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

8/14/2019 Form: 036-21478-001 Rev. a (0802) Supersedes: Nothing

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


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Zone

Zone

How Meridian Works ........................................................................................................... 5

Why Should I Use Meridian? ............................................................................................... 6

What Is Unique About Meridian

? ......................................................................................6-8Zoning 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 unitsare for ease of communication. Meridian can also be used onsplit systems.

Form: 036-21478-001 Rev. A (0802) Supersedes: NothingCopyright 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.


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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 ......................................................... .14Figure 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 .................................................................... 17Figure 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


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5/28Meridian Systems 5

Zoning Design Guide036-21478-001 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 degreeoff setpoint. At this time a vote is placed for heating orcooling. Next the controller evaluates the total cooling

demand or heating demand within the entire buildingto see which requirement is more critical. Finally, thesystem looks for any priority conditions, which wouldtake precedence over other zones. All three of these el-ements working together provide accurate and stablecontrol of comfort.

Additional control features are taken into account toprovide a very effective control of the system. Some ofthese include priority override, supply air temperaturelimits, outside air temperature lockouts, and min./max.control over damper position.

Substantial savings can be realized using the Meridian

Zoning system instead of having to install multiple roof-top units to accommodate multiple zone requirements.The Meridian Zoning system is versatile and can beused with any packaged roof top unit or split system. Itcontrols a variety of terminal unit functions includingsingle duct pressure dependent, pressure independent,series fan and parallel fan terminals.

The Meridian control system converts single-zone con-stant volume rooftop packaged or split system HVACunits into variable air volume/variable temperaturemultiple 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 ZoneManager then directs the HVAC unit to provide theappropriate amount of heating, cooling, and ventilationto satisfy each zones requirements. A bypass dampercontrolled, by a static air pressure sensor, modulatesto maintain constant duct pressure.

The Meridian system uses a unique 3 tier approach tocontrolling the system:

Voting Zones

System Demand

Priority

This 3 tier system works in an integrated fashion tomaintain proper control of the equipment and effectivecontrol of comfort in the zone.

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6/286 Meridian Systems

Zoning Design Guide 036-21478-001 Rev. A (0802)

Why Should I Use Meridian ?

Meridian is a proven system with a long history ofsuccessful installations. Our systems have been refinedover the years with the help of feedback from people inthe field who work and live with these systems on adaily basis. Our success is greatly due to the fact thatwe have implemented changes and enhancements based

on real world experience not from tinkering with equip-ment in an isolated lab environment. This real worldapproach provides engineers, contractors, and end us-ers with a zone control system that is efficient, reliable,and most importantly, keeps the customers comfortable!

What Is Unique About Meridian?

Meridian is unique because it has many features notfound on other systems. These features include

Non-Proprietary Design

Meridian will work on any manufacturers HVACequipment that will accept a standard thermostat con-nection. This protects the end user from being locked into one source for service and support. In addition,Meridian systems include very comprehensive docu-mentation, which is written in a format designed for thecontractor. This allows a contractor with limited con-trols experience to easily install the Meridian system.

Pre-Engineered Software

System design, software, and documentation has alreadybeen done for you. This eliminates the costly expense

usually associated with conventional DDC systems,making the Meridian system more competitive andeasier to install and operate.

One System for Zoned or Single ZoneSystems

Not only does Meridian provide a networked zonecontrol system for one or multiple zoned HVAC units,

you can also connect individual single zone units to thesystem 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. Thisreduces the chance of ordering errors and makes sys-tem layout effortless!

User Friendly Set Up

Since the Meridian

system is designed for menu driven,fill in the blank programming, system setup is simple.The system manual takes you step by step through theset up process. Default parameter values are pro-grammed into permanent memory so the system can beoperational at start-up. Specialized training is not re-quired.

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True Network Communications

The Meridian uses a three wire, RS-485 loop for com-munication between all controllers in the system. Thisprovides a very reliable form of communication withflexibility of installation. The loop can be wired in adaisy chain or star configuration. Many other zon-ing systems utilize home run wiring that requires allcommunication cables to be brought back to a centralpoint adding additional cost to the project and compli-cating wiring.

High Integrity Communications

Many communicating control systems are susceptibleto electrical interference. One major manufacturer ofzoning systems recommends that their communication

cable should not be strapped to conduit because of po-tential interference. The Meridian Systems have a com-munication bus that is almost immune to any noise 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 othersystems.

Stand-Alone Systems

All Meridian Systems are true stand-alone and do notrequire 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 anddisplay 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 backlightedmaking it easy to read even in low light environments.

Menu driven programming makes the system extremelyuser 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 theCommLink II communications interface and a localphone 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 frontend software package.

Memory BackupInstead of batteries, which have to be replaced,Meridian utilizes super capacitors to provide powerfor memory backup during power outages. The majoradvantages to this approach is that super capacitors aremore reliable than batteries and they recharge in a mat-ter of seconds instead of hours. Typical memory backupis good for a minimum of 10 days.

Modulating, Heavy Duty Actuators withReal Time Feedback

All Meridian

actuators utilize true modulating con-trol unlike many systems, which are two position. Thisgives the system-improved control, which translates, tobetter comfort levels. Our actuators are also rated for2- million cycles, making our actuators some of themost reliable in the industry. One other critical featureis the real time feedback. Many other systems have nofeedback at all. They blindly estimate the travel time oftheir actuator, which, in the real world, is not a veryrepeatable estimate. To help correct the problems in-herent with this approach, they recycle all the actuatorsin 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 RoundZone Dampers

Meridian only uses commercial grade zone dampers,not cheap, flimsy, light commercial or residentialstyle dampers like many other manufacturers. Our rounddamper is ARI certified and comes from the factory fullyinsulated. Why? When many zone dampers are installedthey 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 contractorwhile insuring the end user will not have problems withcondensation dripping down onto the ceiling.

