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Step 5: Set the SMC55-HWQS Advanced Parameters to Modify the
Functionality of the HVAC System
Parameters Applicable for Radiant Underfloor Heating System
Radiant Underfloor Heating Control Summary
Pulse Width Modulation (PWM) Temperature Control (for relay signals only)
Both indoor air temperature control and floor temperature control uses a PWM control algorithm when using relays. PWM works
by turning the heat on during a calculated percentage of the cycles per hour (parameter 94A).
For example, if the controller is configured to have 3 cycles per hour, there will be three 20-minute time periods in an hour. Every
time period will have the heat on for a calculated percentage of the period, known as a "duty cycle". The duty cycle is calculated
mostly by the temperature difference from the setpoint.
• The duty cycle equals 100% of the time period when the temperature is at or below the setpoint minus the floor 100%
differential (parameter 92A).
Example: If the setpoint equals 70 °F, the duty cycle is 100% when the temperature is at or below 68°F (70 °F − 2 °F).
• The duty cycle equals 0% of the time period when the temperature is at or above the setpoint plus the floor 0% differential
(parameter 93A)
Example: If the setpoint equals 70 °F, the duty cycle is 0% (off) when the temperature is at or above 72 °F (70 °F + 2 °F).
Figure 12: Simplified Graph of the Duty Cycle Calculation
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Short Cycle Prevention: To prevent the controller from cycling too quickly, duty cycle rounding is used if the cycle is almost fully
on or off. If the duty cycle value is 95% or higher, the duty cycle is rounded to 100%. If the duty cycle value is below the minimum
pulse width (Parameter 54A), the duty cycle is rounded to 0%.
0–10 V- Control (for 0–10 V- signal only)
If the valve control is set to 0–10 V-, the controller provides a continuous voltage output to the valve actuator. Similar to PWM
with relay control, the duty cycle calculated determines the output, but now in a voltage instead of an on / off interval. For
example, a duty cycle of 30% is similar to a 3.0 V output signal to the valve actuator.
Duty Cycle Sample Adaptation (for both relay and 0–10 V- signals)
The radiant floor control algorithm also uses a duty cycle sample adaptation. The purpose of the adaptation is to dynamically
change the duty cycle according to the newly sampled temperature.
Included with SMC55-HWQS version 7420 or newer and HomeWorks Palladiom Thermostat version 1.10 or newer.
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Temperature (°F)
(continued)
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P/N 032498h
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