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Sequence Of Operation SOO for HVAC Systems

Below is a typical sequence of operation for the HVAC system & equipments like packaged units, Fan Coil Units, Split Units, Extract fans, Kitchen Extract fans and general ventilation fans etc. This sequence of operation is demonstrated by using the BMS building management system software during testing & commissioning of the project.

Below information is useful for HVAC engineers in order to develop a new sequence strategy or to understand how the HVAC equipment is synchronized with each other.

Package Air Conditioning Unit (PACU) for Substation’s, LV/HV Room


The unit shall consist of:

1 Package assembly (evaporator, condenser, filters) complete with control panel.

2 Sensors and controls (refer to BMS Schematic Diagram)

The HV and LV switch rooms shall be cooled by means of ducted Package Air Cooled Unit (PACU) located outside (rooftop of Substation) of the rooms and shall be set to operate continuously to maintain the rooms at the set point of 24 °C (adjustable) via a the inbuilt Package unit Display. In the event of a failure of either of the PACU, an alarm shall be provided via the BMS. The BMS shall control and monitor the PACU’s start/stop operation from DDC to VCF at PACU control panel. An independent temperature and humidity sensor shall be provided connected to the BMS for monitoring purposes only which shall raise an alarm via the BMS in the event of the set points being exceeded.

Monitor the status and alarm condition of each PACU by independent monitoring and linking into integral controls as supplied complete with the package unit.

A fire alarm interlock shall be hard wired into the control circuit of the fans to ensure that they shut down in an alarm condition.

General Exhaust Systems / Kitchen Exhaust System

Gen. Exhaust Fans:       Various Locations

The unit shall consist of:

1 Fan assembly

2 Attenuators (as required only)

3 Sensors and controls (refer to BMS Schematic Diagram)

The Extract Fan systems will operate under the dictates of one of the DDC controller inbuilt time schedules (adjustable) to suit the school operation requirement thru volt free contact (VFC) from fan control panel and control in the following manner.

When called on to operate the respective fan damper will be driven to the fully open position and when the inbuilt damper feedback confirms this, the fan will be enabled.

Indication of fan running is provided by means of a differential air pressure switch fitted across the fan which will alarm in the event of failure. Individual indication of “fan trip” and “switch not in auto position” will be provided through the DDC controller.

A graphical representation of the plant will be produced with all set points, alarms and time schedules displayed with simple mouse clicks. Access to the graphic will be through a system of site plans, plant rooms and systems.

All values are to be historically recorded at controller level so that locally any laptop or Portable operator’s terminal may retrieve the data as well as the network BMS Supervisor.

A fire alarm interlock shall be hard wired into the control circuit of the fans to ensure that they shut down in an alarm condition.

Toilet Extract Fans

The unit shall consist of:

1   Package Fan assembly complete with control panel

2   Sensors and controls (refer to BMS Schematic Diagram)

The system shall comprise of roof mounted package twin extract fan unit (duty/standby) serving toilets.

The unit shall have the facility of adjustable time program demand from the BMS.

The duty extract fans shall enable to run if the following conditions are satisfied:-

Damper position

Start / Stop command

Dfan Trip alarm and fan status

The fire alarm signal is not active.

The toilet extract fans shall be arranged for duty-standby operation with weekly duty rotation to ensure equal running of each fan.

A differential pressure switch installed across the unit shall monitor flow, and in the event of flow failure the duty extract fan, an alarm shall be raised at the BMS and the standby fan shall then be enabled.

A fire alarm interlock shall be hard wired into the control circuit of the fans to ensure that they shut down in an alarm condition.

Transformer Room Ventilation

Exhaust Fan & Motorized Dampers: Substation Room

The Transformer room ventilation system is comprising of exhaust fan complete with distribution ductworks, intake louvres with motorized dampers and room thermostat.

The Transformer rooms shall be ventilated only. In the event of the room temperature exceeding a pre-set limit initially set at 10˚C above ambient condition (adjustable), the DDC shall signal the extract fan thru volt free contact (VFC) with proof of operation sensed via the differential pressure switch located across the positive and negative sides of the impeller. In the event of a failure of the fan operation, an alarm shall be raised on the BMS.

In the event fire, an alarm from Main Fire Alarm panel or the clean agent gas extinguishing panel shall send the signal to BMS (DDC) to stop the extract fan operation and shall close the motorized smoke fire curtain damper to fully seal the Transformer room as required by the type of room automatic extinguishing system.

Smoke Clearance (Auditorium/Gym Stage Area)

Smoke Extract Fans:

Motorized Dampers:      Various Locations (refer to Mech. and Elect. Drawings)

The system will provide 14 m3/s smoke clearance rate on Stage area in the event of a fire.

The smoke extract system will operate in response to the signal from the fire detection system. The system will utilize the air conditioning system return duct (fire rated construction) as smoke extract duct. On fire mode, the normally open (NO) motorised fire smoke damper (MSFD) connected to the return duct of AHU shall close by Fire Alarm Panel and the MSFD connected to the smoke extract fan side shall open thru volt free contacts (VFC) through Fire Alarm Panel to effect the smoke route and discharge to outside. All other motorised smoke dampers (MSD) connected to return duct serving other areas shall closed to effect the smoke extraction in Stage area only.

The make-up air is source thru the wall openings beneath the stage floor complete with MSFD and Sand trap louvre. Air outlet openings in front of the stage area sized at least to deliver 1.5 m/s air velocity to ensure that that the make-up air will not disturb the smoke flume pattern. The motorised fire and smoke damper of make-up air louvre shall open upon a receive of signal from Fire Alarm Panel.

A fireman’s override panel shall be provided in the Fire Command room which shall allow the Fire Brigade to override the automatic system and switch on/off the fans. All switches on the Fireman’s panel shall be key operated and red and green indicator lamps provided to confirm if fans are operating.

FCU Controls

The system shall be 3 speed volume package Fan Coil Unit either ceiling exposed (free blow), ceiling concealed (ducted) or wall mounted. The unit shall consist of following:

1 Cooling Coil

2 Fan

3 Washable Air Filter

4 Drain Pan (with optional drain pump if required)

5  Sensors and controls (refer to BMS Schematic Diagram)

BMS shall start/stop the FCU thru FCU controllers (DDC) and shall be standalone. These controllers will be pre configured to control the cooling valve (thru 0-10 VDC) at the desired temperature to the satisfaction of their space/return air temperature detectors as applicable.

All fan coil units shall be controlled by an individual DDC controllers being provided with an individual room/space wall mounted intelligent controllers with thermostatic, fan speed, and time schedule functions. Where it is not possible to have a space mounted thermostat controller the fan coil units shall be controlled based on wall mounted or return air mounted sensors at the discretion of the engineer.

The BMS DDC shall modulate the valve based on the difference of the space temperature and desired set-point. The BMS shall switch the FCU’s (on/off) based on preset programmable time schedule. The speed adjustment shall be controlled by the controller in Auto mode. All room unit controllers will also allow the user to override the system on/off. All fan coil units shall be disabled on receipt of signal from the fire alarm system.

Split Air Conditioning Unit / Direct Expansion (DX) Unit

IDU / ODU : Various Locations

The unit shall consist of:

Package indoor (evaporator) and outdoor (condenser) assembly complete with control panel

Provide monitoring, control and power to the split air conditioning units.

Each linked indoor and outdoor unit system will be controlled from a remote mounted proprietary controller supplied and wired by the system installer. A volt free contact (VFC) shall be made available from the control panel to DDC.

Allow for control by BMS the following functions:-

Start / Stop command

A fire alarm interlock shall be hard wired into the control circuit of the fans.


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