Reznor RPB Unit Installation Manual User Manual

Page 31

Form I-RPB, P/N 131782 R12, Page 31

Computer Controlled

Electronic Modulation between

50% and 100% Firing Rate

With this option the furnace is equipped with a Maxitrol signal conditioner

which operates much the same way as the amplifier above to control the reg-

ulator valve. The conditioner accepts an input signal of either 4-20 milliamps

or 0-10 volts from a customer-supplied control device such as a computer.

With the dip switches on the conditioner in the "on" positions, the conditioner

accepts a 4-20 milliamp signal. In the "off" positions, the conditioner accepts

a 0-10V signal. The conditioner converts the signal to the 0 to 20 volt DC

current required to control the modulating valve. Temperature selection is

through the field-supplied computer software.

Electronic Modulation

between 20-28% and

100% Firing Rate,

Option AG39

Depending on the size, furnaces equipped with electronic modulation Option AG39

have a 20-28% turndown ratio. The furnace will ignite at any input rate in the available

range and will maintain average thermal efficiencies equal to or greater than the ther-

mal efficiency at full fire. (

natural gas only; not available on Size 350)

The gas supply (see pressure requirements in the table above) connects to the single-

stage gas valve. To compensate for additional pressure loss through the modulating

valve, the single-stage gas valve has a custom outlet pressure setting higher than

when it is used on a standard gas manifold. The pilot tubing connects to the pilot port

on the single-stage gas valve. When the valve receives a call for heat from the amplifier

and pilot is established, gas flow from the single-stage valve goes to both the modulat-

ing valve and the regulated lighter tube system. When the signal from the amplifier to

the modulating valve requires less-than-high fire operation, the modulating valve func-

tions to lessen the gas flow to the burner to reduce the input rate to that required to

maintain the desired temperature. When the input rate is reduced enough to decrease

the gas pressure to 1.1" w.c., the primary gas pressure switch in the manifold activates

the gear motor that controls the bypass damper in the venter/combustion air system.

The bypass damper opens diverting some of the incoming air directly into the flue duct,

Carryover

Regulator

Modulating

Valve

Single-

Stage Gas

Valve

P rimary Gas

Flow Pressure

Switch

White Label

1.1 w.c.

Gas Flow

Pressure Switch

White Label

1.1 w.c.

FIGURE 33 - Option

AG39 Manifold

Arrangement

Note: Arrangement may vary slightly depending on

gas valve; components are the same.

Description of

Operation of

Option AG39

The gas train includes a single-stage gas valve, a modulating valve, and two gas pres-

sure switches. The burner rack is equipped with one flash carryover and a regulated

gas lighter tube system. The carryover lighter tube receives its gas supply through the

regulator, simultaneously with the gas to the burner. Control of the system is through a

Maxitrol amplifier with a corresponding remote temperature dial.

Model Size

125

150

175

200

225

250

300

400

Maximum Turndown (%)

Inlet Range (MBH)

25-125 40.3-150 40.3-175 51.8-200 51.8-225 69-250 36-300 100-400

Inlet Pressure to Modulating Valve ("w.c.)

3.9

3.7

3.9

4.0

4.4

Gas Supply Pressure Required ("w.c.)

Electronic modulation for heating controlled by a specially designed room thermo-

stat (60°-85°F) is identified as Option AG7. Electronic modulation control systems for

makeup air applications controlled by a field-installed duct sensor (See Paragraph

6.4.2.) and temperature selector (55-90°F) are identified as either Option AG8 or Option

AG9. The temperature selector setting for Option AG8 is on the amplifier; Option AG9

has a remote temperature selector. Both systems are available with an override ther-

mostat.

FIGURE 32A -

Amplifier in Options

AG7, AG8, and AG9

FIGURE 32B -

Signal

Conditioner

used in Options

AG21 & AG40