Issue
Suggested configuration for Xenta 121, STR-150 in single occupancy zones (Hotel Operation):
- Single setpoint display for ease of use for hotel guests
- Erasing setpoint offsets between guests automatically on transition from unoccupied to occupied
- Disable fan overrides
Product Line
TAC Vista
Environment
- Hotel rooms
- Xenta 121, ZBuilder
- STR-150
Cause
A hotel room is a unique application of the Xenta 121 and must be tailored to fit the temporary residents and be as easy to use and understand via an STR-150 as possible to reduce the amount of calls to the on-call maintenance department.
Resolution
The important thing to remember is that the Xenta 121 and STR-150 do not have duplex communication capabilities. Communication is one way from the stat to the controller. There is no capability for the controller to override/control the stat display. Because of this, it will be very important to standardize setpoints between the stat, the controller, and system-wide.
Set Up the STR-150
Refer to the STR-150 User’s Manual for additional information.
Push the fan and bypass buttons simultaneously for 2 seconds to enter P0. In P0, hold down the bypass button and push the fan button three times. The wrench symbol is lit when the STR-150 is in configuration mode.
| Parameter | Function | Value/Range | Set Value |
| P0 | Software Version | - | - |
| P1 | °C or °F temperature display | 1=°C, 2=°F | 2 |
| P2 | Reference temperature (Reftemp) | 15-30°C / 60-90°F | 72 1 |
| P3 | Setpoint or room temp. as default | 1=Setpt, 2=Room | 1 |
| P4 | Timeout | 5-90 seconds | 10 |
| P5 | Fan settings | 0= No fan 1= On/Off fan 2= Two-speed fan 3= Three-speed fan |
0 2 |
| P6 | Room temperature and setpoint display resolution | 0.1 or 0.5°C 0.2 or 1.0°F |
0.2 |
| P7 | Max adjustable setpoint span above or below Reftemp (P2). | ±0 - ±5°C ±0 - ±10°F |
10 |
| P8 | Bypass button and occupancy indication When = 2, no bypass command is sent to the controller | 1= Symbol on, off or flashing 2= Symbol always off |
2 |
1 Reference temperature should equal the average of the Xenta 121 occupied heating and cooling setpoints. Assuming 70°F heating and 74°F cooling for this example.
2 There is no way to give only AUTO/ON override control to hotel guests, so fan override capabilities should be disabled.
Wire STR-150 to Xenta 121
| STR-150 | Xenta 121 | ||
| Mode | 11 | Y1 | 5 |
| Data | 12 | X1 | 7 |
| M | 13 | M | 6 |
Set Up the Xenta 121 - ZBuilder
Connected devices > Room unit
Select STR-150 and Check the box for "Activate STR-150 reset offset function."
Engineering TAC Xenta 120 Manual Chapter 9.1.2 states:
There is a so-called hotel reset function for room unit STR-150. When activated, an 'old' offset value is not taken into account when going from Unoccupied to Occupied until the Offset is changed (probably by a new hotel guest).
Control > Setpoints
- Center all control setpoints around reference temperature of the STR-150. In this example, the reference temperature is 72°F, so cooling and heating setpoints have been centered around that.
- Setpoint calculation mode is set to method A which preserves symmetry around a base setpoint, but since these setpoints are already symmetrical, that is not of great importance.
- Expose normalize setpoint is important for the hotel staff to see the same setpoint as the stat is displaying to the hotel guest.
Operation
- STR-150 defaults to reference temperature as setpoint 72°F. Xenta 121 uses default setpoints. In cooling maintaining 74°F. If the stat is set to display setpoint by default, the customer will only see the setpoint and won't be aware of the 2-degree dead band offset.
- Hotel guest decides 72°F is too hot and lowers the setpoint on the stat to 70°F. Xenta 121 interprets this as a -2°F offset on setpoints and now maintains 68°F heating/72°F cooling.
- Guest checks out and the room is set to unoccupied. Stat continues to display 70°F but the larger unoccupied dead band actually controls to set default of 80°F for cooling.
- Next guest checks in and the room is set to occupied. Stat continues to display 70°F but the Xenta 121 has erased the offset from its calculation and maintains 74°F.
- Guest feels this is too warm and lowers the stat from 70°F to 69.8°F. A new offset of -2.2°F is sent to the Xenta 121 which now controls the cooling setpoint to 71.8°F. The guest believes they have lowered their setpoint by 0.2°F but in reality have effectively lowered it 2.2°F. As soon as they make a change to the setpoint, they resume control of the offsets.
