Carrier 33ZCSECTRM Especificaciones descargar pdf (Pagina 34)

Zone Pressure control can also be used to control systems

utilizing dual duct terminals to supply a constant amount of

ventilation air to each zone. In these systems, a separate venti-

lation air source delivers conditioned, ventilation air to the sec-

ondary inlet of each dual duct terminal. The primary inlet is

connected to a standard VAV air source. The primary airflow is

controlled to maintain the desired space temperature in the

same way as a single duct terminal. A secondary airflow sensor

is installed in the total airflow from terminal and connected to a

secondary damper control. The actuator is installed on the sec-

ondary damper (hot deck or ventilation inlet). As the load

changes and the primary airflow modulates, the airflow sensed

by both the primary inlet and total outlet probes vary. If a nega-

tive value in the amount of the required ventilation airflow is

configured, that difference is introduced by the secondary

damper as ventilation air. In these applications, heating is typi-

cally provided by an auxiliary heat source controlled by the ter-

minal, but may be supplied through the air source as well (VAV

heating). See Fig. 28.

LIMITATIONS — The zone controller can not be located in

corrosive and contaminated environments. The terminal con-

troller maximum size damper is limited to 500 sq in. and

9000 CFM. Applying the zone controller in this manner for

zone pressure control will work only if all the air entering the

zone is measured. Therefore all the air supplied to the space

must be supplied through a single duct type terminal. This is

the same for the return zone exhaust air. Only single duct termi-

nals or exhaust dampers can be controlled by a secondary ter-

minal control. The 33ZCFANTRM zone controller and

33ZCESECTRM secondary damper terminal control must be

configured for single duct control. The type of supply and ex-

haust damper do not need to be the same design and stroke

(i.e., opposed blade, 90 degree butterfly, or 35 / 45 degree blade

type).

To maintain a zone at a constant desired pressure (either

negative or positive), the zone controller modulates the second-

ary damper to control the return airflow from the zone. The re-

turn airflow is controlled to an airflow set point that is offset

from the current primary damper airflow set point by a config-

ured delta. If the secondary airflow set point is less than the pri-

mary airflow set point, more air will flow into the zone than

leaves the zone and the zone will be pressurized.

If the secondary airflow set point is greater than the primary

set point, then more air will leave the zone than is entering it

and the zone will be depressurized. As the zone’s temperature

load changes and the primary damper modulates to maintain

the desired temperature set point, the zone controller will mod-

ulate the secondary damper position to maintain the required

difference in airflow and maintain the zone’s static pressure.

TERMINAL TRACKING — For applications where pres-

sure control is required in the occupied space in order to pro-

vide isolation, zone pressure control provides volumetric flow

tracking to maintain the proper return airflow by controlling

a secondary damper connected to the return air system. See

Fig. 27. Zone Pressure Control can only work properly if all the

air entering and leaving the space is measured. Therefore all air

supplied to the space should be supplied through a single duct

type terminal. No provision can be made to disable pressure

control if other than a single duct terminal (fan powered termi-

nal) is configured as the primary air device. In these systems,

the primary air damper is modulated in order to maintain the

space temperature within the desired set points. The primary air

terminal is a single duct terminal, therefore all sequences of

operation, for a single duct terminal apply to the primary

terminal.

Only single duct type terminals should be used for return air

control. If other terminals are used, no provision can be made

to disable pressure control. As the primary airflow set point

changes, the pressure control modules the return damper to

maintain the secondary airflow at a fixed delta (either positive

or negative) from the current primary airflow reference.

Dual Duct Terminal Applications —

The zone con-

troller provides control of a second damper in a dual duct ter-

minal. A dual duct terminal has two primary air inlets, referred

to as the cold deck and the hot deck. The second damper is the

hot deck damper. The dampers are controlled by the

33ZCFANTRM and 33ZCSECTRM zone controllers. The two

inlets provide a source of heating and cooling to the zone. Dual

duct terminals can be controlled in a constant volume mode or

a variable volume mode. Additionally, the constant volume

mode can be controlled using a second inlet airflow probe or a

total airflow probe. These three configurations are shown in

Fig. 29-31. The main difference between the configurations is

the placement of sensors and output control signals.

SECONDARY

AIRFLOW SENSOR

PRIMARY DAMPER

CONTROL OUTPUT

PRIMARY AIRFLOW

DAMPER

SECONDARY

AIRFLOW DAMPER

TOTAL AIRFLOW

PRIMARY AIRFLOW

SENSOR

PRIMARY AIR

VENTILATION AIR

SECONDARY DAMPER

CONTROL OUTPUT

SECONDARY

CONTROLLER

ZONE

CONTROLLER

CONSTANT VENTILATION USING DUCT DUCT TERMINAL

WITH ZONE PRESSURE CONTROL

Fig. 28 — Secondary Damper for Zone Pressurization

1 2 ... 29 30 31 32 33 34 35 36 37 38 39 ... 43 44

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