Supply and exhaust ventilation system automation project

We have developed a project for installing automation systems for supply and exhaust ventilation.

ventilation system automation design documentation

Design of Supply and Exhaust Ventilation System Automation

The project provides for the possibility of dispatching these systems.

Main Automation Solutions

For automation, control and dispatching tasks, a set of technical means is used, which includes programmable controllers for supply and exhaust systems, drainage and sewage pumping stations, and expansion modules for exhaust systems. A local area network is provided for information exchange between controllers. Control cabinets for supply and exhaust ventilation systems and automation cabinets with built-in controllers or expansion modules are located in ventilation chambers.

Ventilation systems have 2 control modes:

  • Local control testing of power units, electric motors of fans, pumps;
  • Automatic and remote control of ventilation systems.

Switching electric motors on and off in local control mode is done by buttons located on control cabinets in ventilation chambers. To switch any unit to local control mode, set the corresponding switch or all switches on control cabinets to "Local" position. If for supply and exhaust systems at least one switch is set to "Local", then all regulation modes are disabled and only the heater freeze protection in winter mode remains active. Local control mode is used only during ventilation system debugging and in emergency cases. Automatic control for all ventilation systems is performed by the controller.

project with supply system automation operation algorithm

The system can be started:

  • Using an operator panel connected to any of the local controllers;
  • Remotely from the dispatch room with workstation.

The operator can set the ventilation system operation mode:

  • "Start" and "Stop" - turning the ventilation system on and off regardless of the time schedule;
  • "Auto" - turning the ventilation system on and off according to a set time program via timer;

"Auto" mode is the best as it doesn't require maintenance personnel intervention. To turn the ventilation system on or off during days or times not provided by the program, switch the ventilation system to "Start" or "Stop" mode.

All supply and exhaust ventilation systems operate in two modes: summer and winter. Switching between summer and winter modes is done directly from ventilation chambers by operator command from the controller or centrally from the dispatch room.

Automation cabinets with controllers provide:

  • Starting all ventilation system units in specific combination and sequence;
  • Implementation of necessary regulation and control laws, interlock dependencies; monitoring and regulation of supply air temperature in the room - based on temperature in exhaust air duct;
  • Monitoring outdoor temperature (1 sensor on building exterior, common for all systems connected to automation cabinet);
  • Monitoring return heat carrier temperature after 1st stage heater;
  • Monitoring temperature after 1st stage heater;
  • Monitoring air pressure after supply fan - to maintain design pressure value using frequency converter; monitoring temperature and humidity after irrigation chamber and in exhaust air duct;
  • Regulating absolute humidity after irrigation chamber;
  • Monitoring coarse and fine filter clogging;
  • Heater freeze protection;
  • Monitoring equipment status (local or automatic control, on or off, alarm);
  • Remote switching on and off of ventilation systems from dispatch room with workstation;
  • Interlock between supply and exhaust systems;
  • Automatic redundancy for supply-exhaust systems and backup electric motors;
  • Monitoring CO concentration in parking areas via local network.

If carbon monoxide concentration reaches 20 mg/m³ and doesn't decrease within 15 minutes, the controller issues a signal to turn on corresponding exhaust systems if they are off.

Dispatching

Transfer of alarm and technological information about technological processes to dispatch room. Turning off ventilation systems at "Fire" signal is ensured by:

  • For exhaust ventilation and thermal curtains - voltage supply to circuit breakers with independent release in distribution panels;
  • For supply ventilation and exhaust fans - turning off fan electric motor via closing contact in fan control circuit.

Local indicating instruments: thermometers and pressure gauges are provided for visual parameter control during setup and operation of ventilation equipment.

Supply and Exhaust Ventilation System Operation Algorithm

This section of explanatory notes and automation diagrams are initial data for software creation. Supply and exhaust fans of systems are equipped with variable speed drives, controlled by air quantity demand for maintaining indoor climate via pressure sensors installed in main air ducts of supply systems. Exhaust fan speeds are regulated by "master-slave" scheme depending on supply fan drive speed.

Winter Mode

Valve on cold water for systems is completely closed. System heating and unit startup sequence. After receiving system start command, controller turns on hot water circulation pump if it wasn't already on by outdoor temperature and opens valve on 1st stage heat carrier by 100%.

