EngineeringBulletin

Gas Heatfor M-Series and T-Series Climate Changer™ Air Handlers

March 2004 CLCH-PRB010-EN

Preface

© 2004 American Standard Inc. All rights reserved CLCH-PRB010-EN

Gas heat can be a good heating option for any of the following applications:

• Climates and applications with large heat loads

• Applications with high outside air requirements to comply with ASHRAE Standard 62

• Buildings without a central boiler plant

• Remote locations where boiler capacity or water piping expense is prohibitive

• Areas with relatively inexpensive natural gas or expensive electricity

The gas heat offering for the M-Series and T-Series Climate Changer™ air handlers uses indirect heat exchangers and is designed for recirculating or 100 percent outside air applications. Only top-quality components are used in the cabinet, heat exchanger and burner. Top-quality components means extended equipment life, even in make-up air applications.

Trane gas heat modules have considerable option flexibility, which is to be expected in applied air handlers. This flexibility allows customization for a specific application.

The M-Series and T-Series Climate Changer air handlers are customized, cataloged air handlers with numerous options. The gas heat option is a pre-designed, highly engineered option available in near standard ship cycles.

CLCH-PRB010-EN 3

Contents

Features and Benefits .......................................................... 4Gas Heat Features ............................................................................. 4Heat Exchanger Features ..................................................................... 5Burner and Gas Train Features ............................................................. 5Extra Cost Options............................................................................... 6

Application Considerations.................................................8Control System Considerations.......................................................... 9

Constant Volume Units................................................................... 9Variable-Air-Volume ........................................................................ 9

Shipping Considerations ................................................... 11

Installation Considerations ...............................................12Field Supplied Items .......................................................................... 12Starting the Gas Heat Module ........................................................... 13Storage Requirements ....................................................................... 13

Guide Specifications.......................................................... 14Heat Exchanger .................................................................................. 14Burner Assembly................................................................................ 14Combustion Assembly ....................................................................... 14Gas Train ............................................................................................ 14Controls.............................................................................................. 14

Submittal Data ................................................................... 16Heat Exchanger .................................................................................. 16Burner Assembly................................................................................ 16Flame Management........................................................................... 16Gas Train ............................................................................................ 16Controls.............................................................................................. 16Control Panel.......................................................................................17Product Options ..................................................................................17

4 CLCH-PRB010-EN

Features and Benefits

Gas Heat Features• Available in unit sizes 6 to 120.

• Available 200 to 2500 MBh output, 2 to 8 MBh selections per unit size.

• Gas heat sections are available in the blow-through position, last in airstream, only.

• Gas heat sections feature double-wall construction.

• Gas train vestibules are provided with an access door. Gas train components are housed in an internal to unit or external “piping cabinet” if necessary. Gas train available on left or right side. The preferred location typically is the drive side of the unit.

• Combustion air inlet.

• Standard bolt up and roof curb interface.

• Horizontal (Figure 2) or vertical down (Figure 3) discharge available.

• Natural gas or propane burners are available.

• Standard M-Series and T-Series air handler sections are UL listed.

• Gas heat sections are UL listed, certifying that units have passed both UL Standard 795 and Canadian standard CGA 3.2-1976; the air handler unit as a whole is UL listed.

• All units are run tested and adjusted before leaving the factory.

Figure 1. Gas heat exchanger module

Figure 2. Horizontal air discharge

Figure 3. Vertical air discharge

Air Flow

Max.Temp

See Page 8

Min. -40 F

Air FlowMax. TempSee Page 8

Min. -40 F

Features and Benefits

CLCH-PRB010-EN 5

Heat Exchanger Features• Drum-and-tube heat exchangers

are made of 14-gauge, 409 stainless steel on both primary and secondary surfaces. This provides long service life especially in make up air applications during partial load, where the heat exchanger may be condensing.

• Sight glass is provided in the burner vestibule for viewing the flame condition (except on the 200 MBh heat exchanger where the sight glass is on the opposite side of unit).

• Heat exchangers are provided with a gasketed cleanout panel.

• Condensate drains and valves provided on all heat exchangers.

