J&R MANUFACTURING 700E, Operation And Service Manual

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AIR BALANCE
The building air balance is very important to the proper operation of your
Oyler Pit. The Oyler design is based on the induction of air into the pit
due to the “stack effect” of the chimney. The “stack effect” is the term
used to describe the upward airflow created in a chimney based on the
chimney height and the temperature difference between the bottom
(inlet) and top (discharge). This “stack effect” induces airflow into the
oven chamber via the front door opening (when the doors are open) and
into the firebox when the firebox is open or when the firebox combustion
air damper is open. Disruptions of this airflow can be caused by
mechanical exhaust fans, building that are too airtight (insufficient
openings for incoming air), and chimney downdrafts created by wind.
Such downdrafts are often created by nearby windbreaks, which are
taller than the chimney top. For this reason, the chimney should be four
feet taller than the surrounding rooftop including nearby parapet walls,
and taller than adjacent buildings and trees.
If air balance cannot be achieved by normal means, you should consider
using a fan to assist the stack effect. A fan inline or on the terminus of a
chimney can solve the problem. We recommend fans manufactured by
Exhausto (www.us.exhausto.com) installed with variable fan speed
controllers. These fans are available through J&R and other sources.
FURDOWN
As shown in Figure 1, we recommend a furdown (or draft curtain) surrounding
the pit. This traps nuisance smoke and allows it to be vented through the
annular space around the smokestack and out of the building. The furdown
can be constructed of metal, sheetrock, or other non-combustible materials. If
a furdown is used, we recommend that a 30-inch diameter metal sleeve be
installed between the ceiling opening and the roof flashing.
EYEBROW HOOD
As shown in Figure 3, another method to capture nuisance smoke is to install a
low volume eyebrow hood over the front of the pit. Please be advised that too
much exhaust volume for such hoods can negate the smoke/air draft design of
the pit, which is predicated on a front to rear air and smoke flow (see “Air
Balance” above).
Such hoods should be sized with fan volumes under 1000 CFM, with means to
adjust the airflow to achieve an appropriate air balance. The eyebrow hood can
be interlocked with the front door limit switch so that it is only energized when
the front doors are opened.
Eyebrow hoods must comply with NFPA 96 and local codes.
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