Bryant 580J*04--12 Installationshandbuch PDF herunterladen (Seite 21)

Supply Fan

The RTU Open supply fan may be configured for 1 of 3

Fan Control modes:

S Single -- The fan operates at one speed only and

provides on/off operation

S Two Speed -- The fan operates at 1 of 2 speeds depending

on the mode of operation and load conditions. During fan

only or single stage cooling, the fan operates at low speed.

During heating, dehumidification, second stage cooling, or

if maximum economizer operation is required, the fan

operates at high speed. This control mode is used when

the 2--Speed Indoor Fan option is provided.

S Variable Speed -- The fan operates at a variable speed to

meet the load conditions and SAT safety requirements to

provide maximum energy savings by minimizing fan

horsepower consumption. Fan speed is NOT controlled by

static pressure.

The RTU Open supply fan may be configured for 1 of 3

Fan Modes:

S Auto -- The fan cycles on/off in conjunction with

heating or cooling.

S Continuous -- The fan runs continuously during

occupancy and intermittently during unoccupied

periods with heating and cooling.

S Always On -- The fan runs continuously regardless of

occupancy or calls for heating and cooling.

Occupancy can be determined by BACnet schedules, BAS

schedules, or in response to a remote occupancy switch.

A Fan Off Delay allows the supply fan to continue

operating after heating or cooling stops.

If the following alarms are active, the fan turns off

immediately, regardless of the occupancy state or demand:

S Fire Shutdown

S Safety chain

S SAT sensor alarm

S SPT sensor alarms

The RTU Open does not include smoke--control functions

such as a smoke--purge, zone--pressurization, or smoke--vent-

ilation. Each of these modes require a field--designed circuit

to operate the following by local fine codes:

S RTU supply fan

S RTU economizer

S RTU power exhaust

The RTU Open many be configured to accept a Supply

Fan Status input to provide proof the supply fan is

operating. When enabled, a loss or lack of fan status will

stop heating and cooling operation.

A supply Fan Alarm Service Timer function is available

to track the number of supply fan run hours and generate

an alarm when the accumulated runtime exceeds the set

threshold.

Economizer

The Economizer dampers are used to provide free cooling

when the outside conditions are suitable and Indoor Air

Quality, if optional CO

sensor is installed.

The following conditions must be true for economizer

operation:

S Indoor Fan is on.

S Enthalpy is Low if the Enthalpy input is enabled.

S SAT reading is available.

S OAT reading is available.

S SPT reading is available.

S OAT <= High OAT economizer lockout configuration

(default = 75).

S OAT <= SPT

If any of the mentioned conditions are not true, the

economizer will be set to its configured minimum position.

If the RTU Open is configured for VFD or 2--speed fan,

and the fan is on or at the highest speed, or if the unit is

configured for single--speed fan, then the economizer will

use the Vent Dmpr Pos/DCV Min Pos setpoint as the

minimum economizer position when occupied. If the unit

is configured for VFD or 2--speed fan, and the fan is on or

at the lowest speed, the economizer will use the Low Fan

Econ Min Pos.

The minimum damper position can be overridden by the

IAQ routine described later in this section.

If the above conditions are true, the Economizer control

will calculate a damper position starting with a minimum

vent position and based on current space temperature and

a setpoint that is one degree less than the effective cool

setpoint. If the SAT drops below the cooling low supply

air setpoint (+ 5_F), the economizer will close as required

but not to less than the to minimum position. The

Calculated Min Econ Pos used for control is displayed in

the Maintenance section.

RTU Open provides Fault Diagnostic and Detection

(FDD) for economizer operation in compliance with

California Title 24. The FDD logic will detect an

economizer that fails to close, fails to open, stuck fully

open, and fails to fully open. Each condition will cause an

Economizer Operation alarm to occur and the specific

condition will be displayed.

Enthalpy Control

You may use an enthalpy switch to indicate the suitability of

outdoor air for economizer cooling. You can use either an

outdoor air or differential enthalpy switch. A differential

enthalpy switch has a sensing device in both the outdoor and

return air streams. A differential enthalpy switch indicates

when outside air is more suitable to be used than the return

air and is available for economizer cooling. If no enthalpy

switch is configured, a network point (Object Name: oae) is

available.

The sequence of operation for economizer cooling is the

same with or without an enthalpy switch, except that an

enthalpy switch imposes one more validation on the

suitability of outside air for economizer cooling. An

Enthalpy Status that is High disables the economizer and the

outside air damper goes to its minimum position. An

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