Orion-system VCC-X Controller Manual do Utilizador descarregar pdf (Página 57)

VCC-X Controller Technical Guide

SEQUENCE OF OPERATIONS

Economizer Operation & Dehumidiﬁ cation

Economizer Operation

Economizer operation is enabled when the Outdoor Air (OA) drybulb,

wetbulb, or dewpoint temperature falls below the Economizer Enable

Setpoint by 1°. Economizer operation is disabled when the OA

temperature rises 1° above the Economizer Enable Setpoint.

The Economizer acts as the 1

stage of cooling and controls to the

Active Supply Air Cooling Setpoint. An Economizer Minimum

Position can be programmed into the controller. During Economizer

Operation, the economizer will modulate between this minimum

position and 100%. If the economizer reaches 100% and the Supply

Air Temperature is still above setpoint, mechanical cooling is then

allowed to stage up while the economizer is held at the full open

position. Any time cooling stages are currently running, and the

economizer becomes enabled, it will immediately open to 100%.

During Heat and Vent Modes, the Economizer will remain at its

minimum position. The only exception to this can occur during “VAV

Operation with Outdoor Air Temperature Control (VAV Tempering)”.

See that section for more details. During Unoccupied Mode, the

Economizer can be used for night setback free cooling; otherwise

it will remain closed.

IAQ (CO

) Override of the Economizer simply resets the Economizer

Minimum Position higher. See IAQ (CO

) Control Operation section

for more details.

If utilizing the Title 24 Economizer option, an Economizer feedback

signal (0-10 VDC) can be wired into the VCCX-EM1 Expansion

Module for status monitoring. Several Title 24 alarm conditions

can also be annunciated and are listed in the Alarms section of this

manual.

Dehumidiﬁ cation Mode

O n VAV, C AV, Single Zone VAV, and High Percentage Outdoor

Units with Space Temperature Control, the Dehumidiﬁ cation Mode

is initiated when the Indoor Humidity rises above the Low Indoor

Humidity Setpoint. The unit will leave the Dehumidiﬁ cation Mode

when the humidity falls 1% below this setpoint.

On 100% Outdoor Air (MUA) units with Outdoor Air Temperature

Control, Dehumidification is initiated when the Outdoor Air

Dewpoint rises above the Outdoor Air Dewpoint Setpoint. The unit

will leave the Dehumidiﬁ cation Mode when the humidity falls 1%

below this setpoint. The Outdoor Air Dewpoint is calculated using

the Outdoor Air Temperature and the Outdoor Air Humidity.

There are four conﬁ guration options for Dehumidiﬁ cation operation.

In Occupied Vent Mode Only—Dehumidiﬁ cation can only be

initiated in the Occupied Mode when there is no call for Heating or

Cooling. This creates a Vent Dehumidiﬁ cation Mode.

In Both Occupied and Unoccupied Vent Mode—Dehumid-

iﬁ cation can be initiated in the Occupied and Unoccupied Modes

when there is no call for Heating or Cooling. This creates a Vent

Dehumidiﬁ cation Mode.

NOTE: Do not use this option on a MUA unit that does not

have return air and which is not conﬁ gured for space

controlled Night Setback operation. Damage to the

unit could occur since the OA damper remains closed

in the Unoccupied Mode.

In All Modes while Occupied—Dehumidiﬁ cation can be initiated

anytime in the Occupied Mode during Cooling, Heating, or Vent

Mode. This can create a Cooling Dehumidiﬁ cation Mode, a Heating

Dehumidiﬁ cation Mode, or a Vent Dehumidiﬁ cation Mode.

In All Modes while Occupied and Unoccupied—Dehumid-

iﬁ cation can be initiated anytime in the Occupied or Unoccupied

Mode during Cooling, Heating, Vent, or Off Mode. This can create

a Cooling Dehumidiﬁ cation Mode, a Heating Dehumidiﬁ cation

Mode, or a Vent Dehumidiﬁ cation Mode. Any calls for Unoccupied

Dehumidiﬁ cation use the same Dehumidiﬁ cation Setpoint as during

the Occupied Mode since you never want humidity to get out of

control.

NOTE: Do not use this option on a MUA unit that does not

have return air and which is not conﬁ gured for space

controlled Night Setback operation. Damage to the

unit could occur since the OA damper remains closed

in the Unoccupied Mode.

There is no Dehumidiﬁ cation allowed during Heat Mode on a Heat

Pump unit.

NOTE: Compressor operation is subject to the Outdoor Air

Temperature Cooling Lockout during Dehumidiﬁ ca-

tion.

Dehumidiﬁ cation Operation

Once in Dehumidiﬁ cation Mode, units with ﬁ xed compressors

will activate the compressors to maintain the Evaporator Coil

Suction (Saturated) Temperature Setpoint. An RSMV Module will

be required for each ﬁ xed compressor or each ﬁ xed compressor

tandem pair in order to monitor the suction (saturated) temperature

and control the compressor(s) accordingly. Each RSMV will

independently activate and stage its compressor(s) to maintain that

circuit’s Suction (Saturated) Temperature Setpoint. The staging of

compressors on an RSMV is subject to Stage Up and Stage Down

Delays as well as compressor Minimum Run Times and Minimum

Off Times.

A suction pressure transducer is used and the VCC-X Controller

converts that to a Suction (Saturated) Temperature value

On units with one or more sets of VFD/Fixed tandem compressors,

each set of tandem compressors (one circuit) will be controlled by

a separate RSMV Module with its own Suction Pressure Transducer

(converted to a Suction (Saturated) Temperature). Once the unit

enters the Dehumidiﬁ cation Mode, each RSMV will initially activate

the VFD compressor as required to maintain the Suction (Saturated)

Temperature Setpoint. At that point each RSMV will modulate its

VFD compressor and enable the ﬁ xed compressor, as necessary,

to maintain the Suction (Saturated) Temperature Setpoint for that

circuit.

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