Application Considerations
A-19 — Stacked Energy Recovery Unit with Fixed-Plate Exchanger
A-20
— Air Blender Module — Mixed Air Temperature Performance
Fixed-Plate Exchanger.(FigureA-19)
Relying on thermal conduction to induce heat transfer, the fixed-plate air- to-air
exchanger consists of alternate layers of plates
separated and sealed to form passages for the outdoor
and exhaust air streams. This design eliminates cross-contamination, and is easy to clean and service. An optional "frost-avoidance"
damper discourages icing, permitting exchanger
operation at ambient temperatures as low as -20F.
Application considerations:
- Recovery is limited to sensible energy only; effectiveness typically ranges from 50 to 80 percent.
- The fixed-plate exchanger may contribute an additional 0.6 to 1.0 in. wg to
system static pressure.
- Face-and-bypass dampers can be used to bypass economizer air through the exchanger.
Economizer Module
This module provides a path for return air to be exhausted, allowing the system
to provide natural, nonmechanical cooling when outdoor
air conditions are suitable.
Air Blender Module.
(Figure A-20) The air
blender module contains air- mixing baffles or
"blenders" that impart rotational energy to
the passing air streams, boosting their velocity for
improved mixing. It is usually placed immediately downstream of a mixing box module, and should always be positioned
upstream of filters and coils. Chart A-1 documents the
air blender’s performance at a coil face
temperature of 55 F and return air temperatures of
70 F and 75 F.
Application considerations:
- Blender face velocity should exceed 400 fpm for proper mixing.
- When operated at temperatures within its design range, an air blender may eliminate the need for preheat.
- Space is required both upstream and downstream of the blender to allow complete air mixing. (The design of the air
blender module satisfies these spatial requirements.)
|
