county hall bp ae mcc7-1 des ops (rev3 - record)_2

7/27/2019 County Hall BP AE MCC7-1 Des Ops (Rev3 - Record)_2

1/13

Description of Operation

Project and Controls Details:

Project Title: County Hall BP AE 6th Floor Refit

Orlanix Project Reference(s): MCC7-1

Orlanix System Description: AHU7-1, AHU 7-2, and Secondary Chilled Beam CCT Pumps

Orlanix System Reference(s): TE/200/902

Specification Reference(s): MEIT MD812 / Jan 2008 (County Hall 6th Floor Cat B Fit-Out)

System Description: MEIT Specification 9 (Automatic Controls)

Panel Reference(s): MCC7-1

Controller Manufacturer(s): Trend Controls

Type / Model: IQ251

Associated Documentation: TE/100/902 - BMS Points and Equipment ScheduleTE/130/902 - Control Valve ScheduleTE/601/902 - MCC Wiring Diagram

Document Index:

Introduction to System Description of System, and Associated Components

Pre-Requisites for System Operation - Hand/Auto Operation, and System Interlocks

System Times - Occupancy Times, and Optimisation Settings

Temperature and Environmental Control Routines - Heating/Cooling

Fabric and Environmental Protection - Water, Frost, Legionella, etc (Scope as Applicable to SpecificPlant/Control Details)

Energy Conservation Control Routines - Free Cooling and Heating, Enthalpy Control, etc (Scope asApplicable to Specific Plant/Control Details)

Miscellaneous Control and Monitoring Ancillary System Alarms, Energy Metering, etc

Health and Safety Functionality Life Safety Systems, and Environmental Systems Cause and Effect

Summary of Control Application Tables and Schedules of: Control Set Points, Times/Dates,Operational Statuses, Configuration Settings, User Adjustable Settings,

Master Doc: TE/202/902Page 1 of 13

Rev: 03 (Record)Date: May 2009


2/13


Introduction to System

The 2off Air Handling Units (AHUs) are supplied and/or manufactured by ECE Ltd, and are positioned in theplant area located on the 7th floor.

The AHUs are electrically powered, and controlled, via a form 2, type 2 Motor Control Centre (MCC); projectidentified as MCC7-1.

The MCC houses all motor starters, controls, and ancillary devices (network display panel, etc) necessary forproviding motive power and control functionality for the AHUs, and associated ancillary plant and services.

In particular the control section of the MCC houses Trend IQ series BMS controllers, which provide the directdigital control functions (DDC) necessary to monitor and control the plant items and ancillary, field mounted,devices.

Each AHU is mechanically comprised of the following components:

Fans:

1off Supply fan with associated scroll/impeller assembly

1off Extract fan with associated scroll/impeller assembly

Motors:

1off Supply fan motor

1off Extract fan motor

Motor Starters:

2off Side section mounted variable speed drives (VSDs)

Dampers:

1off Fresh air opposed blade type isolation type damper section c/w open/close type damper

actuator

1off Extract air opposed blade face/bypass type damper section c/w with modulating type damper

actuator

Thermal Controls, Pumps, and Associated Valve/Actuators:

1off LTHW Frost Coil c/w 2-Port Control Valve / Modulating Type Actuator

1off CHW Cooling Coil c/w 2-Port Control Valve / Modulating Type Actuator

1off LTHW Reheat Coil c/w 2-Port Control Valve / Modulating Type Actuator

Filters:

2off Supply air filters (bag and panel type)

1off Extract air filter (panel type)




3/13


Miscellaneous Items:

Misc noise attenuation sections

Misc access sections

Manometer(s)

Packaged sump pumps (2off)

AHU pod lighting




4/13


Pre-Requisites for System Operation

In order for the AHUs to operate a number of power supply, and control, pre-requisites must be satisfied.

These items and operational conditions are as follows:

Supply Fan - Starting and Stopping

Hand Operation

In order for the fan to operate the following conditions must be proven:

I. All safety interlocks (typically: motor isolators, fan overloads, VSD status, fire alarm signals,override switches, frost stat ccts, pod door interlocks, damper positions, etc) must be in theirnormal operational condition.

