Auto-Zone Control Systems Auto-Zone Plus User Manual

Design, Installation

Plus System

and Operations Manual

Revision 03A

Auto-Zone Plus

Design, Installation & Operations Manual

Section 1..............................................................................System Overview

Section 2...................................................................Installation and Wiring

Section 3....................................................................................Programming

Section 4....................................................... Start-Up and Troubleshooting

This document is subject to change without notice.

WattMaster Controls, Inc. assumes no responsibility

for errors or omissions herein.

Auto-Zone Plus Design, Installation & Operations Manual - Form WM-AZP-IO-03A

Auto-Zone is a registered trademark of WattMaster Controls, Inc.

Copyright 2008 WattMaster Controls, Inc.

All rights reserved.

Section 1

Table of Contents

Conventions ....................................................................................................1

General Information .....................................................................................3

Description of System Components.................................................................................5

Design Considerations.................................................................................10

Zone Diversity................................................................................................................10

Cooling - Partial Load Conditions .................................................................................10

Heating - Partial Load Conditions .................................................................................13

Override Conditions.......................................................................................................13

Building Pressurization..................................................................................................14

Design Guide ................................................................................................15

Step #1 - Zoning.............................................................................................................15

Step #2 - Sizing the Central Unit ...................................................................................18

Step #3 - Duct Design Considerations ...........................................................................18

Step #4 - Room Air Motion/Diffuser Selection.............................................................19

Step #5 - Bypass Damper Sizing....................................................................................19

Step #6 - VFD Considerations .......................................................................................20

Step #7 - Sizing Zone Dampers .....................................................................................22

Auxiliary Heat Control Options.................................................................25

Index: ............................................................................................................27

Table of Figures

Figure 1-1: Auto-Zone Plus System ..............................................................................2

Figure 1-2: Typical HVAC Unit Installation.................................................................3

Figure 1-3: Incorrect Zoning of Typical Building .......................................................16

Figure 1-4: Correct Zoning of Typical Building..........................................................17

Figure 1-5: Locating the Static Pressure Sensor..........................................................21

Table 1-1: Round Damper Sizing Chart ......................................................................22

Table 1-2: Round Damper Dimensional Data .............................................................23

Table 1-3: Pressure Independent “K” Factors..............................................................23

Table 1-4: Rectangular Damper Sizing Information....................................................24

Design Guide

Auto-Zone Plus Section 1

Conventions

This document uses the following definitions throughout as a guide to the user in
determining the nature of information presented:

Note: Additional information which may be helpful.

Tip: Suggestion to make installation, set-up, and troubleshooting easier.

Caution: Items which may cause the equipment not to function correctly but will

not otherwise damage components.

Warning: Errors which can result in damage to equipment and void warranties.

Design Guide 1-1

Section 1 Auto-Zone Plus

Figure 1-1: Auto-Zone Plus System

1-2 Design Guide

Auto-Zone Plus Section 1

General Information

The Auto-Zone Plus control system converts single-zone Constant Volume HVAC units
into variable air volume/variable temperature multiple zone systems. The microprocessor
based Zone Manager calculates the heating and cooling requirements for each zone based
on real time information received from each Zone Controller. The Zone Manager then
directs the HVAC unit to provide the appropriate amount of heating, cooling, and
ventilation to satisfy each zone's requirements. A static air pressure sensor located in the
supply duct measures air pressure and the Zone Manager controller sends a signal to
modulate a bypass damper to maintain the static pressure setpoint. The Zone Manager has
been updated with a new feature so that it can instead be configured to provide a 0-10
VDC signal output to control a Variable Frequency Drive (VFD) which in turn varies the
HVAC units supply air fan motor speed to maintain the static pressure setpoint.

Typical HVAC Unit

(Packaged or Split System)

LOCAL COMM LOOP

ZONE CONTROLLER

Above Corridor

( Preferred Location )

Zone Sensor

(4-1/2' to 5'; Shoulder Height)

TWISTED PAIR

WITH SHIELD TO

LOCAL COMM LOOP

TWISTED PAIR WITH

SHIELD TO OTHER

ZONE CONTROLLERS

OR CV CONTROLLERS

Static Pressure Pickup

(2/3 Of The Way Down Main Duct)

Supply Duct

Supply Temp Sensor

(Ahead of Bypass Takeoff)

Zone Damper and Control

( Over Corridor for Easy Service )

LOCAL COMM LOOP

ZONE CONTROLLER

TWISTED PAIR

WITH SHIELD TO

Diffuser at Perimeter Wall

(Direct Airflow Inward Towards Center of Area)

Bypass Damper

( Locate Where Easily Accessible )

Duct to Return

(Preferred)

Outdoor Air Sensor

(Mount Away From Direct Sunlight))

Zone Manager

NETWORK COMM LOOP

WITH SHIE LD TO

NEXT ZONE MANAGER

TWISTED PAIR

Return Duct

Return Temp Sensor

(Avoid Mixed Air Area)

Figure 1-2: Typical HVAC Unit Installation

Design Guide 1-3

Section 1 Auto-Zone Plus

Other new features provided with the Zone Manager controller include the ability to
control a modulating chilled water valve for cooling and/or a modulating hot water valve
or SCR electric heater for heating. This modulating cooling and/or heating requires the
addition of the OE352 2 Slot Expansion Base Board with an OE355 4 Analog Output
Board mounted on it. The base board/expansion board assembly connects to the Zone
Manager via a modular cable. The Zone Manager has the ability to control up to 2 stages
of cooling and 2 stages of heating. When more stages are required the same OE352 2
Slot Expansion Base Board can be populated with up to (2) OE357 4 Relay Output
Expansion Boards to provide up to 4 additional stages of heating and/or cooling.

