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Form: 036-21478-001 Rev. A (0802) Supersedes: Nothing

Zone
Zone
How MeridianWorks ...........................................................................................................5
Why Should I Use Meridian?...............................................................................................6
What Is Unique About Meridian?......................................................................................6-8
Zoning Systems Versus True VAV Systems.......................................................................... 9
Basics Of Designing A Zoning System ................................................................................ 10
Design Considerations ................................................................................................... 11-12
Zoning Design Procedures.............................................................................................13-21
System Installation .........................................................................................................22-26
Application Notes ................................................................................................................27
Table Of Contents
NOTE: Any reference in this document to roof top HVAC unit
s
are for ease of communication. Meridiancan also be used on
split systems.
Form: 036-21478-001 Rev. A(0802) Supersedes: Nothing
Copyright 2002 York International Corp..
Meridianis a registered trademark of York International Corp.
York International Corp. assumes no responsibility for errors, or omissions.
This document is subject to change without notice.
All rights reserved.

Figure 1-1: MeridianPlus System Overview ..................................................................... 5
Figure 1-2: Zones Affected By Outdoor Load...................................................................13
Figure 1-3: Zone Layout With External Zones Only ..........................................................14
Figure 1-4: Zones With North And South Exposures ........................................................14
Figure 1-5: Zoning And Constant Volume Units ............................................................... .14
Figure 1-6: Round Bypass Damper.................................................................................. .16
Figure 1-7: Rectangular Bypass Damper & Kit..................................................................16
Figure 1-8 Preferred Sensor Location .............................................................................. 17
Figure 1-9: Acceptable Sensor Location ...........................................................................17
Figure 1-10: Least Desirable Sensor Location .................................................................... 17
Figure 1-11: Pressure Dependent Damper ......................................................................... 18
Figure 1-12: Pressure Independent Damper....................................................................... 18
Figure 1-13: York Communications Wire.............................................................................23
Figure 1-14: MeridianBasic System Communications Loop Wiring .................................24
Figure 1-15: MeridianPlus System Communications Loop Wiring ................................... 24
Figure 1-16: Transformer & Wire Sizing Considerations ..................................................... 26
Table 1-1: Round Damper Selection Data..........................................................................19
Table 1-2: Rectangular Damper Selection Data .................................................................20
Table Of Figures & Tables

MeridianSystems 5
Zoning Design Guide
036-21478-001 Rev. A (0802)
How MeridianWorks
Figure 1-1: MeridianPlus System Overview
First the zone must initiate a vote to the HVAC unit.
This occurs when a zone becomes more than 1 degree
off setpoint.At this time a vote is placed for heating or
cooling. Next the controller evaluates the total cooling
demand or heating demand within the entire building
to see which requirement is more critical. Finally, the
system looks for any priority conditions, which would
take precedence over other zones.All three of these el-
ements working together provide accurate and stable
control of comfort.
Additional control features are taken into account to
provide a very effective control of the system. Some of
these include priority override, supply air temperature
limits, outside air temperature lockouts, and min./max.
control over damper position.
Substantial savings can be realized using the Meridian
Zoningsysteminstead ofhaving toinstall multiple roof-
top units to accommodate multiple zone requirements.
The MeridianZoning system is versatile and can be
used with any packaged roof top unit or split system. It
controls a variety of terminal unit functions including
single duct pressure dependent, pressure independent,
series fan and parallel fan terminals.
TheMeridiancontrolsystem convertssingle-zone con-
stant volume rooftop packaged or split system HVAC
units into variable air volume/variable temperature
multiple zone systems. The microprocessor based Zone
Manager calculates the heating and cooling require-
ments for each zone based on real time information re-
ceived from each Zone Controller/Damper. 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 bypass damper
controlled, by a static air pressure sensor, modulates
to maintain constant duct pressure.
The Meridiansystem uses a unique 3 tier approach to
controlling the system:
•Voting Zones
•System Demand
•Priority
This 3 tier system works in an integrated fashion to
maintain proper control of the equipment and effective
control of comfort in the zone.
H
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AC Line
Outside Air
Exhaust Air
Supply Air Duct
24 VAC
Local Communication Loop
Network
Comm
Loop
Ground
Fan
Up To 16 Zones
To Other
Meridian Plus
Zone Controllers
Zone #1
Temperature Sensor
Modulating
Bypass Damper Return Air
Sensor
Static Pressure
Sensor & Pickup Tube
Supply Air
Temperature
Sensor
Computer
(Optional)
Outside Air
Temperature
Sensor
Avoid Direct
Sunlight
Meridian Plus
Zone Manager
Typically Mounted
in the HVAC Unit
Zone #2
Temperature Sensor
With Override and Setpoint Adjust
NORMAL
WARMER
COOLER
OVR
To Other
Meridian Plus
Zone Managers
Remote Link
(Optional)
CommLink II
WCLI
ATTMASTERONTROS,NC
COMMLINKII
COMM LINK II
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Zone Damper Zone Damper
Zone Controller
Zone Controller
24VAC
24VAC
SychronousDataLink
CONTROLS
SIG
DET
RDY
SND
REC
PWR
System Manager
Mixed
Air
Return Air
24VAC
ClearWindowArea
6
5
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DEC
7
MINUS
0
CLEAR
9
8
13
2
MENU
Override
Communication
ENTER
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Alarm
SystemManager
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Meridan
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6MeridianSystems
Zoning Design Guide 036-21478-001 Rev. A (0802)
Why Should I Use Meridian ?
Meridianis a proven system with a long history of
successful installations. Our systems have been refined
over the years with the help of feedback from people in
the field who work and live with these systems on a
daily basis. Our success is greatly due to the fact that
wehaveimplemented changesand enhancements based
on real world experience not from tinkering with equip-
ment in an isolated lab environment. This real world
approach provides engineers, contractors, and end us-
ers with a zone control system that is efficient, reliable,
andmostimportantly,keepsthe customerscomfortable!
What Is Unique About Meridian ?
Meridianis unique because it has many features not
found on other systems. These features include
Non-Proprietary Design
Meridianwill work on any manufacturers HVAC
equipment that will accept a standard thermostat con-
nection. This protects the end user from being locked in
to one source for service and support. In addition,
Meridiansystems include very comprehensive docu-
mentation, which is written in a format designed for the
contractor. This allows a contractor with limited con-
trols experience to easily install the Meridiansystem.
Pre-Engineered Software
Systemdesign,software, anddocumentation hasalready
been done for you. This eliminates the costly expense
usually associated with conventional DDC systems,
making the Meridiansystem more competitive and
easier to install and operate.
One System for Zoned or Single Zone
Systems
Not only does Meridianprovide a networked zone
control system for one or multiple zoned HVAC units,
you can also connect individual single zone units to the
system eliminating the need to use programmable ther-
mostats.
Easy to Configure
Since Meridiancomponents are grouped into pack-
ages, configuring a system has been simplified. This
reduces the chance of ordering errors and makes sys-
tem layout effortless!
User Friendly Set Up
Sincethe Meridiansystemis designedfor menudriven,
fill in the blank programming, system setup is simple.
The system manual takes you step by step through the
set up process. Default parameter values are pro-
grammed into permanent memory so the system can be
operational at start-up. Specialized training is not re-
quired.
ClearWindowArea
6
5
4
DEC
7
MINUS
0
CLEAR
98
132
MENU
Override
Communication
ENTER
ESC
Alarm
System Manager
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MeridianPlus
05/17/0003:38PMWED
OCCUPIED
NOALARMS
HeatingandAir Conditioning
®