Rectangular Dampers

Meridian uses only top of the line, aluminum air foilrectangular control dampers. No other zone system onthe market today utilizes a damper of this quality andperformance!




What Is Unique About Meridian?

Patented Flush Mount Room Sensors

Our flush mount room sensors are so unique, they arepatented (U.S. Patent No. 4,659,236). Even though part

of the sensor is recessed into the wall to provide anattractive yet tamper proof flush mounting, internal walltemperatures do not influence the sensor. A special plateon the face of the sensor accurately senses space tem-perature. Even though the attractive off white plastichousing is a preferred color, the sensor housing can bepainted 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 thecontrollers via modular plugs like the ones used on tele-phones. This simplifies installation and eliminates thepossibility of wiring errors. The devices, which utilizethis method, are damper actuators for zone and bypasscontrol, auxiliary relay boards, and static pressure/air

flow sensors. There is one interesting side note aboutthe auxiliary relay board and airflow sensors. Thesedevices are typically used on the zone controllers in theMeridian Basic & Plus systems. When the system ispowered up, it automatically looks to see if these de-vices are connected to the controller. If they are, the

controller automatically reconfigures itself to utilizethese devices and activates the appropriate set up screensback at the operators interface. Pretty neat dont youthink!

FREE! Windows Graphics Software

Each Meridian system can be monitored on site or re-motely using a PC and our Prism computer front endsoftware software. This full-featured package is veryuser friendly and can be used to monitor one system orhundreds. The Prism software is not copy protectedso it can be installed on multiple PCs without addi-tional expense. Just some of its many features includebut 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 allowingother manufacturers to develop direct interfaces to thecommunications loop. This gives you the ability to in-tegrate the Meridian system into products from othervendors. Our engineering staff will be glad to assist anyvendor in this process.




General

Even though there are some similarities between zonecontrol systems and Variable Air Volume (VAV) sys-

tems, there are some major differences. In many casessystems will be called VAV when in fact they are reallya zoning system or are referred to as a zoning systemwhen they are really a VAV system. Always make surethat you do not try to adapt a zoning system to a VAVdesign system. Understanding the differences will helpyou to prevent misapplication of the Meridian zoningsystem. In the paragraphs that follow we will try to ex-plain the differences, advantages and disadvantages ofeach 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 locatedin the downstream ductwork that are used to controlthe amount of constant temperature air delivered to thevarious building zones. Sometimes the HVAC unit mayhave gas or electric heat, but it is typically sized andapplied for morning warm-up purposes. The HVAC unitis designed to vary the volume of air that is supplied tothe 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. VAVsystems typically use high velocity VAV terminal unitsto distribute the air to the zones. As the various VAVterminal units in the different zones open and close tosupply the constant temperature air to the spaces, theHVAC unit varies the volume of constant temperatureair based on the static pressure in the ductwork. TheHVAC unit is designed to maintain a constant cold sup-ply air temperature regardless of the air flow volume inthe system. The HVAC unit cycles its cooling stages tomaintain 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 areused to supply heated air to the space. Many times fanpowered terminal boxes are used and in many casesalso incorporate electric or hot water heating coils toprovide perimeter zone heating. In summary a true VAVsystem uses a variable volume fan supplying constanttemperature 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 differentin operation and design from the VAV system previ-

ously discussed. One of the major differences betweenthe zoning system and a true VAV system is that theHVAC unit used on a zoning system utilizes a constantvolume fan. Air volume control of the zoning system isachieved by bypassing air from the HVAC unit supplyduct back into the HVAC unit return air duct on the unitinlet. This bypass air is controlled based on a static pres-sure sensor located in the supply air duct downstreamof the unit supply air discharge. The bypass dampermodulates open and closed based on the static pressurein the duct. The temperature at the HVAC unit dischargevaries in relation to the demand from the zones. Typi-

cally the HVAC units used for the zoning system willhave both heating and cooling capabilities. The fan sup-plies a constant volume of cold or hot air to the ductsystem which is then fed to the individual zones bymodulating zone dampers. Each zone controller relaysits heating or cooling demand to the HVAC unit con-troller. The HVAC unit controller determines its modeof operation (heating, cooling or vent mode) depend-ing on the demand from the zone controllers. The unitcontroller utilizes a voting system to determine the cor-rect mode of operation. Each zone controller determines(based on its heating and cooling setpoints) whether ornot to use the air being supplied by the HVAC unit. Forexample, one of the zones is calling for cooling whenthe temperature in the duct is above the zones coolingsetpoint. This zone will move to its minimum coolingposition to prevent warm air being introduced into thespace. With the zoning system the zone dampers aregenerally pressure dependent. Pressure independentoperation is available but is not very common. Reheatand/or fan powered terminal units can be used but arentcommonly part of the typical zoning system.

ConclusionIn many cases VAV systems go over budget because ofthe increased cost of a VAV, HVAC unit and the expen-sive VAV controls associated with the system. Manytimes the system can be redesigned to a zoning systemusing Meridian controls with a significant cost sav-ings and equal or better performance and comfort thanthe VAV system would provide. Be sure to follow theinstructions in this design guide for your zoning sys-tem.




This is a summary of the key items you need to con-sider for the design and layout of a successful zoningsystem.

It is important that you study the design guide for a

more in depth understanding of proper system design .