This new version also has Optimal Start capabilities. A target zone can be selected as a
control point and the Zone Manager will start the system at the correct time to make sure
the zone setpoint temperature is reached according to the scheduled start time based on
the soak time that the user configures. The new Zone Manager can now also be
configured to allow control of your HVAC unit based on the heating or cooling Supply
Air Temperature.

The Auto-Zone Plus System Manager allows multiple Zone Managers to be programmed
and monitored from a central operator's panel. Single-zone constant volume rooftop
HVAC units can also be connected to the Auto-Zone Plus communication network,
allowing for both multizone and single-zone equipment to be controlled from the same
system.

Substantial savings can be realized using the Auto-Zone Plus system instead of having to
install multiple single zone Constant Volume rooftop units to accommodate multiple
zone requirements. The Auto-Zone Plus system is versatile and can be used with any
packaged roof top or indoor HVAC unit or any split system HVAC unit. It controls a
variety of terminal unit functions including pressure dependent or pressure independent
single duct terminals and series or parallel flow fan terminals.

The optional Prism color graphics software package is available to provide for on site or
remote monitoring via a personal computer.

1-4 Design Guide

Auto-Zone Plus Section 1

Description of System Components

A typical Auto-Zone Plus system is comprised of the following basic components.

System Manager
The microprocessor based System Manager allows multiple Zone Managers and any
single-zone constant volume HVAC units to be programmed and monitored from a
central operator's panel. The System Manager is connected to the Auto-Zone Plus
communication network and can be wired to any local loop connection on the system.

The System Manager is mounted in an attractive, white plastic housing, suitable for wall
mounting. A four line by twenty character backlighted LCD display and membrane
keypad provide a user friendly interface. All system variables, setpoints, and values can
be viewed and modified from the System Manager. Menu driven programming makes the
Auto-Zone Plus easy to set up and operate without the need for specialized training.

CommLink IV

The OE361-12 CommLink IV Communications Interface allows computer access into the
Auto-Zone controls system and also provides communications across multiple local
communications loops on the control system.

The CommLink IV comes packaged in an attractive beige colored plastic enclosure. The
CommLink IV is powered by a small plug-in transformer that is included. Locally, an
optional on-site personal computer with Prism software installed may be connected to the
CommLink IV to provide direct access to system control parameters. A USB cable (6 ft.
long) is provided with the CommLink IV for connection to your computer.

Design Guide 1-5

Section 1 Auto-Zone Plus

Remote telephone access to the control system can be obtained by purchasing the optional
OE419-06 Remote Link II modem. With the optional Remote Link II modem installed,
the control system can be accessed remotely by using another Remote Link II modem
(purchased separately) connected to a personal computer with Prism software installed at
the remote location. With the Remote Link installed at the job site, the CommLink IV can
be configured to call a pager or cell phone number if an alarm condition occurs.

An optional OE415-02 IP Module Kit is also available that provides an Ethernet
connection to the controls system from any computer connected to your building’s LAN.
It can also be configured to allow access to the control system from the Internet if your
Ethernet firewall is configured for this option.

Zone Manager

The Zone Manager is a microprocessor based controller which monitors up to sixteen
zones in the system. The zone manager controls the zoned HVAC unit to satisfy the
requirements of each individual zone while maintaining efficient operation and comfort.
The Zone Manager operates the fan, heating, cooling, duct static pressure, and
economizer functions. Each Zone Manager also features time scheduling, night set back,
trend logging of sensor values, and automatic changeover.

1-6 Design Guide

Auto-Zone Plus Section 1

Bypass Damper or VFD Control

A Bypass damper or Variable Frequency Drive (VFD) is used to control the duct static
pressure. When using bypass damper control, the Zone Manager sends a signal to the
bypass damper actuator to maintain duct static pressure by opening and closing a damper
in order to bypass a portion of the discharge air stream back into the return air duct of the
HVAC unit in response to the duct static pressure.

When a VFD is used, the Zone Manager sends a 0–10 VDC signal to the VFD to
maintain duct static pressure by causing the VFD to change the Supply Fan motor speed
thereby increasing or decreasing the air flow in response to the duct static pressure.
Minimum airflow requirements of the heat exchanger must be considered when using a
VFD on units that have heating. See the design section of this manual for specific
recommendations and information.

