FORCED AIR ZONE CONTROL

Presented by

Tom Jackson, CEO and Ron Jackson, President

JACKSON SYSTEMS, LLC

RESIDENTIAL

LIGHT COMMERCIAL

BRIEF HISTORY & FACTS

The first forced air zone control system was brought to fruition over 44 years ago.

Today, there are over a dozen major manufacturers of forced air zoning systems and the list keeps growing.

Forced air zone control represents a Hundred-Million dollar industry.

In 2007, zone control systems for residential and light commercial applications exceeded 350,000 systems.

Forced air zoning is no longer a niche market but plays a major part in energy conservation and improved comfort in the home and workplace.

Over 67% of US homeowners are uncomfortable in their homes.

Zone control can solve the problem.

PROBLEMS THAT CAN BE SOLVED

• Comfort problems between different floors

• Comfort problems in finished basements

• Comfort problems in home additions

• Comfort problems in added sun rooms

• Comfort problems in rooms with cathedral or vaulted ceilings

• Comfort problems between external and internal areas

• Comfort problems due to external influences (sun and wind)

• Comfort problems in bonus rooms located over garages

• Comfort problems from heat producing equipment

BASIC PRINCIPLE OF OPERATION

The basic principle of operation for a zone control system is to allow a single HVAC system to be controlled by multiple thermostats strategically placed in areas called zones.

The conditioned air entering each zone is controlled by a zone damper located in a main supply trunk line or multiple dampers located in branch runs serving the zone.

The operation of the zone thermostats and dampers is controlled by a zone panel which provides the logic to energize the HVAC system in the proper mode of operation as well as controlling the zone damper positions based on each zone thermostat’s demand for heating, cooling or ventilation.

TYPICAL SYSTEM LAYOUT

TYPES OF ZONING SYSTEMSELECTRONIC:

A typical electronic zone control system utilizes UL Class II, 24 Volts AC to provide power for the zone panel, zone thermostats, and electro-mechanical zone dampers.

ZONE THERMOSTAT

ZONE THERMOSTAT

ELECTRO-MECHANICALZONE DAMPER

ELECTRO-MECHANICALZONE DAMPERLOGIC

PANEL

ELECTRO-PNEUMATIC: A typical electro-pneumatic zone control system utilizes UL Class II, 24 Volts AC to provide power for the zone panel, zone thermostats, and an air pump that creates both vacuum and pressure for air actuated dampers.

TYPES OF ZONING SYSTEMS

ZONE THERMOSTAT

ZONE THERMOSTAT

LOGICPANEL

AIR PUMP

AIR ACTUATED DAMPER

AIR ACTUATED DAMPER

ZONE CONTROL PANELSZone control panels provide the basic logic required in using multiple zone thermostats and zone dampers with a single HVAC system. Selecting the right panel involves knowing the application specifics and provides the base for selection of the remaining system components.

THINGS TO KNOW:

• Number of individual zones

• Type of equipment• Heat/Cool (single stage or multi-stage)• Heat Pump (2 heat/1cool or 3 heat/2 cool)• Hybrid (fossil fuel/dual fuel)

• Type of zone dampers ( 2-wire, 3-wire or air actuated)

• Cooling tonnage (important when sizing the bypass damper)

BASIC SYSTEM COMPONENTS

ZONE THERMOSTATSIn today’s world, low-voltage mechanical thermostats are basically a thing of the past due to the tremendous advancements in digital and micro-computer technology. Digital thermostats are extremely accurate and come packed with numerous features that require an onboard microprocessor. When selecting zone thermostats for any application, system compatibility is the key along with user preference.

BASIC THERMOSTAT CLASSIFICATIONS:

• Non-Programmable• Single Stage Heat/Cool (manual or auto-changeover)• Multi-stage Heat/Cool (manual or auto-changeover)• Heat pump (2 heat/1cool or 3 heat/2 cool)

• Programmable• Single Stage Heat/Cool (manual or auto-changeover)• Multi-stage Heat/Cool (manual or auto-changeover)• Heat pump (2 heat/1 cool or 3 heat/2 cool)

BASIC SYSTEM COMPONENTS

ZONE DAMPERS

BASIC TYPES:

• 2-wire (spring open/powered close)• 3-wire (powered open/powered close)• 3-wire retrofit (slides into existing ductwork) • Pneumatic (air actuated)

When selecting zone dampers, the following considerations should be made:

• New construction or retrofit• Total number of dampers required• Compatibility with zone panel• Total VA requirement

BASIC SYSTEM COMPONENTS

ELECTRO-MECHANICAL TWO-POSITION

Electro-mechanical two-position dampers are widely used for forced air zone control applications. Both rectangular and round dampers are available in a wide range of sizes to fit most standard trunk and branch duct configurations. Two-position dampers are either fully open or fully closed. Most have a mechanical minimum position adjustment to allow a percentage of air flow (leakage) when in the closed position.

Rectangular dampers slide into the duct work and are available in side mount (actuator on the vertical plane) and bottom mount (actuator on the horizontal plane) to accommodate for restrictions such as ceiling joists.

