| The forced-draft configuration provides the simplest and most convenient fan arrangement. With all blower components located below the tube bundle, they are easily accessible for maintenance and are not exposed to the heated air leaving the unit. However, these exchangers are susceptible to hot air recirculation due to the low velocity of the air leaving the unit. Induced-draft operation gives more uniform air flow over the tube bundle and the exit air velocity is several times higher than in forced-draft operation, thereby reducing the potential for hot air to be recirculated back to the intake of the unit or other nearby units. Hot air recirculation tends to reduce the capacity of the heat exchanger, thereby requiring a higher air flow rate and/or more heat-transfer surface. The induced-draft configuration also provides some protection from the elements for the tube bundle, which helps to stabilize the operation of the unit when sudden changes in ambient conditions occur |