Design Guide 1-7

Section 1 Auto-Zone Plus

Zone Controller

The Zone Controller monitors space temperature and positions a damper to maintain
proper air flow to the assigned zone in order to achieve desired comfort and ventilation
levels.

If the current supply air temperature in the duct will benefit the local zone temperature
setpoint, the zone damper will modulate the air flow across the damper as needed to in
order to satisfy the setpoint temperature. If the supply air will not benefit the zone (such
as hot air in the duct when the space is calling for cooling), the controller will direct the
damper actuator to a minimum position and wait for a change in the supply air
temperature to occur that will help achieve the heating or cooling setpoint.

Constant Volume Controller

The Constant Volume (CV) Controller is a microprocessor based controller designed to
operate packaged roof top HVAC units. Up to thirteen stand alone CV controllers can be
connected to each Zone Manager's local communications loop to provide a fully
integrated multizone/single-zone control system. The CV controller operates the fan,
heating, cooling, and economizer functions. Each CV controller also features time
scheduling, night set back, trend logging of sensor values, and automatic changeover.

1-8 Design Guide

Auto-Zone Plus Section 1

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Zone Sensor

The patented zone sensor is of a flush, wall mounted design. A special plate on the face
of the sensor accurately senses space conditions. As a result of its unique design, the zone
sensor rejects the influence of internal wall temperature effects. The sensor comes in four
different configurations:

• Sensor only

• Sensor w/push-button override (Override time fixed at 2 hours)

• Sensor w/setpoint adjustment

• Sensor w/override & setpoint adjustment

Any combination of these sensor configurations can be used with the system.

Expansion Boards

The Zone Manager is designed to utilize expansion boards to provide additional
versatility to the control system. The OE352 2 Slot Expansion Base Board connects to the
Zone Manager via a modular cable and with the OE355 4 Analog Output Expansion
Board mounted on it can provide for 2 additional analog outputs to control a modulating
hot water heating valve or SCR electric heater and/or modulating chilled water valve. The
OE357 4 Relay Output Board can also be mounted on the 2 Slot Expansion Base Board
and provides for up to 6 total stages of heating and/or cooling combined when two
OE357 Boards are used.

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Design Guide 1-9

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R6

Section 1 Auto-Zone Plus

Design Considerations

Consider the following items when designing an Auto-Zone Plus system.

Zone Diversity

An Auto-Zone Plus system is designed to improve tenant comfort by dynamically re­balancing the air distribution when used with a typical constant volume rooftop
heating/cooling unit. If zones with extremely different load conditions are serviced by a
single rooftop unit, the result will be poor control and excessive wear due to cycling of
the equipment.

It is especially important to avoid mixing interior zones (which require cooling all year)
with exterior zones (which may require constant heat during winter months). If you must
mix zones under these conditions, consider using either VAV boxes with heat or separate
baseboard heat on exterior zones. Auto-Zone Plus systems offer a variety of methods to
control additional zone heat to help you avoid problems.

Group similar loads on an individual unit and use more than one zoned unit if required.
Any special loads can be handled by using separate constant volume units.

The Auto-Zone Plus system offers the designer considerable flexibility by allowing both
multiple-zoned units and single-zone units to be connected within a single simple system.

Cooling - Partial Load Conditions

The engineer must be aware of several potential problems when applying an Auto-Zone
Plus system during cold weather operation.

Low Ambient Temperature Lockout

During very cold weather it is common for mechanical systems to have “low temp
lockouts” which protect equipment from damage if operated under these conditions.
Auto-Zone Plus also provides user programmed lockouts for protection purposes,

although mechanical safeties should always be used as the final stage of protection.

If the rooftop unit services interior zones with thermal loads which require cooling when
outside temperatures are below the safe operating limits for your equipment, you should
seriously consider installing an economizer on your rooftop unit. The Auto-Zone Plus
control system is designed to take advantage of an economizer if it is installed. The use of
an economizer will save money on utilities and provide comfort under conditions when it
is not possible to operate the mechanical cooling system.

1-10 Design Guide

Auto-Zone Plus Section 1

Low Supply Air Temperatures

Under lightly loaded conditions much of the supply air may be bypassed back into the
return air side of the system. This bypassing will result in the lowering of the supply air
temperature, which may result in the supply air temperature reaching the low temp safety
limit. If the supply air low temp safety limit is exceeded, the control system will “cut-off”
the mechanical cooling to protect it from damage. Excessive cycling of the mechanical
system will result if this condition persists. Comfort may also suffer if the system cannot
run long enough to satisfy cooling demands.

A number of things can be done to reduce this problem. Some of these things depend
upon the type of installation.

• Avoid oversizing the unit. Do your load calculations carefully. Since Auto-Zone Plus

directs the heating or cooling to the zones which require it, you may find that you can
use a smaller unit in many cases. Oversizing is the number one cause of excessive low
supply air temperature cycling.

• Increase your cooling minimum airflow or damper position settings to allow more air

during cooling operation. Be careful to avoid settings which are so high you cause
over cooling of the spaces. Find a compromise position.

