which locks out the electric heater when it senses warm water in the system, thereby preventing electric heat when hot water heat is available.

This unit employs continuous water circulation through the riser heat-exchanger. Fan operation is continuous. The thermostat cycles an internal face and bypass damper which directs the air either over the riser heat-exchanger or through the bypass section which contains the auxiliary electric heater.

A decrease in room temperature from full cooling will first cause the face dampers to close against the cold riser heat-exchanger, while simultaneously opening the bypass damper to bypass air through the inactive heater. A further decrease in room temperature will then turn on the electric heater if there is chilled water in the system. The thermostat cycles the dampers and electric heater as required to give each individual unit the capability of providing either heating or cooling. In the winter, the system is changed over from chilled water to hot water, and warm water is circulated through the riser heat-exchanger for heating. The user has manual fan speed selection of HI, LO, or OFF.

Two-Pipe Face and Bypass Damper Control With Total Electric Heat
This unit design also has the advantage of providing the user with heating at any time of the year and cooling whenever chilled water is circulating through the riser heat-exchanger. Fan operation is continuous. The thermostat cycles an internal face and bypass damper which directs the air either over the riser heat-exchanger or through the bypass section which contains the electric heater.

A decrease in room temperature from full cooling will first cause the face dampers to close against the cold riser heat-exchanger, while simultaneously opening the bypass damper to bypass air through the inactive heater. A further decrease in room temperature will then turn on the heater.

In cold climates, a two-stage electric heater can be furnished.

The thermostat cycles the dampers and electric heater as required to give each individual unit the capability of providing either heating or cooling. The electric heater provides all the necessary heat, and no system changeover to hot water is required during the winter. The user has manual fan speed selection of HI, LO, or OFF.