Despatch LAD Series WITH PROTOCOL PLUS - Manual (Page 15)

7
Full Open Position
When the fresh air damper is in the full open position, the chamber will operate at its
minimum operating temperature.
Friction heat from the air recirculation system builds up in the chamber. This causes
chamber temperature to rise slightly even though the heating system is not turned on.
After the recirculation motor has been on for an extended period of time, the chamber
will reach a thermal equilibrium temperature.
When the damper is not set to the full open position, the chamber has no way to readily
dissipate the heat generated by the friction. With the fresh air damper fully open, the
thermal equilibrium temperature is the minimum operating temperature of the chamber.
Other Damper Settings
The damper can be set to several other distinct operating positions. In most cases the
damper setting is influenced by two specific performance factors. The two performance
factors are uniformity and cool down rates.
The uniformity of the chamber is influenced by the inside chamber pressure of the
system. The pressure inside the chamber is dependant on the amount of fresh air
flowing into the chamber. When a large volume of fresh air is flowing into the chamber,
the chamber becomes slightly pressurized and the overall temperature uniformity
improves. The slightly pressurized chamber produces the effect of "pushing" the air to
the corners of the chamber. Typically the corners of the chamber will improve with
respect to temperature distribution while the core of the chamber will maintain excellent
uniformity characteristics regardless of the damper position. Therefore, the
pressurization of the chamber typically is a factor when the chamber is loaded heavily.
Adjusting the exhaust damper will aid in pressurizing the chamber. The best uniformity
results, with respect to the product, are achieved when no more than two-thirds of any
inside chamber dimension are used. The best overall results are achieved when the
product(s) are located in the center of the chamber.