MeridianSystems 7
Zoning Design Guide
036-21478-001 Rev. A (0802)
True Network Communications
The Meridianuses a three wire, RS-485 loop for com-
munication between all controllers in the system. This
provides a very reliable form of communication with
flexibility of installation. The loop can be wired in a
“daisy chain” or “star” configuration. Many other zon-
ing systems utilize “home run” wiring that requires all
communication cables to be brought back to a central
point adding additional cost to the project and compli-
cating wiring.
High Integrity Communications
Many communicating control systems are susceptible
to electrical interference. One major manufacturer of
zoning systems recommends that their communication
cable should not be strapped to conduit because of po-
tentialinterference.The MeridianSystemshave acom-
municationbus thatisalmost immuneto anynoise prob-
lems that may be found in most commercial facilities.
Microprocessor Controllers
All controllers in the Meridiansystem have an on-
board microprocessor. This is what gives the Meridian
powerful features and capabilities not found in other
systems.
Stand-Alone Systems
All MeridianSystems are true stand-alone and do not
require a computer to operate. Unit controllers main-
tain their own 7 day time clock, 365 day holiday sched-
uling, and setpoints within each controller.
Menu Driven Operators’ Interface
All Meridiansystems have an operators’ keypad and
display terminal. This gives you access to system sta-
tus and parameter values without the need for a com-
puter. The 4 line by 20 character display is backlighted
making it easy to read even in low light environments.
Menudrivenprogramming makesthe system extremely
user friendly. In addition, the interface panel is pass-
word protected to keep unauthorized users from access-
ing the system.
Communications Via Optional Modem
The Remote Link is used for achieving remote commu-
nications with the Meridiansystem. It connects to the
CommLink II communications interface and a local
phone line. With the Remote Link, the Meridiansys-
tem can be monitored and controlled from a remote lo-
cation, using a computer and the Prismcomputer front
end software package.
Memory Backup
Instead of batteries, which have to be replaced,
Meridianutilizes super capacitors to provide power
for memory backup during power outages. The major
advantages to this approach is that super capacitors are
more reliable than batteries and they recharge in a mat-
ter of seconds instead of hours.Typical memory backup
is good for a minimum of 10 days.
Modulating, Heavy Duty Actuators with
Real Time Feedback
All Meridianactuators utilize true modulating con-
trol unlike many systems, which are two position. This
gives the system-improved control, which translates, to
better comfort levels. Our actuators are also rated for
2-½ million cycles, making our actuators some of the
most reliable in the industry. One other critical feature
is the real time feedback. Many other systems have no
feedback at all. They blindly estimate the travel time of
their actuator, which, in the real world, is not a very
repeatable estimate. To help correct the problems in-
herent with this approach, they recycle all the actuators
in the system once or twice a day. They may save a few
dollars by not including feedback but they sacrifice sys-
tem performance. Not so with Meridian.
Commercial Grade – Insulated Round
Zone Dampers
Meridianonly uses commercial grade zone dampers,
not cheap, flimsy, “light commercial” or “residential”
styledampers likemanyothermanufacturers.Our round
damperisARIcertified andcomes fromthefactoryfully
insulated.Why?When many zonedampers areinstalled
they are improperly insulated or not insulated at all.
This can cause problems with the damper “sweating”
from condensation. With factory insulated zone damp-
ers, we eliminate a common problem for the contractor
while insuring the end user will not have problems with
condensation dripping down onto the ceiling.
Rectangular Dampers
Meridianuses only top of the line, aluminum air foil
rectangular control dampers. No other zone system on
the market today utilizes a damper of this quality and
performance!