By following the design guide and these tips you caneliminate many unnecessary headaches that occur whenthe basic rules of zoning are not followed. Always con-tact your York 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




Design Considerations

Load Diversity

A zoning system is designed to improve tenant comfortby 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 resultwill be poor control and excessive wear due to cyclingof 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, considerusing either VAV boxes with heat or separate externalheat on perimeter zones. Meridian Zoning systems

offer a variety of methods to control additional zoneheat to help you avoid problems.

Group similar loads on an individual unit and use morethan one zoned unit if required. Any special loads canbe handled by using separate constant volume units.

The Meridian Plus system offers the designer consid-erable flexibility by allowing both multiple-zoned unitsand single-zone units to be connected within a singlesimple system.

Cooling - Partial Load Conditions

The engineer must be aware of several potential prob-lems when applying a zoning system for cold weatheroperation.

1.) Low Ambient Temperature Lockout. During verycold weather it is common for mechanical systems tohave low temperature lockouts which protect equip-ment from damage if operated under these conditions.Meridian also provides user programmed lockouts forprotection purposes, although mechanical safeties

should always be used as the final stage of protection.

If the rooftop unit services interior zones with thermalloads, which require cooling when outside temperaturesare below the safe operating limits for your equipment,you should seriously consider installing an economizeron your rooftop unit. The Meridian control system isdesigned to take advantage of an economizer if it isinstalled. The use of an economizer will save money on

utilities and provide comfort under conditions when itis not possible to operate the mechanical cooling sys-tem.

2.) Low Supply Air Temperatures. Under lightlyloaded 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 supplyair temperature, which may result in the supply air tem-perature reaching the low temperature safety limit. Ifthe 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 themechanical 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 oversizing the unit. Do your all load calculationscarefully. Since the zoning system directs the heatingor cooling to the zones which require it, you may findthat you can use a smaller unit in many cases. Oversizingis the number one cause of excessive low supply airtemperature cycling.

Use an economizer. Although this is not a cure-all, itgreatly improves operation during cool weather whencooling loads are minimal. Using an economizer alsoimproves ventilation and lowers operating costs.

Increase cooling minimum airflow. Increase your cool-ing minimum airflow or damper position settings to al-low more air during cooling operation. Be careful toavoid minimum settings that are so high they may causeover cooling of the spaces.

Bypass the air into the ceiling plenum. If you have asystem without ducted return, bypass the air into theceiling plenum instead of into the return air intake. Becareful if you use this method since you may get dump-ing of cold air from your return air grilles. This methodworks best with plenum returns.Do not use this methodwith ducted returns.




Design Considerations

Increase your static pressure setpoint. This will helpreduce the amount of air being bypassed. Be aware ofincreased noise levels and the cost of operation if youuse excessive static pressures. This will not work if youare using pressure independent zone controllers, sincethey will maintain a constant flow of air to the zonesregardless of duct static pressure. This technique willlikely cause over cooling of the spaces due to increased

airflow at minimum positions.

Warning:

If the fan system has the capability of producing static

pressures which could damage ductwork you must pro-

vide a manual reset, high pressure limit switch (Dwyer

1900-5-MR or equal) to cut off the fan system in theevent 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 thecures are generally the same. Again, a number of thingscan be done to reduce the effects of this problem.

Increase heating minimum airflow. Increase your heat-

ing minimum airflow or damper position settings toallow more air during heating operation. Be careful toavoid minimum settings that are so high they may causeover heating of the spaces.

Increase the static pressure. Set the static pressuresetpoint to be as high as practical. Increasing static pres-sure does not help if you are using pressure indepen-dent control operation.

Avoid oversizing the unit. Do your all load calculationscarefully. Since the zoning system directs the heatingor cooling to the zones which require it, you may findthat you can use a smaller unit in many cases.

Bypass the air into the ceiling plenum. If you have asystem without ducted return, bypass the air into theceiling plenum instead of into the return air intake. This

method works best with plenum returns. Do not usethis method with ducted returns

Use auxiliary heat . Use an auxiliary heat source ineither your VAV boxes or use baseboard heaters.

Meridian has a number of auxiliary heat control op-tions which provide solutions to most problems. Referto theAuxiliary Heat Control Options topic near theend of this section.

Override ConditionsAfter-hours overrides can produce aggravated partialload conditions in both the heating and cooling modes.A single zone being overridden for after-hours use most

commonly causes the problem. This causes the rooftopequipment to operate for only one zone. The Meridian

system offers an improved solution to this commonproblem by allowing a single override to trigger a groupof zones via a global override. This allows the sys-tem to operate with sufficient load to reduce cyclingcaused by light load conditions.

Building Pressurization

If you are using an economizer, building pressurizationmust be addressed. Failure to properly handle buildingpressurization may result in doors remaining open whenthe economizer is operating. Pressurization problemscan render economizer operation useless. The follow-ing suggestions will help to avoid potential problems.

Use powered exhaust. A power exhaust fan(s) must beused 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 wheneverthe 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




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 AndLocation Of Zones

A single air handler unit can have no more than sixteenzones and no fewer than 3 zones. If the number of zonesexceeds sixteen then more than one Zone Manager willbe required.

The primary precaution to be taken in applying theMeridian 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 oppositetemperature air to satisfy its load. For example, depend-

ing on the wall, ceiling and floor material and locationwithin the building (e.g. top or middle floor), a typicalfloor of a building usually has several distinct tempera-ture or control zones that are affected uniquely by theoutdoor 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 11could be multiple conference or computer rooms whereadditional zoning would be required, or it could be assmall as a corridor where no zoning is required. Simi-larly, zones 7 and 8 could have no external windowsand no partitions between them and could be consid-ered a single zone. Some zones could be divided intomultiple 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 ZoneControllers, the greater the comfort. The designer willhave to look at the specific building, balancing the costsof multiple zones with the added comfort possible withmultiple zones, to match the owners requirements.