When air temperature after heater is above +5°C and return heat carrier temperature is above +35°C, guaranteeing heater freeze prevention, ventilation system units start in following sequence:

  • Supply fan turns on; outdoor air damper opens (electrically interlocked with supply fan);
  • After 1 minute delay, exhaust fan turns on with subsequent opening of damper on exhaust air duct, electrically interlocked with exhaust fan (interlock between supply and exhaust systems is implemented via software);
  • 10 minutes before supply fan turns on, irrigation chamber pump turns on, and turns off 10 minutes before supply fan turns off for supply systems. This keeps irrigation chamber nozzles dry on non-operating systems and significantly reduces microbe formation.
Regulation

After starting ventilation systems, valve on heat carrier switches to maintaining supply or exhaust air temperature mode: when air temperature is below normal - valve opens slightly, increasing hot water flow through heater; when air temperature is above normal - valve closes slightly, decreasing hot water flow through heater. After starting ventilation systems, valve on 1st stage heat carrier switches to maintaining constant absolute humidity mode (humidity sensor located directly after irrigation chamber):

  • When air humidity is below normal - valve opens slightly, increasing hot water flow through heater;
  • When air humidity is above normal - valve closes slightly, decreasing hot water flow through heater.

Valve on 2nd stage heat carrier switches to maintaining constant supply air temperature mode:

  • When air temperature is below normal - valve opens slightly, increasing hot water flow through heater;
  • When air temperature is above normal - valve closes slightly, decreasing hot water flow through heater.

Regulation law is proportional-integral. When air humidity in exhaust air duct >50%, irrigation chamber pump turns off if it was previously on from dispatch room. When air humidity in exhaust air duct <50%, irrigation chamber pump turns on, but only 10 minutes before supply-exhaust system turns on.

Heater Freeze Protection

Heater freeze protection operates in two ventilation modes:

  • Operating mode;
  • Standby mode.

In winter period, both in operating mode and standby mode when outdoor temperature is below +2°C, automatic monitoring of return heat carrier temperature and maintaining it at safe level is performed depending on air temperature after 1st stage heater by regulating valve position on heat carrier, while pump on hot water works constantly. In operating mode if air temperature after 1st stage heater is below +5°C or return heat carrier temperature is below +20°C:

  • Alarm signal of heater freeze threat is issued to operator on control cabinets, automation cabinets and to dispatch room;
  • Valve on 1st stage heat carrier opens 100%;
  • Supply and exhaust fans turn off;
  • Outdoor air damper closes;

Program blocks ventilation system from starting, pump on heat carrier continues working, valve controls return heat carrier temperature, maintaining it at safe level (+25°C). Restarting ventilation system is done manually by operator command from automation cabinet in ventilation chamber or remotely from dispatch room with workstation only after operator manually removes block via keyboard.

In standby mode when freeze protection thermostat activates by air (air temperature after heater drops below +5°C) or when return heat carrier temperature drops below +20°C:

  • Freeze protection activation alarm is issued;
  • Pump on hot water turns on if it wasn't already on by outdoor temperature sensor;
  • Valve on heat carrier opens;

If within 10 minutes freeze protection thermostat returns to normal and return heat carrier temperature exceeds +35°C, program cancels protection mode and ventilation system returns to standby mode. If within 10 minutes thermostat doesn't return to normal, program blocks ventilation system, pump continues working, valve maintains +25°C temperature. Unblocking ventilation system and returning system to normal state is possible by pressing "Alarm Reset" button by operator command on automation cabinets. Critical return heat carrier temperature values are specified during setup.

Summer Mode

Valves on 1st stage heat carriers are completely closed, pumps on hot water are off.

Control

These supply and exhaust systems in summer mode operate without air temperature regulation.

Supply Ventilation Units

After starting ventilation systems, valve on cold water switches to maintaining air temperature (supply or exhaust) mode. When air temperature is above normal - valve opens slightly, increasing cold water flow through cooler; when air temperature is below normal - valve closes slightly, decreasing cold water flow through cooler. Ventilation systems after starting, valve switches to maintaining constant absolute humidity mode (humidity sensor installed after irrigation chamber):

  • When air humidity is above normal - valve opens slightly, increasing cold water flow through cooler;
  • When humidity is below - valve closes slightly, decreasing flow through cooler.

Valve on 2nd stage heat carrier switches to maintaining constant supply air temperature mode:

  • When air temperature is below normal - valve opens slightly, increasing hot water flow through heater;
  • Above normal - valve closes slightly, decreasing hot water flow.

