Requirements for an air-conditioning system
An air-conditioning system supplies fresh air into a room and exhausts the contaminated air. Let us look at the following sample system:
A room contains an extractor fan and a fresh-air fan.
Each fan is monitored by means of a flow sensor.
The pressure in the room may rise above the atmospheric pressure.
The fresh-air fan may only be switched on if the flow sensor signals the safe operational state of the extractor fan.
A warning lamp indicates failure of one of the fans.
Standard solution
The fans are monitored by means of flow sensors. If no air flow is registered after a short delay time has expired, the system is switched off and an error message is generated, which can be acknowledged by pressing the off button.
Fan monitoring requires an analyzer circuit with several switching devices, in addition to the flow sensors. A single LOGO! device can replace this analyzer circuit.
LOGO!Soft Comfort solution
The use of LOGO! reduces the amount of switchgear. Thus, you save installation time and space in the control cabinet. You may even be able to use as a smaller control cabinet.
With LOGO! you can also switch off the fans sequentially after the system is switched off.
The circuit in LOGO!Soft Comfort
The system is switched on and off at the inputs I1 and I2. The fans are connected to outputs Q1 and Q2, the flow sensors are connected to the inputs I3 and I4. Blocks B007 and B008 are used to set the watchdog times after which the flow sensors should send a signal to the fault output Q3.
You can invert output Q3 to use output messages at Q4. Relay Q4 only drops out if main power is lost or if there is a fault in the system. The output can then be used for a remote message.