What is Energy Recovery? Energy Recovery Devices Energy Recovery Devices While Energy Recovery units can be custom manufactured to optimize any application, each unit is defined by one of four typical devices found inside an energy recovery unit: Plate Type Air-to-Air Heat Exchangers-recover sensible only energy with no cross contamination of air stream. Rotary Energy Recovery Wheels-which can recover both sensible and latent energy. Heat Pipes-which are coils filled with a specific amount of refrigerant. Run-Around Loops-which circulate a liquid between two different air streams. Plate Air-to-Air Heat Exchangers Plate Air-to-Air Heat Exchangers recover energy by crossing discarded exhaust air and ventilation (supply) air in side-by-side air streams with common recovery plates. The process "preconditions" the ventilation air so the primary conditioning media is required to do less work. Because it lacks moving parts, a Plate Air-to-Air Heat Exchanger is an extremely low maintenance energy recovery product. One drawback to this device is that it recovers only sensible energy-causing the dry bulb temperature of the ventilation air to change while maintaining a constant dew point. Rotary Energy Recovery Wheels Energy Recovery Wheel units retrieve a portion of exhausted energy by using a total energy wheel, which rotates between the supply and exhaust air streams. The advantage of this device is that it can recover both sensible and latent energy and use the latent energy to vastly increase its effectiveness-especially in hot, humid environments. Partial loads are accounted for by varying the speed of the rotating wheel or by bypassing air. Cross contamination is a concern of the Energy Recovery Wheel device. Designing wheels to transfer only moisture and not airborne contaminants averts the problem. A purge also can be built into the wheel to wipe it with clean outside air. When properly applied, a purge section on an energy recovery wheel can reduce cross contamination to 0.1%. Sensible only wheels are also available. Heat Pipes Heat Pipes can be incorporated into Energy Recover Units to recover energy. They require side-by-side air streams, similar to Energy Recovery Wheels and Plate Air-to-Air Heat Exchangers. Heat Pipes are simply coils filled with a specific amount of refrigerant that naturally changes phase based on exhaust and supply temperatures, using vapor pressure to transmit energy. Because they lack moving parts, Heat Pipes are low maintenance and very rarely fail. Sensible effectiveness of this device is between 45% and 65%. Heat Pipes recover only sensible energy. Run-Around Loops Run-Around Loops circulate a liquid between two different air streams. By simply adding pumps and coils, a cost-effective energy recovery solution is attained. Unlike other devices, a Run-Around Loop can take advantage of air streams that are not next to one another. If the system is properly sized, pre-heat coils can function as the energy discharge side of the loop in the outdoor air unit. Run-Around Loops are typically controlled by varying water flow with a VFD driven pump, or by using a three-way bypass valve. Sensible effectiveness is estimated between 55 and 65%. Run-Around Loops have limited moving parts and no cross-contamination issues. However, due to the typical distance between the outdoor air unit and the heat recovery unit, this type of system may also requires on-site interconnecting piping. Using cooling tower water or evaporative media can also save energy. This method is typically called indirect evaporative recovery, and is classified as a form of run-around loop.