It is important to recognize that there are purely inter-nal zones, such as Zone 11 in Figure 1-2, which maycontain separate offices/conference/computer rooms.

These internal zones could easily have high cooling re-quirements while external zones (1,2,3, etc.) could beat or near design heating load. This is a misapplication of the Meridian , zoning (or any heating/cooling

change-over) system. The interior zones with coolingonly loads should be served by a separate single zonerooftop HVAC unit (that could be zoned between mul-tiple rooms with a similar load profile). Supplementalheat could be added to the perimeter zones and con-trolled with the auxiliary heat control board from theZone Controller. System performance will generally be

compromised and frequent change-over from the heat-ing to the cooling mode will occur during the heatingseason if purely internal zones are combined on the sameair-conditioning unit serving perimeter zones. The ex-posure to the sun has a large affect on the loading of thebuilding. With the building zoned as shown below, forthe best control, zones 6, 7, 8, 9 and 10 should be puton one HVAC unit, and zones 1, 2, 3, 4 and 5 on an-other HVAC unit. Zone 11 should be on a separate singlezone constant volume HVAC unit.Figure 1-2: Zones Affected by the Outdoor Load

2 3 4

5

678

10 11

1

9

N





Figure 1-3: Zone Layout With External Zones Only.

1

2

3

4 5

6

7

N

Here is another example of the buildings exposure af-fecting the zoning. Figure 1-3 below shows a buildinglayout with 7 zones, it has 3 zones with an eastern ex-posure, 4 zones with a western exposure and two eachnorth and south exposures. This building can be con-trolled from a single, constant volume air handler. Allof the zones have exterior exposures and there are nototally internal zones, so they will have similar loadrequirements.

Figure 1-4 shows a building with 7 zones, 4 of the zoneshave a north exposure and the other 3 have a south ex-posure. Since there is a big difference in the affect onthe building between north and south exposures, instal-

lation of two separate zoned HVAC units is recom-mended.

Figure 1-5 shows a combination manufacturingfacility and office area. The space temperature in theindividual zones numbered 1 through 7, would all becontrolled by a single HVAC unit. A single constantvolume HVAC unit would be used for each of thezones 8 through 12.

1 2 3 4

567

N

1

2

3

4 5

6

7

8

9 12

10 11

Figure 1-5: Zoning And Constant Volume Units

Figure 1-4: Zones With North And South Exposures.




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 ofloads to be taken into account and will often providebetter comfort with a smaller HVAC unit.

In sizing the system, the individual zone loads shouldbe calculated using any dependable load estimating pro-gram. Because of diversity, the central unit should beselected for the instantaneous peak load, not the sum ofthe peak loads, as would be done with a constant vol-ume single zone system. Consider the following whensizing the central unit.

Size the peak cooling load based on themonth day hour of the greatest total buildingsystem load

Heating should be sized for the lowest designtemperature with an additional margin formorning pickup. This margin is generallyrecommended to be 20 to 25 percent of basedesign.

Step #3 - Duct Design Considerations

The Meridian

system uses a typical low pressure ductdesign. To reduce noise problems duct pressures shouldnot exceed 1 inch W.C.

Primary trunk ducts should not be undersized. Thisis especially true for pressure dependent systems.Pressure dependent refers to the typical Meridian,Zone Controller without the airflow sensor. With largertrunk ducts, it is easier to assure relatively constant pres-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 zonedampers above corridors to reduce the noise in the spaceand facilitate service of the units. Trunk ducts shouldbe sized for no more than 0.1 inch W.C. drop per 100feet., and a maximum duct velocity of 2000 FPM.

Note For pressure independent terminal unitswith velocity sensors and conventionalVAV boxes properly selected for

quiet operation, this 2000 FPM rulecan be exceeded by up to 50 percent. Thedesigner, however, should be veryexperienced in VAV system design beforeconsidering modification of this generalrule.

Typical VAV systems with pressure independent termi-nals use the static regain method for sizing ducts. Thetypical Meridian Zoning system is a low-pressure,pressure dependent system that utilizes conventional

unitary air-conditioning units. These systems should usethe equal-friction method of sizing the ducts, and usethe maximum loss of 0.1 inch per 100 feet as describedabove.

Step #4 - Air Motion/Diffuser Selection

Air motion is a consideration for occupant comfort. Theselection of diffusers for an Meridian Zoning systemrequires more care than a constant volume system dueto varying flow of air into the zones. Slot diffusers arerecommended 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 unsatisfactorywith an Meridian Zoning system. These diffusers mayresult in dumping of the cold air at low flows in thecooling mode, and insufficient room air motion at lowair 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 comesfrom a ceiling diffuser. Linear slot diffusers should beproperly selected for the airflow and throw suited to

the specific installation or zone.

Additional factors to consider in diffuser selection aresound level and throw at design flow. Generally, mul-tiple diffusers will result in lower sound levels in thespace, but this must be balanced with the additionalhardware and installation costs. It is commonly recom-





mended that slot diffusers be located near the perim-eter or outside wall with the airflow directed into theroom. Consult your diffuser supplier or catalog forproper diffuser sizing and location.

