Trane Round In/Round Out Seznam dílů stáhnout pdf (Strana 92)

92 VAV-PRC011M-EN

DDC Controls

Single-Duct: On/Off Electric Reheat

One, two, or 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

One to three stages of pulse-width modulation of electric heat are available. Energizing for a

portion of a three-minute time period modulates the electric heater. 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 the 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 activated. Caution: Care should be taken when sizing electric heaters. Discharge

air temperatures should not exceed between 100°F and 110°F, with a temperature between 85°F and

95°F being optimal for space temperature control. If too hot of air is delivered to the space through

ceiling-mounted diffusers, and then leaves the space through ceiling-mounted return-air grilles,

the buoyancy of this hot air will tend to cause some of the air to bypass from the supply-air diffusers

to the return-air grilles, resulting in uneven air distribution and possible comfort complaints. To

prevent stratification, the warm air temperature should not be more than 20°F (6.7°C) above zone

air temperature. (See Diffuser, “D”, section for additional application details).

Ventilation Control

Ventilation control enhances the usability of Trane DDC controllers in more select applications that

require measurement of outside air (ventilation). Ventilation control is designed for use with

constant volume single-duct VAV units which modulate the primary damper and associated reheat

to maintain an average constant discharge air temperature. The reheat is modulated to provide

discharge air temperature consistent with AHU supply air temperature (typically 50º–60ºF). This is

critical to ensure that ASHRAE Standard 62.1 Ventilation standards are attained, consistently

maintained, and monitored. When connected to a Trane Building Automation System control

system, trend logging, remote alarming, etc. is available. In fact, the Trane Tracer Control System

can provide unmatched “peace of mind” by calling/paging the appropriate person(s) when specific

alarms occur.

Flow Tracking Control

This enhanced VAV DDC controller feature allows two Trane VV550 controllers to coordinate

modulation simultaneously. This allows a specific CFM offset to be maintained. The CFM offset

provides pressurization control of an occupied space, while maintaining the comfort and energy

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