SEQUENCE OF OPERATION

1)  FAN COIL UNITS ON/OFF Type with return Temperature sensor

Each Fan Coil Unit shall consist of a supply fan and a cooling coil complete with a 3 port On/Off control valve and a filter section.

The FCU’s will be controlled via wall mounted Temperature controller type XXX. A remote return air temperature sensor situated in the common return air path shall sense the actual return temperature and shall compare the actual temperature with its preset set point. The controller shall in turn sequence the On/Off control valve to open or close therefore maintaining the required room temperature. A 3 speed selector switch shall be available on the controller to allow the occupant to control the Fan speed at Low, Medium and High speed options.

Drawing Reference :- ATE-STD-FCU-01

2)  FAN COIL UNITS ON/OFF Type with Room sensing

Each Fan Coil Unit shall consist of a supply fan and a cooling coil complete with a 3 port On/Off control valve and a filter section.

The FCU’s will be controlled via wall mounted Temperature controller type XXX. A Temperature sensor within the controller shall sense the actual space temperature and shall compare this with its preset set point. The controller shall in turn sequence the On/Off control valve to open or close, therefore maintaining the required room temperature. A 3 speed selector switch shall be available on the controller to allow the occupant to control the Fan speed at Low, Medium and High speed options.

Drawing Reference :- ATE-STD-FCU-02

FAN COIL UNITS – Modulating Remote set point BMS

Each FCU shall comprise of supply fan a chilled water cooling coil complete with a 3 port control valve and a filter section.

A Temperature sensor (Type TT555/1000A) situated in the return air path to each of the fan coil unit shall relay the actual temperature to a unitary DDC controller (type XXXXX).

The controller shall in turn modulate a 3 port control valve, situated on the cooling coil to maintain the required room temperature; a room potentiometer as indicated in the drawing shall be installed. It shall be possible to set a minimum and maximum change from the designed setpoint to the engineer's approval. Each potentiometer shall have a temperature setpoint, On/Off and 4-position selector switch to provide auto, 1, 2 and 3 speeds.

Rooms with more than one FCU shall have a common Potentiometer to set the same temperature. The potentiometer shall be connected to a single controller acting as a master and this controller shall signal to the other controllers within the room which shall act as a slave.

When selected in Auto position the controller shall maintain the 2nd fan speed control when the setpoint is maintained and on a demand cooling the valve shall modulate open. If the temperature continues to rise the controller shall select the higher fan speed to meet the additional cooling requirement. If the temperature falls below its setpoint, the valve shall modulate closed and the controller shall select the low fan speed.

Each of the Fan Coil Unit controllers shall be arranged to allow for remote control and temperature indication from the Building Management System.

Drawing Reference :- ATE-STD-FCU-03

FAN COIL UNITS Modulating

Each FCU shall comprise of supply fan a chilled water cooling coil complete with a 3 port control valve and a filter section.

A Temperature sensor (Type TT555/1000A) situated in the return air path to each of the fan coil unit shall relay the actual temperature to a unitary DDC controller (type XXXX).

The controller shall in turn modulate a 3 port control valve situated on the cooling coil to maintain the required room temperature; a special gold plated room potentiometer shall be installed. It shall be possible to set a minimum and maximum change from the designed setpoint to the engineer's approval. Each potentiometer shall have a temperature setpoint, and 4-position selector switch to provide Off 1, 2 and 3 speeds.

AHU – SINGLE ZONE

Each AHU shall comprise of supply and extract fans??? each with variable speed drives (VFD) controlled by differential pressure sensors, a chilled water cooling coil complete with a 3 port control valve, a Fresh Air Damper and a filter section.

Temperature Control

A duct temperature and Humidity sensor Type( xxx ) situated in the common return air shall relay the actual return temperature to a DDC controller Type (XXXXX), the controller shall compare this with its internal set point and on a demand for cooling shall modulate in a linear fashion the 3 port control valve on the cooling coil or in the event of heating the controller shall modulate a Thyristor unit controlling the electric duct heater battery to maintain the required return air temperature .

A duct temperature and Humidity sensor Type ( xxx ) located in the common supply duct shall in the event of over cooling limit the control valve to protect the system from over cooling.

The VFD shall also be controlled to vary its speed according to the cooling demand within the controlled space. The fresh air damper will adjust its position according to the speed of the VFD to supply the required fresh air.

A potentiometer with on/off switch shall be provided for setpoint adjustment and remote on/off of AHU. (non-circulating AHU’s only)

Humidity Control

A Duct Temperature and Humidity sensor Type( xxx ) situated in the common return air shall relay the actual return temperature to a DDC controller Type (XXXX), the controller shall compare this with its internal set point and on a demand for dehumidification shall modulate in a linear fashion the 3 port control valve on the cooling coil to bring the system into a dehumidification cycle, during this period in the event of the system over cooling the controller shall modulate the Thyristor unit controlling the electric duct heater battery to maintain the required return air temperature.

Air flow Sensing

A differential pressure switch (PA-930-xx) situated across the supply fan shall be interlocked with the controls such that in the event of a fan failure it will cut off the electric heater battery and the valve shall return the fully closed position the supply/exhaust fan motor will be switched off and an alarm will indicate an air flow failure alarm on the control panel. The same will be relayed back to the BMS terminal for indication of a priority maintenance alarm condition.

Dirty Filter Indication

A differential pressure switch (PA-930/xx) situated across the filter section shall monitor the filter condition and shall on a dirty filter condition indicate in the control panel a dirty filter alarm. The same will be relayed back to the controller for indication of maintenance alarm condition in the BMS terminal.