Damper actuators are available in 2-wire (Spring Open/Power Closed) or 3-wire (Power Open/Power Closed) models. A typical actuator motor is 24 Volts AC but the VA rating (the amount of power required to drive the motor) may vary within a range of 2VA to 10VA. This becomes an important factor when selecting zone control dampers as the total system VA must not exceed the transformer VA rating.

TYPES OF ZONE DAMPERS

2-POSITION ZONE DAMPERSTYPICAL 2-WIRE RECTANGULAR SIDE MOUNT

ACTUATOR ANDSPRING RETURN

MECHANISM

DAMPERBLADES

MOUNTINGFLANGE

MINIMUM POSITIONADJUSTMENT

SCREW

MOUNTING DIRECTION

2-POSITION ZONE DAMPERSTYPICAL 2-WIRE RECTANGULAR BOTTOM MOUNT

ACTUATOR ANDSPRING RETURN

MECHANISM

DAMPER BLADES

MOUNTING FLANGE

MINIMUMPOSITION

ADJUSTMENTSCREW

MO

UN

TIN

G D

IRE

CT

ION

FRONT VIEW

2-POSITION ZONE DAMPERSTYPICAL 2- WIRE ROUND

ACTUATOR ANDSPRING RETURN

MECHANISM

DAMPERBLADE

MINIMUM POSITIONADJUSTMENT

SCREW

2-POSITION ZONE DAMPERSTYPICAL 3-WIRE RECTANGULAR SIDE MOUNT

ACTUATOR

MINIMUMPOSITION

ADJUSTMENTSCREW

DAMPER BLADESMOUNTING DIRECTION

2-POSITION ZONE DAMPERSTYPICAL 3- WIRE ROUND

MINIMUMPOSITION

ADJUSTMENTSCREW

DAMPER BLADE

ACTUATOR

2-POSITION ZONE DAMPERSTYPICAL 3- WIRE RETROFIT DAMPER

ACTUATOR

DAMPER BLADE

EXISTINGDUCT WORK

RETROFITDAMPER

PNEUMATIC (AIR ACTUATED)

Pneumatic dampers operate on either air pressure or vacuum provided by an air pump as part of the zone control system. There are two basic types of pneumatic air dampers.

BLADDER TYPEA rubber bladder inside a damper shell or duct work retracts when a vacuum is applied allowing air to flow through the duct and inflates when pressure is applied to restrict air flow.

DIAPHRAGM TYPEA diaphragm (air actuator) is incorporated with mechanical linkage to move a damper blade when either a vacuum or pressure is applied.

TYPES OF ZONE DAMPERS

BYPASS DAMPERS

Since forced air zone control systems are designed to be used with constant volume equipment, a bypass damper may be required depending on the total number of zones in the system. As zone dampers open and close, the static pressure is constantly changing. In order to maintain the system design static pressure, a bypass damper is installed.

BASIC BYPASS DAMPERS:

• BarometricBarometric bypass dampers utilize a mechanical counterweight attached to a shaft connected to an offset damper blade. When all zone dampers are in the open position and with the air handler running, the bypass damper counterweight is adjusted so that the damper blade is closed. As zone dampers close and the static pressure increases, the bypass damper relieves the pressure increase by modulating open and discharging the air back into the return air duct.

BASIC SYSTEM COMPONENTS

TYPICAL BAROMETRIC BYPASS DAMPER ARRANGEMENT

BASIC SYSTEM COMPONENTS

TYPICAL BAROMETRIC BYPASS DAMPERS

BASIC SYSTEM COMPONENTS

ROUND RECTANGULAR

BYPASS DAMPERS

• ELECTRONICElectronic bypass dampers incorporate a motorized 24 Volt, 3-wire actuator and a static pressure control with an adjustable static pressure setting. As zone dampers open and close, the static pressure control sends a signal to the actuator which modulates the bypass damper to maintain the system static pressure setting.

It is important to note that when using an electronic bypass damper, the zone damper actuators should be equal to or slower than the speed of the bypass damper actuator to prevent over or under compensation of bypass air. Typical electronic bypass dampersuse 60 or 90 second actuators. This is the time that it takes the damper blade to go from full closed to full open.

BASIC SYSTEM COMPONENTS

TYPICAL ELECTRONIC BYPASS DAMPER ARRANGEMENT

BASIC SYSTEM COMPONENTS

TYPICAL ELECTRONIC BYPASS DAMPERS

BASIC SYSTEM COMPONENTS

ROUND RECTANGULAR

SYSTEM PERIFERALS

• LOW LIMIT PROTECTIONSince many zone control systems use bypass dampers to

maintain the system static pressure, a cooling low limit is an important part of any system. When in the cooling mode of operation, cold air that is bypassed back into the return begins to super cool the air passing through the evaporator coil. If the condition persists for any length of time, the coil will freeze. Most zone control panels have dedicated terminals that accept either an electronic discharge air sensor or mechanical freeze stat that mounts on the suction line. When the discharge air temperature or suction line temperature drops below a fixed point, the panel de-energizes the compressor while allowing the air handler to run to prevent coil freezing.

