Table of Contents
Advertisement
FAN OPERATION
When the subbase fan switch is in the ON position, the
fan is energized continuously in the occupied mode. The
AUTO position energizes the fan with the heating or cool-
ing system. If the subbase is Q7300D, during unoccupied
mode, the fan cycles with Y1 and W1.
NOTE: The Q7300 switch no. 4 has no effect when the
thermostat is configured for heat pump.
EMERGENCY HEAT
When the system switch is in the EM. HEAT position
(on select Q7300 subbases), the auxiliary heat is stage 1 and
the compressor stages are locked off. The fan cycles with
the auxiliary heat.
GENERAL OPERATION INFORMATION
Cycle Rates
The thermostat control algorithm maintains the tem-
perature by cycling stages of heating or cooling to meet
setpoint. See Table 9 for the nominal cycle rates provided.
TABLE 9—NOMINAL CYCLE RATES
FOR HEATING AND COOLING.
System Type
Conventional
Heat Pump
Subbase Auxiliary Relay
The Q7300 auxiliary relay output acts as a time-of-day
switch to be used with an economizer minimum position
control. The normally open (A1) auxiliary relay contacts
are closed during the occupied period and open during the
unoccupied period. The normally closed (A3) auxiliary
relay contacts are open during the occupied period and
closed during the unoccupied period. The contacts are in
the normal state during recovery.
Interfacing with Electromechanical Economizers
(Subbases with Auxiliary Relay)
Mechanical cooling is often used when outside tempera-
tures are in the 50° to 60°F range and humidity is below 50
percent. In central and northern climates, hundreds of hours
fall into this temperature category. By permitting 80 to 100
percent outside air into the system, mechanical cooling
may not be needed at all, particularly during spring and fall.
An economizer is used to take advantage of the outside
air. The typical economizer consists of an outside air damper,
motor, outdoor air changeover control and a minimum
position potentiometer. The motor controls the dampers.
Suitability of the outside air for cooling is determined by
the outdoor air changeover control. The potentiometer is
used for adjusting the minimum position of the economizer
dampers, which provide a minimum amount of fresh air for
ventilation.
The economizer reduces compressor run time, thereby
saving energy and extending the compressor life. The
drawback to the economizer is that during the unoccupied
H1
H2
C1
C2
C3
8
8
4
4
4
4
8
4
4
—
period, if there is no call for cooling or outdoor air is not
suitable for free cooling, the economizer is controlled to
minimum position. This position allows some percentage
of outdoor air to enter the building, regardless of air suit-
ability. The situation can cause the heating or cooling to run
more often than if suitable outdoor air is permitted to enter
the building.
The thermostat can take advantage of an economizer by
connecting the auxiliary relay contacts (A1 and A2) of the
subbase to control the economizer minimum position po-
tentiometer. The contacts close during the occupied period,
allowing the economizer to operate normally. The contacts
are open duirng the unoccupied period, disabling the mini-
mum position feature of the economizer. The open contacts
cause the economizer to drive dampers fully closed instead
of staying at minimum open position. This reduces the
possibility of unsuitable outdoor air from entering the
building, which lowers the internal load on the HVAC
system are saves additional energy.
Other Uses for the Auxiliary Relay
Examples of other uses of the auxiliary relay are hot
water heaters, lighting or baseboard heat. The additional
loads are connected to the auxiliary relay contacts on the
subbase. The contacts are rated for 1.6A at 30 Vac, but can
be adapted to higher current applications with the use of an
external relay and transformer. See Fig. 22.
Duty Cycle Interface
Duty cycling HVAC equipment controlled with a T7200
or T7300 is recommended because the thermostat is al-
ready maintaining an optimum control cycle rate. Adding
another external duty cyle increases the P+I error being
sensed and results in degradation of temperature control
and equipment efficiency.
Fig. 22—Use of external relay and transformer
for auxiliary loads greater than 1.6A.
Q7300 SUBBASE
A1
A2
A3
3
AUXILIARY
RELAY
CONTACTS
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
1
PROTECTION AS REQUIRED.
RELAY REQUIRED (R8222 OR SIMILAR).
2
TERMINAL A3 AVAILABLE ON Q7300A,B,D,E AND G MODELS ONLY
3
17
T7200/T7300/Q7300
OPERATION
L1
L2
1
(HOT)
2
M4383
63-4038—7
TO
LOAD
Advertisement
Table of Contents
