McQuay ART7 Installation Manual

Operation Manual

MicroTech Applied Rooftop Unit Controller: CAV-ZTC Control

Programs ART5 and ART7

Dehumidification/Reheat Control Sequence

OM 109 Supp. #1

Group: Applied Systems Part Number: 629960Y

Date: May, 1998

Contents

Introduction .................................................................................................................................................. 3

Dehumidification Enable/Disabled .............................................................................................................. 3

Occupied Dehumidification ......................................................................................................................... 3

Dehumidify from Cooling/Economizer ................................................................................................ 3

Dehumidify from Heating ..................................................................................................................... 4

Dehumidify from Fan On/Fan On Heat ................................................................................................ 4

Unoccupied Dehumidification ..................................................................................................................... 4

Dehumidify from Unoccupied Cooling/Unoccupied Economizer ........................................................ 4

Dehumidify from Unoccupied Heating ................................................................................................. 5

Dehumidify from Off Unoccupied ........................................................................................................ 5

Dehumidification Unit Configuration ......................................................................................................... 6

Dehumidification Cooling With Compressors ............................................................................................ 8

Dehumidify from Cooling/Economizer ................................................................................................ 8

Dehumidify from Fan On/Fan On Heat/Heating ...................................................................................9

Dehumidify from Off Unoccupied/Unocc. Cooling/Unocc. Economizer/Unocc. Heating .................. 9

Dehumidification Cooing With Chilled Water .......................................................................................... 10

Dehumidify from All Possible States .................................................................................................. 10

Heat/Reheat Control ...................................................................................................................................10

Configuration #1 ..................................................................................................................................10

Dehumidify from Economizer/Unoccupied Economizer/Cooling/Unoccupied Cooling ............. 10

Dehumidify from Heating/Unoccupied Heating ........................................................................... 11

Dehumidify from Fan On/Fan On Heat ........................................................................................ 11

Dehumidify from Off Unoccupied ................................................................................................12

Configuration #2 ..................................................................................................................................12

Configuration #3 ..................................................................................................................................12

Dehumidification Menu items ................................................................................................................... 13

Inputs/Outputs ............................................................................................................................................ 14

CAV-Zone Temperature Control w/Return Air .................................................................................. 14

CAV-Zone Temperature Control w/100% Outside Air ...................................................................... 15

Dehumidification Compressorized Staging Sequences ............................................................................. 16

Input Schematic ......................................................................................................................................... 20

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INTRODUCTION

This document describes the sequence of operation of the dehumidification sequence incorporated into the standard Constant Volume Zone Control (ART5 & ART7) software packages.

A DX or chilled water cooling coil is controlled to cool the air low enough to wring out moisture. Reheat is then supplied as necessary to provide properly conditioned air to the space. Although the unit will most likely have an optional space temperature installed, the dehumidification sequence does not require one. The unit reheat is always controlled to maintain the Menu # 12 “Cntl Temp=” input at the reheat set point. Generally the unit would have an optional space temperature sensor installed and this parameter would be set to “Space”. From this point forward in this document it is assumed that “Cntl Temp=Space”. When dehumidification is not required the unit operates as described in operation manual OM 109.

An humidity sensor is mounted in either the space or return air to sense relative humidity. The sensor is wired to field terminals 101, 126 and 127 as shown on the attached input schematic. Terminals 126 and 127 are factory wired to analog input AI12 on the unit ADI board. This signal from the humidity sensor to the ADI board varies from 0-5VDC as the humidity varies from 0-100% RH. Dew point is calculated using this RH value and either the space or return air temperature depending on the location of the humidity sensor. Relative humidity and dew point are both displayed on Menu # 10 of the keypad (“Humidity=” and “Dew point=”). Dehumidification control parameters are located on Menu # 18. "Humidity" or "Dew point" can be selected as the type of humidity control (“Control=“). "Space" or "Return" can be selected for the location of the humidity sensor (“Sensor=”). Note: “Space” cannot be selected if the “Space Sensor=” parameter on Menu 28 is set to “No”. A relative humidity set point and dead band (“Humidity Spt=” and “Humidity DB=”) and dew point set point and a dead band (“Dewpt Spt =” and “Dewpt DB=”) are also adjustable through Menu #18. Refer to the “Dehumidification Menu Items” section of this document for a listing of all menu items added related to dehumidification operation.

