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.)