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CP-Open Global Libraries Documentation

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Comfort Point Open - Global Library Documentation

APPLICATION DOCUMENTATION

PAC-AHU-SZ-005 (Pacific Application)

Table of Contents

1. System Synopsis ................................................................................................................................................. 2

2. Schematic .......................................................................................................................................................... 2

3. Theory of Operation ............................................................................................................................................ 3

4. Sequence of Operation ........................................................................................................................................ 3

5. Zone Temperature Control ................................................................................................................................... 9

6. Zone Temperature Alarm ................................................................................................................................... 14

7.

Version History ................................................................................................................................................. 15

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1. System Synopsis

This is a single zone air cooled heat pump fan coil unit with four stages of cooling and four stages of reverse cycle

heating.

Temperature control is from a zone temperature sensor.

Manual day extension of the air handling unit is included as a standard feature.

The control strategy also includes separate fire override facilities for general and zone fire alarms.

2. Schematic

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3. Theory of Operation

This application uses heating & cooling P + I control loops to stage the fan coil unit air cooled heat pump

compressor stages On and Off from a temperature sensor located in the area or zone served by the unit.

4. Sequence of Operation

Time Schedule Control

The unit is activated from a dedicated time schedule within the Honeywell DDC Controller, as detailed in thefollowing table.

Day Of Week Occupied Time Unoccupied Time

Monday 0800 1800

Tuesday 0800 1800

Wednesday 0800 1800

Thursday 0800 1800

Friday 0800 1800

Saturday - -

Sunday - -

Day Extension Control (After Hours)

A dedicated push button is provided to allow the plant to be activated outside of occupied times.

When pressed, the button will activate the unit for an operator adjustable period of 2 hours.

Once activated the day extension may be cancelled by the operator by pressing the button a second time.

The day extension function will not operate during normal occupied times.

An output is provided which will activate during day extension mode and drive an indicator to inform the operatorthat the plant is running in day extension mode.

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Fire Mode Override Control

The signals for the Fire Mode Control System are derived from the main fire indicator panel and are wired to theDDC panel.

General Fire Alarm (Supply Air Fan Stop)

A general fire alarm typically represents a shutdown scenario!

When the fire indicator panel initiates a general fire alarm condition the following control action will occur:-

a) The supply air fanwill be commanded Off.

b)

The unit heat pump compressor outputs are de-energised.

Zone Fire Requiring Smoke Exhaust (Supply Air Fan Start)

The fire indicator panel will discriminate between fire conditions in each area served by individual AHUs, theseareas are referred to as Fire Zones.

The fire indicator panel may place the plant (Fire Zone) in to a smoke exhaust condition; a smoke exhaustcondition will take precedent over a general fire alarm condition.

When the fire indicator panel initiates a smoke exhaust condition the following control action will occur:

a) The supply air fanwill be commanded On.

b) The unit heat pump compressor outputs are de-energised.

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Plant Mode

The operating mode for the fan coil unit plant is displayed in a Multistage Value point called xxxxPlantMode(where xxxxrefers to the actual plant name). All of the main operating functions for the plant are controlled by

xxxxPlantMode.

There are up to 32 possible values for xxxxPlantModehowever not all modes are used in this application.

The modes used in this application are displayed in the following table.

Nr Mode Comment

03 UnOccupied Time Scheduled Control Unoccupied Mode

05 Occupied Time Scheduled Control Occupied Mode

06 Day Extension After Hours Mode

18 User Defined 6 (Delayed start) Power Fail Delayed Restart Mode

29 Fire_Off General Fire Alarm

30 Smoke_Exh Zone Fire Alarm

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Temperature Control Mode

The temperature control mode for the air handling plant is displayed in a Multistage Value point calledxxxxTempCtlMd (where xxxx refers to the actual plant name). The operating functions for the temperature

control plant are interlocked with xxxxTempCtlMd.

There are up to 5 possible values for xxxxTempCtlMdhowever not all modes are used in this application.

The modes used in this application are displayed in the following table.

Nr Mode Comment Enable Condition

01 Disabled Heating and Cooling Disabled All remaining plant modes and low ambient lockout

03 Clg Cooling only enabled

Plant Mode 02,05,06 and 07 (Optimise start in

cooling, Occupied, Day extension and Optimise start

in heating) with HtgSP/ClgSP switching reference

and depending on the low ambient lockout status

04 Htg Heating only enabled

The heating and cooling mode change operation is detailed in the following diagram:

HtgSP ClgSP

Zone temperature

Deg C

TempControl

Mode

Clg Mode

Htg Mode

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Low Ambient Lockout Control

If the temperature control mode is in Cooling Mode and the ambient temperature is less than the low ambient lockout setpoint, the temperature control mode will be overridden and will be switched to Disabled. In this mode the

heat pump will not be available for cooling.The low ambient lockout control will take priority over the zone temperature override for cooling mode.

The low ambient lockout mode change to Disabled operation is detailed in the following diagram:

The low ambient lockout control of the temperature control mode will initially be set up with the following defaultvalues:-

Set Points

a) Low limit 8.0C

b) Hysteresis 2.0K

Low OaTempLimit SP

Outside Air temperature

Deg C

Clg Mode Disabled

Clg Mode Available

+Hyst

TempControl

Mode

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Fan Fail Alarm

A fan failed alarm is generated whenever there is a mismatch between the fan start-stop signal and the fan statusinput. An adjustable delay will prevent nuisance alarms from occurring.