• Bypass the air into the plenum instead of into the return air intake. Be careful if you

use this method since you may get “dumping” of cold air from your return air grilles.
This method works best with plenum returns, do not use this method with ducted
returns unless you have carefully considered the consequences.

• Increase your static pressure setpoint to help reduce the amount of air being bypassed.

Be aware of increased noise levels and the cost of operation if you use excessive static
pressures. This will not work if you are using pressure independent zone controllers,
since they will maintain a constant flow of air to the zones regardless of duct static
pressure. This technique will likely cause over cooling of the spaces due to increased
airflows at minimum positions.

Design Guide 1-11

Section 1 Auto-Zone Plus

Warning: If the fan system has the capability of producing static pressures which

could damage ductwork you must provide a manual reset, high
pressure limit switch to cut-off the fan system in the event of high
duct static. Do not use your Auto-Zone Plus system as

a safety device!

• Use an Economizer. Although this is not a cure-all, it greatly improves operation

during cool weather when cooling loads are minimal. Using an Economizer also
improves ventilation and lowers operating costs.

1-12 Design Guide

Auto-Zone Plus Section 1

Heating - Partial Load Conditions

Heating difficulties are less common than cooling difficulties. They are similar in nature,
however, and the cures are generally the same.

• Increase the Heating minimum setpoints on as many zones as possible.

• Increase the static pressure setting as high as is practical. Increasing static pressure

does not help if you are using pressure independent operation.

• Bypass to plenum instead of the return air intake if acceptable.

• Do not oversize your equipment.

• Use auxiliary heat in either your VAV boxes or baseboard.

Caution: When using a VFD for duct static pressure control, the VFD control

must have its minimum speed setting configured to meet the minimum
airflow requirements of the installed heating equipment. This is
especially critical when using indirect fired gas heating since the heat
exchanger could be damaged if the heating airflow falls below the
minimum airflow recommended for the heat exchanger. If the unit is
equipped with electric heat, failure to meet minimum airflow
requirements of the electric heater could cause nuisance tripping of the
electric heaters safety devices. The minimum heating airflow required
for your HVAC unit should be available from your HVAC unit
manufacturer. See your VFD installation manual for information on
setting the minimum airflow.

Auto-Zone Plus has a number of auxiliary heat control options which provide solutions to
most problems. Refer to the Auxiliary Heat Control Options topic near the end of this
section.

Override Conditions

After-hours overrides can produce aggravated partial load conditions in both the heating
and cooling modes. The problem is most commonly caused by a single zone being
overridden for after-hours use. This causes the rooftop equipment to operate for only one
zone. The Auto-Zone Plus system offers an improved solution to this common problem
by allowing a single override to trigger a group of zones via a “global” override. This
allows the system to operate with sufficient load to reduce cycling caused by light load
conditions.

Design Guide 1-13

Section 1 Auto-Zone Plus

Building Pressurization

If you are using an economizer, building pressurization must be addressed. Failure to
properly handle building pressurization may result in doors remaining open when the
economizer is operating. Pressurization problems can render economizer operation
useless. The following suggestions will help to avoid potential problems.

• Use powered exhaust when the system uses ducted returns. The return duct pressure

drop will cause most barometric relief dampers to function poorly or not at all. Auto­Zone Plus has the ability to control a powered exhaust whenever the economizer is
operating.

• Use a separate building pressure control which operates a relief fan or dampers.

1-14 Design Guide

Auto-Zone Plus Section 1

Design Guide

There are seven basic steps to designing an Auto-Zone Plus system:

1. Zoning

2. Sizing the Central Unit

3. Duct Design Considerations

4. Room Air Motion / Diffuser Selection

5. Bypass Damper Sizing

6. VFD Considerations

7. Sizing Zone Dampers

Step #1 - Zoning

Determine the number of zones. A single air handler unit can have no more than sixteen
zones. If the number of zones exceeds sixteen then more than one Zone Manager will be
required.

The primary precaution to be taken in applying the Auto-Zone Plus System is to select the
zoning so that no zone will be at maximum (design) heating (or cooling) load when any
other zone requires the opposite temperature air to satisfy its load. For example,
depending on the wall, ceiling and floor material and location within the building (e.g.
top or middle floor), a typical floor of a building usually has a minimum of nine distinct
temperature or control zones that are affected uniquely by the outdoor load. These zones
are depicted in Figure 1-3 & Figure 1-4.

Depending on the size of the building and partition layout, some of these zones may
overlap or be insignificant from a zoning standpoint. For example, Zone 9 could be
multiple conference or computer rooms where additional zoning would be required, or it
could be as small as a corridor where no zoning is required. Similarly, zones 7 and 8
could have no external windows and no partitions between them and could be considered
a single zone. Zone 6 could be divided into multiple offices with full partitions between
them, thus requiring separate Zone Controllers because of different internal loads, but the
same external load.

Generally speaking, the greater the number of individual Zone Controllers, the greater the
comfort. The designer will have to look at the specific building, balancing the costs of
multiple zones with the added comfort and energy savings possible with multiple zones,
to match the building owner's requirements.