The Duct Temperature and Humidity sensor situated in the common supply duct will measure the actual supply temperature and relative humidity and this can be monitored on the BMS.

A Duct Smoke detector provided in the supply duct will sense the smoke and will shutdown the AHU in case of fire condition. The same will be relayed back to the controller for indication of critical alarm condition in the BMS.

The immersion temperature sensor situated in the common supply and return chilled water lines to the AHU will indicate the actual temperature back to the BMS

Drawing Reference :- ATE-STD-AHU-05

AHU – MULTI ZONE (Feeding to VAV’s)

Each Multizone AHU shall comprise of supply and extract fans each with variable speed drives (VFD) controlled by differential pressure sensor in the supply air duct, a chilled water cooling coil complete with a 3 port control valve, and a filter section.

Temperature Control

A duct temperature and Humidity sensor Type( xxx ) situated in the common supply air shall relay the actual supply temperature to a DDC controller Type (XXXX), the controller shall compare this with its internal set point and on a demand for cooling shall modulate in a linear fashion the 3 port control valve on the cooling coil or in the event of heating the controller shall modulate a Thyristor unit controlling the electric duct heater battery to maintain the required supply air temperature .

Humidity Control

A Duct Temperature and Humidity sensor Type( xxx ) situated in the common return air shall relay the actual return temperature to a DDC controller Type (XXXX), the controller shall compare this with its internal set point and on a demand for dehumidification shall modulate in a linear fashion the 3 port control valve on the cooling coil to bring the system into a dehumidification cycle, during this period in the event of the system over cooling the controller shall modulate the Thyristor unit controlling the electric duct heater battery to maintain the required return air temperature.

Pressure Control

A pressure sensor (type PA267-300) situated in the common supply air duct and one on the common exhaust duct shall sense the actual pressure and relay this to a DDC controller (type XXXX), the controller shall signal to the respective VFD to maintain a constant pressure in the duct at all times. If there is a change of state on any of the VAV terminal units the duct pressure shall maintain a constant pressure. The fresh air damper will adjust its position according to the speed of the VFD to supply the required fresh air.

A pressure switch (typePA980—) situated across the supply fan shall be interlocked with the controls and shall indicate an airflow failure on the relevant control panel in the event of an airflow failure and shall also signal an alarm condition to the BMS.

A differential pressure switch (type PA980—) situated across the filter shall indicate on the control panel in the event of a dirty filter condition shall also signal a maintenance alarm condition to the BMS.

In addition to the above, in the event of a fire condition signaled from the fire panel, all controls shall be shut down and the fan shall stop and a priority alarm shall be signaled to the BMS.

Air flow Sensing

A differential pressure switch (PA-DL4.5K) situated across the supply fan shall be interlocked with the controls such that in the event of a fan failure it will cut off the electric heater battery and the valve shall return the fully closed position the supply/exhaust fan motor will be switched off and an alarm will indicate an air flow failure alarm on the control panel. The same will be relayed back to the BMS terminal for indication of a priority maintenance alarm condition.

Dirty Filter Indication

A differential pressure switch (PA-DL4.5K) situated across the filter section shall monitor the filter condition and shall on a dirty filter condition indicate in the control panel a dirty filter alarm. The same will be relayed back to the controller for indication of maintenance alarm condition in the BMS terminal.

The Duct Temperature and Humidity sensor situated in the common supply duct will measure the actual supply temperature and relative humidity and this can be monitored on the BMS.

Drawing Reference :- ATE-STD-AHU-06

Fire and Smoke

A Duct Smoke detector provided in the supply duct will sense the smoke and will shutdown the AHU in case of fire condition. The same will be relayed back to the controller for indication of critical alarm condition in the BMS.

The system shall also be interlocked with the Fire alarm system such that in the event there the fire system detects an alarm condition the system shall shut down the AHU. The same will be relayed back to the controller for indication of critical alarm condition in the BMS.

Chilled Water Indication

The immersion temperature sensor situated in the common supply and return chilled water lines to the AHU will indicate the actual temperature back to the BMS

VAV Terminal Units

Each terminal unit shall be controlled as follows

A temperature sensor (type TT555/1000A) situated in the return air path shall relay the actual return air temperature to a unitary DDC controller (type XXXX). The controller shall in turn sequence the VAV actuator to modulate open on a demand for cooling to maintain the required room temperature. The controller shall include a differential pressure transducer and built in air velocity sensor to measure the average differential pressure in the duct. The controller shall convert this value to actual airflow.

Each controller shall also incorporate an algorithm that allows for resetting of the associated air handling unit discharge temperature to satisfy space-cooling requirements. This algorithm shall function to signal the DDC Controller to perform the required discharge temperature reset in order to maintain the space temperature cooling setpoint.

VAV UNITS with re-heater

These units shall have an electric heater battery and the controller shall on an a requirement for heating open the damper to the necessary level and the controller shall modulate the Thyristor on the heater battery to maintain the set temperature within the controlled space. The heater output shall be interlocked such that if there is insufficient airflow the heater will not be allowed to operate. The heater output shall also be interlocked with the potentiometer switch inside the room to switch off the heater when the Off position is selected. The heater battery shall also be protected by a factory fitted high limit cut-out supplied by the heater manufacturer.

Drawing Reference: - ATE-STD-VAV-04

FAN COIL UNITS