8MeridianSystems
Zoning Design Guide 036-21478-001 Rev. A (0802)
What Is Unique About Meridian ?
Patented Flush Mount Room Sensors
Our flush mount room sensors are so unique, they are
patented (U.S. Patent No. 4,659,236). Even though part
of the sensor is recessed into the wall to provide an
attractiveyettamper proofflush mounting, internalwall
temperatures do not influence the sensor.Aspecial plate
on the face of the sensor accurately senses space tem-
perature. Even though the attractive off white plastic
housing is a preferred color, the sensor housing can be
painted or wallpapered to blend with room decor with-
out affecting sensor performance. The sensors are of-
fered in four different configurations:
•Sensor
•Sensor w/override
•Sensor w/setpoint adjustment
•Sensor w/setpoint adjustment & override
Modular Connections
Many Meridianauxiliary devices are connected to the
controllers via modular plugs like the ones used on tele-
phones. This simplifies installation and eliminates the
possibility of wiring errors. The devices, which utilize
this method, are damper actuators for zone and bypass
control, auxiliary relay boards, and static pressure/air
flow sensors. There is one interesting side note about
the auxiliary relay board and airflow sensors. These
devices are typically used on the zone controllers in the
MeridianBasic & Plus systems. When the system is
powered up, it automatically looks to see if these de-
vices are connected to the controller. If they are, the
controller automatically reconfigures itself to utilize
thesedevices andactivates theappropriate setup screens
back at the operators interface. Pretty neat don’t you
think!
FREE! Windows™ Graphics Software
Each Meridiansystem can be monitored on site or re-
motely using a PC and our Prismcomputer front end
software software. This full-featured package is very
user friendly and can be used to monitor one system or
hundreds. The Prismsoftware is not copy protected
so it can be installed on multiple PC’s’ without addi-
tional expense. Just some of its many features include
but are not limited to:
•Pre-designed status screens for all controllers
•Alarm dial out capability
•Programming of all system parameters
•Trend logging to Excel™ spreadsheets
•Alarm Handling
•Custom graphics capability
Open Protocol System
Meridianis an open protocol based system allowing
other manufacturers to develop direct interfaces to the
communications loop. This gives you the ability to in-
tegrate the Meridiansystem into products from other
vendors. Our engineering staff will be glad to assist any
vendor in this process.

MeridianSystems 9
Zoning Design Guide
036-21478-001 Rev. A (0802)
General
Even though there are some similarities between zone
control systems and Variable Air Volume (VAV) sys-
tems, there are some major differences. In many cases
systems will be called VAV when in fact they are really
a zoning system or are referred to as a zoning system
when they are really a VAV system. Always make sure
that you do not try to adapt a zoning system to a VAV
design system. Understanding the differences will help
you to prevent misapplication of the Meridianzoning
system. In the paragraphs that follow we will try to ex-
plain the differences, advantages and disadvantages of
each and explain their operation.
VAV Systems
These systems consist of an HVAC unit that is gener-
ally a cooling only unit and VAV terminal units located
in the downstream ductwork that are used to control
the amount of constant temperature air delivered to the
various building zones. Sometimes the HVAC unit may
have gas or electric heat, but it is typically sized and
appliedformorning warm-uppurposes.The HVAC unit
is designed to vary the volume of air that is supplied to
the duct system by using either inlet vanes or an elec-
tronic variable frequency drive. These devices modu-
late to control the air flow through the supply fan in
response to the static pressure in the duct system. VAV
systems typically use high velocity VAV terminal units
to distribute the air to the zones. As the various VAV
terminal units in the different zones open and close to
supply the constant temperature air to the spaces, the
HVAC unit varies the volume of constant temperature
air based on the static pressure in the ductwork. The
HVAC unit is designed to maintain a constant cold sup-
ply air temperature regardless of the air flow volume in
the system. The HVAC unit cycles it’s cooling stages to
maintain a constant predetermined supply air tempera-
ture. It typically runs continuously based on a sched-
ule. For perimeter zones requiring heat, reheat coils
(electric or hot water) located in the terminal units are
used to supply heated air to the space. Many times fan
powered terminal boxes are used and in many cases
also incorporate electric or hot water heating coils to
provide perimeter zone heating. In summary a true VAV
system uses a variable volume fan supplying constant
temperature air to the system with variable volume ter-
minal units used to control the volume of constant tem-
perature air delivered to the space. Generally these sys-
tems use pressure independent damper control.
Zoning Systems Versus True VAV Systems
Meridian