Figure 4. Gas Heat Exchanger

Burner and Gas Train Features

• Full-modulation burners:

– 3:1 turndown ratio (standard offering) available on 200-2,000 MBh output, forced draft burners

– 10:1 turndown ratio (optional offering) available on 200-2,000 MBh output, forced draft burners

– 20:1 turndown ratio (optional offering) available on 1,250-2,000 MBh output forced draft burners

• Power burner with forced draft centrifugal fan and direct drive motor.

• Induced draft fans mounted and wired (for MBh sizes 1,250, 1,500, 1,750, 2000 and 2,500.

• Control power transformer provided standard on 1,250 MBh and larger burners.

• Honeywell electronic flame relay with UV flame sensor, purge cycle and low fire start interlock.

• Intermittent spark ignition with ignition transformer pre-wired.

• Safeties provided by burner manufacturer; built into the burner controls.

• Main and pilot gas pressure regulators. Main regulator is included as a part of the gas solenoid safety shutoff valve. Maximum pressure is 14 inches wc (0.5 psig). Optional high gas pressure regulators are available.

• Main and redundant solenoid safety shutoff valves.

• Two manual shutoff cocks.

• Pilot manual and solenoid shutoff valves.

• Gas train has unions for ease of service.

• Combustion airflow switch mounted and wired.

• Main airflow switch mounted and wired.

• High temperature cutout.

• Pre-wired control panel, including system circuit breaker, low fire start relay and numbered terminal strip.

• Gas train built in accordance with Underwriter’s Lab (UL) and Factory Mutual (FM) insurance ratings as standard. Optional Industrial Risk Insurers (IRI) rated gas train is available.

Features and Benefits

6 CLCH-PRB010-EN

• Gas pressure requirements: 7 to 14 inches wc (0.25 to 0.5 psig). Note that a minimum of 9 inches wc (0.32 psig) is required for 1250-2500 MBh heaters with 10:1 turndown capability. Higher pressures require an optional high gas pressure regulator. Lower pressures may require an oversized gas train.

• On T-Series Climate Changer air handlers, a stainless steel flue stack is included for field mounting. M-Series Climate Changer air handlers require a field-provided flue stack.

• High and low gas pressure switches.

• Gas train controls:

– 120-volt power or line voltage if control transformer is supplied

– Dry contact on/off and 0 to 10 Vdc control signal required

– Terminal blocks for all field control and power wiring terminations

• Propane configuration is available.

Factory Testing

All units are run tested and logged before leaving factory.

Extra Cost Options• 200-2000 MBh: Burners with

turndown ratios of 10:1 (required for 100 percent outside air or VAV applications).

• 1250-2500 MBh: Burners with turndown ratio of 20:1 for extra control modulation.

• High-pressure (greater than 14 inches wc [0.5 psig]) gas regulators.

• Control power transformer mounted and wired. Reduces line voltage to 120-volt power for gas train. Note the control power transformer is standard on 1,250 MBh and larger burner sizes. Note that if the transformer is not ordered, 120-volt, 60 Hz, single-phase power will need to be supplied to the gas train.

• Motorized gas valve with proof of closure switches on automatic gas valves (required by some local codes).

• Gas train built in accordance with Industrial Risk Insurers (IRI).

• Honeywell digital readout for flame relay: a very effective diagnostic tool.

Figure 5. Complete burner and gas train assembly

Figure 6. Another view of burner and gas train assembly

Features and Benefits

CLCH-PRB010-EN 7

Table 1. Gas heat benefitsBenefit DescriptionCompete Package Complete central station air handler with chilled water, filtration and gas

heating in one packageQuality • Using industry proven components, Trane offers a superior quality,

highly functional heating section that complements the attributes of our M-Series and T-Series Climate Changer air handlers.

• Industrial quality forced draft burners from industry leaders in combustion technology form the heart of the system. These, combined with heavy-duty heat exchangers of 14-gauge, 409 stainless steel (primary and secondary surfaces), complete a heating system worthy of being called an applied product.

Safety Integral to the gas heating section is a state-of-the-art flame management system. Tried and proven flame relays from Honeywell employ an ultraviolet flame scanner typically used on larger output systems

Cleanliness Gas trains and piping are inside the burner vestibule, keeping the unit appearance neat and clean. Gas trains are constructed in accordance with UL and FM guidelines.