Series fan boxes may be used instead of zone damperswhere higher induction rates are desirable. If the heatloss on perimeter walls is high, such as large areas ofglass, the use of series fan boxes may be indicated tomaintain higher induction rates to offset downdrafts.If the heat loss is greater than 275 BTUH/LINEARFOOT, you should use high quality slot diffusers nextto the outer wall with the airflow directed inward tocounteract downdrafts during heating. Seriousdowndraft problems occur when heat losses exceed 400

BTUH/linear foot and both high induction diffusers andseries 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 variablevolume zone dampers. The bypass damper modulateson a signal from a duct static pressure sensor to by-pass air from the supply duct back into the return airduct. If the duct static pressure exceeds the adjustable

setpoint, then the damper opens to bypass more air, andif the static pressure drops below the setpoint, it closesto bypass less air.

Using a load calculation program, the bypass dampershould be sized to give you the maximum CFM of airto be bypassed, typically 60 to 70 percent of the HVACunits rated capacity.

To size the damper, select a damper from the table basedon calculated bypass CFM and a maximum velocitybetween 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 Tables1-1 & 1-2: Damper Sizing Charts)

Whenever possible, use a single bypass damper andround duct for the bypass. If space limitations or totalairflow requires it, multiple bypass dampers can be con-trolled in parallel or a rectangular damper may be used.For proper control of the Bypass Damper, the static pres-sure sensor location is very important. Refer to Fig-ures 1-8 Thru 1-10 for proper sensor installation loca-tion information and guidelines.

Figure 1-6: Round Bypass Damper Figure 1-7: Rectangular Bypass Damper & Kit




Fan

RA SensorSA 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 closeto 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 eachzone. These calculations will be used in selecting theappropriate zone damper sizes.

Using the maximum acceptable velocity for a branchduct (typically 1000-1500 FPM for minimal noise), find

the smallest damper that will deliver the required CFMas 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 damperwhich will provide the acceptable CFM to meet yourspecific zone requirements.

Note Compare the damper size selected againstthe duct size to determine if the next size

up or down will provide acceptableperformance without requiring a transi-tion fitting.

One additional damper may be slaved together for largezones. See zone wiring diagram for details. This shouldbe reserved for situations when it is not practical to usea single large damper. Round zone dampers can be speci-fied to be either pressure dependent or independent.

Fan

RA SensorSA Sensor

3D

Min.

2D

Min.

Return Air Duct

Supp

lyAir

Duc

t

SP Pickup

Bypass Damper

SP Sensor

Fan

RA Sensor

SA Sensor

Return Air Duct

Supply Air Duct

Tubing To Be EqualLength And Size

Bypass Damper

SP SensorSP Pickups

If the trunk ducts are properly sized for minimum pres-sure drop, the location of the static pickup probe is notparticularly critical. It should ideally be located at rightangles to the airflow in a straight section of the supplyduct approximately 2/3 the distance of the total lengthof the supply duct. Also the probe should be locatednot less than 3 duct diameters downstream and 2 ductdiameters 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 aninstallation, a location in the main trunk where the tipis not in a negative pressure area (e.g. just downstreamof the inside curve of an elbow) or an area where thetube opening is directly impacted by the velocity of thesupply air. See Figure 1-9.





Pressure Dependent Dampers

With pressure dependent (PD) dampers, the minimumand maximum airflow is set based on damper position.During the final commissioning of the system, each zoneis typically balanced with a flow hood and the min/maxposition is fixed either mechanically or the preferredmethod, in the controller software. Since this min/maxsetting is based only on position, as the static pressurefluctuates it will cause the actual airflow at the zonedamper to increase or decrease. Therefore the name,pressure dependent since the airflow is dependent onthe static pressure. Pressure dependent dampers areavailable in round or rectangular configurations. SeeFigure 1-11 for a diagram of a typical pressure depen-dent zone damper.

Pressure Independent Dampers

When using pressure independent (PI) dampers thisminimum and maximum is set based on actual CFM ofairflow through the damper. Airflow is measured usinga pickup tube mounted in the zone damper and an elec-

tronic air flow sensor. Using this method you alwaysknow 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 actualairflow reading. As the static pressure fluctuates, theflow sensor reads the variation and automatically repo-sitions the damper to maintain the minimum or maxi-mum flow setpoints. Since the minimum or maximumairflow 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 Figure1-12 for a diagram of a typical pressure independentzone damper.

When pressure independent dampers are used they mustbe 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 thecommissioning portion of the system installation. TheK-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 usedby the controller software to maintain the correct mini-

mum or maximum airflow setpoint regardless of thestatic pressure at the flow sensor. The K-factor and theminimum and maximum damper CFMs can be enteredat the Zone Manager on Basic systems, or using theSystem Manager on Meridian Plus systems. K-factorscan also be entered using a personal computer with thePrism 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-tors and minimum and maximum damper CFM setpointsare entered, the damper will modulate to try to main-tain these CFM airflows during damper operation. If

zone dampers or fan terminal units manufactured byothers are used, the correct K-factors must be obtainedfrom the equipment manufacturer.




can cause air flow problems. These slide-in dampersrequire that the damper frame be inside the duct. Imag-ine an 8 x 10 rectangular duct using a slide in damperwith a frame thickness of 1. The frame alone wouldreduce 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 bladesfor superior control and have both blade and jamb sealsfor tight shut off. The dampers are installed using amounting flange. The purpose for the flange mountingis to allow as much unrestricted free space within theduct as possible.

