Bryant 580J*04--12 Manual de Instalação descarregar pdf (Página 22)

Enthalpy Status that is Low enables the economizer if a call

for cooling exists and the remaining preconditions are met.

Space Air Quality

Space Air Quality (AQ) is controlled on rooftop

equipment using the economizer. The Space AQ sequence

utilizes an air quality (CO2) sensor to monitor conditions

within the occupied space. A CO

sensor may be

terminated at the RTU Open, or a subordinate zone

controller, when part of a zoned system.

An outdoor air quality sensor may also be installed and

terminated at the RTU Open, but is not required. When an

outdoor air quality sensor is not installed, the algorithm

uses 400ppm as the fixed outdoor air CO

level.

The following conditions must be true for the Space AQ

algorithm to operate:

S The system is occupied

S The supply fan has been operating for at least 30 seconds

S The Space AQ sensor has a valid reading

As the air quality in the space decreases (Space AQ CO2

value increases), the minimum position of the economizer

increases, allowing more outdoor air to enter the space.

The amount of increase depends on the relationship

between the Space AQ level and the DCV Max Ctrl

Setpoint.

The Space AQ algorithm calculates a minimum position

value using a PID loop. The CO2 minimum damper position

is then compared against the Vent Dmpr Pos / DCV Min Pos

setpoint and the greatest value becomes the minimum

damper position utilized for the economizer. When the

minimum economizer position is being reset by the Space

AQ algorithm, the System Mode displays IAQ Override.

The maximum amount the economizer may be opened to

outdoor air by the Space AQ algorithm is limited by the

DCV Max Vent Damper Pos, which is adjustable between

10 and 75%.

Power Exhaust

RTU Open may enable and disable an exhaust fan based

on either the controller’s occupancy or its economizer

damper position. If configured for continuous occupied

operation, it will be energized whenever the controller is

in the occupied mode and disabled when in the

unoccupied mode. If configured for damper position

control, it will be energized whenever the economizer

exceeds the power exhaust setpoint and disabled when the

economizer drops below the setpoint by a fixed hysteresis

of 10%. If the Fan Control is set to Two Speed or Variable

Speed, the Power Exhaust Setpoint is automatically

adjusted based on the fan’s air delivery. The Calculated

PE Setpoint used for control is displayed in the

Maintenance section.

Pre--Occupancy Purge

Pre--Occupancy Purge allow the rooftop equipment with

an economizer damper to utilize outdoor air to purge the

space of contaminates just prior to the beginning of the

occupied period.

The following conditions must be true for pre--occupancy

purge to operate:

S Pre--Occupancy Purge set to Enable

S Economizer Exists set to Yes

S A local time schedule is configured

S The local time schedule is currently unoccupied and the

remaining time is less than the configured Purge Time

When the RTU Open schedule is unoccupied and the

remaining unoccupied time is less than the purge time, the

supply fan starts. The economizer damper opens to the

configured Economizer Purge Min Pos. The RTU Open

continues to operate in this mode until the occupied start

time is reached. The Pre--Occ Purge state is displayed in

the Maintenance section.

Heating

The heat outputs are controlled by the Heating Control

PID Loop and Heating Stages Capacity algorithm. They

will be used to calculate the desired number of stages

needed to satisfy the space by comparing the SPT to the

Occupied Heat Setpoint the T56 slider offset when

occupied and the Unoccupied Heat Setpoint plus the T56

slider offset if unoccupied. The following conditions must

be true in order for this algorithm to run:

S Indoor Fan is ON for any unit with electric heat.

S Cool mode has not been active for 5 minutes.

S If occupied and SPT <(occupied heat setpoint plus T56

slider offset)

S SPT and supply air temperature values are available

S If it is unoccupied and the SPT < (unoccupied heat

setpoint plus T56 slider offset).

S OAT < High OAT lockout temperature.

If all of the above conditions are met, the controller uses a

PID logic loop to energize or de--energize heat outputs to

satisfy the heat demand. If the SAT begins to exceed the

high supply air setpoint, a ramping function will cause the

Heat Stages Capacity algorithm to decrease the number of

stages until the SAT has dropped below the setpoint. There

is a fixed one minute minimum on time and a one minute

off time for each heat output. There is a 10 minute minimum

stage up delay if the heat demand is  3_F,anda2minute

minimum stage up delay if heat demand is > 3_F.

Indoor Air Quality

If the optional indoor air quality sensor is installed, the

RTU Open will maintain indoor air quality within the

space at the user configured differential set point. The set

point is the difference between the indoor air quality and

an optional outdoor air quality sensor. If the outdoor air

quality is not present then a fixed value of 400ppm is

used. The following conditions must be true in order for

this algorithm to run:

S The mode is occupied.

S Indoor Fan is ON.

S Indoor Air Quality is a valid reading.

As air quality within the space decreases, the minimum

position of the economizer damper will be increased thus

allowing more outdoor air into the space depending on the

relationship of the indoor air quality to the differential

setpoint. If all the above conditions are true, the IAQ

algorithm will run and calculates an IAQ minimum

position value using a PID loop. The IAQ minimum

damper position is then compared against the user

configured economizer minimum position and the greatest

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