II. The Hand-Off-Auto switch on the front fascia of the MCC must be switched to the Handposition (and/or the Hand Icon on the relevant BMS pc graphic page must be initiated).

Auto Operation

In order for the supply fan to operate the following conditions must be proven:

I. All safety interlocks (typically: motor isolators, fan overloads, VSD status, fire alarm signals,override switches, frost stat ccts, damper positions, pod door interlocks, etc) must be in their

normal operational condition see MCC diagrams for full details of interlock circuitry.

II. The Hand-Off-Auto switch on the front fascia of the MCC must be switched to the Autoposition.

III. The associated BMS controller programmable time schedule for the unit must be registering ascheduled period of occupancy (and/or a user demand signal may be sent via the BMS pc, orvia the MCC display screen overriding the unit on).

On confirmation that the conditions in the list above have been met the fan is enabled via the BMS controller.

After the enable signal has been initiated the fan has its running status proven (after a suitable graceperiod; via the operation of, and associated feedback signal from, a duct mounted differential pressure

switch.

Extract Fan - Starting and Stopping

Hand Operation

In order for the extract fan to operate the following conditions must be proven:

I. All safety interlocks (motor isolator and overloads, fire alarm signal, overrideswitches, pod door interlocks, etc) must be in their normal condition see MCC diagramsfor full details of interlock circuitry.

II. The Hand-Off-Auto switch on the front fascia of the MCC must be switched

to the Hand position (and/or the Hand Icon on the relevant BMS pc graphic page must beinitiated)




5/13


Auto Operation

In order for the extract fan to operate the following conditions must be proven:

I. All safety interlocks (typically: motor isolators, fan overloads, VSD status, fire alarm signals,override switches, frost shutdown, pod door interlocks, damper positions, etc) must be in theirnormal operational condition.

II. The Hand-Off-Auto switch on the front fascia of the MCC must be switched to the Auto

position.

III. The associated BMS controller programmable time schedule for the unit must be registering ascheduled period of occupancy (and/or a user demand signal may be sent via the BMS pc, orvia the MCC display screen overriding the unit on).

On confirmation that the conditions in the list above have been met the fan is enabled via the BMS controller.

After the enable signal has been initiated the fan has its running status proven (after a suitable graceperiod; via the operation of, and associated feedback signal from, a duct mounted differential pressureswitch.

System Timed Operation (Occupancy Times)

The 6th Floor AHUs are started and stopped according to a user adjustable time schedule, this scheduleresides in the associated BMS controller, and may be adjusted as required from the network display panel(IQVIEW), located on the front fascia of the MCC, or via the main BMS supervisor pc (subject to the correctuser level codes being available for system access).

In general the plant items, and associated services, conform to the following control strategy:

Optimised / Timed Start Core Operating Hours Optimised / Timed Stop

The core operating hours are as detailed in the operational timed schedule (see summary section at end ofthis document for further details):

During system commissioning the operational time schedule, and associated set-points, will initially be set tothe settings detailed in the summary tables located at the end of this document (or as subsequently advisedby the system users representatives): -

Note: The days, times, and some of the system set points scheduled are user adjustable, and aretherefore indicative only at time of document publication; as they may be subsequently changed bythe system users, and/or their system maintenance representatives.

Plant Optimisation (Start/Stop)

The controlled plant operates on an optimised start/stop (OSS) routine. This allows for the plant to start up to2hrs prior to occupation, or to shut down up hr prior to the end of occupation (if required). The OSS will beinitiated such that the space reaches a set point of -1 oC from the actual space set point (i.e. if the space set

point has been programmed for 21oC then the OSS will aim to achieve a space set point of 20 oC immediatelyprior to the scheduled occupancy, and vacancy, times).




6/13


Note: In order for correct operation of the thermal and environmental control routines the relevant plant

and/or medium for heating, cooling, humidity control etc, must be functional/available (i.e. LTHW, CHW ,etc).

