Set Temperature Mode Function Block

This function automatically calculates the effective temperature control mode based on the control type, system switch setting, network mode command, temperature set points, supply temperature and space temperature.

EffTempMode indicates the current Mode determined by input states and arbitrated by control logic. The valid enumerated values have the following meanings:

effTempMode

Meaning

COOL_MODE = 0

Cool air is being supplied to the node via the central air supply, and cooling energy is being supplied to the controlled space.

REHEAT_MODE = 1

Cool air is being supplied to the node via the central air supply. The air is being reheated by a local Heat source.

HEAT_MODE = 2

Heated air is being supplied to the node via the central air supply, and heated air is being supplied to the controlled space.

EMERG_HEAT = 3

Emergency Heat is being supplied to the node via the central air supply.

OFF_MODE = 255

A controller is commanded off.

 

 

 

 

 

 

 

 

 

Figure 1: SetTemperatureMode Function Block

Figure 2: SetTemperatureMode Property Sheet

Inputs

Input Name

Description

SysSwitch

System switch-This input comes from wall module. Users will be able to switch to Auto, Cool, Heat, Emergency Heat , off modes.

0 = Auto

1 = Cool Mode

2 = Heat Mode

3 = Emergency Heat Mode (Emergency Heat is being supplied to the node via the central air supply.). Emergency Heat, also known as "auxiliary heat", is the second stage of heat that your thermostat runs on when the temperature is too cold for your heat pump to extract heat from the outside. Emergency Heat is triggered when it is 35 deg F and below outside.

Emergency heat should really be switched on by the users in emergency situations, when something happens to the first stage heat source "heat pump".

255 = Off Mode.

Numeric: 32-Bit Integer value 0, 1, 3, 255. Default: Null

CmdMode

CmdMode- This input comes from operator. From the supervisor operator can command to Auto, Heat , Cool, Emergency Heat , off modes.

0 = Auto

1 = Heat Mode

2 = Cool Mode

3 = Off

4 = Emergency Heat Mode

255 = Off Mode.

Numeric: 32-Bit Integer value 0, 1, 3, 4, 255. Default: Null

SupplyTemp

Supply Temperature-This input is used in VAV applications to switch the temperature mode based on supply temperature.

If the supply temperature is less than 70 °F / 21 °C, then VAV box will switch to cool mode.

Else if supply temperature is greater than 75 °F / 24 °C, then VAV box will switch to heat mode.

Else VAV box will switch to cool, heat, reheat based on room temperature , effective heat and cool setpoint.

Numeric: 32-Bit Floating value -50-150°C or -58-302°F Default: Null

SpaceTemp

Space temperature.

Numeric: 32-Bit Floating value -50-150°C or -58-302°F Default: Null

EffHeatSp

Effective heat set point.

Numeric: 32-Bit Floating value -50-150°C or -58-302°F Default: Null

EffCoolSp

Effective cool set point.

Numeric: 32-Bit Floating value -50-150°C or -58-302°F Default: Null

AllowAutoChange

AllowAutoChange-This is the binary input used to allow temperature mode change based on additional validations.

Application will be written to make sure cooling coil is completely closed before switching to heat mode or vice versa using this input.

0 = Don't Allow Auto Change

1 = Allow Auto Change.

If allowAutoChange = 1 then allow to switch between HEAT_MODE and COOL_MODE. Must have valid effHeatSP and effCoolSP. If allowAutoChange = 1 and effHeatSp > effCoolSp, then effHeatSp will be internally set to effCoolSP.

Numeric: Binary value 0, 1, Default: Null

Table 1: Inputs of Set Temperature Mode Function

Output

Output Name

Description

EffSp

Effective setpoint.

It is a calculated setpoint derived by its temperature control modes.

If effTempMode=COOL_MODE then val= effCoolSetPt, else val=effHeatSetPt.

Numeric: 32-Bit floating point value, 0-255.

EffTempMode

Effective temperature mode.

0 = Cool Mode

Cool air is supplied from a network workstation or a node via the central air supply and cooling energy is supplied to the controlled space.