DEHUMIDIFICATION ENABLE/DISABLED

The dehumidification function is enabled or disabled through Menu # 18 (“DehumidCntl=”). Setting this parameter to “No” disables and “Yes” enables dehumidification. Caution: This parameter should never be set to “Yes” unless the unit can be classified as one of the three configurations described in the “Dehumidification Unit Configuration” section of this document.

Dehumidification is disabled if mechanical cooling is disabled for any reason. It also is disabled if heating is disabled for any reason except outside air temperature lockout. Refer to Menu #7 (Cool Status) and Menu #8 (Heat Status). Dehumidification is allowed if heat is disabled due to high OAT since it may be required during warm periods.

OCCUPIED DEHUMIDIFICATION

The unit is allowed to enter the Dehumidify state from the following “occupied” operating states: Fan On, Fan On Heat, Economizer, Mechanical Cooling or Heating. Dehumidification operation is initiated when the humidity/dew point rises above the set point by more than the dead band. Refer to Figure 4 (ART5) and Figure 5 (ART7) for sequence charts showing the possible transitions in and out of the Dehumidify state.

Dehumidify from Cooling/Economizer

If the humidity/dew point rises above the set point by more than the dead band while the unit is in either the Economizer or Mechanical Cooling state, the unit enters the Dehumidify state in which dehumidification cooling is turned on and reheat is controlled to maintain the space temperature at the reheat set point (Menu 14 “Reheat Spt=”). This set point is not adjustable from the keypad but is set equal to the zone cooling set point (Menu 12 “Cooling Spt=” ) by the controller. When both the humidity/dew point set point and the reheat set point are satisfied, the unit will leave the Dehumidify and enter the Fan On state. Note: The unit can leave the Dehumidify and enter the Mechanical Cooling state under certain conditions if the unit has DX cooling (refer to the “Dehumidification Cooling With Compressors” section of this document). While in the

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Dehumidify state, the outside air dampers are driven fully open if the outside air enthalpy is suitable for free cooling. Otherwise the dampers are driven to minimum position.

Dehumidify from Heating

If the humidity/dew point rises above the set point by more than the dead band while the unit is in the Heating state, the unit enters the Dehumidify state in which dehumidification cooling is turned on and reheat is controlled to maintain the space temperature at the reheat set point (Menu 14 “Reheat Spt=”). This set point is not adjustable from the keypad but is set equal to the zone heating set point (Menu 12 “Heating Spt=” ) by the controller. When both the humidity/dew point set point and the reheat set point are satisfied, the unit will leave the Dehumidify and enter the Fan On state. While in the Dehumidify state, the outside air dampers are driven to minimum position.

Dehumidify from Fan On/Fan On Heat

If the humidity/dew point rises above the set point by more than the dead band while the unit is in the Fan On or Fan On Heat state, the unit enters the Dehumidify state in which dehumidification cooling is turned on and reheat is controlled to maintain the unit discharge temperature at the reheat set point (Menu 14 “Reheat Spt=”). This set point is not adjustable from the keypad but is set equal to the fan on heating set point (Menu 14 “Fan On Htg=” ) by the controller. When the humidity/dew point set point is satisfied, the unit will leave the Dehumidify and enter the Fan On state. While in the Dehumidify state, the outside air dampers are driven to minimum position.

If the space temperature should rise above the zone cooling set point (Menu 12 “Cooling Spt=”) while the unit is in this “Dehumidify from Fan On/Fan On Heat” operating mode, the unit will change to the “Dehumidify from Cooling/Economizer” operating mode.

If the space temperature should fall below the zone heating set point (Menu 12 “Heating Spt=”) while the unit is in this “Dehumidify from Fan On/Fan On Heat” operating mode, the unit will change to the “Dehumidify from Heating” operating mode.

UNOCCUPIED DEHUMIDIFICATION

The default dehumidification parameters on Menu # 18 are set so that the unit will not provide dehumidification during unoccupied time periods. If unoccupied dehumidification is desired, the Menu # 18 parameter “UnocDehumid=” must be set to “Yes”.

When unoccupied dehumidification is enabled, the unit is allowed to enter the Dehumidify state from the following “unoccupied” operating states: Off Unoccupied, Unoccupied Heating, Unoccupied Economizer or Unoccupied Cooling. The unit enters the Dehumidify state if the humidity/dew point rises above the set point by more than the dead band. If the unit is in the Off Unoccupied state, it will start up and enter the Dehumidify state. Unoccupied dehumidification operation is the same as occupied dehumidification except that dehumidification cooling is cycled off and the unit leaves the Dehumidify state as soon as the humidity/dew point set point is satisfied even if the reheat set point is not yet satisfied.