On start up the supply, and extract fan shut-off dampers are driven to their open positions, and positivefeedback of the damper status is obtained via the damper actuator end switches operating. This action alsoenables the associated fan VSD for operation, and hence starts the respective fan motor at its minimumspeed setting initially set to 15hz (subsequent supply and extract fan speed tracking takes place; with theresultant extract fan volume having an offset applied, to reduce its volume from that of the supply fan).

Subject to the above start-up sequence taking place as programmed; one of the following modes ofoperation will then commence:

There will be three available normal start-up modes depending on space/outside temperature conditions.

I. Boost warm-up mode

II. Boost pre-cool mode

III. Normal mode

When the plant is enabled, under Optimum Start mode, the AHU will initially be started in a boost mode, thiswill be based on the average space temperature compared to outside temperature.

I. Boost Warm-Up Mode

If the average space temperature is greater than 5 oC below the desired occupancy set point, the AHU will bestarted in a boost warm-up mode. During this mode the supply air temperature will be limited to 26 oC and theassociated on-floor VAV terminal units will be driven to the Vmax position via a global commandOnce the desired space temperature has been achieved the AHU will revert to Normal mode.

II. Boost Pre-Cool Mode

If the average space temperature is greater than 5 oC above the desired occupancy set point and the outsideair is above 7oC, the AHU will be started in a boost pre-cool mode. During this mode the supply airtemperature will be limited to 11oC, the AHU will be in full fresh air mode and the associated on-floor VAVterminal units will be driven to the Vmax position via a global command. Once the desired space temperaturehas been achieved the AHU will revert to Normal mode.

III. Normal Mode

If the average space temperature is less than 5oC above or below the desired occupancy set point the AHUwill be started in normal mode.

Fan Failure Condition

If a healthy running signal is not received from either fan 30 seconds after being enabled; termed as thegrace period, or if the flow proven signal is lost during normal operational conditions, then a critical alarmnotification occurs at the associated BMS controller (for transmittal to the local display panel, and the BMSsupervisor pc). A manual reset will be required to re-enable the failed fan once the fault has been rectified.

Should either fan fail to start, the AHU will enter shutdown mode and the associated chilled beam valves willbe driven closed.




7/13


Temperature and Environmental Control Routines

Once the supply and extract fans have been proved to be running, as detailed above, then the temperaturecontrol routines, and associated controls devices, are enabled.

Heating Demand Signal

A heating demand signal is sent to the primary heating plant once either AHU heater battery signal reaches ademand level =/>10% for a period 1 minute. Should this condition occur, and the heating plant is deemed tobe in a healthy condition, then the heater battery will be controlled via the dictates of its own control loop.

This primary heating plant enable signal shall remain in an active state until the AHU heater battery control

demand signal has been inactive for a period of 10 minutes.

Frost Heater Battery Temperature Control

The frost heater battery is controlled via a 2-term (P+I) control loop in order to maintain a minimum off coiltemperature set point of 5oC; this value is user adjustable via the BMS. A duct mounted temperature sensor,mounted downstream of the battery elements, measures the off element air temperature in order to maintainthis temperature setting. If the outside air temperature is at 4oC or lower during the plant start sequence, thefrost coil will be driven to 100% open, prior to allowing the fresh air damper to open. Provided the off coiltemperature is above set point with the dampers open to fresh air, the frost coil control loop will revert to itsnormal operating mode.

Cooling Demand Signal

A cooling demand signal is sent to the primary cooling plant once the AHU cooling battery demand signalreaches a demand level =/>10% for a period 1 minute. Should this condition occur, and the cooling plant isdeemed to be in a healthy condition, then the cooling battery will be controlled via the dictates of its owncontrol loop.

Supply Air temperature control.

Cooling and Re-heat Valve Temperature Control

The main re heat control valve is controlled sequentially along with the cooling valve via 2-term control loops(P+I) in order to maintain a controlled supply air set point of 11 oC; this value is user adjustable via the BMS.

Note: the supply air set-point is compensated to allow for a nominal 1oC system gain, as the chilled beamsactually require a nominal supply air temperature of 12oC

Should the supply air temperature rise 2oC above the desired set point an alarm will be initiated on the BMS.