Systems
The Meridianzoning system is completely different
in operation and design from the VAV system previ-
ously discussed. One of the major differences between
the zoning system and a true VAV system is that the
HVAC unit used on a zoning system utilizes a constant
volume fan.Air volume control of the zoning system is
achieved by bypassing air from the HVAC unit supply
duct back into the HVAC unit return air duct on the unit
inlet. This bypass air is controlled based on a static pres-
sure sensor located in the supply air duct downstream
of the unit supply air discharge. The bypass damper
modulates open and closed based on the static pressure
in the duct. The temperature at the HVAC unit discharge
varies in relation to the demand from the zones. Typi-
cally the HVAC units used for the zoning system will
have both heating and cooling capabilities. The fan sup-
plies a constant volume of cold or hot air to the duct
system which is then fed to the individual zones by
modulating zone dampers. Each zone controller relays
its heating or cooling demand to the HVAC unit con-
troller. The HVAC unit controller determines its mode
of operation (heating, cooling or vent mode) depend-
ing on the demand from the zone controllers. The unit
controller utilizes a voting system to determine the cor-
rectmodeof operation.Each zonecontrollerdetermines
(based on its heating and cooling setpoints) whether or
not to use the air being supplied by the HVAC unit. For
example, one of the zones is calling for cooling when
the temperature in the duct is above the zones cooling
setpoint. This zone will move to its minimum cooling
position to prevent warm air being introduced into the
space. With the zoning system the zone dampers are
generally pressure dependent. Pressure independent
operation is available but is not very common. Reheat
and/or fan powered terminal units can be used but aren’t
commonly part of the typical zoning system.
Conclusion
In many cases VAV systems go over budget because of
the increased cost of a VAV, HVAC unit and the expen-
sive VAV controls associated with the system. Many
times the system can be redesigned to a zoning system
using Meridiancontrols with a significant cost sav-
ings and equal or better performance and comfort than
the VAV system would provide. Be sure to follow the
instructions in this design guide for your zoning sys-
tem.

10 MeridianSystems
Zoning Design Guide 036-21478-001 Rev. A (0802)
This is a summary of the key items you need to con-
sider for the design and layout of a successful zoning
system.
It is important that you study the design guide for a
moreindepth understandingofproper system design.
By following the design guide and these tips you can
eliminate many unnecessary headaches that occur when
the basic rules of zoning are not followed.Always con-
tact yourYork applications group if you have any ques-
tions.
•Always group zones with similar load
profiles on the same HVAC unit.
•Never mix perimeter zones with interior
zones on the same HVAC unit.
•Each zoned HVAC unit should have a
minimum of 3 to 4 zones. Any less and you
should consult the factory.
•Each zoned HVAC unit can support a
maximum of 16 voting zones. Any more
zones and you should contact the factory.
•When using auxiliary heat for individual
zones, perimeter heat such as baseboard is
always preferred and more economical to
operate than a fan terminal unit with reheat.
•If you have electric reheat coils mounted on
VAV boxes, it is recommended that a fan
powered box be used. Consult the factory for
further details concerning this application.
•If there is an economizer on the HVAC unit,
it is highly recommended, though not
required, that the Zone Manager control the
economizer.
•Pressure Independent Zones must always use
round dampers or VAV boxes, never
rectangular - no exceptions!
•Never attempt to use a zone control system
on a true VAV application. See “ Zoning
Systems Versus True VAV Systems” on page
9 of this guide for detailed information.
•Bypass dampers should always be sized for
60%-70% of the HVAC units rated CFM.
•Even though the Meridiansystem has
certain features to help protect your
equipment, never override or disconnect any
safety devices associated with the HVAC
unit.
Basics of Designing A Zoning System

MeridianSystems 11
Zoning Design Guide
036-21478-001 Rev. A (0802)
Design Considerations
Load Diversity
A zoning 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 con-
ditions 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
(whichmay requireconstant heatduring wintermonths).
If you must mix zones under these conditions, consider
using either VAV boxes with heat or separate external
heat on perimeter zones. MeridianZoning 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 MeridianPlus system offers the designer consid-
erable 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 prob-
lems when applying a zoning system for cold weather
operation.
1.)LowAmbientTemperature Lockout.During very
cold weather it is common for mechanical systems to
have “low temperature lockouts” which protect equip-
ment from damage if operated under these conditions.
Meridian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 Meridian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 sys-
tem.
2.) Low Supply Air Temperatures. Under lightly
loaded conditions much of the supply air may be by-
passed back into the return air side of the HVAC unit.
This bypassing will result in the lowering of the supply
air temperature, which may result in the supply air tem-
perature reaching the low temperature safety limit. If
the supply air low temperature safety limit is exceeded,
the control system will “cut off” the mechanical cool-
ing 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 installa-
tion.
Avoid oversizingtheunit. Do your all load calculations
carefully. Since the zoning system directs the heating
or cooling to the zones which require it, you may find
thatyou canuse asmallerunitinmanycases.Oversizing
is the number one cause of excessive low supply air
temperature cycling.
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.
Increasecoolingminimumairflow.Increaseyour cool-
ing minimum airflow or damper position settings to al-
low more air during cooling operation. Be careful to
avoid minimum settings that are so high they may cause
over cooling of the spaces.
Bypass the air into the ceiling plenum. If you have a
system without ducted return, bypass the air into the
ceiling plenum instead of into the return air intake. Be
carefulifyou usethis methodsince you mayget “dump-
ing” of cold air from your return air grilles. This method
works best with plenum returns. Do not use this method
with ducted returns.

