Despatch RFD Series - Manual (Page 18)

T HEORY OF O PERATION RFD Oven Series Owner’s Manual
18 Version 1
Copyright © 2012 by Despatch Industries.
All rights reserved. No part of the contents of this manual may be reproduced, copied or transmitted in any form or by any
means including graphic, electronic, or mechanical methods or photocopying, recording, or information storage and
retrieval systems without the written permission of Despatch Industries, unless for purchaser's personal use.
3.2.1. Determining Damper Settings
The optimum setting for the amount of fresh air that should be distributed into the chamber
depends on several factors. These factors include ambient environment temperature, load
conditions, load distribution, heat-up rates, cool-down rates, desired temperature uniformity and,
most importantly, the desired operating temperature. Carefully consider existing engineering
tradeoffs while using guidelines to determine the fresh air damper setting.
In general, the damper should be set so that the amount of fresh air flowing into the chamber
agrees with the desired operating temperature conditions. The following paragraphs show the
considerations involved with various damper position settings.
3.2.1.1. Fresh Air Damper Fully Closed Position
The chamber achieves maximum attainable heat-up rates when the fresh air damper lies in the full
closed position. With the damper in the full closed position, the chamber will operate at the
desired temperature using the minimum amount of power. In most cases, the oven also efficiently
operates at the chamber’s maximum operating temperature when in the full closed position.
3.2.1.2. Fresh Air Damper Fully Open Position
The chamber operates at its minimum operating temperature with the fresh air damper in full
open position.
Friction heat from the air recirculation system builds up in the chamber. This causes chamber
temperature to rise slightly even without the heating system on. The chamber reaches thermal
equilibrium temperature after the recirculation motor runs for an extended period of time.
The chamber cannot readily dissipate heat generated by friction without a fully open fresh air
damper. With the fresh air damper fully open, the thermal equilibrium temperature is the mini-
mum operating temperature of the chamber.
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When the damper is in full open position, the oven may not be
able to heat to the maximum oven operating temperature.
3.2.1.3. Exhaust Damper Control
Adjusting the exhaust damper (Figure 6) aids in pressurizing the chamber.