If the on-floor VAV terminal units are all at Vmin, indicating the area is unoccupied without a coolingrequirement, the supply air set point shall be increased to 18oC.

Thermal Routine Dead Band

A dead band of 2oC (+/- 1oC) is programmed into these thermal control routines, to prevent huntingoccurring between the heating and cooling functions of the unit.

Re-cuperator Control




8/13


The re-cuperator fitted to the AHU is an aluminium fixed block type unit, fitted with face / bypass damper, and

will be controlled in sequence with the cooling and reheat coils.

The recuperative effect is obtained by the thermal transfer that takes place when air of differingtemperatures passes into and out of the re-cuperator unit. If the temperature differential, between supply andextract air, is of sufficient magnitude then a significant free cooling, (or heating) effect will be obtained.

This in turn can help energy costs by scaling back the overall demand for mechanically induced heating orcooling; as the requirements for heated or cooled water through the respective coils will be reduced.

Fan Speed Control

Located within the distribution supply ductwork (as associated with each AHU) is a static air pressure sensor.The supply air fan inverter is controlled via a 2-term (P+I) control loop in order to maintain the desired static

pressure set point of 275pa; this value is user adjustable via the BMS.

The extract fan inverter is controlled to maintain a fixed volume, with a reduced off-set relative to that of thesupply fan.

The supply and extract fans are ramped up to the desired speed under the pressure control loop. Uponreaching 30Hz, a global signal is transmitted to enable the relevant VAV terminal units.

The chilled beam circuit mixing valve will remain in the bypass position, until the AHU is proven operational.

Note: further details of these components, their settings, and locations, are required in order to refine thecontrol routine for this element of the plants operation.

High Space Temperature Purge (Unoccupied)

In high temperature conditions, if the temperature within the space, as measured by the wall mounted spacesensor, rises to 28C, or above, and free cooling is available (Outside air temperature is between 4-12Clower than the space condition), the AHU will be started in full fresh air mode, with the supply air temperaturelimited to a minimum value of 11C.

Purge operation will be inhibited if outside air temperature is below 7C.

No cooling demands will be transmitted during the purge operation, the AHU fans will operate at maximumspeed with the associated VAV terminal units set to Vmax via a global command.

The AHU will continue to run until a maximum space temperature of 22C is achieved, at which point the

plant will revert to normal shutdown mode.

Frost Protection Shutdown

An auto reset frost thermostat is fitted to the system; positioned directly after the frost coil. This device ishardwired into the AHU control circuit, at the MCC, and will shut down the air handling unit supply fan, andclose the supply and extract dampers, on sensing an inlet duct temperature of approx 3 oC.

Note: This shutdown operation is a hardwired function, is operational 24hrs, and will operate even if the AHUis running under hand control.

Frost Protection Reset

The frost thermostat will automatically reseton detection of a temperature rise to a point above its switchingdifferential (set at 2oC). Once this has been achieved the air-handling unit will return to its normal mode ofcontrol; as operationally programmed at the time.




9/13


Note: In these conditions, prior to start-up, the frost coil will have been pre-loaded. This will have been

achieved by the frost coil valve having been driven fully open during the frost condition; and the resultantheating demand starting the associated LTHW pumps. This series of cause and event actions shouldprevent occurrences of nuisance tripping of the frost stat when the fans re-start.

The historical alarm condition will be maintained on the BMS (for information purposes, and to aidtroubleshooting) until a manual alarm reset is instigated by the relevant system user or maintenancepersonnel.

Secondary chilled water circuit (Chilled Beams)

The secondary chilled water circuit is mechanically comprised of the following components:

Duty/standby pump-set c/w integral VSDs

Plate heat exchanger Pressurisation unit

3-port mixing valve

2-port pressure relief valve

Pre-Requisites for System Operation

In order for the Secondary Chilled Water pumps to operate a number of power supply, and control, pre-requisites must be satisfied.

These items and operational conditions are as follows:

Secondary Chilled Water pumps - Starting and Stopping

Hand Operation

In order for the duty selected pump to operate the following conditions must be proven:

I. All safety interlocks (typically: motor isolators, VSD status, pressurisation unit, condensationalarm, override switches, etc) must be in their normal operational condition see MCCdiagrams for full details of interlock circuitry.