12 MeridianSystems
Zoning Design Guide 036-21478-001 Rev. A (0802)
Design Considerations
Increase your static pressure setpoint. This will 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
airflow at minimum positions.
Warning:
Ifthefan system hasthecapability of producingstatic
pressureswhich coulddamage ductworkyou mustpro-
videamanual reset,highpressure limitswitch(Dwyer
1900-5-MR or equal) to cut off the fan system in the
event of high duct static. Do not use your Meridian
Zoning system as a safety device!
Heating - Partial Load Conditions
Heating difficulties are less common than cooling dif-
ficulties. They are similar in nature, however, and the
cures are generally the same.Again, a number of things
can be done to reduce the effects of this problem.
Increaseheatingminimumairflow.Increaseyour heat-
ing minimum airflow or damper position settings to
allow more air during heating operation. Be careful to
avoid minimum settings that are so high they may cause
over heating of the spaces.
Increase the static pressure. Set the static pressure
setpoint to be as high as practical. Increasing static pres-
sure does not help if you are using pressure indepen-
dent control operation.
Avoid oversizingtheunit. Do your all load calculations
carefully. Since the zoning system directs the heating
or cooling to the zones which require it, you may find
that you can use a smaller unit in many cases.
Bypass the air into the ceiling plenum. If you have a
system without ducted return, bypass the air into the
ceiling plenum instead of into the return air intake. This
method works best with plenum returns. Do not use
this method with ducted returns
Use auxiliary heat . Use an auxiliary heat source in
either your VAV boxes or use baseboard heaters.
Meridianhas a number of auxiliary heat control op-
tions 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.
Asingle zone being overridden for after-hours use most
commonly causes the problem. This causes the rooftop
equipment to operate for only one zone. The Meridian
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 sys-
tem to operate with sufficient load to reduce cycling
caused by light load conditions.
Building Pressurization
If you are using an economizer, building pressurization
must be addressed. Failure to properly handle building
pressurizationmayresult indoors remaining openwhen
the economizer is operating. Pressurization problems
can render economizer operation useless. The follow-
ing suggestions will help to avoid potential problems.
Use powered exhaust. Apower exhaust fan(s) must be
used when the system utilizes ducted returns. The re-
turn duct pressure drop will cause most barometric re-
lief dampers to function poorly or not at all. Meridian
has the ability to control a powered exhaust whenever
the economizer is operating.
Use a separate building pressure control. Use a con-
trol that operates a relief fan or dampers to relieve build-
ing pressure

MeridianSystems 13
Zoning Design Guide
036-21478-001 Rev. A (0802)
Zoning Design Procedures
General
There are six basic steps to designing an Meridian
Zoning system:
1.) Determining the number and location of zones
2.) Sizing the central unit
3.) Duct Considerations
4.) Room air motion and diffuser selection
5.) Bypass damper sizing
6.) Sizing the zone dampers
Step #1 - Determining The Number And
Location Of Zones
A single air handler unit can have no more than sixteen
zones and no fewer than 3 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
MeridianZoning System is to select the zoning so that
no zone will be at maximum (design) heating (or cool-
ing) load when any other zone requires the opposite
temperature air to satisfy its load. For example, depend-
ing 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 several distinct tempera-
ture or control zones that are affected uniquely by the
outdoor load. These zones are depicted in Figure 1-2.
Depending on the size of the building and partition lay-
out, some of these zones may overlap or be insignifi-
cant from a zoning standpoint. For example, Zone 11
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. Simi-
larly, zones 7 and 8 could have no external windows
and no partitions between them and could be consid-
ered a single zone. Some zones could be divided into
multiple offices with full partitions between them, thus
requiring separate Zone Controllers because of differ-
ent internal loads, but the same external load.
Generally, 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 possible with
multiple zones, to match the owner’s requirements.
It is important to recognize that there are purely inter-
nal zones, such as Zone 11 in Figure 1-2, which may
contain separate offices/conference/computer rooms.
These internal zones could easily have high cooling re-
quirements while external zones (1,2,3, etc.) could be
at or near design heating load. This is a misapplication
of the Meridian, zoning (or any heating/cooling
change-over) system. The interior zones with cooling
only loads should be served by a separate single zone
rooftop HVAC unit (that could be zoned between mul-
tiple rooms with a similar load profile). Supplemental
heat could be added to the perimeter zones and con-
trolled with the auxiliary heat control board from the
Zone Controller. System performance will generally be
compromised and frequent change-over from the heat-
ing to the cooling mode will occur during the heating
seasonif purelyinternal zonesare combinedon thesame
air-conditioning unit serving perimeter zones. The ex-
posure to the sun has a large affect on the loading of the
building. With the building zoned as shown below, for
the best control, zones 6, 7, 8, 9 and 10 should be put
on one HVAC unit, and zones 1, 2, 3, 4 and 5 on an-
otherHVACunit.Zone 11 shouldbe onaseparate single
zone constant volume HVAC unit.
Figure 1-2: ZonesAffected by the Outdoor Load
234
5
67
8
10 11
1
9
N

14 MeridianSystems
Zoning Design Guide 036-21478-001 Rev. A (0802)
Zoning Design Procedures
Figure 1-3: Zone Layout With External Zones Only.
1
2
3
45
6
7
N
Here is another example of the building’s exposure af-
fecting the zoning. Figure 1-3 below shows a building
layout with 7 zones, it has 3 zones with an eastern ex-
posure, 4 zones with a western exposure and two each
north and south exposures. This building can be con-
trolled from a single, constant volume air handler. All
of the zones have exterior exposures and there are no
totally internal zones, so they will have similar load
requirements.
Figure1-4shows abuildingwith 7zones, 4of thezones
have a north exposure and the other 3 have a south ex-
posure. Since there is a big difference in the affect on
the building between north and south exposures, instal-
lation of two separate zoned HVAC units is recom-
mended.
Figure 1-5 shows a combination manufacturing
facility and office area. The space temperature in the
individual zones numbered 1 through 7, would all be
controlled by a single HVAC unit. A single constant
volume HVAC unit would be used for each of the
zones 8 through 12.
12 3 4
567
N
1
2
3
45
6
7
8
912
10 11
Figure 1-5: Zoning And Constant Volume Units
Figure 1-4: Zones With North And South Exposures.