Many companies utilize slide-in type dampers which

Bypass & Slave Dampers Zone Dampers

1/2" Foil FacedInsulation

Actuator

Zone Controller

Round DamperBlade Assembly

Control Enclosure(Cover Removed)

AIRF

LOW AIRFLO

W

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 PressureAir Flow Probe K Factor- For Pressure

Independent Applications Only474 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)


(0.15)

676

(0.10)

1064

(0.07)

1538

(0.07)

2100

(0.07)

2749

(0.05)


(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 FacedInsulation

Actuator

Round DamperBlade Assembly

Control Enclosure(Cover Removed)

AIRFLOW AIRFLOW

Bypass & Slave Interface





damper has a height of 10. In this case the damperwould utilize an 8 blade and a 2 blade stop or damwould be installed across the base of the damper. Tak-ing into consideration the blade stop and the frame, a10 x 10 damper would have a reduced opening of 6 x 8inside the duct. Many contractors have experienced lowair 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 widthsin order to accommodate the size of the damper insteadof the damper trying to accommodate the size of theblade.

Rectangular Dampers

Table 1-2: Rectangular Damper Selection Data

DamperHeightB

8 10 12 14 16 18 20 22 24 26 28 30 32 34 36

DamperWidthA

Airflow Data with Full Open DamperCFM @ 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

(0.01)

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




Auxiliary Heat Control Options

The Meridian Zoning system offers the user a varietyof methods to deal with zone heating requirements. In

order to control zone heat, an optional Relay Expan-sion Board is required. When deciding how to handlezone heating requirements the user should consider thefollowing:

Does the rooftop unit have heat? Are you using fan-powered boxes with reheat? Is auxiliary heat such as baseboard or radiant

ceiling panels used?

If the zone has some type of heat, the user must con-sider how the heat is to be used. Typical questions thatshould be asked:

Q: Should the zone heat be used as a first stage whereit will become active before a heating demand iscreated at the rooftop unit?

A: This mode is useful if you expect to have bothheating and cooling demands at the same time. Thezone will use its own heat and allow the rooftopunit to continue to provide cooling for other zones.This mode is also useful if the roof top 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 roof top unitcannot maintain the space temperature, such asduring very cold weather?

A: In this mode of operation the rooftop will examinethe heating and cooling demands and try to satisfyall of the zones by switching between heating andcooling as required. The zone heat will only beactivated if the zone temperature falls below a

selected limit.

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

A: Many times it is desirable to use the rooftopheating whenever possible and only use zone heatwhen the rooftop unit is in cooling. This mode ofoperation will lockout zone heat if the rooftop isdelivering heated air.

Relay Expansion Board Outputs

The following describes the operation of each of therelays on the optional relay expansion board. The user

can choose the appropriate relays for any given appli-cation.

Relay #1 - Parallel Fan

If the Zone is in cooling or vent mode, the parallel fancan activate anytime the zone temperature drops 0.5 Fbelow the heating setpoint. It deactivates when the tem-perature rises above the heating setpoint.

Relay #2 - Box Heat

If the zone is in cooling or vent mode then the box heatcan activate anytime the zone temperature drops 1.5 F

below the heating setpoint. It deactivates when the tem-perature rises to within 1.0 F of the heating setpoint.Box heat is not allowed to activate in the heating modewhen there is hot air being supplied by the air handlingunit. This output was intended to allow zone reheat whilethe Zone Manager is satisfying cooling demands in otherzones.

Relay #3 - Aux. Heat

In the occupied mode, the aux heat can activate any-time the zone temperature is 0.5 F below the aux heat

setpoint. It deactivates when the temperature rises 0.5F above the aux heat setpoint. In the unoccupied mode,the aux heat uses the unoccupied heating setpoint withthe same deadband values mentioned above. This pre-vents the zone from maintaining the same aux heatsetpoint at night that it does during the daytime. TheParallel Fan and Box Heat are prevented from comingon until the aux heat is energized.

This output was intended to allow zone heating to aug-ment the normal heating mode and also to allow a zonean attempt to satisfy its own heating needs before cre-

ating 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 fancan only start running when the zone damper is closed,so it determines that the damper is closed before start-ing the fan.




System Installation

Mounting Of Controllers

All Meridian Round Dampers or Rectangular DamperKits have the required controllers, actuators etc. fac-

tory mounted in an indoor rated control enclosure. Ifyou wish to use another manufacturers dampers for zon-ing control you must purchase Zone or Bypass Pack-ages from York. These are furnished without a mount-ing enclosure. Most local codes require these compo-nents be mounted in an enclosure. If yours does notrequire this it is still strongly recommended that you domount them in an enclosure. Components that are notin an enclosure are in danger of being damaged, andare susceptible to dirt and moisture contamination. Youmay furnish your own enclosure or one is available fromYork. The part number for the York enclosure is

2ZCE0047001024. This is an indoor rated enclosure. Ifthe zone mounting location is susceptible to water dam-age, watertight enclosures can be purchased at any lo-cal electrical supply. Mounting location for the control-lers should not violate any local, state or national codes.

System Wiring

Wiring requirements for Meridian systems can be bro-ken down into four main categories:

1.) Power Wiring

2.) Communications Wiring

3.) Controller Wiring

4.) Sensor Wiring

Each category should be thoroughly understood andimplemented in order to have a trouble free installa-tion.

Power Wiring

All Meridian devices are powered by 24 VAC. It ispossible to power the system using one or more com-mon transformers or individual transformers for eachdevice. Possible problems you may encounter using

common transformers to power multiple devices are:

If polarity is not maintained between devices,shorting of the transformer will occur resultingin damage to the electronics.

When using one transformer to power multipledevices it is possible to lose most or all of yoursystem if the transformer fails.

It is important when powering multiple devicesfrom one transformer that total VA load andwiring voltage drops be taken into account forproper sizing of the transformer and wire.(See Figure 1-16 on page 26)

It is therefore recommended that in most installationsindividual transformers be installed for each device. Thiswill greatly reduce the possibility of errors and pos-sible damage to the system.