II. The Hand-Off-Auto switch on the front fascia of the MCC must be switched to the Handposition orthe Hand Icon on the relevant BMS graphic page must be initiated.

Auto Operation

In order for the supply fan to operate the following conditions must be proven:

III. All safety interlocks (typically: motor isolators, VSD status, pressurisation unit, condensationalarm, override switches, etc) must be in their normal operational condition see MCCdiagrams for full details of interlock circuitry.

IV. The Hand-Off-Auto switch on the front fascia of the MCC must be switched to the Autoposition.

V. The associated BMS controller programmable time schedule for the unit must be registering ascheduled period of occupancy (and/or a user demand signal may be sent via the BMS pc, or

via the MCC display screen overriding the unit on).




10/13


On confirmation that the conditions in the list above have been met the pump is enabled via the BMS

controller.

After the enable signal has been initiated the pump has its running status proven (after a suitable graceperiod); via the operation of, and associated feedback signal from, a pipe mounted flow switch.

Start Sequence

i. Enable duty secondary pump at minimum speed (15Hz)ii. Once flow is proven, enable secondary circuit temperature controliii. Enable secondary circuit pressure control.

Stop Sequence

i. Shut 3-port mixing cooling valve to by-pass and disable temperature control loop.ii. After a time delay of 60secs, stop the duty pump and disable the pressure control loop.

Pressure Control

The chilled beam circuit pressure differential set point is fixed (to be determined on site at the commissioningstage by others).

The duty pump speed demand is modulated between 15Hz and 50Hz, to maintain a constant dischargepressure, and are monitored for run, fault, speed, and hours run.

The pumps are duty/standby and will auto changeover on a weekly basis and if the duty pump has failed.

Should both pumps fail the system will be shutdown an alarm raised and a manual reset will be required torestart the system.

In addition, the secondary circuit differential pressure set point (as measured across the secondary chilledwater flow and return pipework serving the chilled beam circuit) is maintained at a pre-determined setpoint(via the BMS controller) by modulating the 2-port automatic control valve installed across the flow and returnpipe-work.

Temperature Control

When the system is been enabled and flow has been proven, the secondary chilled water flow temperature iscontrolled via the 3-port mixing valve to maintain the desired set point of 12oC.

Should the temperature fall to 10oC or below for a period of more than 5 minutes the chilled water valve willbe closed to the by-pass position.

Miscellaneous Control and Monitoring Ancillaries Items(Miscellaneous System Alarms, Fire Event Cause and Effect, Leak Detection, Energy Metering, etc)

Air Filter Alarms

The AHU filter sets are monitored via their respective differential pressure switches. When any filter becomessufficiently dirty to cause a significant differential pressure to occur across it then the output from itsassociated differential pressure switch will change state. This action causes the BMS to raise an alarm onMCC display panel, and also at the BMS supervisor pc.

This alarm condition is intended to act as a warning to maintenance personnel, for action as, and when,appropriate. It should be noted that when an alarm (or a number of alarm events) of this type is raised the air




11/13


handling unit will continue to operate in its normal condition (i.e. such an alarm event does not disable or

change the current operational status of the AHU).

Pressurisation Unit Alarms

The ChW pressurisation unit is monitored for a common fault condition via the BMS controller (via on boardOEM VFCs within the units controls cubicle).

On receipt of a fault condition status, the BMS will signal an alarm condition to the system operators via theBMS pc graphics and/or the MCC display screen.

In addition, the pressurisation unit fault circuit is hardwired interlocked with the operation of the pump sets;such that a fault condition on the pressurisation unit will cause the pump sets to be disabled from operation.

This system disable condition will prevail, until such times as the cause of the pressurisation fault isinvestigated / corrected, and a reset on the OEM controls cubicle is carried out (also required via the BMS).

Valve Exercise Routine

All valves shall be subject to a regular exercise routine; and as such each will be driven to their fully open,and closed, positions for two complete cycles on a daily basis (exercise routine instigated at each dailyscheduled plant shutdown).