When air humidity in exhaust air duct >55%, irrigation chamber pump turns off if it was previously on from dispatch room. When humidity <55%, irrigation chamber pump turns on, but only 10 minutes after supply-exhaust system turns on. For all above-mentioned ventilation systems in winter and summer modes, regulation law is proportional-integral. Supply-exhaust ventilation systems are mutually redundant - if one system fails, another turns on. Fan electric motors are mutually redundant - if one electric motor fails, another turns on.

Automatic Supply Fan Operation

In winter and transitional mode at +5°C < outdoor air temperature < +25°C, system operates with variable quantity of recirculation air. After receiving ventilation system start command, controller starts ventilation system units in following sequence:

  • Exhaust fan turns on;
  • Recirculation air damper opens;
  • After exhaust fan turns on with 1 minute delay, supply fan turns on, interlocked with exhaust fan.

Start sequence is achieved by program via controller. Regulation. Supply-exhaust system works to maintain +12°C temperature in exhaust air duct by variable recirculation quantity. When air temperature is above normal - recirculation damper closes slightly, and exhaust air dampers open slightly, increasing outdoor air flow; when air temperature is below normal - recirculation damper opens slightly, and outdoor and exhaust air dampers close slightly, decreasing outdoor air flow. Regulation law is proportional-integral.

Summer Mode. Ventilation system unit startup sequence. In summer mode when outdoor air temperature > +25°C, system operates at 100% direct flow (outdoor and exhaust air dampers open, recirculation damper closed). After receiving ventilation system start command, controller starts ventilation system units in following sequence:

  • Supply fan turns on;
  • Outdoor and exhaust air dampers open;
  • After supply fan turns on with 1 minute delay, exhaust fan turns on, interlocked with supply fan.

Thermal Curtains

Systems operate in automatic mode according to factory supply scope. Heating units.

Possible Malfunctions and Errors

Normal operation disruption of supply or exhaust fans (possible belt break or any air circulation obstruction) is registered by differential pressure sensors.

Fan alarm is considered to have occurred if: 10 seconds after receiving fan start command or during its operation for 10 seconds, there's no response from magnetic starter; or if 1 minute after start command or during its operation for 1 minute, there's no pressure differential. In this case, start command is removed, alarm signal is issued to automation cabinet and dispatch room about system malfunction, and message that "Alarm Reset" point is switched to manual control mode.

Normal operation disruption of pumps on heat carrier and air cooling chamber: pump alarm is considered to have occurred if 10 seconds after pump start command or during its operation for 10 seconds, there's no response from magnetic starter.

Outdoor air damper position is controlled by limit switches. If 4 minutes after damper open command there's no signal from limit switch indicating its 100% opening, alarm signal is issued, and message that "Alarm Reset" point is switched to manual control mode. If current consumption of any fan or pump electric motor (thermal relay) exceeds permissible value or built-in electric motor protection thermal contact activates, then fan or pump automatically turns off. In case of any above-mentioned malfunction, ventilation system start is impossible until it's eliminated, only after that ventilation system can be unblocked by operator command from cabinet or remotely from dispatch room.

Ventilation System Operation Signaling

When connecting portable operator panel to controller, following information can be obtained from each system:

  • Supply and exhaust fan status: on and off based on fan magnetic starter contact state;
  • Normal - based on magnetic starter contact and signal from frequency converter about normal operation;
  • Alarm - based on signal from frequency converter, thermal protection relay contact state or signal from differential pressure sensor.

Pump status:

  • On and off - based on pump magnetic starter state;
  • Normal - based on magnetic starter contact;
  • Alarm - based on motor thermal protection relay contact;

Air filter status:

  • Clean and dirty - based on filter differential pressure sensor;
  • Supply and exhaust air temperature;
  • Return heat carrier temperature;
  • Outdoor air temperature (common for all systems);
  • Air pressure after supply fan for supply ventilation units;
  • Heater "freeze" threat;
  • Absolute humidity after irrigation chamber for supply systems;
  • Relative humidity of exhaust air for mechanical supply ventilation systems;
  • Outdoor, supply and exhaust air damper positions;
  • Outdoor, exhaust and recirculation air damper positions (by control signal);
  • "Local/Auto" switch position;
  • CO concentration in parking areas.

Drainage and sewage pumping station operation signaling. "Alarm" signal from drainage and sewage pumping stations is displayed on screen of portable panel connected to automation cabinet controller located in ventilation chamber.