Operation of the Thermostat Input The thermostat has two terminals, labeled CK1 and CK2, which are used to connect the thermostat to an external device. Whenever there is continuity between CK1 and CK2 the thermostat will be forced into Occupied mode. The CK1 and CK2 connection will be referred to in this manual as the "input." Programmable models - T2900 & T2900SCH The thermostat will maintain Occupied 1 set temperatures for as long as CK1 and CK2 are activated. When the continuity between CK1 and CK2 is broken, the thermostat will then operate according to its regular program. The thermostat MUST be in Program On mode to use the input; if the thermostat is in Heat, Cool, Auto, or Off mode the input will be ignored. CK1 and CK2 will always force the thermostat into Occupied 1, even if the thermostat was already in an Occupied mode. Non-programmable model - T2700. The non-programmable models work differently. They do not have a Program On mode, just Heat Cool, Auto or Off. In any mode except Off, the thermostat will control to the displayed setpoints 24 hours a day, 7 days a week. When the input is activated, it forces the thermostat to an Unoccupied mode, with user-determined Unoccupied setpoints. If desired, the operation of the input can be reversed - this is done in the thermostat setup, where the input is set to Normally Open (NO) or Normally Closed (NC). The thermostat is factory programmed with the input set to Normally Open, which means the thermostat is normally in Occupied mode, until the input forces the thermostat to Unoccupied mode. If set to Normally Closed, the thermostat will be in the Unoccupied mode until the input is activated to force it into Occupied mode. Thinking of Normally Open (NO) as Normally Occupied may help you remember which is which! Note: Hereafter these instructions will refer to the input as forcing the stat into Occupied mode. For non-programmable models, that can always be reversed, forcing the stat in to Unoccupied mode instead.

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A useful feature of the programmable thermostats is the hierarchy of programming which allows one Occupied period to override another. This allows "nesting" of programs, greatly enhancing programming flexibility. Occupied 1 takes precedence over Occupied 2, which takes precedence over Occupied 3. Therefore, if the Occupied 1 period overlaps the Occupied 2 or 3 periods, Occupied 1 will override Occupied 2 or 3. A good example of an application for nested programs is a health club. The owner wants the club to operate at 72 degrees from 6am to 9pm. From 10am to 11am there is an aerobics class, and the desired setpoint is 68 degrees. To program this scenario, set Occupied 2 to run from 6am to 9pm, at 72 degrees, and Occupied 1 to run from 10 am to 11am at 68 degrees. At 10 am Occupied 1 will override Occupied 2 and the setpoint will change to 68 degrees. At 11 am the thermostat will return to Occupied 2 at 72 degrees.

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The T2900SCH thermostat features an Auxiliary output that can be used to turn on or off an external device. Most commonly this output is used to open an economizer damper, but it can also be used to turn on lights, exhaust fans, sprinklers, etc. The output is a dry contact type output. The auxiliary output is energized when the thermostat is in Occupied 1 or in a Pre-Occupancy Purge. The output is often used to control and economizer or outside air damper. Whenever the thermostat is in Occupied 1 or a in a purge cycle, the damper is forced open, and whenever the thermostat is in Unoccupied (or Occupied 2 or 3), the damper will be closed. If the thermostat is forced in to Occupied 1 with the override button or through the dry contact input, the damper will also open. The output is used similarly for light and exhaust fans The output can be used for other types of devices such as sprinklers or security lights, which may run on a much different schedule than the HVAC. In this case, use Occupied 1 only to control the output (set the heat / cool setpoints to setback temperatures), and use Occupied 2 or 3 to control the HVAC.************

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It is possible to control multiple thermostats using a single external timeclock. Simply connect two wires from the timeclock to each thermostat, or daisy chain them together (see installation section.) When the timeclock reaches the preset time, all connected thermostats will be forced into Occupied mode. If it is not desirable for all thermostats to start simultaneously, there is a Soft Start function available in the thermostats to start them in sequence. Up to 100 units can be started sequentially with no two starting at the same time. Please see installation section for wiring diagrams, warnings, and Soft Start programming.

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An Energy Management System (EMS) can be connected to the thermostat(s) using the CK1 and CK2 terminals. Connect the desired output relay from the EMS with two wires to CK1 and CK2 on the thermostat. Whenever the EMS relay is closed, the thermostat will use the Occupied setpoints.

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Any light sensor with a dry contact type output can be connected to the thermostat(s). Whenever the lights are on, the thermostat will go to Occupied mode. On programmable models the regular program can be used for morning warm-up, different occupied setpoints, etc. See installation section for programming details. There are also thermostat models available with a built-in light sensor, which requires no extra wiring or configuration. Models with built in light sensor: T2900.

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Many models of motion detectors are available with a dry contact type output. Any of these sensors can be connected to the thermostat at the CK1 and CK2 terminals. Whenever the motion detector senses motion, the thermostat will be forced into Occupied mode. See Appendix A for a list of vendors and model numbers, and approximate prices.

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A door or window sensor indicates when a door or window is open. This type of sensor can be used to turn off the air conditioning or heating if a window or door is opened. Just connect CK1 and CK2 on the thermostat to the two sensor wires. On thermostat models with a configurable input, the input should be set to normally closed, so that the thermostat goes to Unoccupied when the door or window is opened. For other thermostat models, a switch with a normally closed relay should be used. See installation instructions for details.

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External Timeclock
To control thermostats using an external timeclock, simply connect the two wires from the relay output on the timeclock to CK1 and CK21 on the thermostat. Whenever the timeclock relay is energized, the thermostat will go to Occupied. IN most cases an isolation relay should be used between the timeclock and the thermostat isolate their respective transformers. See wiring diagram below and notes below.

