Page 30 - Air Handling Units.cdr

AIR Handling UNITS

PLATE EXCHANGER - PWT

The most important part of the PWT heat recovery section is a recuperatory cross-ow heat
exchanger, intended to recover the heat from the exhaust air. External and exhaust air ows
alternately in the channels between the exchanger plates (the plates are made of aluminium,
as an option they can be additionally epoxy coated). The streams of air do not contact each
other, so there is no humidity recovery. If the temperature of exhaust air behind the exchanger
falls below the dew-point, condensation of moisture in the air takes place, contributing to heat
recovery intensication (heat of condensation is transferred to the supplied air). At low external
temperatures in the cross-ow exchanger the condensed moisture freezes, ow resistance
increases and heat recovery efciency drops. The methods of preventing this phenomenon
is the use of a system for controlling the by-pass throttles. The purpose of such system is to make
it impossible to let the temperature of exhaust air stream behind the exchanger fall below
permissible value. In such case only a part of the external air ows through the exchanger, the
rest ows through the by-pass. Air temperature after the cross-ow exchanger (tm) is the air
temperature after mixing the two streams. To calculate the required power of the heater after
the cross-ow exchangers the tm temperature should be assumed as starting temperature. Total
efciency of cross-ow exchangers is about 68%. GS heat exchangers are a kind of cross-ow
exchangers. In the GS exchangers the air is directed in reverse streams of ow in dened air
channels. High efciency can be obtained, at low air pressure losses. The GS exchangers are
made of aluminium, resistant to sea water, optionally with an epoxy coating. We produce the
PWT sections with tanks for condensate with a drain, zinc coated versions and versions made of
acid resistant steel. After the exchanger, on the exhaust air side, a droplet eliminator is installed.
The section is equipped with revision covers.

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