EngA ENGINEERED AIR DJM2.4, Инструкция по установке, эксплуатации и обслуживанию, Страница: 32 / 37

DJM2.4 MANUAL
32 Oct 00 R2
On heat/cool units the combustion air is normally drawn by the combustion fan from the intake
screen located on the compressor floor area. As this floor area is cantilevered it can plug up with
blowing snow, especially if the unit is mounted on a low level roof curb. This can cause
combustion air to starve and result into sooting or the heat exchanger.
Smell From Flue (Products of Combustion)
Smells are usually created by improper combustion set up. This can be due to a sticking valve
(note above) , low inlet gas pressure, or just a bad combustion set up. Note the following
comments about combustion set up.
Water and Ice From Combustion
These heat exchangers are very efficient. Water is one of the major products of combustion and
as such must be controlled. The units are equipped with a drain. It is however best to allow
water to leave the unit in the flue gases in vapour form. Combustion that is set at maximum
efficiency will produce excess moisture. Often it is desirable to have 1% to 2% higher excess
oxygen readings then those normally listed to assist in keeping the flue gases drier. Also note that
extended chimneys can contribute to condensation problems
(especially if they are not insulated
or at least double walled) . Water in the heat exchanger can lead to premature failure due to
thermal stress or freezing. Another source of excess condensation is when a unit designed with
capacity to heat 100% outside air is operating with very little outside air, therefore operating at a
low fire or cycling. This allows the cool flue gases from low fire to cool and condense in the
chimney.
Burner Pulsing, Backfiring
An improper air/fuel mixture usually causes this condition. Do not attempt to do any combustion
analysis until the inlet fuel pressure has been checked. If inlet fuel pressure falls too low then the
air velocity on the burner
(which is likely set for proper fuel pressure) would be too high for the
quantity of fuel being supplied to the burner. If the inlet fuel pressure is correct, then the
combustion air is possibly set too high for the burner and combustion analysis should be done.
If an explosion occurs after the burners flame has definitely extinguished, and the burner is being
re-lit on a heat call, the explosion is likely due to a fuel build-up from a slow leaking gas valve. It is
recommended that both pilot and main manifold valves be changed if you cannot prove the
source of a leak.
Also note that a possible cause of burner rumble on standard (round) burners is having the
turndown rate set too low. If the combustion blower is at low speed and the manifold pressure is
set below the 40% turndown, then there is too much air for the quantity of fuel, correct by
increasing low fire manifold pressure. Refer to notes in “
Rumble During Light Off ”, page 30.