1 = Reheat Mode

Cool air is supplied from a network workstation or a node via the central air supply. The air is reheated by a local Heat source.

2 = Heat Mode

Heated air is supplied network workstation or a node via the central air supply and heated air is supplied to the controlled space.

3 = Emergency Heat Mode

Emergency Heat is supplied network workstation or a node via the central air supply.

Numeric: 32-Bit integer point value, 0-3.

Table 2: Output of Set Temperature Mode Function


Parameters

Parameter Name

Description

AllowAutoChange Par

Occupancy sensor

0 = Don't Allow Auto Change

1 = Allow Auto Change.

If allowAutoChange = 1 then allow to switch between HEAT_MODE and COOL_MODE. Must have valid effHeatSP and effCoolSP. If allowAutoChange = 1 and effHeatSp > effCoolSp, then effHeatSp will be internally set to effCoolSP.

Numeric: Binary value 0, 1, Default: Allow Auto Change

ControlType

ControlType.

0 = CVAHU (Constant Volume Air Handling Unit)

Constant air volume (CVAHUV) is a type of heating, ventilating, and air-conditioning (HVAC) system. In a simple CVAHU system, the supply air flow rate is constant, but the supply air temperature is varied to meet the thermal loads of a space

1 = VAV (VAV stands for variable air volume, it is a device used to control flow of air to space. It shuts air supply to minimum flow once temperature in room is reached. )

Basic difference between CVAHU and VAV Box

The CVAHU boxes are mainly used in the small buildings as they are less expensive. Whereas, the VAV box provides variable air inside a building. The temperature of the air is constant and similar as the control unit delivers.

Property Value: CV-AHU, VAV, Default: CV-AHU

Out Save

Master Sync Enabled : If you set it to "true" the last output will be set as output for one cycle after the controller restarts. The application can use it to return to the same state before the controller restart.

Eff Sp: To enable or disable the Effective Setpoint feature.

Eff Temp Mode:To enable or disable the Effective Temperature Mode feature.

Table 3: Parameters of Set Temperature Mode Function

Figure 3: CVAHU Arbitration Logic

Figure 4: VAV Mode Arbitration Logic

Examples

  1. SysSwitch = Auto, ControlType = 1 (VAV), CmdMode = Auto, SupplyTemp =68°F, SpaceTemp=70°F, EffHeatSp =68°F, EffCoolSp =75°F, EffectiveSp will be EffCoolSp and effTempMode is COOL i.e. If SupplyTemp <70°F, effTempMode will be On Cool Mode.

  2. SysSwitch = Auto, ControlType = 1(VAV), CmdMode = Auto, SupplyTemp =68°F, SpaceTemp=70°F, EffHeatSp =68°F, EffCoolSp =75°F, EffectiveSp will be EffCoolSp and effTempMode is HEAT i.e. If SupplyTemp >75°F, effTempMode will be On Heat Mode.

  3. SysSwitch= Sscool, ControlType = 1(VAV), CmdMode = Auto, SupplyTemp =60°F, SpaceTemp=56°F, EffHeatSp =68°F,EffCoolSp =75°F, EffectiveSp will be EffCoolSp and effTempMode is COOL i.e. If SupplyTemp >75°F, effTempMode will be On Heat Mode.

  4. SysSwitch= Sscool, ControlType = 1(VAV), CmdMode = Auto, SupplyTemp =80°F, SpaceTemp=60°F, EffHeatSp =68°F, EffCoolSp =75°F, EffectiveSp will be EffHeatSp and effTempMode is HEAT i.e. If SupplyTemp >75°F, then effTempMode will be On Heat Mode.

    Note: If the system is in COOL Mode and SpaceTemp < EffHeatSp & SpaceTemp < EffCoolSp - 1, system goes to reheat mode. If the system is in Reheat Mode and SpaceTemp > EffCoolSp & SpaceTemp > EffHeatSp + - 1 system goes to cool mode

Refer to General Description for general information about IRM N4 Function Blocks.