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100 VAV-PRC011M-EN

DDC Controls

is below the active heating setpoint and the amount of time that the space temperature has been

below the active heating setpoint.

If the discharge air temperature reaches the Discharge Air Temperature Design Setpoint, the air

valve opens further and modulates between Airflow Setpoint Reset Minimum Local Heat and

Airflow Setpoint Reset Maximum Local Heat to maintain space temperature at the active heating

setpoint, while the water valve modulates to maintain discharge air temperature at the Discharge

Air Temperature Design Setpoint. If the air valve reaches Airflow Setpoint Reset Maximum Local

Heat, the water valve opens further and modulates to maintain space temperature at the active

heating setpoint, while the air valve remains at Airflow Setpoint Reset Maximum Local Heat.

An additional on/off remote heat output is available and energized when the water valve is driven

100% open and de-energized when the water valve reaches 50% open.

When reheat is de-energized, the cooling Airflow Minimum Setpoint is enforced.

Single-Duct: On/Off Electric Reheat

Three stages of staged electric reheat are available. The heating minimum airflow setpoint is

enforced during reheat.

Stage 1 is energized when the space temperature falls below the active heating setpoint and

minimum airflow requirements are met. When the zone temperature rises above the active heating

setpoint by 0.5°F (0.28°C), stage 1 is de-energized. Stage 2 energizes when the space temperature

is 1°F (0.56°C) or more below the active heating setpoint, and is de-energized when the space

temperature is 0.5°F (0.28°C) below the active heating setpoint. Stage 3 energizes when the zone

temperature is 2°F (1.11°C) or more below the active heating setpoint, and de-energizes when the

space temperature is 1.5°F (0.83°C) below the active heating setpoint. When reheat is de-energized,

the cooling minimum airflow setpoint is enforced.

Single-Duct: Pulse-Width Modulation of Electric Heat

Electric heat is modulated by energizing for a portion of a three-minute time period. One of two

stages can be used. This allows for closer matching of heating capacity to the heating load,

resulting in more stable temperature control. The heating minimum airflow setpoint is enforced

during reheat.

The amount of reheat supplied is dependent on both the degree that space temperature is below

the active heating setpoint and the time that the space temperature has been below the active

heating setpoint. If not already off, reheat de-energizes when the zone temperature rises more than

0.5°F (0.28°C) above the heating setpoint.

The Stage 1 “on” time is proportional to the amount of reheat required. For example, when 50%

of stage 1 capacity is required, reheat is on for 90 seconds and off for 90 seconds. When 75% of

stage 1 capacity is required, reheat is on for 135 seconds and off for 45 seconds. When 100% of

stage 1 capacity is required, reheat is on continuously.

Stage 2 uses the same “on” time logic as stage 1 listed above, except stage 1 is always energized.

For example, when 75% of unit capacity is required, stage 1 is energized continuously, and stage

2 is on for 90 seconds and off for 90 seconds. When reheat is de-energized, the cooling minimum

airflow setpoint is enforced.

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