Note: When using the auxiliary input (CK1 & CK2) or if attempting to control multiple HVAC units with a single thermostat, it is possible to encounter transformer phasing problems that will interfere with thermostat operation. Connecting transformers that are not phased properly may result in a direct short, which could damage the transformers and/or the thermostat. Phasing problems are more likely if the units share a common ground with grounded secondary transformers.

Solution: If possible, phase all HVAC units together. If phasing is impractical, isolation relays may be used to isolate the transformers. To isolate the auxiliary input, use a separate transformer for the auxiliary control device (usually a timeclock). Connect the control device to an isolation relay coil*. Connect one set of isolated contacts to each thermostat at CK1 and CK2. See diagram A.

To prevent phasing problems when controlling multiple HVAC units with one thermostat, phase the HVAC units or use isolation relays* to isolate the unit transformers. One unit will be connected directly to the thermostat, and it will power the stat. All other units will require one set of isolated contacts for each of the following: heat, cool, fan, and/or reversing valve, etc. See diagram B.

* There is an optional accessory available that can be used instead of an isolation relay - it is an opto-coupler, which isolates voltage using an LED. It is wired exactly like a relay.

Energy Management System (EMS)
Most Energy Management systems will include some type of dry-contact or relay output. To control the thermostat, connect CK1 and CK2 from the thermostat to the desired relay output. Polarity of the wires does not matter. When the EMS relay is closed, the thermostat will control to the Occupied setpoints. When the relay is open, the thermostat will revert to normal operation.

Light Sensor - External Sensor
Connect the two control wires from the light sensor to the CK1 and CK2 terminals on the thermostat. ***Power?***

Light Sensor - Internal sensor - (T2900)
The light sensor is built in to the thermostat. The light sensor is adjustable to accommodate different light levels. The sensor adjustment screw is located in the inner cover of the thermostat near the down arrow button. A small screwdriver is included with the thermostat. Turning the screw clockwise increases the sensitivity, counterclockwise decreases the sensitivity. The light sensor responds to overhead light only, so it is not affected by side windows. The minimum light level that will put the thermostat into occupied mode is approx. 24 fcd at the highest sensitivity setting, and approx. 96 fcd at the lowest sensitivity setting. The easiest way to test light level is to use a flash meter from a camera store, such as the Minolta Flash Meter V. Make sure to test the light level right up against the wall where the thermostat will be mounted.

Whenever the thermostat senses light, it is forced into Occupied 1. The thermostat must be in Program On mode to use the light sensor, in all other modes the sensor is ignored. When the lights are off, the thermostat reverts to its regular program, which allows programming of morning warm-up, different setpoints, etc.

Morning warm-up: It may be desirable to start the heating (or cooling) in the morning before the building is occupied in order to have the building comfortable by the time the occupants arrive. This is easy to do with the light activated thermostats, just use the regular program and set any of the Occupied periods for the desired time and setpoint. When the occupants arrive and turn on the lights, the stat will be forced into Occupied 1. For example, if the desired normal occupied temperature is 72 degrees and the building is occupied at 8 am, set Occupied 1 to start at 7am and end at 8am with a setpoint of 72 degrees. This will provide one hour of morning warm-up. If the lights are not on at 8 am, the thermostat will go to Unoccupied. If the lights are on, the stat will go to Occupied 1 at 72 degrees and stay there as long as the lights remain on.

Different setpoints: It may be desirable to have two (or more) different setback temperatures, based on the time of day. For example, consider a building that is normally occupied from 8 am to 5 pm. The building owner wishes to save energy by using a light activated stat to set the temperature back when the offices are unoccupied (lights are off). The owner sets the cooling Occupied setpoint to 72 and the cooling Unoccupied setpoint to 85. Now, whenever the lights are off, the thermostat will go to Unoccupied at 85 degrees. But, if an office worker goes to lunch just for an hour (and the lights are off during that time), he/she may not want to return to a room that's 85 degrees! In this case, simply set Occupied 2 to run from 8 am to 5 pm at 75 degrees. Whenever the lights are on, the stat will go to Occupied 1 at 72 degrees, because Occupied 1 overrides Occupied 2. When the lights are off, if it is between 8 and 5 the stat will revert to Occupied 2 at 75 degrees, giving a 3 degree setback which will save energy without allowing to room to heat up too much.

Motion Sensors
To connect a motion sensor to the input of a thermostat, use a motion sensor with a relay or dry contact type output and a timer that will keep the sensor on for a length of time after motion is detected. The timer is necessary so that the sensor doesn't require constant motion, just occasional movements. Most motion detectors are infrared devices and require a 9 - 12 VDC power source. See Appendix A for model numbers and sources.

Connect the power source to the motion detector, then run two wires from the Normally Closed contacts on the sensor to the CK1 and CK2 terminals on the thermostat (polarity doesn't matter.) Whenever the sensor detects motion it will close its relay, which will put the thermostat into Occupied mode.

Remote Control Activator (on/off relay)
Radio Shack
RSU 10037752 $18.99

Home Controls
XT506 $20.95

Home Automation Systems, Inc.
2010 $20.95

Telephone Responders (requires remote control activator, above)

Radio Shack
RSU 10037778 $79.99

Home Controls
HCTMS $169.95
XT551 $67.95

Home Automation Systems, Inc.
5000 $64.95

Motion Sensors

Home Controls
RK7001 $21.95

Home Automation Systems
7481 $24.99

Wireless Motion Sensor
7402 $129.95 motion sensor (transmitter)
7412 $47.95 receiver