Carrier 37HS specifications Ð Cooling/Heating Wall Thermostat, Ð Wall-MountedHeating Thermostat

VAV Heating and Cooling With Changeover Ð (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 con®guration 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 Ð (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.

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Fig. 46 Ð System-Powered Changeover Switch Arrangement with Heating/Cooling Wall Thermostat

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Fig. 47 Ð Cooling/Heating Wall Thermostat

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Fig. 48 Ð Wall-Mounted Heating Thermostat

SYSTEM-POWERED CONTROLS WITH ELECTRIC INTERFACE

VAV Cooling With Electric Warm-Up Ð (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 satis®ed 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 Ð (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 con®guration 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.

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Fig. 49 Ð VAV Control Arrangement

for Electric Warm-Up

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Fig. 50 Ð VAV Control Arrangement

for Electric Changeover

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