5.13 Heat Recovery Systems

Heat recovery systems shall be utilized in all ventilation units (100 percent outside air units) and where the temperature differentials between supply air and exhaust air is significant. Heat recovery systems shall operate at a minimum of 70 percent efficiency. The heat recovery systems must be capable of connecting to a microprocessor controller that in turn can be connected to a direct digital control (DDC) Building Automation System. Prefilters shall be provided in all heat recovery systems before the heat recovery equipment.

Heat Pipe. For sensible heat recovery a run around type heat pipe shall use refrigerant to absorb heat from the air stream at the air intake and reject the heat back into the air stream at the discharge of the air-handling unit. System shall have solenoid valve control to operate under partial load conditions.

Run-around Coil. A glycol run-around coil could be used with control valves and a pump for part load conditions. The run-around coils shall be used at the exhaust discharge from the building and at the fresh air intake into the building. The run-around coil system shall be capable of connecting to a microprocessor controller that in turn can be connected to a DDC Building Automation system.

Enthalpy Wheel. A desiccant-impregnated enthalpy wheel with variable speed rotary wheel may be used in the supply and exhaust systems.

Sensible Heat Recovery. For sensible heat recovery, a cross-flow, air-to-air (z-duct) heat exchanger shall recover the heat in the exhaust and supply air streams. Z-ducts shall be constructed entirely of sheet metal. Heat-wheels may also be used for sensible heat recovery. Unit shall have variable speed drive for controlling the temperature leaving the unit.

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