MeridianSystems 15
Zoning Design Guide
036-21478-001 Rev. A (0802)
Step #2 - Sizing the Central Unit
Because the zones are controlled with variable air vol-
ume, 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
becalculatedusing anydependable load estimatingpro-
gram. 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 vol-
ume single zone system. Consider the following when
sizing the central unit.
•Size the peak cooling load based on the
month day 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 Meridian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 Meridian,
Zone Controller without the airflow sensor. With larger
trunkducts,it iseasier toassurerelatively constantpres-
sure to each zone. Runs should be as short as possible,
and the trunk duct system kept as symmetrical as pos-
sible to facilitate system balancing. Wherever possible,
run the trunk ducts above corridors and locate the zone
dampersabovecorridors toreduce thenoisein thespace
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 termi-
nals use the static regain method for sizing ducts. The
typical MeridianZoning system is a low-pressure,
pressure dependent system that utilizes conventional
unitaryair-conditioning units.These systemsshould use
the equal-friction method of sizing the ducts, and use
the maximum loss of 0.1 inch per 100 feet as described
above.
Step #4 - Air Motion/Diffuser Selection
Air motion is a consideration for occupant comfort. The
selection of diffusers for an MeridianZoning 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
airflows. Because the zone airflow is variable volume,
lower cost round or rectangular diffusers that were sat-
isfactory for constant volume may prove unsatisfactory
with an MeridianZoning 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 mo-
tion in the heating mode can be undesirable, a slot dif-
fuser with a high induction ratio generally helps to re-
duce room air “stratification” when the heating comes
from a ceiling diffuser. Linear slot diffusers should be
properly selected for the airflow 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, mul-
tiple 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 recom-

16 MeridianSystems
Zoning Design Guide 036-21478-001 Rev. A (0802)
Zoning Design Procedures
mended that slot diffusers be located near the perim-
eter 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
The function of the bypass damper is to allow a con-
stant volume air handling unit to be used with variable
volume zone dampers. The bypass damper modulates
on a signal from a duct static pressure sensor to “by-
pass” air from the supply duct back into the return air
duct. If the duct static pressure exceeds the adjustable
setpoint, then the damper opens to bypass more air, and
if the static pressure drops below the setpoint, it closes
to bypass less air.
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 by-
pass duct size, be sure to take into account any transi-
tion fittings and associated pressure drops. (See Tables
1-1 & 1-2: Damper Sizing Charts)
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 con-
trolled in parallel or a rectangular damper may be used.
Forproper controlofthe BypassDamper,the staticpres-
sure sensor location is very important. Refer to Fig-
ures 1-8Thru 1-10 for proper sensor installation loca-
tion information and guidelines.
Figure 1-6: Round Bypass Damper Figure 1-7: Rectangular Bypass Damper & Kit

MeridianSystems 17
Zoning Design Guide
036-21478-001 Rev. A (0802)
Fan
RA Sensor
SA Sensor
Return Air Duct
Supply Air Duct
SP Pickup
Bypass Damper
SP Sensor
Figure 1-10: Least Desirable Sensor Location
If the supply duct comes directly from the unit and im-
mediately splits in opposite directions, the pressure
pickup should be located ahead of the split, or as close
to it as possible, even if the bypass damper(s) are lo-
cated downstream of the split.
Step #6 - Sizing the Zone Damper
Use a load program to determine the peak load for each
zone. These calculations will be used in selecting the
appropriate zone damper sizes.
Using the maximum acceptable velocity for a branch
duct(typically1000-1500 FPMfor minimal noise),find
the smallest damper that will deliver the required CFM
as determined by the load program.
Locate the branch velocity used in the duct design pro-
gram 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 your
specific 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 transi-
tion 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
asingle largedamper. Roundzone damperscan bespeci-
fied to be either pressure dependent or independent.
Fan
RA Sensor
SA Sensor
3D
Min.
2D
Min.
Return Air Duct
Supply Air Duct
SP Pickup
Bypass Damper
SP Sensor
Fan
RA Sensor
SA Sensor
Return Air Duct
Supply Air Duct
Tubing To Be Equal
Length And Size
Bypass Damper
SP Sensor
SP Pickups
If the trunk ducts are properly sized for minimum pres-
sure 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. See Fig-
ure 1-8.
Figure 1-8: Preferred Sensor Location
Figure 1-9: Acceptable Sensor Location
Since the “ideal” location is often difficult to find in an
installation, a location in the main trunk where the tip
isnot ina“negative pressurearea” (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. See Figure 1-9.