Agency Listings M-Series and T-Series gas heating sections bear the UL label for Commercial and Industrial Gas Heating Equipment (ANSI/UL Standard 749) and ETL Canada label for Industrial Gas Fired Package Units (CGA Standard 3.2-1976).

Flexibility Various heat outputs and unit size combinations to allow for closely matching heater size to jobsite requirements. Various control options to tailor the heating system to design requirements.

Checkout All units are fully run tested before shipment to ensure proper operation and burner setup reducing start up costs.

8 CLCH-PRB010-EN

ApplicationConsiderations

Applying gas heat in air-handling systems is fairly straightforward; however, as with any applied product, there are application guidelines that should be reviewed before making final selections:

• Apply indirect fired gas heating sections in the blow-thru configuration only with the gas heating section as the last component in the airstream. In this configuration, the gas heat section is under positive static pressure to ensure that combustion products will not enter the airstream.

Note: A special end-of-unit shipping split must be ordered with all T-Series units.

• The discharge air temperature must be controlled to modulate when the airflow is modulated.

• When reducing airflow, the control system should not allow the temperature rise through the gas heat section to exceed the nominal at full airflow.

• Standard discharges include both front horizontal and vertical--- down.

• Minimum entering air temperature is -40ºF.

• Maximum discharge air temperature is limited by the downstream components. For example, the maximum temperature for a plenum is 180 degrees F. For any other downstream components, consult the manufacturer's temperature guidelines.

• Note this does not imply that the gas section can deliver a 180 degree F temperature rise. The maximum temperature rise across the heat exchanger is 101 degrees F. See the selection table for the allowable temperature rise for the specific unit size and burner capacity.

• Gas heating sections are constructed with a vestibule to house the burner and gas train components. Smaller capacity heating sections are housed entirely within the footprint of the standard casing. Larger capacity sections use an external vestibule. Refer to the quick selects (CLCH-SLB004-EN and CLCH-SLB005-EN) and submittal drawings for details.

• Air pressure drop through the gas heat section needs to be determined. Heat exchangers and air block-off baffles in the gas heating section have been sized to provide a specific air velocity over the heat exchanger at design CFM. This gives a 0.5 inches wg pressure drop at design airflow. This pressure drop is applicable to all unit sizes. The outlet opening, if less than full size, has a small exit loss. Use CLCH blow-thru fan curves when calculating fan hp and rpm.

• Most comfort heating applications for “full modulating” burners require only a 3:1 turndown ratio. “Turndown” refers to the burner’s modulation range. A 3:1 turndown ratio indicates the burner can operate at a capacity as low as 33 percent or one-third

Figure 7. Horizontal air discharge

Air Flow

Max.Temp

See Page 8

Min. -40 F

of its rated high fire output. Likewise, a 10:1 turndown ratio indicates the burner can operate at a capacity as low as 10 percent or one-tenth of its rated high fire output. 10:1 turndown is typically used for 100 percent makeup air applications. Similarly, a 20:1 turndown ratio indicates the burner can operate at a capacity as low as 5% or one-twentieth. 20:1 is typically used in an industrial process application where much tighter control is required.

• A condensate drain with shutoff valve is provided on the heat exchanger. For M-Series Climate Changer air handlers, the valve is located in the piping vestibule. For T-Series Climate Changer air handlers, the valve is located on the opposite side of the piping vestibule and accessed through the access door.

• Provide for a “cool-down” cycle in the control system. Allow the air handler fan to run for a minimum of 3 minutes after gas heat shut down to cool the heat exchanger to dissipate any residual heat.

• On high altitude applications, derate the heating capacity (MBh) by 4 percent for every 1,000 feet over 2,000 feet.

Application Considerations

CLCH-PRB010-EN 9

Exhaust Flue

T-Series Climate Changer air handlers are provided with a short exhaust gas flue stack. It is attached to the unit during installation. A field provided exhaust flue stack is not required.

M-Series gas heat modules require a field-engineered and field-installed flue stack. Local codes and practices vary throughout the country. The engineer should size the flue based on MBh output, horizontal and vertical run lengths, type of flue material, NFPA 54 Fuel Gas Code, and local codes. The flue should be designed for 800 degrees F (430 degrees C). If horizontal runs over 20 feet or other static-increasing transitions are necessary, a flue booster fan will be required.

