Controls both vav and cv units – Trane RT-DS-10 User Manual

Page 34

Controls

Both VAV and

CV Units

Control Sequences of Operation That are Common to Both VAV and CV Units

Ventilation Override (VOM)

Ventilation override allows an external

system to assume control of the unit

for the purpose of exhaust or

pressurization. There are two inputs

associated with ventilation override,

the initiate input and the select input.

When the UCP senses a continuous

closed condition on the initiate input at

the low voltage terminal board the unit

will begin ventilation override

depending on the condition of the

select input. The default condition of

the select input is exhaust (input open).

A closed select input will yield

pressurization. The component state

matrix for ventilation override is as

follows:

System

Component

Exhaust

Pressurization

Heat/Cool

off

IGV

closed

open

Supply Fan

off

Exhaust Fan

off

Outside Air Damper

closed

open

Return Air Damper

open

closed

VAV Boxes

n/a

open

Coil Freeze Protection FROSTAT

The FROSTAT system eliminates the

need for hot gas bypass and adds a

suction line surface temperature sensor

to determine if the coil is in a condition

of impending frost. If impending frost is

detected primary cooling capacity is

shed as necessary to prevent icing. All

compressors are turned off after they

have met their minimum three minute

on times. The supply fan is forced on

until the FROSTAT device no longer

senses a frosting condition or for 60

seconds after the last compressor is

shut off, which ever is longer.
Occupied/Unoccupied Switching

There are three ways to switch

Occupied/Unoccupied:

NSB Panel

Field-supplied contact closure

TRACER

Night Setback Sensors

Tranes night setback sensors are

programmable with a time clock

function that provides communication

to the rooftop unit through a two-wire

communications link. The desired

transition times are programmed at the

night setback sensor and

communicated to the unit.
Night setback (unoccupied mode) is

operated through the time clock

provided in the sensors with night

setback. When the time clock switches

to night setback operation, the outdoor

air dampers close and heating/cooling

can be enabled or disabled. As the

building load changes, the night

setback sensor communicates the need

for the rooftop heating/cooling (if

enabled) function and the evaporator

fan. The rooftop unit will cycle through

the evening as heating/cooling (if

enabled) is required in the space. When

the time clock switches from night

setback to occupied mode, all heating/

cooling functions begin normal

operation.
When using the night setback options

with a VAV heating/cooling rooftop,

airflow must be maintained through

the rooftop unit. This can be

accomplished by electrically tying the

VAV boxes to the VAV heat relay

contacts on the Low voltage terminal

board or by using changeover

thermostats. Either of these methods

will assure adequate airflow through

the unit and satisfactory temperature

control of the building.

Timed Override Activation ICS

When this function is initiated by

pushing the override button on the ICS

sensor, TRACER will switch the unit to

the occupied mode. Unit operation

(occupied mode) during timed override

is terminated by a signal from TRACER.
Timed Override Activation Non-lCS

When this function is initiated by the

push of an override button on the

programmable zone sensor, the unit

will switch to the occupied mode.

Automatic Cancellation of the Timed

override Mode occurs after three hours

of operation.
Comparative Enthalpy Control

of Economizer

The Unitary Economizer Module (UEM)

receives inputs from optional return air

humidity and temperature sensors and

determines whether or not it is feasible

to economize. If the outdoor air

enthalpy is greater than the return air

enthalpy then it is not feasible to

economize and the economizer

damper will not open past its minimum

position.
Emergency Stop Input

A binary input is provided on the UCP

for installation of field provided switch

or contacts for immediate shutdown of

all unit functions. The binary input is

brought out to Low Voltage Terminal

Board One (LTB1).
Conventional Thermostat Interface

(CV ONLY)

An interface is required to use a

conventional thermostat instead of a

zone sensor module with the UCP. The

Conventional Thermostat Interface

(CTI) is connected between

conventional thermostat and the UCP

and will allow only two steps of heating

or cooling. The CTI provides zone

temperature control only and is

mutually exclusive of the Trane

Communications Interface.