Power wiring should always be done in accordance withany local, state, or national codes.

It is also important to note that THE HVAC UNITSFACTORY TRANSFORMER SHOULD NEVER

BE USED TO POWER Meridian

devices! Normallytransformers on typical HVAC units are sized to onlyhandle the load of the units factory installed controls. Aseparate transformer must be used.

Communication Loops

The Meridian system utilizes two different communi-cations loops. The Basic system uses a 9600 Baud RS-485 communications loop (Local Loop) only. The Plussystem uses two different communications loops. It hasa 9600 Baud RS-485 communications loop (Local Loop)like the Basic system but also has an RS-485 19200

baud communication loop (Network Loop) that con-nects the Zone Managers together and connects theCommLink II communications interface.




York requires that all communication wire be 18 gaugeminimum, two wire shielded cable, Belden #82760 orequivalent. York offers communications cable for thispurpose. The 18 gauge color coded and labeled wire isavailable for the local loop and the network loop com-munications wiring. The local loop wire is supplied in1000 ft. spools and is labeled Local Loop with agreen candy stripe. The network loop wire is suppliedin 500 ft. spools and is labeled Network Loop with ared candy stripe.

The loop is best connected in adaisy chain configura-

tion, meaning the loop is connected from one control-ler to another. It is not necessary to sequentially ad-dress the zone controllers in relation to their locationon the loop.

Even though the daisy chain configuration is preferred,thestar configuration can also be used. If required, acombination of the two can also be used. Remember,the best communications loop wiring is the one whichutilizes the minimum number ofends while using theshortest wiring path.

Communication Wiring terminals on most Meridian

controllers are marked T, R and SHLD (Note:instead of SHLD the CommLink is marked G andthe Basic Zone Manager is marked SH). All wiringshould be connected T to T, R to R and SHLD to SHLDthroughout the entire loop system. Communication wire

should be color coded to facilitate error free wiring.The communication loops will not work if any of thewires are reversed or otherwise landed incorrectly. Com-munications loops can be run up to a maximum of ap-proximately 4000 ft. in total length. If your system ex-ceeds this length, please consult the York factory formore information regarding extended communicationloop lengths and solutions.

Caution: Unless the communications loopis installed in conduit, be careful toposition the cable away from highnoise devices like fluorescentlights, transformers, VFDs, etc.Conduit is not required for com-

munications loop wiring unlessrequired by local codes.

Tip: Incorrect wiring of the communicationsloop is the most common mistake madeduring installation. Before beginninginstallation, write down the wire colorused on each terminal connection andconsistently maintain that color code. Itis recommended that a continuous wirerun be made between devices. Anytimea splice is made in the cable you increaseyour chance of problems. If a splice mustbe made, Never use wire nuts! Cableshould be soldered and wrapped or ifsoldering is not possible use butt splicecrimp connectors and wrap tightly withelectrical tape.

Caution: Make sure when you are insertingwires into the terminal blocks thatstrands of wire do not stick out and

touch the adjacent terminals. Ifadjacent wires touch each other oranother terminal, shorting andsubsequent damage to the circuitboard could result

Figure 1-13: York Communications Wire

Local Loop Wire Network Loop Wire


24/28




Zone Controller 24 VAC Supply Voltage (10 VA)

(2) Conductors - Determine minimum

wire size from Figure 1-16 on page 26. Communications Loop

(2) Conductors 18 gauge minimumtwisted pair with shield(York communication wire,

Belden #82760 or equal)

Room Sensor(2) Conductors 24 gauge minimum(3) Conductors if using optional slide

Sensor Wiring

Meridian

temperature sensors utilize a type III ther-mistor element that is one of the most commonly usedsensors in the building controls industry. Sensor wireshould be a minimum of 24 gauge however larger wiresuch as 18 gauge is commonly used.

Conventional thermostat cable is acceptable in mostcommercial and institutional installations. In some in-stallations which have the potential for high electricalnoise, such as broadcast facilities (radio, TV, etc.), heavyindustrial (machinery, welding equipment, etc.), andmedical (x-ray, scanning, etc.), it is advisable to use

shielded cable on sensors which are located in or closeto these environments. The same cable used for the com-munication bus can be used in these situations.

Sensor requirements are: Supply Air Sensor

(2) Conductors 24 gauge minimum

Return Sensor(2) Conductors 24 gauge minimum

Outside Air Sensor

(2) Conductors 24 gauge minimum

Room Sensor(2) Conductors 24 gauge minimum(3) Conductors if using optional slide

adjust

Controller Wiring

All controller wiring should be in accordance with alllocal, state, and national codes. It is recommended thatall wire be a minimum of 18 AWG unless otherwisespecified in the charts below. Controller connectionsand wire sizing is as follows:

Zone Manager 24 VAC Supply Voltage (25 VA)

(2) Conductors - Determine minimumwire size from Figure 1-16 on page 26.

Communications Loop(2) Conductors 18 gauge minimumtwisted pair with shield

(York communication wire,Belden #82760 or equal)

Supply Air Temperature Sensor(2) Conductors 24 gauge minimum

Return Air Temperature Sensor(2) Conductors 24 gauge minimum

Outside Air Sensor(2) Conductors 24 gauge minimum

Supply Static Pressure Sensor(2) Conductors 24 gauge minimum

Bypass Damper(4) Conductors 24 gauge minimum

HVAC Unit Control Wiring(6) Conductors 24 gauge minimumR (Common), G (Fan), Y1 (Cool 1),Y2 (Cool 2), W1 (Heat 1), W2 (Heat 2)For Meridian Plus System With

Optional Staging Expansion Board up to

an additional (8) conductors Y3 through

Y6, W3 Through W6

System Manager 24 VAC Supply Voltage (25 VA)

(2) Conductors - Determine minimumwire size from Figure 1-16 on page 26.