Use best practice to ensure adequate draft is ensured for exhausting flue gases. An induced draft fan or exhauster may be required to overcome friction losses from long horizontal runs or flue restrictions. Conversely, a barometric damper may be required if exhausting into a tall chimney which produces excessive draft.

The flue should be installed in accordance with NFAPA 54 (ANSI Z223.1) National Fuel Gas Code, NFPA 211 Standard for Chimneys, Fireplaces, Vents and Solid Fuel-Burning Appliances and any other relevant local building codes or regulations. Vent material must have resistance to corrosion and heat equal or greater than 304 stainless steel.

Control System Considerations

Constant Volume Units

Air handler controller requirements for gas heat section operation in constant volume units:

• One (1) binary output signal is needed for on - off control of the gas burner.

• A continuous 10 vdc signal to ramp unit to full fire position after start up. This is needed for on - off gas heat control only.

• One (1) analog output signal for 0 - 10 vdc to modulate the gas burner with 10 vdc being full fire. An alternate to the 0 - 10 vdc signal is to use an analog output for 4 - 20 mA. Note this requires an optional signal converter in the gas heat module. This is needed for modulating gas heat control.

Trane supplied air handler controllers have the capability to operate the gas heat section. Note that wiring between the controller and the gas heat section would be done in the field. Consult with the local Trane sales office for design assistance.

Minimum Air Flow Requirements -

Constant Volume Units

Table 2 shows the minimum air flow requirements for a constant volume air handler. The burner firing rate does not have to be reduced if these minimum CFM values are maintained.

Variable-Air-Volume

Air handler controller requirements for gas heat section operation in variable-air-volume units:

• One (1) binary output signal is needed for on - off control of the gas burner.

• Two (2) analog inputs for temperature sensors are required. A discharge temperature sensor and a supply air temperature sensor are required to monitor temperature rise across the gas heater.

• One (1) analog output signal for 0 - 10 vdc to modulate the gas burner with 10 vdc being full fire. An alternate to the 0 - 10 vdc signal is to use an analog output for 4 - 20 mA. Note this requires an optional signal converter in the gas heat module.

Trane supplied air handler controllers have the capability to operate the gas heat section. Note that wiring between the controller and the gas heat section would be done in the field. Consult with the local Trane sales office for design assistance.

Table 2. Minimum cfm for constant volume units

Unit size Minimum CFM6 21988 282810 361512 461314 532517 630021 780025 915030 10,87535 12,78840 14,73850 18,53657 21,38666 24,61980 29,531100 37,650120 44,843

Application Considerations

10 CLCH-PRB010-EN

Monitor Air Temperature Rise -

Variable Air Volume Units

On variable air volume systems, as the air handler's air volume decreases in response to zone load, the gas burner firing rate must modulate also so as not to exceed the nameplate temperature rise rating. To do this requires a temperature sensor on the entering and leaving air side of the gas heat section to monitor the temperature rise across the heat exchanger. The temperature rise set point should not exceed the nameplate rating.

Minimum Air Flow Requirements -

Variable Air Volume Units

Variable air volume units have minimum CFM limits for proper operation of the gas heat. Refer to the table below for minimum air handler CFM limits. At these CFM limits, the firing rate of the gas heater must be reduced as described previously. The temperature rise across the heat exchanger must not exceed the nameplate temperature rise rating.

Note: VAV applications require reduced fire rates. Do not exceed nameplate temperature rise rating.

Table 3. Minimum cfm for variable-air-volume units

Unit Size Minimum CFM6 15008 200010 250012 300014 350017 425021 525025 625030 750035 875040 1000050 1250057 1425066 1650080 20000100 25000120 30000

CLCH-PRB010-EN 11

Shipping Considerations

The gas heating section ships with the burner and heat exchanger installed. The external piping vestibule, if required, ships attached to the heating section. The exhaust gas flue on T-Series gas heat sections ships inside the burner vestibule and must be field installed.

The gas heat section ships separately and must be field installed to the air handler at the jobsite. The heating sections for T-Series Climate Changers can accept roof curb or pier mounting.

12 CLCH-PRB010-EN

InstallationConsiderations

Field-Supplied Items

Controls

The gas heat control system requires a binary input signal for on/off control. The control system also requires a 0 to 10 Vdc analog signal for modulation where 10 Vdc is full heat.

