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c. Detailed sequence of operation. Microprocessor-based room thermostat TuP-XX01 is equipped
with "HEAT-OFF-COOL" and "AUTO-ON" switches. It can be programmed to maintain separate
occupied and unoccupied heating mode and occupied cooling mode temperatures. When the system
switches are indexed to "HEAT" and "AUTO", the thermostat cycles the heating unit and the fan to
maintain the programmed temperature; the cooling unit remains de-energized. When the thermostat is
indexed to "COOL" and "AUTO", the thermostat cycles the cooling unit and the fan to maintain the
programmed temperature; the heating unit remains de-energized. At the conclusion of the cooling
occupied mode, the system is de-energized and remains de-energized throughout the unoccupied mode.
When indexed to "ON" the unit fan runs continuously. When the "HEAT-OFF-COOL" switch is indexed
to "OFF", neither heating nor cooling can be energized.
8. DUAL-TEMPERATURE FAN COIL UNIT CONTROL SYSTEM.
a. Description of dual-temperature fan coil system. The system consists of a fan and a dual-
temperature coil that is supplied with cold water during the cooling season and hot water during the
heating season. Figure 4-5 shows the schematic and ladder diagrams and equipment schedule for this
type of system.
Figure 4-5. Dual-temperature fan coil unit temperature control system.
b. General sequence of operation. A wall-mounted two-stage thermostat cycles the fan in winter to
maintain its lower setpoint and in summer to maintain its higher setpoint. Fan speed is manually indexed
by the room occupants.
c. Detailed sequence of operation.
(1) Wall-mounted two-stage thermostat TS-XX01 has two setpoints. The lower setpoint is a
heating mode setpoint, which, on a fall in temperature, cycles the fan to maintain the setpoint. The
higher setpoint is a cooling mode setpoint, which, on a rise in temperature, cycles the fan to maintain the
(2) Strap-on aquastat TS-XX02, located on the return line downstream of the fan coil 3-way
valve, senses whether hot water or cold water is being supplied to the dual-temperature coil, and its
snap-acting contacts determine which thermostat contact and setpoint will cycle the fan.
(3) Whenever the fan is energized, a three-way electric valve VLV-XX01 is also energized, to
open the hydronic medium to the coil. Whenever the fan is de-energized, VLV-XX01 is also de-
energized and closes the hydronic medium to the coil and opens it to coil bypass.
9. CONTROL SYSTEMS THAT REQUIRE SINGLE-LOOP CONTROLLER PANELS.
a. An HVAC control panel is required for each system that requires the control capabilities of the
single-loop controller. The designer will show all the details of the standard HVAC control panel on the
contract drawings. These details will describe the construction, mounting, and general arrangement of
the standard HVAC control panel.