Communications Loop(2) Conductors 18 gauge minimumtwisted pair with shield(York communication wire,

Belden #82760 or equal)




System Installation

Figure 1-16: Transformer And Wire Sizing Considerations

FILENAME

DATE: B. CREWS

DESCRIPTION:PAGE

DRAWN BY:

Wire & Transformer Sizing

JOB NAME

11/30/99

MWIRSIZ1.CDR

Meridian1

24VAC Power - Transformer & Wire Sizing Considerations

Component Power Requirements

120 / 24VAC

120 / 24VAC

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Distance A to B cannot exceed 46.30 Ft. Distance from A to B cannot exceed 92.60 Ft.Distance from A to C cannot exceed 92.60 Ft.

Distance from A to B cannot exceed 185.20 Ft.Distance from A to C cannot exceed 185.20 Ft.Distance from A to D cannot exceed 185.20 Ft.Distance from A to E cannot exceed 185.20 Ft.

120 / 24VAC

Some installers like to use one large 24VAC transformer to power several controllers. This is allowable as long as polarity is maintained to eachcontroller on the transformer circuit.

Usingseparate transformers also allows redundancy in case of a transformer failure. Instead of having 8 controllers inoperative because of a malfunctioningtransformer you have only 1 controller off line. If the installer does decide to use a large transformer to supply power to several controllers, the

following transformer and wire sizing information is presented to help the installer correctly supply 24VAC power to the controllers.

Following is a typical example to help the installer to correctly evaluate transformer and wiring designs.

Each Zone Controller with actuator requires 10 VA @ 24VAC power. In the examples below we have a total of 8 Zone Controllers.

8 Zone Controllers @ 10VA each................ 8 x 10VA = 80VA.

The above calculation determines that our transformer will need to be sized for a minimum of 80VA if we are to use one transformer to power all thecontrollers.

Next we must determine the maximum length of run allowable for the wire gauge we wish to use in the installation. Each wire gauge below has avoltage drop per foot value we use to calculate total voltage drop.

18ga wire.................................0.00054 = voltage drop per 1 length of wire16ga wire.................................0.00034 = voltage drop per 1 length of wire14ga wire.................................0.00021 = voltage drop per 1 length of wire

For our example we will use 18 gauge wire. York recommends 18 gauge as a minimum wire size for all power wiring.

Next use the voltage drop per foot value for 18 gauge wire from the list above and multiply by the total VA load of the 8 controllers to be installed.

0.00054 (Voltage drop per foot for 18 gauge wire) x 80VA controller load = Volts/Ft.

Meridian controllers will operate efficiently with a voltage drop no greater than 2 Volts. Divide the total allowable voltage drop of 2 Volts by the numberyou arrived at above and you have the maximum number of feet you can run the 18 gauge wire with an 80VA transformer with no more than a 2 Voltdrop at the farthest controller from the transformer..

2 (Volts total allowable voltage drop)=

0.0432 (Voltage drop per 1 ft. @ 80VA load)

Parallel circuiting of the wiring instead of wiring all 8 controllers in series allows for longer wire runs to be used with the same size wire (as shown inour examples below).

Warning: If polarity is not maintained, severe damage to the controllers may result. York recommendsusing a separate transformer for each controller in order to eliminate the potential for damaging controllers due to incorrect polarity.

0.0432

46.30 feet

It is often necessary for the installer to calculate and weigh the cost and installation advantages and disadvantages of wire size,transformer size, multiple transformers, circuiting, etc., when laying out an installation. No matter what layout scheme is decided upon, it is mandatorythat the farthest controller on the circuit is supplied with a minimum of 22 Volts.

System Manager ......................25VA GPC Controller.........................20VA

Zone Manager..........................25VA Wetbulb Module .......................20VA

Zone Controller ........................10VA Lighting Panel Controller ..........25VA

CV Controller............................20VA Zone Relay Expansion Board ...10VA

CV-C Controller........................20VA Staging Expansion Board.........20VA

Optimal Start Scheduler ...........25VA

A

A

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B C D EBB C




Application Notes:

Zoning 30 And 40 Ton Units

When using large HVAC units for zoning applications,several rules must be considered to prohibit potential

problems.

Because of the large air flow capacities of the 30 and40 ton units, great care must be taken in sizing zoneand bypass dampers.

Use these guidelines to help keep you out of trouble.

Always use the Meridian Plus system evenif you only have one unit that you are zoning.

Generally you should use constant volume

units in your zoning system design. If yourunits are to be equipped with variablefrequency drives or inlet vanes, pleaseconsult York Controls for assistance.

The 2ZEB004701024 - 8 Relay StagingExpansion Board is usually required as theseunits typically have more than 2 stages ofcooling and heating.

Bypass dampers should be sized for 60 to70% of the rated CFM of the unit. Because ofthe large air volumes involved, rectangulardampers should be used instead of rounddampers. Consult the rectangular dampersizing guide (Table 1-2 on page 20), for CFMratings.

Large units should always have a minimumof 6 zones due to the high air flow capacities.

To prevent excessive noise in the system,zone damper total minimum airflow settingsshould be equal to or preferably greater than

30% of the units rated CFM.

As an added precaution, we recommend a high ductstatic safety switch be installed (Dwyer Model 1900-5-MR or equal) to prevent over pressurization of theductwork.

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

Documents

Transcript of Form: 036-21478-001 Rev. a (0802) Supersedes: Nothing