Avoid using a zone sensor to control leaving air temperature from the gas heat section. This could cause excessive discharge air temperature due to over-firing of the burner. A discharge air sensor is the preferred method of control.

For VAV applications when airflow is reduced, the control system should not allow the temperature rise through the gas heat section to exceed the nominal at full airflow. The discharge air temperature must be controlled to modulate when the airflow is modulated.

Gas Supply

A supply of natural gas must be connected to the gas train. See Table 4 for gas connection sizes. Required gas pressure to the gas train is 7 to 14 inches wc (0.25 to 0.5 psig) for units through 2000 MBh.

Table 4. Gas connection sizesGas Output (MBh) 200–560 700–1,000 1,250–1,750 2,000, 2,500Connection Size (inches) 1 1Z\v 1Z\x 2

Table 5. Power supply requirementsGas Output (MBh) 200–1,000 200–1,000 with control

transformer1,250–2,500

Amperage (Amps) 11 (single-phase) 11 (three-phase) 20 (three-phase)

Note that a minimum of 9 inches wc (0.32 psig) is required for 1250-2000 MBh heaters with 10:1 turndown capability. For all size units, do not exceed 14 inches wc (0.5 psig) inlet gas pressure.

Gas pressure and volume must be maintained and stable at high fire. Higher inlet gas pressure requires a field-provided high gas pressure regulator. Lower gas pressure will require an oversized gas train—contact Lexington Marketing.

Note: A propane configuration is also available.

Exhaust Flue

T-Series Climate Changer air handlers are provided with a short exhaust gas flue stack. It is attached to the unit during installation. A field provided exhaust flue stack is not required.

M-Series Climate Changer air handlers require a field provided exhaust flue stack. The flue stack should be selected for a maximum flue gas temperature of 800 degrees F (430 degrees C). Type B flue stacks are not recommended as they are only suitable for a maximum flue temperature of 450 degrees F (230 degrees C).

Use best practice to ensure adequate draft is ensured for exhausting flue gases. An induced draft fan or exhauster may be required to overcome friction losses from long horizontal runs or flue restrictions. Conversely, a barometric damper may be required if exhausting into a tall chimney which produces excessive draft.

The flue should be installed in accordance with NFAPA 54 (ANSI Z223.1) National Fuel Gas Code, NFPA 211 Standard for Chimneys, Fireplaces, Vents and Solid Fuel-Burning Appliances and any other relevant local building codes or regulations. Vent material must have resistance to corrosion and heat equal or greater than 304 stainless steel.

Wiring

All power and control wiring for the gas heat section must be field provided. All power and control wiring for any modules downstream of the gas heat section must be field provided.

Power

Gas heaters with 200 to 1,000 MBh output require a separate 120V power source to operate the control panel, gas valves, actuators, etc. If the optional control power transformer is ordered, line voltage may be supplied to the control panel. Be sure to order the same voltage as the supply fan.

Installation Considerations

CLCH-PRB010-EN 13

Gas heaters with 1,250 to 2,500 MBh output require three-phase power for the forced draft exhaust fans. Therefore, these sizes are supplied with a standard control power transformer to power the control panel, gas valves, actuators, etc. Be sure to order the same voltage as the supply fan. A separate 120V is not required.

Refer to Table 5for the power supply and amperage requirements.

Starting the Gas Heat ModuleEven though the gas heat section has been run tested in the factory, minor adjustments may be needed at startup. These are usually limited to adjustment of pilot and main burner gas pressure regulators. Detailed start-up procedures are discussed in the Installation and Maintenance manual.

Storage RequirementsFollow the recommendations in CLCH-SVX03B-EN or CLCH-IM-16A installation and maintenance manuals provided with M-Series and T-Series Climate Changer air handlers.

Gas Heat Quick SelectsRefer to the M-Series and T-Series Climate Changer gas heat quick selects (CLCH-SLB004-EN and CLCH-SLB005-EN, respectively) to find the combination of unit size and MBh output (or temperature rise) to suit design requirements. Gas heat section piping vestibules, configurations, lengths and weights are also given.