BASIC SYSTEM COMPONENTS

SYSTEM PERIFERALS

• HIGH LIMIT PROTECTIONHigh limit protection is also an important part of any zone control system. When in the heating mode of operation, hot air that is bypassed back into the return begins to super heat the air

passing across the heat exchanger. If the condition persists for any length of time, the HVAC system will trip out on high safety limit. Again, most zone control panels have dedicated terminals that accept either an electronic discharge air sensor or mechanical high limit stat that

mounts in the discharge air plenum. When the discharge air temperature goes above a fixed setpoint, the heating system will be de-energized while the system fan continues to run.

BASIC SYSTEM COMPONENTS

SYSTEM PERIFERALS

• SYSTEM TRANSFORMERMost zone control system logic panels use a separate 24 Volt transformer to power the panel, thermostats and zone dampers.

A separate transformer also isolates the panel, thermostats and dampers from the equipment transformer. The important thing is knowing the total VA requirement of the system when selecting

a transformer.

The Golden RuleNever use the equipment transformer regardless of the VA

rating.

BASIC SYSTEM COMPONENTS

There are numerous control logic methods used in forced air zone control and many logic panels are designed to provide a selection of control algorithms to chose from based on the specific zoning application.

COOLING PRIORITYCooling Priority logic is designed to provide cooling first over heating. This means that if one zone calls for heating and another zone calls for cooling, cooling wins. After the cooling call is satisfied, the system will changeover to heating.

HEATING PRIORITYHeating Priority logic is designed to provide heating first over cooling.If a zone calls for cooling and another zone calls for heating, heating wins. After the heating call is satisfied, the system will changeover to cooling.

CONTROL LOGIC

FIRST CALL PRIORITYFirst Call Priority logic is designed to allow the equipment to energize in the mode of operation that matches the first zone thermostat to call. If a zone calls for heating and shortly thereafter another zone calls for cooling, heating will receive priority. Once the heating call is satisfied, the system will changeover to the cooling mode.

MAJORITY WINSMajority Wins logic looks at the difference in the number of heating calls versus cooling calls. Whichever is greater receives priority. If there is a tie, most systems prioritize cooling.

CONTROL LOGIC

OTHER LOGIC OPTIONS:

• Time ShareTime Share logic, when offered as a system option, provides an additional feature to the control logic. Time Share limits the equipment from running in one mode of operation (typically 20 minutes) if there are opposite calls taking place. If the first call is not satisfied within the time limit the system will changeover to the opposite mode. Time Share logic is a continuous loop and will change the mode of operation within the time limit providing opposite calls take place.

CONTROL LOGIC

OTHER LOGIC OPTIONS:

• Capacity ControlCapacity Control logic when offered as an option with the control logic is used to control second stage heating or cooling based on a selectable minimum number of zones that have to call before upstaging will occur. This feature is beneficial in applications that have a number of small zones that can be satisfied using first stage only until the minimum number is reached. Capacity Control also prevents short second stage run times as well as equipment cycling off on high or low limit.

CONTROL LOGIC

• Zone control begins with good HVAC design.

• Proper load calculations used to determine duct and equipment sizing are essential in achieving optimum performance.

• Install zone thermostats in their respective zones!

• System wires should be tagged to match the panel terminal designations and zone identification.

• Zone dampers should be installed at least 10’ from discharge air grills whenever possible.

• Zone dampers need to be located where they can be accessed for trouble shooting.

• Flex or lined duct is recommended on the last 5’ of branch runs.

SYSTEM DESIGN CONSIDERATIONS

• Thermostats and zone dampers usually can be located up to 300’ from the control panel when 18AWG copper thermostat wire is used.

• Always use a separate 24VAC transformer rated at the proper VA to power the panel, dampers and zone thermostats.

• Never use the equipment transformer regardless of its VA rating!

• When using forced air zoning with a variable speed HVAC system, high speed fan should be set at 400 CFM per ton of cooling.

• When a bypass damper is required, proper sizing is important.

SYSTEM DESIGN CONSIDERATIONS

BYPASS DAMPER SIZING CHART

COOLING TONNAGE BYPASS DAMPER SIZE

2.5 8”

3 10”

4 - 5 12”

7.5 14”

10 16”

12.5 18”

15 20”

SYSTEM DESIGN CONSIDERATIONS

Sizing is based on bypassing 75% of the total system CFM

PUTTING IT ALL TOGETHERZONE CONTROL SYSTEM INFORMATION CHART

NUMBER OF ZONES: ________

TYPE OF EQUIPMENT: [ ] HEAT/COOL [ ] HEAT PUMP [ ] DUAL FUEL [ ] SPLIT [ ] RTU

STAGES OF COOLING ______ COOLING TONNAGE ______ STAGES OF HEATING _____

TYPE OF THERMOSTATS: [ ] NON-PROGRAMMABLE [ ] PROGRAMMABLE

TYPE OF DAMPERS: [ ] ROUND [ ] RECTANGULAR [ ] RETROFIT [ ] 2-WIRE [ ] 3-WIRE

TRANSFORMER VA REQUIREMENT: _______VA

BYPASS DAMPER SIZE: ___________

QUESTIONS AND ANSWERS