Dehumidify from Unoccupied Cooling/Unoccupied Economizer

If the unit is in the Unoccupied Economizer or Unoccupied Cooling state and the humidity/dew point rises above the set point by more than the dead band, the unit enters the Dehumidify state. Unoccupied dehumidification operation is then similar to that describe above for occupied “Dehumidify from Economizer/Cooling” except the outside air dampers are fully closed if the outside air enthalpy is high rather than driven to minimum position.

When the humidity/dew point set point is satisfied, dehumidification cooling is cycled off and the unit leaves the Dehumidify state and enters the Off Unoccupied state even if the reheat set point is not satisfied.

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Dehumidify from Unoccupied Heating

If the unit is in the Unoccupied Heating state and the humidity/dew point rises above the set point by more than the dead band, the unit enters the Dehumidify state. Unoccupied dehumidification operation is then similar to that describe above for occupied “Dehumidify from Heating” except the outside air dampers are fully closed rather than driven to minimum position.

Dehumidify from Off Unoccupied

1) If the unit is in the Off Unoccupied state and the space temperature is above the occupied zone cooling set point (Menu 12 “Heating Spt=” ) at the time the humidity/dew point rises above the set point by more than the dead band, the unit starts up and enters the Dehumidify state. Unoccupied dehumidification operation is then similar to that describe above for occupied “Dehumidify from Economizer/Cooling” except the outside air dampers are fully closed if the outside air enthalpy is high rather than driven to minimum position.

2) If the unit is in the Off Unoccupied state and the space temperature is below the occupied zone heating set point (Menu 12 “Heating Spt=” ) at the time the humidity/dew point rises above the set point by more than the dead band, the unit starts up and enters the Dehumidify state. Unoccupied dehumidification operation is then similar to that describe above for occupied “Dehumidify from Heating” except the outside air dampers are fully closed rather than driven to minimum position.

3) If the unit is in the Off Unoccupied state and the space temperature is between the occupied zone cooling and heating set points (Menu 12 “Cooling Spt=” and “Heating Spt=” ) at the time the humidity/dew point rises above the set point by more than the dead band, the unit starts up and enters the Dehumidify state. Unoccupied dehumidification operation is then similar to that describe above for occupied “Dehumidify from Fan On/Fan On Heat” except the outside air dampers are fully closed rather than driven to minimum position.

OM 109 Supplement #1 / Page 5

DEHUMIDIFICATION UNIT CONFIGURATION

The dehumidification function can be configured to control one of three different heat/reheat/cooling unit arrangements:

Configuration # 1 Unit has one heat source downstream of cooling coil. This heat source functions as

both the primary unit heat and the dehumidification reheat (refer to Figure 1).

Configuration # 2 Unit has a primary heat source upstream of the cooling coil and a dedicated

dehumidification reheat source downstream of cooling coil (refer to Figure 2).

Configuration # 3 Unit has a primary heat source and a dedicated dehumidification reheat source

downstream of cooling coil (refer to Figure 3).

This configuration is set up through two parameters in Menu #18.

1) “DedRHCfg=” defines whether or not the unit has a source of heat that is dedicated to reheat. If the unit is Configuration # 1, this parameter is set to “None”. If the unit is either Configuration # 2 or Configuration # 3, this parameter is set to indicate the type of dedicated reheat. If the dedicated reheat is modulating, this parameter is set to “Modulating”. If the dedicated reheat is staged, this parameter is set to Stage 1, Stage 2, Stage 3, Stage 4, Stage 5, Stage 6, Stage 7 or Stage 8, depending on the number of dedicated reheat stages. Note: More than 2 stages of dedicated reheat requires reheat staging board hardware. In order to change this parameter in the field, the user is prompted to enter a password before the value can be changed. To enter the password, the user must press “ENTER”, “ENTER”, “-“, “-“ on the unit keypad. This password is different than the standard keypad password.

2) “Supplmntl RH=” defines whether or not the standard unit heat should supplement the dedicated reheat during dehumidification if the reheat source is insufficient to meet the reheat requirements. If the unit is Configuration # 1 or Configuration # 2, this parameter should be set to “No”. If the unit is Configuration # 3, this parameter can be set to “Yes” and the standard heat will supplement the reheat in the event that the reheat source cannot meet the reheat requirements.

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