DISCHARGE AIR SENSOR
A discharge air sensor suitable for installation in the duct at the discharge of the cooling/hearing unit shall be provided with each SMC. The
discharge air sensor shall operate at 12 VDC and shall be a thermistor molded into the end of a metal tube suitable for insertion through a 3/8
inch hole in the duct. The thermistor shall be factory wired to a terminal strip located in a NEMA I enclosure mounted at the other end of the
tube. The enclosure shall be foam backed to provide an air seal when it is screwed to the duct.
The SMC shall be field adjustable to disable the internal discharge air sensor when discharge thermostats provided by others are used.
Discharge thermostats by others may be used to provide more than two stages of cooling or heating, to provide modulating control or to
provide pneumatic control.
REMOTE SENSORS
A remote sensor shall be located in up to five Therma-Fuser TF-HC units designated on the plans. The remote sensors shall operate at 12
VDC. Sensors shall be a thermistor molded into a protective clear plastic tube open at both ends for air flow This sensor shall be mounted
adjacent to the thermal elements in a TF-HC Therma-Fuser so that it senses the temperature of the secondary air from the space below
induced past the thermal elements. The sensors shall be factory wired to a terminal strip inside a NEMA I enclosure, factory mounted on the
top of the Therma-Fuser. Factory wiring shall be NEC CL2P cable approved for installation in space used for environmental air.
The SMC shall be field adjustable to disable unused sensors.
DELAY TIMERS
The SMC shall have time delays (delay on make) in the heating and cooling output circuits adjustable from 6 seconds to 9 minutes. The
function of these time delays is to impose a delay between cooling and heating to purge the ducts and allow the system to settle out in
ventilation if possible before changing mode and to improve control stability. They shall be factory set at 5 minutes.
WARRANTY
Manufacturer shall warrant the SMC to be free from defects for 1 year.
LOCATION
The SMC shall be enclosed in a NEMA I enclosure with a hinged front panel latched with a keyed lock. It shall be located as shown on the
plans.
INTERFACE
The SMC shall interface with the cooling/heating unit through 24v relays requiring not more than 1 amp. (24 VA.) See the specification of the
cooling/heating unit for details of fan, cooling and hating relays. Delay on break anti short cycle time delays by others may be required for
compressor protection. (See the recommendations of the cooling/compressor unit manufacturer and note 10 to the SMC jobsite wiring.)
The SMC circuits shall be fused and have a surge suppressor to protect against voltage spikes above 26.8 volts. Separate fusing shall be
provided for the cooling/heating unit outputs, the 24 VAC mode signals and, where used, for the duct heating station outputs.
POWER
The SMC shall be provided with 24v (+10% - 15%) power. Minimum power required shall be 12 VA plus the requirement for the fan relay and
either the cooling or heating relay. The cooling/heating unit transformer shall be used when sized to power the relays in the cooling/heating unit
plus external controls. The relays shall have a maximum requirement of 12 VA steady state each.
A transformer to 24v fused and protected as necessary shall be provided by others when the cooling/heating unit transformer does not have
adequate power, when using the 24 VAC mode signals or when using duct heating stations.
OPTIONAL REMOTE OVERRIDE
The SMC shall be capable of interface to an isolated set of dry contacts of a windup timer(s) by others. When the contacts are closed, the
SMC shall switch to the occupied mode. The dry contacts of the windup timer shall operate at 12v and have a capacity of 10 VA.
OPTIONAL 24 VAC MODE SIGNALS
The SMC shall have terminals providing a 24 VAC signal suitable for operating a relay holding coil of 12 VA maximum in each of the three
modes: occupied, unoccupied and preoccupancy.
OPTIONAL ADD FOR DUCT HEAT
See separate specifications for use of the SMC to control a duct heating station for each of the five sensors. These duct heating stations can
be reheat coils or fan powered boxes.
EXTERNAL WIRING
External wiring shall be in accordance with the wiring diagram(s) and specifications. All wiring shall be low voltage and shall be in accordance
with the National Electrical Code and local electrical codes. Minimum wire size shall be as shown in the Acutherm table of wire size vs. wire
length. All wires to be tagged to match terminal numbers. NEC CL2P cable approved for installation in ducts, plenums and other spaces used
for environmental air is recommended when wiring to the sensors through return air plenums.
Upon completion the contractor shall conduct a total system test.