14 CLCH-PRB010-EN

Guide Specifications

GeneralThe gas heat section shall be natural gas, indirect fired and shall be completely factory assembled, wired and tested to form an integral part of the unit. It shall bear an ETL or UL label for Commercial and Industrial Gas Heating Equipment (ANSI / UL Standard 795) and for Industrial Gas Fired Packaged Units (CGA Standard 3.2-1976).

Heat ExchangerThe heat exchanger shall be a two- or four-pass design. The primary surface shall be one or two passes, constructed of welded 409 stainless steel. The secondary heat exchanger shall consist of multiple tubes of 409 stainless steel in a single- or two-pass arrangement. Tubes shall be fitted with multi-plane metal turbulators, and both primary and secondary surfaces shall be minimum 14-gauge thickness. Lighter metal gauges will not be acceptable. The heat exchanger shall be fitted with a cleanout plate to facilitate cleaning and inspection of tubes and turbulators as well as a condensate drain connection that is piped to an accessible shutoff valve.

Burner AssemblyThe burner shall be forced draft, industrial type capable of efficient firing over its operating range without producing excessive CO, CO2 or NOX. It shall be fitted with a combustion air damper assembly for control of fuel-air ratio through its modulating range. The burner uses a modulating gas valve design, not a step-controlled gas valve, to provide precise capacity control. Two-speed fan motors will not be acceptable for this application. The burner modulation range (i.e., turndown) shall be as specified on the equipment schedule. The combustion air damper and modulating gas valve shall be linked either internally or through a control linkage that is factory preset. The burner shall have a low fire start interlock and shall be manufactured by Maxon, Power Flame or Eclipse only.

Combustion AssemblyThe combustion blower shall be centrifugal type, direct drive, capable of delivering the proper amount of combustion air to the burner nozzle. The blower motor shall have an internal thermal overload protection, and an air proving switch shall be mounted on the scroll, interlocking burner operation with the gas train controls to prevent burner operation when the combustion air fan is shut down. On unit sizes 1,250 MBh and larger, an induced draft fan shall be employed for positive venting of combustion products. An induced draft (ID) fan shall be centrifugal type, capable of withstanding high temperatures associated with flue gas. The unit shall be equipped with a stainless steel flue stack that rises above the roof level.

Gas TrainThe gas train shall meet FM approval and shall include the following:

• A modulating gas valve

• Automatic gas valve with gas pressure regulator

• Redundant automatic gas valve (above 400 MBh)

• Main gas shutoff valve with pressure tap and second ball shutoff cock

• Pilot solenoid

• Pilot gas pressure regulator

• Pilot solenoid valve

ControlsThe gas safety controls shall include the following:

• Electronic flame relay with UV flame sensor

• High limit control

• Combustion air flow

• Primary air flow interlocks

The unit shall be programmed to start in low-fire mode, and the flame relay shall be Honeywell Model 7895A or equal and shall be equipped with annunciation lights indicating pilot on, safeties satisfied, combustion airflow and flame failure. The unit shall have a purge cycle that provides a minimum of four air changes of the heat exchanger interior. The purge time shall not exceed four minutes.

Guide Specifications

CLCH-PRB010-EN 15

The heating system shall have an intermittent spark ignition to establish the pilot flame. The ignition transformer shall be factory wired into the control system.

All control components shall be factory pre-wired to numbered terminal strips in the burner control panel. All wiring shall be run in conduit. The control circuit shall have a circuit breaker as a disconnecting device and for overcurrent protection. Field connections shall require only main power (120 Vac or line voltage if supplied with a control power transformer), a heat start contact closure and a modulating 0 to 10 Vdc (4 to 20 Ma optional) signal.

Avoid using a zone sensor to control leaving air temperature from the gas heat section. This could cause excessive discharge air temperature due to over-firing of the burner. A discharge air sensor is the preferred method of control.

For VAV applications when airflow is reduced, the control system should not allow the temperature rise through the gas heat section to exceed the nominal at full airflow. The discharge air temperature must be controlled to modulate when the airflow is modulated.

