Figure A-17 — Stacked Energy Recovery Unit with Total Energy Recovery Wheel

Energy Recovery Module

This custom module houses an energy-recovery device that, depending on ambient conditions, uses the exhaust air stream to precondition (warm or cool/dehumidify) entering outdoor air. Following are three energy- recovery methods for use in Modular Climate Changer applications.

Total-Energy Wheel.

(Figure A-17) This energy-recovery device consists of a rotating wheel coated with a desiccant medium suited for total energy transfer. Adjacent outdoor and exhaust air streams pass through the wheel in a counterflow arrangement, exchanging sensible energy through thermal conduction and latent energy through moisture adsorption and desorption. Along with its ability to recover both sensible and latent energy, the total- energy wheel’s advantages include its compact size and reliable, mature technology. Application considerations:

• Recovery effectiveness typically ranges from 68 to 86 percent.
  
• The total-energy wheel may contribute an additional 0.7 to 0.9 in. wg to system static pressure.
  
• This method of energy recovery is particularly well-suited to dehumidification cooling applications with low sensible heat ratios.

Run-Around Loop.

(Figure A-18) A run- around loop consists of two finned-tube coils (air-to-water heat exchangers) piped together; one coil resides in the outdoor air stream and the other in the exhaust air stream. An expansion tank, pump, three-way temperature control valve and working fluid (usually an inhibited solution of ethylene glycol and water) complete the recovery system.

Figure A-18 — Typical Run-around Energy Recovery Loop

Since the outdoor and exhaust air streams need not be adjacent, the run- around loop provides design flexibility well-suited to building renovations — at a lower first cost than other methods of energy recovery. Complete separation of the air streams also eliminates the risk of cross- contamination.

Application considerations:

• Recovery is limited to sensible energy with an effectiveness that typically ranges from 60 to 65 percent.

• Together, the two finned-tube coils may contribute approximately 0.3 to 0.6 in. wg to system static pressure.