Design Guide 1-15

Section 1 Auto-Zone Plus

It is important to recognize that all buildings have some purely internal zones, such as
Zone 10, which may contain separate offices/conference/computer rooms. These internal
zones will normally have high cooling requirements year around while external zones
(1,2,3, etc.) could be at or near design heating load requirements during the winter
months. This diversity can be used (if properly zoned with multiple HVAC units serving
similar loads and zones) to save energy. However, a single HVAC unit is used to serve
zones with opposed cooling and heating demands as shown in Figure 1-3 the resulting
system will be very energy inefficient and comfort levels in the building will not be
satisfactory.

9

8

7

1

10

6

2

3

5

4

Figure 1-3: Incorrect Zoning of Typical Building

As previously mentioned, Figure 1-3 shows a misapplication of an Auto-Zone Plus (or
any heating/cooling changeover) system. Supplemental heat could be added to the
perimeter zones and controlled with the auxiliary heat control board from the Zone
Controller which would improve the performance of the system but still would not be
ideal. System performance would still generally be compromised and frequent
changeover from the heating to the cooling mode will occur during the heating season if
purely internal zones are combined on the same air-conditioning unit serving perimeter
zones.

1-16 Design Guide

Auto-Zone Plus Section 1

The best approach would be to serve the interior zones with cooling only loads with a
separate constant volume HVAC unit (that could be zoned if desired between multiple
rooms with a similar load profile) instead of zoned with perimeter zones. Also perimeter
zones with South and West exposures typically have a higher cooling load than North and
East exposures. It is best to group the South and West perimeter zones together on the
same HVAC unit and the North and East perimeter zone together on another HVAC unit.
This will provide the best energy savings, prevent the HVAC units from changing over
from heating to cooling frequently and provide the best comfort for the occupants. This
recommended ideal system is depicted in Figure 1-4. If you use this approach you will
have the best flexibility and energy saving system design that is
possible.

9

8

7

10

6

5

4

Figure 1-4: Correct Zoning of Typical Building

1

2

3

Design Guide 1-17

Section 1 Auto-Zone Plus

Step #2 - Sizing the Central Unit

Because the zones are controlled with variable air volume, it is unlikely that all zones will
be at design load at the same time. The zoning allows for the diversity of loads to be
taken into account and will often provide better comfort with a smaller HVAC unit.

In sizing the system, the individual zone loads should be calculated using any dependable
load estimating program. Because of diversity, the central unit should be selected for the
instantaneous peak load, not the sum of the peak loads, as would be done with a constant
volume single zone system. Consider the following when sizing the central unit.

• Size the peak cooling load based on the month and hour of the greatest total

building/system load.

• Heating should be sized for the lowest design temperature with an additional margin

for morning "pickup". This margin is generally recommended to be 20 to 25 percent
of base design.

Step #3 - Duct Design Considerations

The AZ Plus system uses a typical low pressure duct design. To reduce noise problems
duct pressures should not exceed 1 inch W.C.

Primary trunk ducts should not be "undersized." This is especially true for "pressure
dependent" systems. Pressure dependent refers to the typical Auto-Zone, Zone Controller
without the air flow sensor. With larger trunk ducts, it is easier to assure relatively
constant pressure to each zone. Runs should be as short as possible, and the trunk duct
system kept as symmetrical as possible to facilitate system balancing. Wherever possible,
run the trunk ducts above corridors and locate the zone dampers above corridors to reduce
the noise in the space and facilitate service of the units. Trunk ducts should be sized for no
more than 0.1 inch W.C. drop per 100 feet., and a maximum duct velocity of 2000 FPM.

Note: For pressure independent terminal units with velocity sensors and

conventional "VAV" boxes properly selected for "quiet" operation, this 2000
FPM rule can be exceeded by up to 50 percent. The designer, however, should
be very experienced in VAV system design before considering modification of
this general rule

Typical VAV systems with pressure independent terminals use the static regain method
for sizing ducts. The typical Auto-Zone Plus system is a low-pressure, pressure
dependent system that utilizes conventional unitary air-conditioning units. These systems
should use the equal-friction method of sizing the ducts, and use the maximum loss of 0.1
inch per 100 feet as described above.

.

1-18 Design Guide

Auto-Zone Plus Section 1

Step #4 - Room Air Motion/Diffuser
Selection

Air motion is a consideration for occupant comfort. The selection of diffusers for an
Auto-Zone Plus system requires more care than a constant volume system due to varying
flow of air into the zones. Slot diffusers are recommended due to their superior
performance at low air flows. Because the zone air flow is variable volume, lower cost
round or rectangular diffusers that were satisfactory for constant volume may prove
unsatisfactory with an Auto-Zone Plus system. These diffusers may result in "dumping"
of the cold air at low flows in the cooling mode, and insufficient room air motion at low
air flows in the heating mode. Although high air motion in the heating mode can be
undesirable, a slot diffuser with a high induction ratio generally helps to reduce room air
"stratification" when the heating comes from a ceiling diffuser. Linear slot diffusers
should be properly selected for the air flow and "throw" suited to the specific installation
or zone.