16 CLCH-PRB010-EN

Submittal Data

Note: Indirect Fired Gas Heating Section for M-Series and T-Series Climate Changer Air Handlers

GeneralThe indirect gas heat section consists of the heat exchanger, power burner, gas train, flame management controls and control panel. The section is completely assembled, pre-wired and flame tested before shipment and bears the UL label for Commercial and Industrial Gas Heating Equipment (ANSI/UL Standard 749) and Industrial Gas Fired Package Units (CGA Standard 3.2-1976). The gas heat section features double-wall construction with fiberglass insulation.

All burner and control components are housed completely within the section in the burner vestibule. The vestibule wall is double-wall construction on the heat exchanger side, and a combustion air intake louver is provided to allow combustion air into the vestibule. A full-sized hinged vestibule access door is standard.

Heat ExchangerThe drum-and-tube heat exchanger is constructed of 14-gauge, 409 stainless steel on both the primary and the secondary surfaces. The drum and tubes are fully welded. 200 to 1,000 MBh is a two-pass design and 1,250 to 2,500 MBh is a four-pass design. The heat exchanger is fitted with a cleanout door on the rear flue box to facilitate cleaning and tube inspection. It is also fitted with a condensate drain, which terminates to an accessible shutoff valve.

Burner AssemblyThe burner is a commercial/industrial forced draft, full modulating type designed to fire natural gas or propane gas. A stainless steel multi-port diffuser and flame retention firing head combine to produce full-range, stable performance. The burner is equipped with an integrally mounted direct drive combustion blower, internal thermal overload protection and a combustion air damper, which controls the fuel-air ratio throughout the modulating range for efficient turndown. The combustion air damper and modulating gas valve are linked either internally or through a factory preset control linkage. The standard turndown is 3:1.

Flame ManagementThe heating section uses a Honeywell 7800 series flame relay to provide the flame safeguard programming. The flame relay has annunciation lights, indicating pilot on, safeties satisfied, combustion airflow and flame failure. The flame relay has a pre-purge cycle, providing for a minimum of four air changes in the heat exchanger before ignition. An ultraviolet (UV) flame detector senses the presence of a flame.

The flame relay uses a spark-ignited gas pilot system to establish an intermittent pilot. The ignition transformer is mounted on the burner wall and provides a 6000-volt spark.

Gas TrainThe standard gas train meets UL and FM requirements and is designed for 7 to 14 inches wc (0.25 to 0.5 psig) incoming gas pressure. Its components include the following:

• Main gas safety shutoff valve

• Redundant safety shutoff valve

• Gas pressure regulator

• Manual gas shutoff valve with pressure taps (primary)

• Manual gas shutoff valve (secondary)

• Modulating gas valve

• Gas pressure taps for servicing and adjusting burner

• Orifice plate

• High gas pressure safety switch

• Low gas pressure safety switch

• Pilot gas pressure regulator

• Pilot gas solenoid

• Pilot gas manual shutoff valve

ControlsOperating and safety controls include the following:

• Modulating actuator to drive the gas control valve and the combustion air damper

• Conditioned airflow switch

• High air temperature limit switch

• Low fire start relay

• Combustion air flow switch

Submittal Data

CLCH-PRB010-EN 17

Control PanelThe system control panel is mounted in the burner vestibule. It houses the incoming power terminal block, circuit breaker, low fire start relay and numbered terminal strip. A terminal is available for wiring an external alarm relay. All wiring is run in flex conduit and is numbered for ease of service. Others must provide the temperature control system.

Product Options

• Full-modulation burners:

– 3:1 turndown ratio (standard offering) available on 200-2,000 MBh output, forced draft burners

– 10:1 turndown ratio (optional offering) available on 200-2,000 MBh output, forced draft burners

– 20:1 turndown ratio (optional offering) available on 1,250-2,000 MBh output forced draft burnersControl power transformer

• High gas pressure regulator: required when inlet gas pressure exceeds 14 inches wg (0.5 psig)

• Digital readout for flame relay: a plug-in module for the flame relay featuring two-line digital English language readout of over 50 parameters

• Industrial Risk Insurers (IRI) approved gas train

Trane

A business of American Standard Companies

www.trane.com

For more information, contact your local Trane office or e-mail us at comfort@trane.com

Literature Order Number CLCH-PRB010-EN

Date March 2004

Supersedes CLCH-PRB010-EN (November 2000)

Stocking Location Inland

Trane has a policy of continuous product and product data improvement and reserves the right to change design and specifications without notice.