Applications Guide Tracer Graphical Programming - Trane
Applications Guide Tracer Graphical Programming - Trane Applications Guide Tracer Graphical Programming - Trane
® Chapter 4 Cooling tower with two-speed fan example Reviewing the sequence of operation In this scenario a cooling tower with a two-speed fan delivers condenser water to a small chiller plant. The following specifications apply to control of the cooling tower. Condenser water pump When condenser water is requested by the chiller plant, command the condenser water pump to start. If condenser water flow fails to be confirmed within 30 seconds, command the pump to stop, indicate a pump failure at the operator display, and turn on the alarm output. A user must be able to reset the alarm at the operator display. Note: The instructions for writing the condenser water pump module are not included in this chapter. If you are working through the book chapter by chapter, you will write this module in Chapter 5. Otherwise, see “Writing the condenser water pump module” on page 94. Cooling tower fan If condenser water flow is established and if the condenser water temperature rises 2.5°F above the setpoint, start the fan at low speed. Switch the fan to high speed if the condenser water temperature rises to 5.0°F above the setpoint. Turn off the fan when the condenser supply water temperature falls below the setpoint minus 2.5°F. A minimum 30-second delay is required between starting the fan at low speed and switching to high speed. Sump heater Turn on the sump heater if the sump temperature falls below 40°F (this value is adjustable at the operator display). If the outdoor air temperature falls below 32°F, turn on the sump heater continuously. If the sump temperature remains below 36°F (this value is adjustable at the operator display) for 15 minutes, or if the sump temperature falls below 32°F, indicate an alarm at the operator display and turn on the alarm output. Alarms In addition to the alarm requirements mentioned in the previous sequence of operation components, indicate an alarm at the operator display and turn on the alarm output when any temperature sensor fails. Theusermustbeabletoresetthealarmsattheoperatordisplay. Analysis of this scenario results in Figure 47 on page 49. The corresponding data definition is presented in Table 5 on page 49, and a wiring diagram is presented in Figure 48 on page 51. 48 CNT-APG001-EN
® Reviewing the sequence of operation Figure 47: Cooling tower with two-speed fan drive data Table 5: Cooling tower with two-speed fan drive data definition Data Type Name Notes Inputs Analog Supply Temp Universal input configured as thermistor or RTD (Balco, Platinum) Return Temp Universal input configured as thermistor or RTD (Balco, Platinum) Sump Temp Universal input configured as thermistor or RTD (Balco, Platinum) Outdoor Air Temp Universal input configured as thermistor or RTD (Balco, Platinum) Binary Flow Status Condenser Water Request Outputs Binary Fan Start/Stop/Low Apply sufficient minimum on/off timers to prevent excessive fan cycling. Fan High Apply sufficient minimum on/off timers to prevent excessive fan cycling. Sump Heater Apply sufficient minimum on/off timers to prevent excessive heater cycling. Pump Start/Stop Apply sufficient minimum on/off timers to prevent excessive pump cycling. Alarm * The binary variable, Alarm Reset, is sourced from both the operator display/service tool and the program. This allows the user to turn on the Alarm Reset variable, and once the alarm is reset, the program turns the Alarm Reset variable off. CNT-APG001-EN 49
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®<br />
Chapter 4 Cooling tower with two-speed fan example<br />
Reviewing the sequence of operation<br />
In this scenario a cooling tower with a two-speed fan delivers condenser<br />
water to a small chiller plant. The following specifications apply to control<br />
of the cooling tower.<br />
Condenser water pump<br />
When condenser water is requested by the chiller plant, command the<br />
condenser water pump to start. If condenser water flow fails to be confirmed<br />
within 30 seconds, command the pump to stop, indicate a pump<br />
failure at the operator display, and turn on the alarm output. A user must<br />
be able to reset the alarm at the operator display.<br />
Note:<br />
The instructions for writing the condenser water pump module<br />
are not included in this chapter. If you are working through the<br />
book chapter by chapter, you will write this module in<br />
Chapter 5. Otherwise, see “Writing the condenser water pump<br />
module” on page 94.<br />
Cooling tower fan<br />
If condenser water flow is established and if the condenser water temperature<br />
rises 2.5°F above the setpoint, start the fan at low speed. Switch the<br />
fan to high speed if the condenser water temperature rises to 5.0°F above<br />
the setpoint. Turn off the fan when the condenser supply water temperature<br />
falls below the setpoint minus 2.5°F. A minimum 30-second delay is<br />
required between starting the fan at low speed and switching to high<br />
speed.<br />
Sump heater<br />
Turn on the sump heater if the sump temperature falls below 40°F (this<br />
value is adjustable at the operator display). If the outdoor air temperature<br />
falls below 32°F, turn on the sump heater continuously. If the sump<br />
temperature remains below 36°F (this value is adjustable at the operator<br />
display) for 15 minutes, or if the sump temperature falls below 32°F, indicate<br />
an alarm at the operator display and turn on the alarm output.<br />
Alarms<br />
In addition to the alarm requirements mentioned in the previous<br />
sequence of operation components, indicate an alarm at the operator display<br />
and turn on the alarm output when any temperature sensor fails.<br />
Theusermustbeabletoresetthealarmsattheoperatordisplay.<br />
Analysis of this scenario results in Figure 47 on page 49. The corresponding<br />
data definition is presented in Table 5 on page 49, and a wiring diagram<br />
is presented in Figure 48 on page 51.<br />
48 CNT-APG001-EN
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