Additional factors to consider in diffuser selection are sound level and throw at design
flow. Generally, multiple diffusers will result in lower sound levels in the space, but this
must be balanced with the additional hardware and installation costs. It is commonly
recommended that slot diffusers be located near the perimeter or outside wall with the
airflow directed into the room. Consult your diffuser supplier or catalog for proper
diffuser sizing and location.

Series fan boxes may be used instead of zone dampers where higher induction rates are
desirable. If the heat loss on perimeter walls is high, such as large areas of glass, the use
of Series Fan Boxes may be indicated to maintain higher induction rates to offset
“downdrafts.” If the heat loss is greater than 275 BTUH/LINEAR FOOT, you should use
high quality slot diffusers next to the outer wall with the airflow directed inward to
counteract downdrafts during heating. Serious downdraft problems occur when heat
losses exceed 400 BTUH/LINEAR FOOT and both high induction diffusers and series
fan boxes are recommended.

Step #5 - Bypass Damper Sizing

Using a load calculation program, the bypass damper should be sized to give you the
maximum CFM of air to be bypassed, typically 60 to 70 percent of the HVAC units rated
capacity.

To size the damper, select a damper from the table based on calculated bypass CFM and a
maximum velocity between 1750-2250 FPM. When determining the bypass duct size, be
sure to take into account any transition fittings and associated pressure drops. (See Table
1-1: Damper Sizing Chart)

Design Guide 1-19

Section 1 Auto-Zone Plus

Whenever possible, use a single bypass damper and round duct for the bypass. If space
limitations or total airflow requires it, multiple bypass dampers can be controlled in
parallel.

For proper control of the Bypass Damper the static pressure sensor location is very
important. See Figure 1-5: Locating the Static Pressure Sensor for proper mounting
locations.

Step #6 - VFD Considerations

When using a VFD instead of a bypass damper for static pressure control, it is important
to consider the minimum fan speed that will still allow for proper airflow across the
electric heating element or gas fired heat exchanger. You should consult the HVAC unit’s
selection and design information regarding the minimum airflow that is allowed to
prevent damage to the heat exchanger in the case of gas fired equipment and prevent
nuisance tripping of the thermal safety devices when you are using an electric heater.

The VFD Controller on your HVAC unit must be configured so that the airflow never
falls below the minimum required by the heat exchanger. The WattMaster controller will
only modulate the VFD to control the fan speed in response to the static pressure setpoint
that you have set.

Also the wiring supplying the 0-10 VDC signal between the Zone Manager and the VFD
should be 18 gauge minimum 2 conductor twisted pair with shield to help prevent signal
feedback to the Zone Manager. This wire is available from WattMaster as part number
WR-LL-WG-18 or you can use Belden #82760 or equivalent wire.

For proper control of the VFD, the Static Pressure Sensor location is very important. See
Figure 1-5: Locating the Static Pressure Sensor for proper mounting locations.

1-20 Design Guide

Auto-Zone Plus Section 1

p

Preferred Location

If the trunk ducts are properly sized for
minimum pressure drop, the location of
the static pickup probe is not particularly
critical. It should ideally be located at
right angles to the airflow in a straight
section of the supply duct approximately
2/3 the distance of the total length of the
supply duct. Also the probe should be
located not less than 3 duct diameters
downstream and 2 duct diameters
upstream of any elbow or takeoff.

Less Than Ideal, But
Acceptable

Since the "ideal" location is often
difficult to find in an installation, a
location in the main trunk where the
tip is not in a "negative pressure area"
(e.g. just downstream of the inside
curve of an elbow) or an area where
the tube opening is directly impacted
by the velocity of the supply air.
Another option is to use (2) Static
Pressure Probes and tie them together
with a tee. Use equal lengths of tubing
for each sensor and run the third leg of
the tee back to the Static Pressure
Sensor. This will average the pressure
readings of the two duct runs.

Least Desirable, But Acceptable

If the supply duct comes directly from
the unit and immediately splits in
opposite directions without a curved
duct split, the pressure pickup should be
located ahead of the split, or as close to
it as possible to it, even if the bypass
damper(s) are located downstream of the
split.

Supply Air

Temp. Sensor

Supply Air

Duct

Supply Air

Supply Air

Duct

Supply Air

Temp. Sensor

Static Pressure

Sensor

Supply

Duct

Tee

Tubing To Be Equal
Length And Size

Fan

Bypass
Damper

Supply

Fan

Static Pressure

Probes

Picku

Supply

Fan

Static Pressure

Pickup Probe

Static Pressure

Pickup Probe

Bypass
Damper

Supply Air

Temp. Sensor

Static Pressure

Sensor

Bypass
Damper

Return Air Duc t

3D
Min.2DMin.