18 MeridianSystems
Zoning Design Guide 036-21478-001 Rev. A (0802)
Zoning Design Procedures
Pressure Dependent Dampers
With pressure dependent (PD) dampers, the minimum
and maximum airflow is set based on damper position.
Duringthe finalcommissioning ofthe system,each zone
is typically balanced with a flow hood and the min/max
position is fixed either mechanically or the preferred
method, in the controller software. Since this min/max
setting is based only on position, as the static pressure
fluctuates it will cause the actual airflow at the zone
damper to increase or decrease. Therefore the name,
pressure dependent since the airflow is dependent on
the static pressure. Pressure dependent dampers are
available in round or rectangular configurations. See
Figure 1-11 for a diagram of a typical pressure depen-
dent zone damper.
Pressure Independent Dampers
When using pressure independent (PI) dampers this
minimum and maximum is set based on actual CFM of
airflow through the damper. Airflow is measured using
a pickup tube mounted in the zone damper and an elec-
tronic air flow sensor. Using this method you always
know the actual airflow through each zone damper in-
stead of just the damper percentage open. The mini-
mum and maximum settings are based on this actual
airflow reading. As the static pressure fluctuates, the
flow sensor reads the variation and automatically repo-
sitions the damper to maintain the minimum or maxi-
mum flow setpoints. Since the minimum or maximum
airflow is maintained independently of the static pres-
sure available in the duct it is called pressure indepen-
Figure 1-11: Pressure Dependent Damper
Figure 1-12: Pressure Independent Damper
dent operation. Pressure independent operation is avail-
able for round zone dampers only. Pressure indepen-
dent rectangular dampers are not available. See Figure
1-12 for a diagram of a typical pressure independent
zone damper.
Whenpressureindependent dampersare used theymust
be field calibrated so the CFM of airflow for the mini-
mum and maximum airflow setpoints will be correct.
This should be done by the field technician during the
commissioning portion of the system installation. The
K-factor is the amount of airflow in CFM that the spe-
cific damper will produce with 1” W.C. duct static pres-
sure on the damper flow sensor. This K-factor is used
by the controller software to maintain the correct mini-
mum or maximum airflow setpoint regardless of the
static pressure at the flow sensor. The K-factor and the
minimum and maximum damper CFMs can be entered
at the Zone Manager on Basic systems, or using the
System Manager on MeridianPlus systems. K-factors
can also be entered using a personal computer with the
Prismcomputer front end software installed. The K-
factors for each damper size are listed in Table 1-1:
Round Air Damper Selection. Once the correct K-fac-
torsand minimumand maximumdamper CFMsetpoints
are entered, the damper will modulate to try to main-
tain these CFM airflows during damper operation. If
zone dampers or fan terminal units manufactured by
others are used, the correct K-factors must be obtained
from the equipment manufacturer.

MeridianSystems 19
Zoning Design Guide
036-21478-001 Rev. A (0802)
can cause air flow problems. These slide-in dampers
require that the damper frame be inside the duct. Imag-
ine an 8 x 10 rectangular duct using a slide in damper
with a frame thickness of 1”. The frame alone would
reduce the opening to 6 x 8.
Another possible problem encountered with rectangu-
lar dampers is the blade width. Many damper manufac-
turers supply dampers with 6” or 8” dampers blades.
This can become a major problem, for example, if the
Rectangular Dampers
Meridianrectangular dampers are high quality alumi-
num construction with opposed/air foil designed blades
for superior control and have both blade and jamb seals
for tight shut off. The dampers are installed using a
mounting flange. The purpose for the flange mounting
is to allow as much unrestricted free space within the
duct as possible.
Many companies utilize slide-in type dampers which
Bypass & Slave Dampers Zone Dampers
1/2" Foil Faced
Insulation
Actuator
Zone Controller
Round Damper
Blade Assembly
Control Enclosure
(Cover Removed)
AIRFLOW
AIRFLOW
Table 1-1: Round Damper Selection Data
Damper Round Duct Size
(Area Ft2)6”
(0.188)
8”
(0.338)
10”
(0.532)
12”
(0.769)
14”
(1.050)
16”
(1.375)
CFM @ 1” Velocity Pressure
Air Flow Probe “K” Factor- For Pressure
Independent Applications Only 474 950 1417 2120 2908 3700
Velocity Through Zone Damper
FPM Airflow Through Zone Damper - CFM
(∆PS inches W.C. With Air Damper Full Open)
750 - Zone 141
(0.03)
254
(0.02)
399
(0.01)
577
(0.02)
788
(0.01)
1031
(0.01)
1000 - Zone 188
(0.05)
338
(0.03)
532
(0.02)
769
(0.03)
1050
(0.02)
1375
(0.01)
1250 - Zone 235
(0.07)
423
(0.04)
665
(0.03)
961
(0.04)
1313
(0.03)
1718
(0.02)
1500 - Zone 282
(0.09)
507
(0.06)
798
(0.04)
1154
(0.05)
1575
0.04)
2062
(0.03)
1750 – Bypass Only 329
(0.12)
592
(0.08)
931
(0.06)
1346
(0.06)
1838
(0.05)
2405
(0.04)
2000 – Bypass Only 376
(0.15)
676
(0.10)
1064
(0.07)
1538
(0.07)
2100
(0.07)
2749
(0.05)
2250 – Bypass Only 423
(0.18)
761
(0.13)
1197
(0.09)
1730
(0.09)
2363
(0.08)
3094
(0.06)
York reserves the right to change specifications without notice
1/2" Foil Faced
Insulation
Actuator
Round Damper
Blade Assembly
Control Enclosure
(Cover Removed)
AIRFLOW
AIRFLOW
Bypass & Slave Interface

