CEMP-E
TI 810-11
30 November 1998
valve), but the fan is controlled. Unit heaters are used to provide heat in mechanical spaces and
stairwells. Figure 4-2 includes the ladder diagram and equipment schedule for this type of system.
Figure 4-2 Unit heater temperature control system.
b. General sequence of operation. A unit thermostat cycles the unit heater fan to maintain its
setpoint temperature. A microprocessor-based thermostat could also be used to provide for a night-
setback setpoint, as shown in chapter 5.
c. Detailed sequence of operation. Space thermostat TSL-XX01 has a manual "OFF-AUTO" switch.
When the switch is indexed to "OFF", the unit-heater motor is de-energized. When the switch is indexed
to "AUTO", the fan starts when the space temperature falls below the thermostat setpoint, and stops
when the temperature rises to its setpoint.
6. GAS-FIRED INFRARED HEATER CONTROL SYSTEM.
a. Description of infrared heater system. This system consists of gas infrared heaters. Figure 4-3
shows the ladder diagram and equipment schedule for this system.
Figure 4-3. Gas-fired infrared heater temperature control system.
b. General sequence of operation. A thermostat cycles the infrared heater (or heaters) to maintain
the programmed setpoint.
c. Detailed sequence of operation. A microprocessor-based room thermostat TuP-XX01 has an
"AUTO-OFF" switch. When the thermostat switch is indexed to the "OFF" position, the infrared heater
remains off. When the switch is indexed to the "AUTO" position, the infrared heater cycles during the
occupied mode to maintain the programmed occupied temperature setpoint and during the unoccupied
mode to maintain the programmed unoccupied temperature setpoint.
7. SMALL PACKAGED UNITARY SYSTEM CONTROL SYSTEM.
a. Description of all-air small packaged unitary system. This system consists of a small self-
contained air handling unit provided with both heating and cooling equipment. Figure 4-4 shows the
ladder diagram and equipment schedule for this system.
Figure 4-4. Small packaged unitary system control system.
b. General sequence of operation. When indexed to "HEAT", a microprocessor-based room
thermostat cycles the unit fan and heating equipment, to maintain the programmed temperature. When
indexed to "COOL", the thermostat cycles the fan and cooling equipment, to maintain the programmed
temperature.
4-3
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