Return Air Duct

Static Pressure

Return Air Duct

Return Air
Tem p. Se ns or

Sensor

Return Air
Tem p. S en sor

Return Air
Temp. Sensor

Figure 1-5: Locating the Static Pressure Sensor

Design Guide 1-21

Section 1 Auto-Zone Plus

Step #7 - Sizing Zone Dampers

Use a load program to determine the peak load for each zone. These calculations will be
used in selecting the appropriate zone damper sizes. WattMaster can provide either round
zone dampers or rectangular zone dampers for your zones

Using the maximum acceptable velocity for a branch duct (typically 1000-1500 FPM for
minimal noise), find the smallest damper that will deliver the required CFM as
determined by the load program.

Round Zone Damper Selection

Locate the branch velocity used in the duct design program on the left hand column of the
damper sizing chart (Table 1-1). Move across the chart and find the damper which will
provide the acceptable CFM to meet zone requirements.

Note: Compare the damper size selected against the duct size to determine if the

next size up or down will provide acceptable performance without requiring a
transition fitting.

One additional damper may be slaved together for large zones. See zone wiring diagram
for details. This should be reserved for situations when it is not practical to use a single
large damper.

Air Damper Round Duct Size

Velocity through Round Air

( Area Ft

Damper

750 - P.I. or P.D. Zone

1000 - P.I. or P.D. Zone

Maximum CFM For P.I. Zone

1250 – P.D. Zone Only

1500 – P.D. Zone Only

1750 - Bypass Only

2000 - Bypass Only

2250 - Bypass Only

2

(FPM)

Damper

)

Round Air Damper Selection

6″

(0.188)

141 254 399 577 788 1031

188 338 532 769 1050 1375

206 413 634 921 1264 1608

235 423 665 961 1313 1718

282 507 798 1154 1575 2062

329 592 931 1346 1838 2405

376 676 1064 1538 2100 2749

423 761 1197 1730 2363 3094

8″

(0.338)

Volume through Round Air Damper

10″

(0.532)

(CFM)

12″

(0.769)

14″

(1.050)

16″

(1.375)

Table 1-1: Round Damper Sizing Chart

1-22 Design Guide

Auto-Zone Plus Section 1

Round Damper
Blade Assembly

Zone Controller

1/2" Foil Faced
Insulation

W

A

O

I

R
L
F

F

L
R
I

O

A

W

Actuator

Control Enclosure
(Cover Removed)

VAV/Zone Round Damper Dimensional

Data

Duct Diameter A B C

6″

8″

10″

12″

14″

16″

19.00 5.88 9.38

19.00 7.88 11.38

19.00 9.88 13.38

22.00 11.88 15.38

22.00 13.88 17.38

22.00 15.88 19.38

Table 1-2: Round Damper Dimensional Data

Pressure Independent Round Damper “K” Factor

Pressure Independent Round Air Dampers utilize “K” factors to correctly measure and
read CFM values. These “K” factors represent the airflow that will pass through a given
size damper at 1” of velocity pressure. These “K” factors must be programmed into the
control system for all pressure independent dampers. See Table 1-3 for a list of “K”
factors by round damper diameter used.

Flow Probe “K” Factor Chart

K Factor = CFM Flow @ 1” Velocity Pressure

Damper Diameter Flow Probe “K” Factor

6″

8″

10″

12″

14″

16″

474

950

1417

2120

2908

3700

Table 1-3: Pressure Independent “K” Factors

Design Guide 1-23

Section 1 Auto-Zone Plus

Rectangular Zone Dampers

The Rectangular Damper is used in applications where rectangular ducts are specified or
required because of space limitations or job requirements. The Rectangular Damper
utilizes opposed blades for improved air flow control. See Table 1-4 for sizing info.

Dimensional Data Typical Installation

Height

(B)

Width

(A)

10″ 510 590 690 800 910 1030 1150 1260 1380 1500 1610 1730 1840 2000 2080

12″ 560 650 730 850 970 1090 1210 1330 1460 1580 1700 1820 1940 2060 2190

14″ 660 770 880 1030 1180 1330 1480 1630 1760 1910 2060 2210 2360 2510 2640

16″ 750 890 1030 1200 1370 1540 1710 1880 2060 2230 2400 2570 2740 2910 3090

18″ 770 980 1180 1380 1580 1780 1980 2180 2350 2550 2750 2950 3150 3350 3540

20″ 850 1090 1330 1550 1770 1990 2210 2430 2650 2870 3090 3310 3530 3750 3990

22″ 930 1210 1480 1730 1980 2230 2480 2730 2950 3200 3450 3700 3950 4200 4440

24″ 950 1290 1630 1900 2170 2440 2710 2980 3250 3520 3790 4060 4330 4600 4880

26″ 990 1390 1780 2080 2380 2680 2980 3280 3550 3850 4150 4450 4750 NA NA

28″ 1070 1500 1930 2250 2570 2890 3210 3530 3850 4170 4500 4820 NA NA NA

30″ 1020 1550 2080 2430 2780 3130 3480 3830 4150 4500 4850 NA NA NA NA

32″ 1090 1660 2230 2600 2970 3340 3710 4080 4450 4820 NA NA NA NA NA

34″ 1150 1770 2380 2780 3180 3580 3980 4370 4750 NA NA NA NA NA NA

36″

″

10″ 12″ 14″ 16″ 18″ 20″ 22″ 24″ 26″ 28″ 30″ 32″ 34″ 36″

8

8″ 410 530 640 740 850 970 1080 1190 1300 1410 1520 1630 1740 1850 1970

1060 1790 2520 2670 3090 3510 3930 4350 5040 NA NA NA NA NA NA

Rectangular Damper Selection Data

Airflow Through Rectangular Damper

CFM @ 1000 FPM Velocity

Notes:

