Engineered air DG series Manual de usuario descargar pdf (Pagina 5)

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109 INTERFACE

PURPOSE

The 109-2 Interface gives improved temperature control to a Engineered Air DG model unit. The

DG style unit uses a power burner that requires modulating air as well as modulating gas.

Therefore a valve such as a Honeywell V9055 or a motor such as a M9185 will be used to

modulate the flow of gas and air to the burner head. At periods when the temperature rise during

low fire setting is too high to properly control the discharge temperature, the 109 will cycle the

burner on and off.

There are two versions of the 109 interface. The original 109 will operate with a Honeywell series

90 temperature controller such as the fast response T991A. It will also operate with a Maxitrol

system such as the series 14. NOTE: when using the Maxitrol system on the 109, a jumper is

required on the 109 terminals 1 and 2. The 109 series 1 will also accept a signal from a

Honeywell W973 system.

The 109-2 is clearly marked as a 109-2. The 109-2 interface will allow the gas valve system to be

controlled by a Honeywell T991A fast response control, a Maxitrol system, a Honeywell W973

system, a signal from a Engineered Air Megatrac control, a 0-10 VDC or a 4-20ma control.

NOTE: only the 109-2 will handle the latter signals.

OPERATION (SIMPLIFIED)

Once the DG unit is running and the prepurge timing system has completed its cycle, the control

of the discharge temperature is handled by the 109 interface. The 109 uses a 24 volt AC power

supply that is connected to terminals “H” and “N”. In most applications the burner motor will run

continuously when outside ambients are below about 60°F.

1. On initial call for heat, the 109 closes a set of internal relay the heat call (usually labelled

“1HR”), which in turn closes its contacts (usually labelled “1HR1”). In most applications this

will energise the flame relay if the pre-purge relay is closed. The prepurge relay is located in

a separate circuit that begins a timing cycle after the combustion fan begins to run. In some

installations with a constant pilot, “1HR1” contacts will energise the gas valve contacts that

are located between the 109 terminals “8” and “9”. This gives power to the relay that controls

directly. The gas valve is usually a Honeywell V9055.

2. Upon completing ignition and proving pilot, the modulation of the gas valve is controlled by a

discharge control feeding a signal into the 109. The 109 modifies this signal and in turn puts

out a signal to the gas valve. The valve will usually overshoot before the discharge control

begins to close the gas valve back towards a modulated fire. Depending on the temperature

rise required, the 109 will modulate the gas valve to maintain the desired setpoint

temperature. Note that the valve will not go to a setting and remain there. There are tow

styles of gas valve in use, the Honeywell V9055 and the servo-motor controlled Neo valve.

Due to the “step” control of the Honeywell V9055, it is not possible to lock on to a setting.

This valve will modulate constantly, usually through a stroke of 3/8” or less.

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Engineered air DG series Manual de usuario Pagina 5