Blocked Filter Alarm

A differential pressure switch is connected across the supply air filter assembly. The switch must be calibrated(when air flow is present) to detect a pressure drop which corresponds to a blocked filter condition. The switchprovides a digital input to the DDC which will be used to generate the blocked filter alarm.

A blocked filter alarm will be raised at any time if the differential pressure switch has been activated continuallyfor a period of 300 seconds.

Once activated, the alarm will be latched until manually reset using the dedicated blocked filter alarm reset point.

FCU Start-up

Whenever the unit is called to run the supply air fan will start and the fan coil unit will operate under fullautomatic control.

FCU Shutdown

Whenever the unit is turned off the following control action will occur:-

a) The unit heat pump compressor outputs are de-energised.

b) The air handling unit supply air fan will be commanded Off.

c) The unit heat pump reversing valve is switch to the Cooling position.

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5. Zone Temperature Control

Whenever the supply air fan is commanded On, and the correct status input has been received, the unit thermal

control system is Enabled.The air handling unit is provided with separate Cooling and Heating setpoints.

The unit heat pump compressors are controlled in sequence to maintain the required zone temperature set pointvalue.

When the zone temperature falls below the heating set point the heat pump reversing valve will be switched tothe heating position and the compressor stages will be sequentially enabled. When the zone temperature risesabove the heating set point the compressor stages will be commanded off.

When the zone temperature rises above the cooling set point the heat pump reversing valve will be switched tothe cooling position and the compressor stages will be sequentially enabled. When the zone temperature falls

below the cooling set point the compressor stages will be commanded off.

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The operation of the heat pump compressors and the reversing valve is detailed in the following sequencediagram, the PI function will be configured with default tuning parameters as detailed in the sequence diagram

which will require adjustment (tuning) for specific conditions at the time of commissioning.The sequence diagram below shows only the proportional component of the PI control to detail the relative stagepositions.

-2.0 -1.5 -1.0 -0.5 HtgSP ClgSP +0.5 +1.0 +1.5 +2.0

Zone temperature

Deg C

ReversingValve

CompressorstagesinCooling

St 1

St 2

St 3

St 4

St 1

St 2

St 3

St 4

CompressorstagesinHeating

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The fan coil unit temperature control module will initially be set up with the following default values:-

Cooling Mode

a) Set Point 22.5C

Heating Mode

a) Set Point 21.5C

Time delays

a) Heat Pump Stage delay On 60.0 s

b) Heat Pump Stage delay Off 60.0 s

c) Heat Pump Mode change delay 120.0 s

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Discharge Air Temperature Override Control

A discharge air temperature sensor is located in the fan coil unit supply air duct work downstream of the heatpump evaporator coil. The sensor is located at a position within the duct work to ensure that the true mixed

discharge air temperature is measured at all times.

The discharge air temperature from the fan coil unit is monitored whenever the heat pump unit is enabled tooperate.

Should the heat pump unit be operating in reverse cycle heating mode and the discharge air temperature risesabove the high limit setpoint then the maximum stage output will be reduced from four to two. The overridecondition will remain active until the discharge air temperature falls to below the setpoint minus the hysteresisvalue. To prevent cycling, the lockout will remain active for at least the duration of the lockout delay time

If the heat pump unit is operating in cooling mode and the discharge air temperature falls to less than the lowlimit setpoint then the maximum stage output will be reduced from four to two. The override condition will remainactive until the discharge air temperature rises above the setpoint plus the hysteresis value. To prevent cycling,the lockout will remain active for at least the duration of the lockout delay time

Hyst Hyst

Low SP High SP

Discharge Air Temperature

Deg C

Lockout Activated

Lockout Deactivated

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The override control will initially be set up with the following default values:-

Setpoints

a) High limit Set Point 28.0C

b)

High limit Hysteresis 1.0K

c) Low limit Set Point 15.0C

d) High limit Hysteresis 1.0K

e) Lockout time period delay 300.0 s

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6. Zone Temperature Alarm

The zone temperature sensor will have alarming capability to indicate high and or low temperature alarms.

An alarm inhibit feature is provided which will allow the alarm to be active during specific times which correspondto the following plant mode values.

Nr Mode Comment

05 Occupied Time Scheduled Control Occupied Mode

06 Day Extension After Hours Mode

When the plant mode changes to a value which enables the alarm, a time delay will be invoked which must expirebefore the alarm will become un-inhibited, this delay will give the plant the necessary running time to stabilise thezone temperature and thus prevent nuisance alarming.

The air handling unit temperature alarm module will initially be set up with the following default values:-

a) High temperature alarm set point Zone cooling mode set point +2.0 Deg K

b) Low temperature alarm set point Zone heating mode set point -2.0 Deg K

c) Delay time to un-inhibit the alarm 1800 Seconds

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7. Version History

DocVersion

Date(dd/mm/yyyy)

Changes Made Author

1.0 17/04/2013 Original version Pacific Library Group

1.1 15/10/2013 Remove R100 references Update control sequence diagram references Pacific Library Group

Honeywell Confidential

This document contains information that is confidential and proprietary to Honeywell International Inc. No part of this docum ent may be

reproduced, copied, or transmitted in any form or for any purpose without express written permission of Honeywell. Any such

reproduction is expressly prohibited by law and violators will be prosecuted to maximum extent possible.

Copyright 2011 Honeywell International Inc.

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