Carrier MODULINE 37HS User Manual

Page 48

VAV Heating and Cooling With Changeover — (Function
5.) A VAV control arrangement for cooling/heating includes
a wall-mounted cooling/heating thermostat and provision to
change the thermostat from cooling to heating configuration
and back again. Figure 46 shows the control arrangement
with Moduline

௡ control for heating and cooling. The wall

thermostat is shown in Fig. 47. The system-powered heating
and cooling changeover uses an assembly consisting of 2
temperature-operated pneumatic switches located inside the
unit plenum and installed in-line between a cooling/heating
thermostat and the volume controller. These switches se-
quence the thermostat between the cooling and heating modes,
depending upon the temperature of the primary air supply.
VAV Heating — (Function 9.) Variable air volume heating
controls are the same as for VAV cooling except that only a
wall-mounted heating thermostat is offered (Fig. 48). The
heating thermostat is reverse acting (RA); thus the output
pressure decreases as the space temperature increases.

SYSTEM-POWERED CONTROLS WITH ELECTRIC
INTERFACE

VAV Cooling With Electric Warm-Up — (Function 6.) Elec-
tric warm-up uses an electric changeover valve to perform
the same function as system-powered warm-up; that is, to
provide heated air to reestablish comfortable temperatures
when occupancy resumes after an extended unoccupied pe-
riod. Since the cooling thermostats are satisfied at the re-
duced temperature, the units will be shut off and the system
will not be able to deliver warm air. It is necessary, there-
fore, to provide a means of temporarily overriding the cool-
ing thermostat.

The changeover control is an electrically operated, re-

motely controlled 3-way solenoid valve. The normally closed
port of the valve is capped. The valve usually is wired to
activate automatically with the supplemental heating switch;
however, it can also be manually activated. This option may
be used with either a unit-mounted or wall-mounted ther-
mostat. See Fig. 49.

VAV Heating and Cooling With Electric Changeover — (Func-
tion 7.) A VAV control arrangement for cooling/heating in-
cludes a wall-mounted cooling/heating thermostat (Fig. 47)
and provision to change the thermostat from a cooling to
heating configuration and back again. System-powered cooling/
heating with electric changeover uses a 3-way electric so-
lenoid valve to switch control between the cooling and heat-
ing functions of a cooling/heating wall-mounted thermostat.
It is installed in-line between the volume controller of a CV
cooling control package and the thermostat. The valve may
be activated separately or interlocked with an electric heat-
ing system. See Fig. 50.

Fig. 46 — System-Powered Changeover

Switch Arrangement with Heating/Cooling

Wall Thermostat

Fig. 47 — Cooling/Heating Wall Thermostat

Fig. 48 — Wall-Mounted Heating Thermostat

Fig. 49 — VAV Control Arrangement

for Electric Warm-Up

Fig. 50 — VAV Control Arrangement

for Electric Changeover