Energy recovery is an option to save on HVAC costs for organizations using a direct exchange system that’s increasingly being written into building codes and ASHRAE standards.

Like VRF, there are two basic types: airside and waterside.

According to Ron Holdaway, an engineer at Smith Seckman Reid, airside energy recovery is the process of using the building’s exhaust air to pre-condition the ventilation air for the building. The exhaust air passes through an energy recovery device such as a rotating heat wheel, a fixed plate heat exchanger, or a run-around coil. The energy from the exhaust air stream is transferred to or from the outside air. In the summer, the temperature of the warmer, humid outside air is reduced before entering the air conditioning system, which trims air conditioning system tonnage. In winter, the cold outside air is warmed before heaters heat the air to maintain the space temperature.

A water-cooled system relies on chillers to cool the water, which is then distributed to air-handling units to condition the space. The heat from the air-handler coils is returned to the chiller where it is returned to the air via fans or a cooling tower. Holdaway notes that waterside energy recovery systems capture some of the heat from the building before it is rejected. This recovered energy is often used to help provide the building’s heating or hot water.

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