VAV Electric Re-Heater Fans Run-On Timer

To prevent possible nuisance tripping occurrences on the electric re-heaters associated with some of theVAV units, the main AHU fans will continue to run for a period of 5-10mins; as timed from the last point that a

terminal unit electric heating signal is present. Dependent on specific requirements for each project, this runon timer control action is a function of either the main plant BMS controller, orvia an inter-network trafficsignal between the associated terminal unit(s) BMS controller(s), and the associated main plant BMScontroller.

Plant Items Running Hours

The pumps, and fan, motors, operational running hours are calculated in the BMS software, via recording ofthe associated dp switches operational status (i.e. the cumulative time that each items associated dp switchis recorded as being in the healthy / running position).

Power Fail Conditions

In the event of a general power supply failure, which impacts on the plant and services controlled via theBMS, the system will either shut-down immediately (i.e. if no power available for plant operation), or it willenter a controlled shutdown sequence (i.e. example; the power to one fan motor is interrupted), generally asdetailed above.

On re-instatement of power the system will reinitiate a controlled start-up sequence and proceed to effectcontrol of the plant and services in line with the control sequence detailed above.

Fire Alarm Conditions

On receipt of a fire alarm signal at the MCC - a hard wired signal received via a locally mounted fire systemInput/Output (I/O) unit - the AHU and associated plant items will be shut down immediately; stopping bothfans, and closing the relevant system dampers.

The unit will remain in the fire shutdown state until; the fire alarm condition is cleared (i.e. the I/O shutdownsignal is removed when the fire system returns to a healthy condition, or some form of manual intervention isachieved; such as maintenance personnel overriding the I/O unit signal by some other means).




12/13


Once the fire alarm system has been reset at the buildings fire command centre the BMS will automaticallyrestart the plant in its, time and temperature dependent, normal operational mode, providing all other safetyinterlocks and switches are in their normal condition.

The MCC BMS controller monitors the fire condition status, as indicated by the I/O unit, to prevent alarmmismatches, and routine testing/nuisance alarms, from being generated at the display panel and BMSsupervisor pc.

Fire Override (Firemans Switch) Future Option (If / As Installed By Others)

At time of writing there is no firemans override switch installed; however, the MCC relay logic will beconfigured such that the following operational sequences are available, should this be required at some point

in the future:

Auto Mode - Plant operates normallyOff Mode - Plant is off Extract Mode - Plant operates as follows:

Supply damper remains closedExtract face / bypass damper drives into full extract position (actuator end switch operates)Extract fan only starts, and runs at full speed

Summary of Control Application

Note that the figures detailed are subject to ongoing amendments during final commissioning, and

post contract end-user / system maintenance adjustments

Weekly Schedule of Occupancy Times:-

Schedule of Control Set Points:-

Schedule of Devices Operational Control:-



Mon Tue Wed Thurs Fri Sat Sun

08:00 08:00 08:00 08:00 08:00 08:00 OFF

18:00 18:00 18:00 18:00 18:00 18:00 OFF

Static Pressure Set Point 275 Pa

Supply Air Temp Set Point 11 Deg C (12Deg Cwith system off-set)

Supply Air High Temp Set Point 13 Deg C

Frost Supply Temp Set Point 5 Deg C

R/H Set Point 50% @ 23 Deg C


13/13



R 03 (R d)

Plant Item Mode of Operation

System Status: Normal SystemStart-up

NormalOperation

Normal SystemShutdown

Fire Shutdown

Supply Fan Starts Running Stops Stops

Extract Fan Starts Running Stops Stops (Can Run In Manual / ExtractOnly if Firemans Switch Installed)

Supply / ExtractAir Dampers

Opens Open Closed Closed

Face / BypassAir Damper

Face Modulating By pass Face

Frost Coil Valve Closed (bypass) Modulating Closed (bypass) Closed

ChW Coil Valve Closed (bypass) Modulating Closed (bypass) Closed

Reheat Coil Valve Closed (bypass) Modulating Closed (bypass) Closed

county hall bp ae mcc7-1 des ops (rev3 - record)_2

Documents