20 MeridianSystems
Zoning Design Guide 036-21478-001 Rev. A (0802)
Zoning Design Procedures
damper has a height of 10”. In this case the damper
would utilize an 8” blade and a 2” blade stop or dam
would be installed across the base of the damper. Tak-
ing into consideration the “blade stop” and the frame, a
10 x 10 damper would have a reduced opening of 6 x 8
inside the duct. Many contractors have experienced low
air flow problems on projects only to discover this hid-
den problem of the dampers actually creating the re-
striction. Meridianutilizes a variety of blade widths
in order to accommodate the size of the damper instead
of the damper trying to accommodate the size of the
blade.
Rectangular Dampers
Table 1-2: Rectangular Damper Selection Data
Damper
Height
“B” 8” 10” 12” 14” 16” 18” 20” 22” 24” 26” 28” 30” 32” 34” 36”
Damper
Width
“A”
Airflow Data with Full Open Damper
CFM @ 1000 FPM Velocity
(∆PS - inches W.C. @ 1000 FPM Velocity)
8” 410
(0.16) 530 (0.10) 640 (0.07) 740 (0.05) 850 (0.04) 970 (0.03) 1080 (0.03) 1190 (0.02) 1300 (0.02) 1410 (0.02) 1520 (0.01) 1630 (0.02) 1740 (0.01) 1850 (0.01) 1970
(
0.0
1)
10” 510
(0.10) 590 (0.07) 690 (0.05) 800 (0.03) 910 (0.03) 1030 (0.02) 1150 (0.02) 1260 (0.01) 1380 (0.01) 1500 (0.01) 1610 (0.01) 1730 (0.01) 1840 (0.01) 2000 (0.01) 2080 (0.01)
12” 560
(0.07) 650 (0.05) 730 (0.03) 850 (0.02) 970 (0.02) 1090 (0.01) 1210 (0.01) 1330 (0.01) 1460 (0.01) 1580 (0.01) 1700 (0.01) 1820 (0.01) 1940 (-) 2060 (-) 2190 (-)
14” 660
(0.05) 770 (0.03) 880 (0.02) 1030 (0.02) 1180 (0.01) 1330 (0.01) 1480 (0.01) 1630 (0.01) 1760 (0.01) 1910 (0.01) 2060 (-) 2210 (-) 2360 (-) 2510 (-) 2640 (-)
16” 750
(0.04) 890 (0.03) 1030 (0.02) 1200 (0.01) 1370 (0.01) 1540 (0.01) 1710 (0.01) 1880 (0.01) 2060 (-) 2230 (-) 2400 (-) 2570 (-) 2740 (-) 2910 (-) 3090 (-)
18” 770
(0.03) 980 (0.03) 1180 (0.01) 1380 (0.01) 1580 (0.01) 1780 (0.01) 1980 (0.01) 2180 (-) 2350 (-) 2550 (-) 2750 (-) 2950 (-) 3150 (-) 3350 (-) 3540 (-)
20” 850
(0.03) 1090 (0.02) 1330 (0.01) 1550 (0.01) 1770 (0.01) 1990 (0.01) 2210 (-) 2430 (-) 2650 (-) 2870 (-) 3090 (-) 3310 (-) 3530 (-) 3750 (-) 3990 (-)
22” 930
(0.02) 1210 (0.01) 1480 (0.01) 1730 (0.01) 1980 (0.01) 2230 (-) 2480 (-) 2730 (-) 2950 (-) 3200 (-) 3450 (-) 3700 (-) 3950 (-) 4200 (-) 4440 (-)
24” 950
(0.02) 1290 (0.01) 1630 (0.01) 1900 (0.01) 2170 (-) 2440 (-) 2710 (-) 2980 (-) 3250 (-) 3520 (-) 3790 (-) 4060 (-) 4330 (-) 4600 (-) 4880 (-)
26” 990
(0.02) 1390 (0.01) 1780 (0.01) 2080 (0.01) 2380 (-) 2680 (-) 2980 (-) 3280 (-) 3550 (-) 3850 (-) 4150 (-) 4450 (-) 4750 (-) NA NA
28” 1070
(0.01) 1500 (0.01) 1930 (0.01) 2250 (-) 2570 (-) 2890 (-) 3210 (-) 3530 (-) 3850 (-) 4170 (-) 4500 (-) 4820 (-) NA NA NA
30” 1020
(0.01) 1550 (0.01) 2080 (0.01) 2430 (-) 2780 (-) 3130 (-) 3480 (-) 3830 (-) 4150 (-) 4500 (-) 4850 (-) NA NA NA NA
32” 1090
(0.01) 1660 (0.01) 2230 (-) 2600 (-) 2970 (-) 3340 (-) 3710 (-) 4080 (-) 4450 (-) 4820 (-) NA NA NA NA NA
34” 1150
(0.01) 1770 (0.01) 2380 (-) 2780 (-) 3180 (-) 3580 (-) 3980 (-) 4370 (-) 4750 (-) NA NA NA NA NA NA
36” 1060
(0.01) 1790 (0.01) 2520 (-) 2670 (-) 3090 (-) 3510 (-) 3930 (-) 4350 (-) 5040 (-) NA NA NA NA NA NA
York reserves the right to change specifications without notice