1.) Zone Dampers should be sized based on the required zone CFM. The table above is calculated based on 1000 FPM velocity through

the Rectangular Damper. Zone Damper recommended velocity is 1000 - 1500 FPM. Select 1000 FPM or less for quiet operation. For

other velocities, use the following multipliers to obtain the correct CFM: 500 FPM = 0.5, 750 FPM = 0.75, 1250 FPM = 1.25, 1500 FPM =

1.5, 2000 FPM = 2.0, 2250 FPM = 2.25.

2.) Bypass Dampers should be selected for 60% to 70% of the HVAC units rated CFM capacity. Recommended Bypass Damper velocity

-

Table 1-4: Rectangular Damper Sizing Information

1-24 Design Guide

Auto-Zone Plus Section 1

Auxiliary Heat Control
Options

The Auto-Zone Plus system offers the user a variety of methods to deal with zone heating
requirements. When deciding how to handle zone heating requirements the user should
consider the following:

• Does the rooftop unit have heat?

• Are you using fan powered boxes?

• Is auxiliary heat used such as baseboard or radiant ceiling panels?

If the zone has some type of heat, the user must consider how the heat is to be used.
Typical questions that should be asked:

Q: Should the zone heat be used as a first stage where it will become active before a

heating demand is created at the rooftop unit?

A: This mode is useful if you expect to have both heating and cooling demands at the

same time. The zone will use it’s own heat and allow the rooftop unit to continue to
provide cooling for other zones. This mode is also useful if the rooftop unit does not
have any heating capabilities.

Q: Is the zone heat only to be used as a second stage, where it will be activated only if

the rooftop unit cannot maintain the space temperature, such as during very cold
weather?

A: In this mode of operation the rooftop will examine the heating and cooling demands

and try to satisfy all of the zones by switching between heating and cooling as
required. The zone heat will only be activated if the zone temperature falls below a
selected limit.

Q: Should the zone heat be locked out if the rooftop unit is supplying warm air?

A: In many instances it is desirable to use the rooftop heating whenever possible and

only use zone heat when the rooftop unit is in cooling or vent mode. This often
provides the most cost effective operation since zone heat is typically electric. This
mode of operation will lockout zone heat if the rooftop is delivering heated air.

Design Guide 1-25

Section 1 Auto-Zone Plus

The following paragraphs describe the operation of each of the relays on the optional
relay expansion board. The user can choose the appropriate relays for any given
application.

Relay #1 - Parallel Fan

If the Zone is in cooling mode or vent mode, the parallel fan can activate anytime the
zone temperature drops 0.5°F below the heating setpoint. It de-activates when the
temperature rises above the heating setpoint. The space temperature must be below the
Aux Heat Setpoint in the occupied mode, before the Parallel Fan relay can be energized.

Relay #2 - Box Heat

If the Zone Manager is in cooling mode or vent mode then the box heat can activate
anytime the zone temperature drops 1.5°F below the heating setpoint. It de-activates when
the temperature rises to within 1.0°F of the heating setpoint. Box Heat is not allowed to
activate in the heating mode when there is hot air being supplied by the air handling unit.
This output was intended to allow zone re-heat while the Zone Manager is satisfying
cooling demands in other zones. The space temperature must be below the Aux Heat
Setpoint in the occupied mode, before the Box Heat relay can be energized.

Relay #3 - Aux Heat

In the occupied mode, the Aux Heat can activate anytime the zone temperature is 0.5°F
below the Aux Heat Setpoint. It de-activates when the temperature rises 0.5°F above the
Aux Heat Setpoint. In the Unoccupied Mode, the Aux Heat uses the Unoccupied Heating
Setpoint with the same deadband values mentioned above. This prevents the zone from
maintaining the same Aux Heat Setpoint at night that it does during the daytime.

This output was intended to allow zone heating to augment the normal Heating Mode and
also to allow a zone an attempt to satisfy its own heating needs before creating a Heating
Demand at the Zone Manager.

Relay #4 - Series Fan

The series fan runs anytime the main fan is running. This includes Occupied and
Unoccupied Modes. The fan can only start running when the Zone Damper is closed, so it
determines that the damper is closed before starting the fan.

Modulating Box Heat Available

Modulating Heat is available by using the OE322 Expansion Board but requires special
consideration. The OE322 board can provide a 0-10 VDC modulating signal for a
Modulating Hot Water Valve or an SCR Electric Heating Coil Controller. Please contact
WattMaster for more information.

1-26 Design Guide